zig/src-self-hosted/ir.zig

const std = @import("std");
const builtin = @import("builtin");
const Compilation = @import("compilation.zig").Compilation;
const Scope = @import("scope.zig").Scope;
const ast = std.zig.ast;
const Allocator = std.mem.Allocator;
const Value = @import("value.zig").Value;
const Type = Value.Type;
const assert = std.debug.assert;
const Token = std.zig.Token;
const Span = @import("errmsg.zig").Span;
const llvm = @import("llvm.zig");
const codegen = @import("codegen.zig");
const ObjectFile = codegen.ObjectFile;
const Decl = @import("decl.zig").Decl;
const mem = std.mem;

pub const LVal = enum {
    None,
    Ptr,
};

pub const IrVal = union(enum) {
    Unknown,
    KnownType: *Type,
    KnownValue: *Value,

    const Init = enum {
        Unknown,
        NoReturn,
        Void,
    };

    pub fn dump(self: IrVal) void {
        switch (self) {
            IrVal.Unknown => std.debug.warn("Unknown"),
            IrVal.KnownType => |typ| {
                std.debug.warn("KnownType(");
                typ.dump();
                std.debug.warn(")");
            },
            IrVal.KnownValue => |value| {
                std.debug.warn("KnownValue(");
                value.dump();
                std.debug.warn(")");
            },
        }
    }
};

pub const Inst = struct {
    id: Id,
    scope: *Scope,
    debug_id: usize,
    val: IrVal,
    ref_count: usize,
    span: Span,
    owner_bb: *BasicBlock,

    /// true if this instruction was generated by zig and not from user code
    is_generated: bool,

    /// the instruction that is derived from this one in analysis
    child: ?*Inst,

    /// the instruction that this one derives from in analysis
    parent: ?*Inst,

    /// populated durign codegen
    llvm_value: ?*llvm.Value,

    pub fn cast(base: *Inst, comptime T: type) ?*T {
        if (base.id == comptime typeToId(T)) {
            return @fieldParentPtr(T, "base", base);
        }
        return null;
    }

    pub fn typeToId(comptime T: type) Id {
        comptime var i = 0;
        inline while (i < @memberCount(Id)) : (i += 1) {
            if (T == @field(Inst, @memberName(Id, i))) {
                return @field(Id, @memberName(Id, i));
            }
        }
        unreachable;
    }

    pub fn dump(base: *const Inst) void {
        comptime var i = 0;
        inline while (i < @memberCount(Id)) : (i += 1) {
            if (base.id == @field(Id, @memberName(Id, i))) {
                const T = @field(Inst, @memberName(Id, i));
                std.debug.warn("#{} = {}(", base.debug_id, @tagName(base.id));
                @fieldParentPtr(T, "base", base).dump();
                std.debug.warn(")");
                return;
            }
        }
        unreachable;
    }

    pub fn hasSideEffects(base: *const Inst) bool {
        comptime var i = 0;
        inline while (i < @memberCount(Id)) : (i += 1) {
            if (base.id == @field(Id, @memberName(Id, i))) {
                const T = @field(Inst, @memberName(Id, i));
                return @fieldParentPtr(T, "base", base).hasSideEffects();
            }
        }
        unreachable;
    }

    pub async fn analyze(base: *Inst, ira: *Analyze) Analyze.Error!*Inst {
        switch (base.id) {
            Id.Return => return @fieldParentPtr(Return, "base", base).analyze(ira),
            Id.Const => return @fieldParentPtr(Const, "base", base).analyze(ira),
            Id.Call => return @fieldParentPtr(Call, "base", base).analyze(ira),
            Id.DeclRef => return await (async @fieldParentPtr(DeclRef, "base", base).analyze(ira) catch unreachable),
            Id.Ref => return await (async @fieldParentPtr(Ref, "base", base).analyze(ira) catch unreachable),
            Id.DeclVar => return @fieldParentPtr(DeclVar, "base", base).analyze(ira),
            Id.CheckVoidStmt => return @fieldParentPtr(CheckVoidStmt, "base", base).analyze(ira),
            Id.Phi => return @fieldParentPtr(Phi, "base", base).analyze(ira),
            Id.Br => return @fieldParentPtr(Br, "base", base).analyze(ira),
            Id.AddImplicitReturnType => return @fieldParentPtr(AddImplicitReturnType, "base", base).analyze(ira),
            Id.PtrType => return await (async @fieldParentPtr(PtrType, "base", base).analyze(ira) catch unreachable),
            Id.VarPtr => return await (async @fieldParentPtr(VarPtr, "base", base).analyze(ira) catch unreachable),
            Id.LoadPtr => return await (async @fieldParentPtr(LoadPtr, "base", base).analyze(ira) catch unreachable),
        }
    }

    pub fn render(base: *Inst, ofile: *ObjectFile, fn_val: *Value.Fn) (error{OutOfMemory}!?*llvm.Value) {
        switch (base.id) {
            Id.Return => return @fieldParentPtr(Return, "base", base).render(ofile, fn_val),
            Id.Const => return @fieldParentPtr(Const, "base", base).render(ofile, fn_val),
            Id.Call => return @fieldParentPtr(Call, "base", base).render(ofile, fn_val),
            Id.VarPtr => return @fieldParentPtr(VarPtr, "base", base).render(ofile, fn_val),
            Id.LoadPtr => return @fieldParentPtr(LoadPtr, "base", base).render(ofile, fn_val),
            Id.DeclRef => unreachable,
            Id.PtrType => unreachable,
            Id.Ref => @panic("TODO"),
            Id.DeclVar => @panic("TODO"),
            Id.CheckVoidStmt => @panic("TODO"),
            Id.Phi => @panic("TODO"),
            Id.Br => @panic("TODO"),
            Id.AddImplicitReturnType => @panic("TODO"),
        }
    }

    fn ref(base: *Inst, builder: *Builder) void {
        base.ref_count += 1;
        if (base.owner_bb != builder.current_basic_block and !base.isCompTime()) {
            base.owner_bb.ref(builder);
        }
    }

    fn copyVal(base: *Inst, comp: *Compilation) !*Value {
        if (base.parent.?.ref_count == 0) {
            return base.val.KnownValue.derefAndCopy(comp);
        }
        return base.val.KnownValue.copy(comp);
    }

    fn getAsParam(param: *Inst) !*Inst {
        param.ref_count -= 1;
        const child = param.child orelse return error.SemanticAnalysisFailed;
        switch (child.val) {
            IrVal.Unknown => return error.SemanticAnalysisFailed,
            else => return child,
        }
    }

    fn getConstVal(self: *Inst, ira: *Analyze) !*Value {
        if (self.isCompTime()) {
            return self.val.KnownValue;
        } else {
            try ira.addCompileError(self.span, "unable to evaluate constant expression");
            return error.SemanticAnalysisFailed;
        }
    }

    fn getAsConstType(param: *Inst, ira: *Analyze) !*Type {
        const meta_type = Type.MetaType.get(ira.irb.comp);
        meta_type.base.base.deref(ira.irb.comp);

        const inst = try param.getAsParam();
        const casted = try ira.implicitCast(inst, &meta_type.base);
        const val = try casted.getConstVal(ira);
        return val.cast(Value.Type).?;
    }

    fn getAsConstAlign(param: *Inst, ira: *Analyze) !u32 {
        return error.Unimplemented;
        //const align_type = Type.Int.get_align(ira.irb.comp);
        //align_type.base.base.deref(ira.irb.comp);

        //const inst = try param.getAsParam();
        //const casted = try ira.implicitCast(inst, align_type);
        //const val = try casted.getConstVal(ira);

        //uint32_t align_bytes = bigint_as_unsigned(&const_val->data.x_bigint);
        //if (align_bytes == 0) {
        //    ir_add_error(ira, value, buf_sprintf("alignment must be >= 1"));
        //    return false;
        //}

        //if (!is_power_of_2(align_bytes)) {
        //    ir_add_error(ira, value, buf_sprintf("alignment value %" PRIu32 " is not a power of 2", align_bytes));
        //    return false;
        //}
    }

    /// asserts that the type is known
    fn getKnownType(self: *Inst) *Type {
        switch (self.val) {
            IrVal.KnownType => |typ| return typ,
            IrVal.KnownValue => |value| return value.typ,
            IrVal.Unknown => unreachable,
        }
    }

    pub fn setGenerated(base: *Inst) void {
        base.is_generated = true;
    }

    pub fn isNoReturn(base: *const Inst) bool {
        switch (base.val) {
            IrVal.Unknown => return false,
            IrVal.KnownValue => |x| return x.typ.id == Type.Id.NoReturn,
            IrVal.KnownType => |typ| return typ.id == Type.Id.NoReturn,
        }
    }

    pub fn isCompTime(base: *const Inst) bool {
        return base.val == IrVal.KnownValue;
    }

    pub fn linkToParent(self: *Inst, parent: *Inst) void {
        assert(self.parent == null);
        assert(parent.child == null);
        self.parent = parent;
        parent.child = self;
    }

    pub const Id = enum {
        Return,
        Const,
        Ref,
        DeclVar,
        CheckVoidStmt,
        Phi,
        Br,
        AddImplicitReturnType,
        Call,
        DeclRef,
        PtrType,
        VarPtr,
        LoadPtr,
    };

    pub const Call = struct {
        base: Inst,
        params: Params,

        const Params = struct {
            fn_ref: *Inst,
            args: []*Inst,
        };

        const ir_val_init = IrVal.Init.Unknown;

        pub fn dump(self: *const Call) void {
            std.debug.warn("#{}(", self.params.fn_ref.debug_id);
            for (self.params.args) |arg| {
                std.debug.warn("#{},", arg.debug_id);
            }
            std.debug.warn(")");
        }

        pub fn hasSideEffects(self: *const Call) bool {
            return true;
        }

        pub fn analyze(self: *const Call, ira: *Analyze) !*Inst {
            const fn_ref = try self.params.fn_ref.getAsParam();
            const fn_ref_type = fn_ref.getKnownType();
            const fn_type = fn_ref_type.cast(Type.Fn) orelse {
                try ira.addCompileError(fn_ref.span, "type '{}' not a function", fn_ref_type.name);
                return error.SemanticAnalysisFailed;
            };

            const fn_type_param_count = fn_type.paramCount();

            if (fn_type_param_count != self.params.args.len) {
                try ira.addCompileError(
                    self.base.span,
                    "expected {} arguments, found {}",
                    fn_type_param_count,
                    self.params.args.len,
                );
                return error.SemanticAnalysisFailed;
            }

            const args = try ira.irb.arena().alloc(*Inst, self.params.args.len);
            for (self.params.args) |arg, i| {
                args[i] = try arg.getAsParam();
            }
            const new_inst = try ira.irb.build(Call, self.base.scope, self.base.span, Params{
                .fn_ref = fn_ref,
                .args = args,
            });
            new_inst.val = IrVal{ .KnownType = fn_type.key.data.Normal.return_type };
            return new_inst;
        }

        pub fn render(self: *Call, ofile: *ObjectFile, fn_val: *Value.Fn) !?*llvm.Value {
            const fn_ref = self.params.fn_ref.llvm_value.?;

            const args = try ofile.arena.alloc(*llvm.Value, self.params.args.len);
            for (self.params.args) |arg, i| {
                args[i] = arg.llvm_value.?;
            }

            const llvm_cc = llvm.CCallConv;
            const fn_inline = llvm.FnInline.Auto;

            return llvm.BuildCall(
                ofile.builder,
                fn_ref,
                args.ptr,
                @intCast(c_uint, args.len),
                llvm_cc,
                fn_inline,
                "",
            ) orelse error.OutOfMemory;
        }
    };

    pub const Const = struct {
        base: Inst,
        params: Params,

        const Params = struct {};

        // Use Builder.buildConst* methods, or, after building a Const instruction,
        // manually set the ir_val field.
        const ir_val_init = IrVal.Init.Unknown;

        pub fn dump(self: *const Const) void {
            self.base.val.KnownValue.dump();
        }

        pub fn hasSideEffects(self: *const Const) bool {
            return false;
        }

        pub fn analyze(self: *const Const, ira: *Analyze) !*Inst {
            const new_inst = try ira.irb.build(Const, self.base.scope, self.base.span, Params{});
            new_inst.val = IrVal{ .KnownValue = self.base.val.KnownValue.getRef() };
            return new_inst;
        }

        pub fn render(self: *Const, ofile: *ObjectFile, fn_val: *Value.Fn) !?*llvm.Value {
            return self.base.val.KnownValue.getLlvmConst(ofile);
        }
    };

    pub const Return = struct {
        base: Inst,
        params: Params,

        const Params = struct {
            return_value: *Inst,
        };

        const ir_val_init = IrVal.Init.NoReturn;

        pub fn dump(self: *const Return) void {
            std.debug.warn("#{}", self.params.return_value.debug_id);
        }

        pub fn hasSideEffects(self: *const Return) bool {
            return true;
        }

        pub fn analyze(self: *const Return, ira: *Analyze) !*Inst {
            const value = try self.params.return_value.getAsParam();
            const casted_value = try ira.implicitCast(value, ira.explicit_return_type);

            // TODO detect returning local variable address

            return ira.irb.build(Return, self.base.scope, self.base.span, Params{ .return_value = casted_value });
        }

        pub fn render(self: *Return, ofile: *ObjectFile, fn_val: *Value.Fn) !?*llvm.Value {
            const value = self.params.return_value.llvm_value;
            const return_type = self.params.return_value.getKnownType();

            if (return_type.handleIsPtr()) {
                @panic("TODO");
            } else {
                _ = llvm.BuildRet(ofile.builder, value) orelse return error.OutOfMemory;
            }
            return null;
        }
    };

    pub const Ref = struct {
        base: Inst,
        params: Params,

        const Params = struct {
            target: *Inst,
            mut: Type.Pointer.Mut,
            volatility: Type.Pointer.Vol,
        };

        const ir_val_init = IrVal.Init.Unknown;

        pub fn dump(inst: *const Ref) void {}

        pub fn hasSideEffects(inst: *const Ref) bool {
            return false;
        }

        pub async fn analyze(self: *const Ref, ira: *Analyze) !*Inst {
            const target = try self.params.target.getAsParam();

            if (ira.getCompTimeValOrNullUndefOk(target)) |val| {
                return ira.getCompTimeRef(
                    val,
                    Value.Ptr.Mut.CompTimeConst,
                    self.params.mut,
                    self.params.volatility,
                );
            }

            const new_inst = try ira.irb.build(Ref, self.base.scope, self.base.span, Params{
                .target = target,
                .mut = self.params.mut,
                .volatility = self.params.volatility,
            });
            const elem_type = target.getKnownType();
            const ptr_type = try await (async Type.Pointer.get(ira.irb.comp, Type.Pointer.Key{
                .child_type = elem_type,
                .mut = self.params.mut,
                .vol = self.params.volatility,
                .size = Type.Pointer.Size.One,
                .alignment = Type.Pointer.Align.Abi,
            }) catch unreachable);
            // TODO: potentially set the hint that this is a stack pointer. But it might not be - this
            // could be a ref of a global, for example
            new_inst.val = IrVal{ .KnownType = &ptr_type.base };
            // TODO potentially add an alloca entry here
            return new_inst;
        }
    };

    pub const DeclRef = struct {
        base: Inst,
        params: Params,

        const Params = struct {
            decl: *Decl,
            lval: LVal,
        };

        const ir_val_init = IrVal.Init.Unknown;

        pub fn dump(inst: *const DeclRef) void {}

        pub fn hasSideEffects(inst: *const DeclRef) bool {
            return false;
        }

        pub async fn analyze(self: *const DeclRef, ira: *Analyze) !*Inst {
            (await (async ira.irb.comp.resolveDecl(self.params.decl) catch unreachable)) catch |err| switch (err) {
                error.OutOfMemory => return error.OutOfMemory,
                else => return error.SemanticAnalysisFailed,
            };
            switch (self.params.decl.id) {
                Decl.Id.CompTime => unreachable,
                Decl.Id.Var => return error.Unimplemented,
                Decl.Id.Fn => {
                    const fn_decl = @fieldParentPtr(Decl.Fn, "base", self.params.decl);
                    const decl_val = switch (fn_decl.value) {
                        Decl.Fn.Val.Unresolved => unreachable,
                        Decl.Fn.Val.Fn => |fn_val| &fn_val.base,
                        Decl.Fn.Val.FnProto => |fn_proto| &fn_proto.base,
                    };
                    switch (self.params.lval) {
                        LVal.None => {
                            return ira.irb.buildConstValue(self.base.scope, self.base.span, decl_val);
                        },
                        LVal.Ptr => return error.Unimplemented,
                    }
                },
            }
        }
    };

    pub const VarPtr = struct {
        base: Inst,
        params: Params,

        const Params = struct {
            var_scope: *Scope.Var,
        };

        const ir_val_init = IrVal.Init.Unknown;

        pub fn dump(inst: *const VarPtr) void {
            std.debug.warn("{}", inst.params.var_scope.name);
        }

        pub fn hasSideEffects(inst: *const VarPtr) bool {
            return false;
        }

        pub async fn analyze(self: *const VarPtr, ira: *Analyze) !*Inst {
            switch (self.params.var_scope.data) {
                Scope.Var.Data.Const => @panic("TODO"),
                Scope.Var.Data.Param => |param| {
                    const new_inst = try ira.irb.build(
                        Inst.VarPtr,
                        self.base.scope,
                        self.base.span,
                        Inst.VarPtr.Params{ .var_scope = self.params.var_scope },
                    );
                    const ptr_type = try await (async Type.Pointer.get(ira.irb.comp, Type.Pointer.Key{
                        .child_type = param.typ,
                        .mut = Type.Pointer.Mut.Const,
                        .vol = Type.Pointer.Vol.Non,
                        .size = Type.Pointer.Size.One,
                        .alignment = Type.Pointer.Align.Abi,
                    }) catch unreachable);
                    new_inst.val = IrVal{ .KnownType = &ptr_type.base };
                    return new_inst;
                },
            }
        }

        pub fn render(self: *VarPtr, ofile: *ObjectFile, fn_val: *Value.Fn) *llvm.Value {
            switch (self.params.var_scope.data) {
                Scope.Var.Data.Const => unreachable, // turned into Inst.Const in analyze pass
                Scope.Var.Data.Param => |param| return param.llvm_value,
            }
        }
    };

    pub const LoadPtr = struct {
        base: Inst,
        params: Params,

        const Params = struct {
            target: *Inst,
        };

        const ir_val_init = IrVal.Init.Unknown;

        pub fn dump(inst: *const LoadPtr) void {}

        pub fn hasSideEffects(inst: *const LoadPtr) bool {
            return false;
        }

        pub async fn analyze(self: *const LoadPtr, ira: *Analyze) !*Inst {
            const target = try self.params.target.getAsParam();
            const target_type = target.getKnownType();
            if (target_type.id != Type.Id.Pointer) {
                try ira.addCompileError(self.base.span, "dereference of non pointer type '{}'", target_type.name);
                return error.SemanticAnalysisFailed;
            }
            const ptr_type = @fieldParentPtr(Type.Pointer, "base", target_type);
            //    if (instr_is_comptime(ptr)) {
            //        if (ptr->value.data.x_ptr.mut == ConstPtrMutComptimeConst ||
            //            ptr->value.data.x_ptr.mut == ConstPtrMutComptimeVar)
            //        {
            //            ConstExprValue *pointee = const_ptr_pointee(ira->codegen, &ptr->value);
            //            if (pointee->special != ConstValSpecialRuntime) {
            //                IrInstruction *result = ir_create_const(&ira->new_irb, source_instruction->scope,
            //                    source_instruction->source_node, child_type);
            //                copy_const_val(&result->value, pointee, ptr->value.data.x_ptr.mut == ConstPtrMutComptimeConst);
            //                result->value.type = child_type;
            //                return result;
            //            }
            //        }
            //    }
            const new_inst = try ira.irb.build(
                Inst.LoadPtr,
                self.base.scope,
                self.base.span,
                Inst.LoadPtr.Params{ .target = target },
            );
            new_inst.val = IrVal{ .KnownType = ptr_type.key.child_type };
            return new_inst;
        }

        pub fn render(self: *LoadPtr, ofile: *ObjectFile, fn_val: *Value.Fn) !?*llvm.Value {
            const child_type = self.base.getKnownType();
            if (!child_type.hasBits()) {
                return null;
            }
            const ptr = self.params.target.llvm_value.?;
            const ptr_type = self.params.target.getKnownType().cast(Type.Pointer).?;

            return try codegen.getHandleValue(ofile, ptr, ptr_type);

            //uint32_t unaligned_bit_count = ptr_type->data.pointer.unaligned_bit_count;
            //if (unaligned_bit_count == 0)
            //    return get_handle_value(g, ptr, child_type, ptr_type);

            //bool big_endian = g->is_big_endian;

            //assert(!handle_is_ptr(child_type));
            //LLVMValueRef containing_int = gen_load(g, ptr, ptr_type, "");

            //uint32_t bit_offset = ptr_type->data.pointer.bit_offset;
            //uint32_t host_bit_count = LLVMGetIntTypeWidth(LLVMTypeOf(containing_int));
            //uint32_t shift_amt = big_endian ? host_bit_count - bit_offset - unaligned_bit_count : bit_offset;

            //LLVMValueRef shift_amt_val = LLVMConstInt(LLVMTypeOf(containing_int), shift_amt, false);
            //LLVMValueRef shifted_value = LLVMBuildLShr(g->builder, containing_int, shift_amt_val, "");

            //return LLVMBuildTrunc(g->builder, shifted_value, child_type->type_ref, "");
        }
    };

    pub const PtrType = struct {
        base: Inst,
        params: Params,

        const Params = struct {
            child_type: *Inst,
            mut: Type.Pointer.Mut,
            vol: Type.Pointer.Vol,
            size: Type.Pointer.Size,
            alignment: ?*Inst,
        };

        const ir_val_init = IrVal.Init.Unknown;

        pub fn dump(inst: *const PtrType) void {}

        pub fn hasSideEffects(inst: *const PtrType) bool {
            return false;
        }

        pub async fn analyze(self: *const PtrType, ira: *Analyze) !*Inst {
            const child_type = try self.params.child_type.getAsConstType(ira);
            // if (child_type->id == TypeTableEntryIdUnreachable) {
            //     ir_add_error(ira, &instruction->base, buf_sprintf("pointer to noreturn not allowed"));
            //     return ira->codegen->builtin_types.entry_invalid;
            // } else if (child_type->id == TypeTableEntryIdOpaque && instruction->ptr_len == PtrLenUnknown) {
            //     ir_add_error(ira, &instruction->base, buf_sprintf("unknown-length pointer to opaque"));
            //     return ira->codegen->builtin_types.entry_invalid;
            // }
            const alignment = if (self.params.alignment) |align_inst| blk: {
                const amt = try align_inst.getAsConstAlign(ira);
                break :blk Type.Pointer.Align{ .Override = amt };
            } else blk: {
                break :blk Type.Pointer.Align{ .Abi = {} };
            };
            const ptr_type = try await (async Type.Pointer.get(ira.irb.comp, Type.Pointer.Key{
                .child_type = child_type,
                .mut = self.params.mut,
                .vol = self.params.vol,
                .size = self.params.size,
                .alignment = alignment,
            }) catch unreachable);
            ptr_type.base.base.deref(ira.irb.comp);

            return ira.irb.buildConstValue(self.base.scope, self.base.span, &ptr_type.base.base);
        }
    };

    pub const DeclVar = struct {
        base: Inst,
        params: Params,

        const Params = struct {
            variable: *Variable,
        };

        const ir_val_init = IrVal.Init.Unknown;

        pub fn dump(inst: *const DeclVar) void {}

        pub fn hasSideEffects(inst: *const DeclVar) bool {
            return true;
        }

        pub fn analyze(self: *const DeclVar, ira: *Analyze) !*Inst {
            return error.Unimplemented; // TODO
        }
    };

    pub const CheckVoidStmt = struct {
        base: Inst,
        params: Params,

        const Params = struct {
            target: *Inst,
        };

        const ir_val_init = IrVal.Init.Unknown;

        pub fn dump(self: *const CheckVoidStmt) void {
            std.debug.warn("#{}", self.params.target.debug_id);
        }

        pub fn hasSideEffects(inst: *const CheckVoidStmt) bool {
            return true;
        }

        pub fn analyze(self: *const CheckVoidStmt, ira: *Analyze) !*Inst {
            const target = try self.params.target.getAsParam();
            if (target.getKnownType().id != Type.Id.Void) {
                try ira.addCompileError(self.base.span, "expression value is ignored");
                return error.SemanticAnalysisFailed;
            }
            return ira.irb.buildConstVoid(self.base.scope, self.base.span, true);
        }
    };

    pub const Phi = struct {
        base: Inst,
        params: Params,

        const Params = struct {
            incoming_blocks: []*BasicBlock,
            incoming_values: []*Inst,
        };

        const ir_val_init = IrVal.Init.Unknown;

        pub fn dump(inst: *const Phi) void {}

        pub fn hasSideEffects(inst: *const Phi) bool {
            return false;
        }

        pub fn analyze(self: *const Phi, ira: *Analyze) !*Inst {
            return error.Unimplemented; // TODO
        }
    };

    pub const Br = struct {
        base: Inst,
        params: Params,

        const Params = struct {
            dest_block: *BasicBlock,
            is_comptime: *Inst,
        };

        const ir_val_init = IrVal.Init.NoReturn;

        pub fn dump(inst: *const Br) void {}

        pub fn hasSideEffects(inst: *const Br) bool {
            return true;
        }

        pub fn analyze(self: *const Br, ira: *Analyze) !*Inst {
            return error.Unimplemented; // TODO
        }
    };

    pub const CondBr = struct {
        base: Inst,
        params: Params,

        const Params = struct {
            condition: *Inst,
            then_block: *BasicBlock,
            else_block: *BasicBlock,
            is_comptime: *Inst,
        };

        const ir_val_init = IrVal.Init.NoReturn;

        pub fn dump(inst: *const CondBr) void {}

        pub fn hasSideEffects(inst: *const CondBr) bool {
            return true;
        }

        pub fn analyze(self: *const CondBr, ira: *Analyze) !*Inst {
            return error.Unimplemented; // TODO
        }
    };

    pub const AddImplicitReturnType = struct {
        base: Inst,
        params: Params,

        pub const Params = struct {
            target: *Inst,
        };

        const ir_val_init = IrVal.Init.Unknown;

        pub fn dump(inst: *const AddImplicitReturnType) void {
            std.debug.warn("#{}", inst.params.target.debug_id);
        }

        pub fn hasSideEffects(inst: *const AddImplicitReturnType) bool {
            return true;
        }

        pub fn analyze(self: *const AddImplicitReturnType, ira: *Analyze) !*Inst {
            const target = try self.params.target.getAsParam();
            try ira.src_implicit_return_type_list.append(target);
            return ira.irb.buildConstVoid(self.base.scope, self.base.span, true);
        }
    };

    pub const TestErr = struct {
        base: Inst,
        params: Params,

        pub const Params = struct {
            target: *Inst,
        };

        const ir_val_init = IrVal.Init.Unknown;

        pub fn dump(inst: *const TestErr) void {
            std.debug.warn("#{}", inst.params.target.debug_id);
        }

        pub fn hasSideEffects(inst: *const TestErr) bool {
            return false;
        }

        pub fn analyze(self: *const TestErr, ira: *Analyze) !*Inst {
            const target = try self.params.target.getAsParam();
            const target_type = target.getKnownType();
            switch (target_type.id) {
                Type.Id.ErrorUnion => {
                    return error.Unimplemented;
                    //    if (instr_is_comptime(value)) {
                    //        ConstExprValue *err_union_val = ir_resolve_const(ira, value, UndefBad);
                    //        if (!err_union_val)
                    //            return ira->codegen->builtin_types.entry_invalid;

                    //        if (err_union_val->special != ConstValSpecialRuntime) {
                    //            ConstExprValue *out_val = ir_build_const_from(ira, &instruction->base);
                    //            out_val->data.x_bool = (err_union_val->data.x_err_union.err != nullptr);
                    //            return ira->codegen->builtin_types.entry_bool;
                    //        }
                    //    }

                    //    TypeTableEntry *err_set_type = type_entry->data.error_union.err_set_type;
                    //    if (!resolve_inferred_error_set(ira->codegen, err_set_type, instruction->base.source_node)) {
                    //        return ira->codegen->builtin_types.entry_invalid;
                    //    }
                    //    if (!type_is_global_error_set(err_set_type) &&
                    //        err_set_type->data.error_set.err_count == 0)
                    //    {
                    //        assert(err_set_type->data.error_set.infer_fn == nullptr);
                    //        ConstExprValue *out_val = ir_build_const_from(ira, &instruction->base);
                    //        out_val->data.x_bool = false;
                    //        return ira->codegen->builtin_types.entry_bool;
                    //    }

                    //    ir_build_test_err_from(&ira->new_irb, &instruction->base, value);
                    //    return ira->codegen->builtin_types.entry_bool;
                },
                Type.Id.ErrorSet => {
                    return ira.irb.buildConstBool(self.base.scope, self.base.span, true);
                },
                else => {
                    return ira.irb.buildConstBool(self.base.scope, self.base.span, false);
                },
            }
        }
    };

    pub const TestCompTime = struct {
        base: Inst,
        params: Params,

        pub const Params = struct {
            target: *Inst,
        };

        const ir_val_init = IrVal.Init.Unknown;

        pub fn dump(inst: *const TestCompTime) void {
            std.debug.warn("#{}", inst.params.target.debug_id);
        }

        pub fn hasSideEffects(inst: *const TestCompTime) bool {
            return false;
        }

        pub fn analyze(self: *const TestCompTime, ira: *Analyze) !*Inst {
            const target = try self.params.target.getAsParam();
            return ira.irb.buildConstBool(self.base.scope, self.base.span, target.isCompTime());
        }
    };

    pub const SaveErrRetAddr = struct {
        base: Inst,
        params: Params,

        const Params = struct {};

        const ir_val_init = IrVal.Init.Unknown;

        pub fn dump(inst: *const SaveErrRetAddr) void {}

        pub fn hasSideEffects(inst: *const SaveErrRetAddr) bool {
            return true;
        }

        pub fn analyze(self: *const SaveErrRetAddr, ira: *Analyze) !*Inst {
            return ira.irb.build(Inst.SaveErrRetAddr, self.base.scope, self.base.span, Params{});
        }
    };
};

pub const Variable = struct {
    child_scope: *Scope,
};

pub const BasicBlock = struct {
    ref_count: usize,
    name_hint: [*]const u8, // must be a C string literal
    debug_id: usize,
    scope: *Scope,
    instruction_list: std.ArrayList(*Inst),
    ref_instruction: ?*Inst,

    /// for codegen
    llvm_block: *llvm.BasicBlock,
    llvm_exit_block: *llvm.BasicBlock,

    /// the basic block that is derived from this one in analysis
    child: ?*BasicBlock,

    /// the basic block that this one derives from in analysis
    parent: ?*BasicBlock,

    pub fn ref(self: *BasicBlock, builder: *Builder) void {
        self.ref_count += 1;
    }

    pub fn linkToParent(self: *BasicBlock, parent: *BasicBlock) void {
        assert(self.parent == null);
        assert(parent.child == null);
        self.parent = parent;
        parent.child = self;
    }
};

/// Stuff that survives longer than Builder
pub const Code = struct {
    basic_block_list: std.ArrayList(*BasicBlock),
    arena: std.heap.ArenaAllocator,
    return_type: ?*Type,
    tree_scope: *Scope.AstTree,

    /// allocator is comp.gpa()
    pub fn destroy(self: *Code, allocator: *Allocator) void {
        self.arena.deinit();
        allocator.destroy(self);
    }

    pub fn dump(self: *Code) void {
        var bb_i: usize = 0;
        for (self.basic_block_list.toSliceConst()) |bb| {
            std.debug.warn("{s}_{}:\n", bb.name_hint, bb.debug_id);
            for (bb.instruction_list.toSliceConst()) |instr| {
                std.debug.warn("  ");
                instr.dump();
                std.debug.warn("\n");
            }
        }
    }

    /// returns a ref-incremented value, or adds a compile error
    pub fn getCompTimeResult(self: *Code, comp: *Compilation) !*Value {
        const bb = self.basic_block_list.at(0);
        for (bb.instruction_list.toSliceConst()) |inst| {
            if (inst.cast(Inst.Return)) |ret_inst| {
                const ret_value = ret_inst.params.return_value;
                if (ret_value.isCompTime()) {
                    return ret_value.val.KnownValue.getRef();
                }
                try comp.addCompileError(
                    self.tree_scope,
                    ret_value.span,
                    "unable to evaluate constant expression",
                );
                return error.SemanticAnalysisFailed;
            } else if (inst.hasSideEffects()) {
                try comp.addCompileError(
                    self.tree_scope,
                    inst.span,
                    "unable to evaluate constant expression",
                );
                return error.SemanticAnalysisFailed;
            }
        }
        unreachable;
    }
};

pub const Builder = struct {
    comp: *Compilation,
    code: *Code,
    current_basic_block: *BasicBlock,
    next_debug_id: usize,
    is_comptime: bool,
    is_async: bool,
    begin_scope: ?*Scope,

    pub const Error = Analyze.Error;

    pub fn init(comp: *Compilation, tree_scope: *Scope.AstTree, begin_scope: ?*Scope) !Builder {
        const code = try comp.gpa().create(Code);
        code.* = Code{
            .basic_block_list = undefined,
            .arena = std.heap.ArenaAllocator.init(comp.gpa()),
            .return_type = null,
            .tree_scope = tree_scope,
        };
        code.basic_block_list = std.ArrayList(*BasicBlock).init(&code.arena.allocator);
        errdefer code.destroy(comp.gpa());

        return Builder{
            .comp = comp,
            .current_basic_block = undefined,
            .code = code,
            .next_debug_id = 0,
            .is_comptime = false,
            .is_async = false,
            .begin_scope = begin_scope,
        };
    }

    pub fn abort(self: *Builder) void {
        self.code.destroy(self.comp.gpa());
    }

    /// Call code.destroy() when done
    pub fn finish(self: *Builder) *Code {
        return self.code;
    }

    /// No need to clean up resources thanks to the arena allocator.
    pub fn createBasicBlock(self: *Builder, scope: *Scope, name_hint: [*]const u8) !*BasicBlock {
        const basic_block = try self.arena().create(BasicBlock);
        basic_block.* = BasicBlock{
            .ref_count = 0,
            .name_hint = name_hint,
            .debug_id = self.next_debug_id,
            .scope = scope,
            .instruction_list = std.ArrayList(*Inst).init(self.arena()),
            .child = null,
            .parent = null,
            .ref_instruction = null,
            .llvm_block = undefined,
            .llvm_exit_block = undefined,
        };
        self.next_debug_id += 1;
        return basic_block;
    }

    pub fn setCursorAtEndAndAppendBlock(self: *Builder, basic_block: *BasicBlock) !void {
        try self.code.basic_block_list.append(basic_block);
        self.setCursorAtEnd(basic_block);
    }

    pub fn setCursorAtEnd(self: *Builder, basic_block: *BasicBlock) void {
        self.current_basic_block = basic_block;
    }

    pub async fn genNode(irb: *Builder, node: *ast.Node, scope: *Scope, lval: LVal) Error!*Inst {
        switch (node.id) {
            ast.Node.Id.Root => unreachable,
            ast.Node.Id.Use => unreachable,
            ast.Node.Id.TestDecl => unreachable,
            ast.Node.Id.VarDecl => return error.Unimplemented,
            ast.Node.Id.Defer => return error.Unimplemented,
            ast.Node.Id.InfixOp => return error.Unimplemented,
            ast.Node.Id.PrefixOp => {
                const prefix_op = @fieldParentPtr(ast.Node.PrefixOp, "base", node);
                switch (prefix_op.op) {
                    ast.Node.PrefixOp.Op.AddressOf => return error.Unimplemented,
                    ast.Node.PrefixOp.Op.ArrayType => |n| return error.Unimplemented,
                    ast.Node.PrefixOp.Op.Await => return error.Unimplemented,
                    ast.Node.PrefixOp.Op.BitNot => return error.Unimplemented,
                    ast.Node.PrefixOp.Op.BoolNot => return error.Unimplemented,
                    ast.Node.PrefixOp.Op.Cancel => return error.Unimplemented,
                    ast.Node.PrefixOp.Op.OptionalType => return error.Unimplemented,
                    ast.Node.PrefixOp.Op.Negation => return error.Unimplemented,
                    ast.Node.PrefixOp.Op.NegationWrap => return error.Unimplemented,
                    ast.Node.PrefixOp.Op.Resume => return error.Unimplemented,
                    ast.Node.PrefixOp.Op.PtrType => |ptr_info| {
                        const inst = try await (async irb.genPtrType(prefix_op, ptr_info, scope) catch unreachable);
                        return irb.lvalWrap(scope, inst, lval);
                    },
                    ast.Node.PrefixOp.Op.SliceType => |ptr_info| return error.Unimplemented,
                    ast.Node.PrefixOp.Op.Try => return error.Unimplemented,
                }
            },
            ast.Node.Id.SuffixOp => {
                const suffix_op = @fieldParentPtr(ast.Node.SuffixOp, "base", node);
                switch (suffix_op.op) {
                    @TagType(ast.Node.SuffixOp.Op).Call => |*call| {
                        const inst = try await (async irb.genCall(suffix_op, call, scope) catch unreachable);
                        return irb.lvalWrap(scope, inst, lval);
                    },
                    @TagType(ast.Node.SuffixOp.Op).ArrayAccess => |n| return error.Unimplemented,
                    @TagType(ast.Node.SuffixOp.Op).Slice => |slice| return error.Unimplemented,
                    @TagType(ast.Node.SuffixOp.Op).ArrayInitializer => |init_list| return error.Unimplemented,
                    @TagType(ast.Node.SuffixOp.Op).StructInitializer => |init_list| return error.Unimplemented,
                    @TagType(ast.Node.SuffixOp.Op).Deref => return error.Unimplemented,
                    @TagType(ast.Node.SuffixOp.Op).UnwrapOptional => return error.Unimplemented,
                }
            },
            ast.Node.Id.Switch => return error.Unimplemented,
            ast.Node.Id.While => return error.Unimplemented,
            ast.Node.Id.For => return error.Unimplemented,
            ast.Node.Id.If => return error.Unimplemented,
            ast.Node.Id.ControlFlowExpression => {
                const control_flow_expr = @fieldParentPtr(ast.Node.ControlFlowExpression, "base", node);
                return await (async irb.genControlFlowExpr(control_flow_expr, scope, lval) catch unreachable);
            },
            ast.Node.Id.Suspend => return error.Unimplemented,
            ast.Node.Id.VarType => return error.Unimplemented,
            ast.Node.Id.ErrorType => return error.Unimplemented,
            ast.Node.Id.FnProto => return error.Unimplemented,
            ast.Node.Id.PromiseType => return error.Unimplemented,
            ast.Node.Id.IntegerLiteral => {
                const int_lit = @fieldParentPtr(ast.Node.IntegerLiteral, "base", node);
                return irb.lvalWrap(scope, try irb.genIntLit(int_lit, scope), lval);
            },
            ast.Node.Id.FloatLiteral => return error.Unimplemented,
            ast.Node.Id.StringLiteral => {
                const str_lit = @fieldParentPtr(ast.Node.StringLiteral, "base", node);
                const inst = try await (async irb.genStrLit(str_lit, scope) catch unreachable);
                return irb.lvalWrap(scope, inst, lval);
            },
            ast.Node.Id.MultilineStringLiteral => return error.Unimplemented,
            ast.Node.Id.CharLiteral => return error.Unimplemented,
            ast.Node.Id.BoolLiteral => return error.Unimplemented,
            ast.Node.Id.NullLiteral => return error.Unimplemented,
            ast.Node.Id.UndefinedLiteral => return error.Unimplemented,
            ast.Node.Id.Unreachable => return error.Unimplemented,
            ast.Node.Id.Identifier => {
                const identifier = @fieldParentPtr(ast.Node.Identifier, "base", node);
                return await (async irb.genIdentifier(identifier, scope, lval) catch unreachable);
            },
            ast.Node.Id.GroupedExpression => {
                const grouped_expr = @fieldParentPtr(ast.Node.GroupedExpression, "base", node);
                return await (async irb.genNode(grouped_expr.expr, scope, lval) catch unreachable);
            },
            ast.Node.Id.BuiltinCall => return error.Unimplemented,
            ast.Node.Id.ErrorSetDecl => return error.Unimplemented,
            ast.Node.Id.ContainerDecl => return error.Unimplemented,
            ast.Node.Id.Asm => return error.Unimplemented,
            ast.Node.Id.Comptime => return error.Unimplemented,
            ast.Node.Id.Block => {
                const block = @fieldParentPtr(ast.Node.Block, "base", node);
                const inst = try await (async irb.genBlock(block, scope) catch unreachable);
                return irb.lvalWrap(scope, inst, lval);
            },
            ast.Node.Id.DocComment => return error.Unimplemented,
            ast.Node.Id.SwitchCase => return error.Unimplemented,
            ast.Node.Id.SwitchElse => return error.Unimplemented,
            ast.Node.Id.Else => return error.Unimplemented,
            ast.Node.Id.Payload => return error.Unimplemented,
            ast.Node.Id.PointerPayload => return error.Unimplemented,
            ast.Node.Id.PointerIndexPayload => return error.Unimplemented,
            ast.Node.Id.ContainerField => return error.Unimplemented,
            ast.Node.Id.ErrorTag => return error.Unimplemented,
            ast.Node.Id.AsmInput => return error.Unimplemented,
            ast.Node.Id.AsmOutput => return error.Unimplemented,
            ast.Node.Id.ParamDecl => return error.Unimplemented,
            ast.Node.Id.FieldInitializer => return error.Unimplemented,
            ast.Node.Id.EnumLiteral => return error.Unimplemented,
        }
    }

    async fn genCall(irb: *Builder, suffix_op: *ast.Node.SuffixOp, call: *ast.Node.SuffixOp.Op.Call, scope: *Scope) !*Inst {
        const fn_ref = try await (async irb.genNode(suffix_op.lhs, scope, LVal.None) catch unreachable);

        const args = try irb.arena().alloc(*Inst, call.params.len);
        var it = call.params.iterator(0);
        var i: usize = 0;
        while (it.next()) |arg_node_ptr| : (i += 1) {
            args[i] = try await (async irb.genNode(arg_node_ptr.*, scope, LVal.None) catch unreachable);
        }

        //bool is_async = node->data.fn_call_expr.is_async;
        //IrInstruction *async_allocator = nullptr;
        //if (is_async) {
        //    if (node->data.fn_call_expr.async_allocator) {
        //        async_allocator = ir_gen_node(irb, node->data.fn_call_expr.async_allocator, scope);
        //        if (async_allocator == irb->codegen->invalid_instruction)
        //            return async_allocator;
        //    }
        //}

        return irb.build(Inst.Call, scope, Span.token(suffix_op.rtoken), Inst.Call.Params{
            .fn_ref = fn_ref,
            .args = args,
        });
        //IrInstruction *fn_call = ir_build_call(irb, scope, node, nullptr, fn_ref, arg_count, args, false, FnInlineAuto, is_async, async_allocator, nullptr);
        //return ir_lval_wrap(irb, scope, fn_call, lval);
    }

    async fn genPtrType(
        irb: *Builder,
        prefix_op: *ast.Node.PrefixOp,
        ptr_info: ast.Node.PrefixOp.PtrInfo,
        scope: *Scope,
    ) !*Inst {
        // TODO port more logic

        //assert(node->type == NodeTypePointerType);
        //PtrLen ptr_len = (node->data.pointer_type.star_token->id == TokenIdStar ||
        //        node->data.pointer_type.star_token->id == TokenIdStarStar) ? PtrLenSingle : PtrLenUnknown;
        //bool is_const = node->data.pointer_type.is_const;
        //bool is_volatile = node->data.pointer_type.is_volatile;
        //AstNode *expr_node = node->data.pointer_type.op_expr;
        //AstNode *align_expr = node->data.pointer_type.align_expr;

        //IrInstruction *align_value;
        //if (align_expr != nullptr) {
        //    align_value = ir_gen_node(irb, align_expr, scope);
        //    if (align_value == irb->codegen->invalid_instruction)
        //        return align_value;
        //} else {
        //    align_value = nullptr;
        //}
        const child_type = try await (async irb.genNode(prefix_op.rhs, scope, LVal.None) catch unreachable);

        //uint32_t bit_offset_start = 0;
        //if (node->data.pointer_type.bit_offset_start != nullptr) {
        //    if (!bigint_fits_in_bits(node->data.pointer_type.bit_offset_start, 32, false)) {
        //        Buf *val_buf = buf_alloc();
        //        bigint_append_buf(val_buf, node->data.pointer_type.bit_offset_start, 10);
        //        exec_add_error_node(irb->codegen, irb->exec, node,
        //                buf_sprintf("value %s too large for u32 bit offset", buf_ptr(val_buf)));
        //        return irb->codegen->invalid_instruction;
        //    }
        //    bit_offset_start = bigint_as_unsigned(node->data.pointer_type.bit_offset_start);
        //}

        //uint32_t bit_offset_end = 0;
        //if (node->data.pointer_type.bit_offset_end != nullptr) {
        //    if (!bigint_fits_in_bits(node->data.pointer_type.bit_offset_end, 32, false)) {
        //        Buf *val_buf = buf_alloc();
        //        bigint_append_buf(val_buf, node->data.pointer_type.bit_offset_end, 10);
        //        exec_add_error_node(irb->codegen, irb->exec, node,
        //                buf_sprintf("value %s too large for u32 bit offset", buf_ptr(val_buf)));
        //        return irb->codegen->invalid_instruction;
        //    }
        //    bit_offset_end = bigint_as_unsigned(node->data.pointer_type.bit_offset_end);
        //}

        //if ((bit_offset_start != 0 || bit_offset_end != 0) && bit_offset_start >= bit_offset_end) {
        //    exec_add_error_node(irb->codegen, irb->exec, node,
        //            buf_sprintf("bit offset start must be less than bit offset end"));
        //    return irb->codegen->invalid_instruction;
        //}

        return irb.build(Inst.PtrType, scope, Span.node(&prefix_op.base), Inst.PtrType.Params{
            .child_type = child_type,
            .mut = Type.Pointer.Mut.Mut,
            .vol = Type.Pointer.Vol.Non,
            .size = Type.Pointer.Size.Many,
            .alignment = null,
        });
    }

    fn isCompTime(irb: *Builder, target_scope: *Scope) bool {
        if (irb.is_comptime)
            return true;

        var scope = target_scope;
        while (true) {
            switch (scope.id) {
                Scope.Id.CompTime => return true,
                Scope.Id.FnDef => return false,
                Scope.Id.Decls => unreachable,
                Scope.Id.Root => unreachable,
                Scope.Id.AstTree => unreachable,
                Scope.Id.Block,
                Scope.Id.Defer,
                Scope.Id.DeferExpr,
                Scope.Id.Var,
                => scope = scope.parent.?,
            }
        }
    }

    pub fn genIntLit(irb: *Builder, int_lit: *ast.Node.IntegerLiteral, scope: *Scope) !*Inst {
        const int_token = irb.code.tree_scope.tree.tokenSlice(int_lit.token);

        var base: u8 = undefined;
        var rest: []const u8 = undefined;
        if (int_token.len >= 3 and int_token[0] == '0') {
            base = switch (int_token[1]) {
                'b' => u8(2),
                'o' => u8(8),
                'x' => u8(16),
                else => unreachable,
            };
            rest = int_token[2..];
        } else {
            base = 10;
            rest = int_token;
        }

        const comptime_int_type = Type.ComptimeInt.get(irb.comp);
        defer comptime_int_type.base.base.deref(irb.comp);

        const int_val = Value.Int.createFromString(
            irb.comp,
            &comptime_int_type.base,
            base,
            rest,
        ) catch |err| switch (err) {
            error.OutOfMemory => return error.OutOfMemory,
            error.InvalidBase => unreachable,
            error.InvalidCharForDigit => unreachable,
            error.DigitTooLargeForBase => unreachable,
        };
        errdefer int_val.base.deref(irb.comp);

        const inst = try irb.build(Inst.Const, scope, Span.token(int_lit.token), Inst.Const.Params{});
        inst.val = IrVal{ .KnownValue = &int_val.base };
        return inst;
    }

    pub async fn genStrLit(irb: *Builder, str_lit: *ast.Node.StringLiteral, scope: *Scope) !*Inst {
        const str_token = irb.code.tree_scope.tree.tokenSlice(str_lit.token);
        const src_span = Span.token(str_lit.token);

        var bad_index: usize = undefined;
        var buf = std.zig.parseStringLiteral(irb.comp.gpa(), str_token, &bad_index) catch |err| switch (err) {
            error.OutOfMemory => return error.OutOfMemory,
            error.InvalidCharacter => {
                try irb.comp.addCompileError(
                    irb.code.tree_scope,
                    src_span,
                    "invalid character in string literal: '{c}'",
                    str_token[bad_index],
                );
                return error.SemanticAnalysisFailed;
            },
        };
        var buf_cleaned = false;
        errdefer if (!buf_cleaned) irb.comp.gpa().free(buf);

        if (str_token[0] == 'c') {
            // first we add a null
            buf = try irb.comp.gpa().realloc(buf, buf.len + 1);
            buf[buf.len - 1] = 0;

            // next make an array value
            const array_val = try await (async Value.Array.createOwnedBuffer(irb.comp, buf) catch unreachable);
            buf_cleaned = true;
            defer array_val.base.deref(irb.comp);

            // then make a pointer value pointing at the first element
            const ptr_val = try await (async Value.Ptr.createArrayElemPtr(
                irb.comp,
                array_val,
                Type.Pointer.Mut.Const,
                Type.Pointer.Size.Many,
                0,
            ) catch unreachable);
            defer ptr_val.base.deref(irb.comp);

            return irb.buildConstValue(scope, src_span, &ptr_val.base);
        } else {
            const array_val = try await (async Value.Array.createOwnedBuffer(irb.comp, buf) catch unreachable);
            buf_cleaned = true;
            defer array_val.base.deref(irb.comp);

            return irb.buildConstValue(scope, src_span, &array_val.base);
        }
    }

    pub async fn genBlock(irb: *Builder, block: *ast.Node.Block, parent_scope: *Scope) !*Inst {
        const block_scope = try Scope.Block.create(irb.comp, parent_scope);

        const outer_block_scope = &block_scope.base;
        var child_scope = outer_block_scope;

        if (parent_scope.findFnDef()) |fndef_scope| {
            if (fndef_scope.fn_val.?.block_scope == null) {
                fndef_scope.fn_val.?.block_scope = block_scope;
            }
        }

        if (block.statements.len == 0) {
            // {}
            return irb.buildConstVoid(child_scope, Span.token(block.lbrace), false);
        }

        if (block.label) |label| {
            block_scope.incoming_values = std.ArrayList(*Inst).init(irb.arena());
            block_scope.incoming_blocks = std.ArrayList(*BasicBlock).init(irb.arena());
            block_scope.end_block = try irb.createBasicBlock(parent_scope, "BlockEnd");
            block_scope.is_comptime = try irb.buildConstBool(
                parent_scope,
                Span.token(block.lbrace),
                irb.isCompTime(parent_scope),
            );
        }

        var is_continuation_unreachable = false;
        var noreturn_return_value: ?*Inst = null;

        var stmt_it = block.statements.iterator(0);
        while (stmt_it.next()) |statement_node_ptr| {
            const statement_node = statement_node_ptr.*;

            if (statement_node.cast(ast.Node.Defer)) |defer_node| {
                // defer starts a new scope
                const defer_token = irb.code.tree_scope.tree.tokens.at(defer_node.defer_token);
                const kind = switch (defer_token.id) {
                    Token.Id.Keyword_defer => Scope.Defer.Kind.ScopeExit,
                    Token.Id.Keyword_errdefer => Scope.Defer.Kind.ErrorExit,
                    else => unreachable,
                };
                const defer_expr_scope = try Scope.DeferExpr.create(irb.comp, parent_scope, defer_node.expr);
                const defer_child_scope = try Scope.Defer.create(irb.comp, parent_scope, kind, defer_expr_scope);
                child_scope = &defer_child_scope.base;
                continue;
            }
            const statement_value = try await (async irb.genNode(statement_node, child_scope, LVal.None) catch unreachable);

            is_continuation_unreachable = statement_value.isNoReturn();
            if (is_continuation_unreachable) {
                // keep the last noreturn statement value around in case we need to return it
                noreturn_return_value = statement_value;
            }

            if (statement_value.cast(Inst.DeclVar)) |decl_var| {
                // variable declarations start a new scope
                child_scope = decl_var.params.variable.child_scope;
            } else if (!is_continuation_unreachable) {
                // this statement's value must be void
                _ = try irb.build(
                    Inst.CheckVoidStmt,
                    child_scope,
                    Span{
                        .first = statement_node.firstToken(),
                        .last = statement_node.lastToken(),
                    },
                    Inst.CheckVoidStmt.Params{ .target = statement_value },
                );
            }
        }

        if (is_continuation_unreachable) {
            assert(noreturn_return_value != null);
            if (block.label == null or block_scope.incoming_blocks.len == 0) {
                return noreturn_return_value.?;
            }

            try irb.setCursorAtEndAndAppendBlock(block_scope.end_block);
            return irb.build(Inst.Phi, parent_scope, Span.token(block.rbrace), Inst.Phi.Params{
                .incoming_blocks = block_scope.incoming_blocks.toOwnedSlice(),
                .incoming_values = block_scope.incoming_values.toOwnedSlice(),
            });
        }

        if (block.label) |label| {
            try block_scope.incoming_blocks.append(irb.current_basic_block);
            try block_scope.incoming_values.append(
                try irb.buildConstVoid(parent_scope, Span.token(block.rbrace), true),
            );
            _ = try await (async irb.genDefersForBlock(child_scope, outer_block_scope, Scope.Defer.Kind.ScopeExit) catch unreachable);

            _ = try irb.buildGen(Inst.Br, parent_scope, Span.token(block.rbrace), Inst.Br.Params{
                .dest_block = block_scope.end_block,
                .is_comptime = block_scope.is_comptime,
            });

            try irb.setCursorAtEndAndAppendBlock(block_scope.end_block);

            return irb.build(Inst.Phi, parent_scope, Span.token(block.rbrace), Inst.Phi.Params{
                .incoming_blocks = block_scope.incoming_blocks.toOwnedSlice(),
                .incoming_values = block_scope.incoming_values.toOwnedSlice(),
            });
        }

        _ = try await (async irb.genDefersForBlock(child_scope, outer_block_scope, Scope.Defer.Kind.ScopeExit) catch unreachable);
        return irb.buildConstVoid(child_scope, Span.token(block.rbrace), true);
    }

    pub async fn genControlFlowExpr(
        irb: *Builder,
        control_flow_expr: *ast.Node.ControlFlowExpression,
        scope: *Scope,
        lval: LVal,
    ) !*Inst {
        switch (control_flow_expr.kind) {
            ast.Node.ControlFlowExpression.Kind.Break => |arg| return error.Unimplemented,
            ast.Node.ControlFlowExpression.Kind.Continue => |arg| return error.Unimplemented,
            ast.Node.ControlFlowExpression.Kind.Return => {
                const src_span = Span.token(control_flow_expr.ltoken);
                if (scope.findFnDef() == null) {
                    try irb.comp.addCompileError(
                        irb.code.tree_scope,
                        src_span,
                        "return expression outside function definition",
                    );
                    return error.SemanticAnalysisFailed;
                }

                if (scope.findDeferExpr()) |scope_defer_expr| {
                    if (!scope_defer_expr.reported_err) {
                        try irb.comp.addCompileError(
                            irb.code.tree_scope,
                            src_span,
                            "cannot return from defer expression",
                        );
                        scope_defer_expr.reported_err = true;
                    }
                    return error.SemanticAnalysisFailed;
                }

                const outer_scope = irb.begin_scope.?;
                const return_value = if (control_flow_expr.rhs) |rhs| blk: {
                    break :blk try await (async irb.genNode(rhs, scope, LVal.None) catch unreachable);
                } else blk: {
                    break :blk try irb.buildConstVoid(scope, src_span, true);
                };

                const defer_counts = irb.countDefers(scope, outer_scope);
                const have_err_defers = defer_counts.error_exit != 0;
                if (have_err_defers or irb.comp.have_err_ret_tracing) {
                    const err_block = try irb.createBasicBlock(scope, "ErrRetErr");
                    const ok_block = try irb.createBasicBlock(scope, "ErrRetOk");
                    if (!have_err_defers) {
                        _ = try await (async irb.genDefersForBlock(scope, outer_scope, Scope.Defer.Kind.ScopeExit) catch unreachable);
                    }

                    const is_err = try irb.build(
                        Inst.TestErr,
                        scope,
                        src_span,
                        Inst.TestErr.Params{ .target = return_value },
                    );

                    const err_is_comptime = try irb.buildTestCompTime(scope, src_span, is_err);

                    _ = try irb.buildGen(Inst.CondBr, scope, src_span, Inst.CondBr.Params{
                        .condition = is_err,
                        .then_block = err_block,
                        .else_block = ok_block,
                        .is_comptime = err_is_comptime,
                    });

                    const ret_stmt_block = try irb.createBasicBlock(scope, "RetStmt");

                    try irb.setCursorAtEndAndAppendBlock(err_block);
                    if (have_err_defers) {
                        _ = try await (async irb.genDefersForBlock(scope, outer_scope, Scope.Defer.Kind.ErrorExit) catch unreachable);
                    }
                    if (irb.comp.have_err_ret_tracing and !irb.isCompTime(scope)) {
                        _ = try irb.build(Inst.SaveErrRetAddr, scope, src_span, Inst.SaveErrRetAddr.Params{});
                    }
                    _ = try irb.build(Inst.Br, scope, src_span, Inst.Br.Params{
                        .dest_block = ret_stmt_block,
                        .is_comptime = err_is_comptime,
                    });

                    try irb.setCursorAtEndAndAppendBlock(ok_block);
                    if (have_err_defers) {
                        _ = try await (async irb.genDefersForBlock(scope, outer_scope, Scope.Defer.Kind.ScopeExit) catch unreachable);
                    }
                    _ = try irb.build(Inst.Br, scope, src_span, Inst.Br.Params{
                        .dest_block = ret_stmt_block,
                        .is_comptime = err_is_comptime,
                    });

                    try irb.setCursorAtEndAndAppendBlock(ret_stmt_block);
                    return irb.genAsyncReturn(scope, src_span, return_value, false);
                } else {
                    _ = try await (async irb.genDefersForBlock(scope, outer_scope, Scope.Defer.Kind.ScopeExit) catch unreachable);
                    return irb.genAsyncReturn(scope, src_span, return_value, false);
                }
            },
        }
    }

    pub async fn genIdentifier(irb: *Builder, identifier: *ast.Node.Identifier, scope: *Scope, lval: LVal) !*Inst {
        const src_span = Span.token(identifier.token);
        const name = irb.code.tree_scope.tree.tokenSlice(identifier.token);

        //if (buf_eql_str(variable_name, "_") && lval == LValPtr) {
        //    IrInstructionConst *const_instruction = ir_build_instruction<IrInstructionConst>(irb, scope, node);
        //    const_instruction->base.value.type = get_pointer_to_type(irb->codegen,
        //            irb->codegen->builtin_types.entry_void, false);
        //    const_instruction->base.value.special = ConstValSpecialStatic;
        //    const_instruction->base.value.data.x_ptr.special = ConstPtrSpecialDiscard;
        //    return &const_instruction->base;
        //}

        if (await (async irb.comp.getPrimitiveType(name) catch unreachable)) |result| {
            if (result) |primitive_type| {
                defer primitive_type.base.deref(irb.comp);
                switch (lval) {
                    //    if (lval == LValPtr) {
                    //        return ir_build_ref(irb, scope, node, value, false, false);
                    LVal.Ptr => return error.Unimplemented,
                    LVal.None => return irb.buildConstValue(scope, src_span, &primitive_type.base),
                }
            }
        } else |err| switch (err) {
            error.Overflow => {
                try irb.comp.addCompileError(irb.code.tree_scope, src_span, "integer too large");
                return error.SemanticAnalysisFailed;
            },
            error.OutOfMemory => return error.OutOfMemory,
        }

        switch (await (async irb.findIdent(scope, name) catch unreachable)) {
            Ident.Decl => |decl| {
                return irb.build(Inst.DeclRef, scope, src_span, Inst.DeclRef.Params{
                    .decl = decl,
                    .lval = lval,
                });
            },
            Ident.VarScope => |var_scope| {
                const var_ptr = try irb.build(Inst.VarPtr, scope, src_span, Inst.VarPtr.Params{ .var_scope = var_scope });
                switch (lval) {
                    LVal.Ptr => return var_ptr,
                    LVal.None => {
                        return irb.build(Inst.LoadPtr, scope, src_span, Inst.LoadPtr.Params{ .target = var_ptr });
                    },
                }
            },
            Ident.NotFound => {},
        }

        //if (node->owner->any_imports_failed) {
        //    // skip the error message since we had a failing import in this file
        //    // if an import breaks we don't need redundant undeclared identifier errors
        //    return irb->codegen->invalid_instruction;
        //}

        // TODO put a variable of same name with invalid type in global scope
        // so that future references to this same name will find a variable with an invalid type

        try irb.comp.addCompileError(irb.code.tree_scope, src_span, "unknown identifier '{}'", name);
        return error.SemanticAnalysisFailed;
    }

    const DeferCounts = struct {
        scope_exit: usize,
        error_exit: usize,
    };

    fn countDefers(irb: *Builder, inner_scope: *Scope, outer_scope: *Scope) DeferCounts {
        var result = DeferCounts{ .scope_exit = 0, .error_exit = 0 };

        var scope = inner_scope;
        while (scope != outer_scope) {
            switch (scope.id) {
                Scope.Id.Defer => {
                    const defer_scope = @fieldParentPtr(Scope.Defer, "base", scope);
                    switch (defer_scope.kind) {
                        Scope.Defer.Kind.ScopeExit => result.scope_exit += 1,
                        Scope.Defer.Kind.ErrorExit => result.error_exit += 1,
                    }
                    scope = scope.parent orelse break;
                },
                Scope.Id.FnDef => break,

                Scope.Id.CompTime,
                Scope.Id.Block,
                Scope.Id.Decls,
                Scope.Id.Root,
                Scope.Id.Var,
                => scope = scope.parent orelse break,

                Scope.Id.DeferExpr => unreachable,
                Scope.Id.AstTree => unreachable,
            }
        }
        return result;
    }

    async fn genDefersForBlock(
        irb: *Builder,
        inner_scope: *Scope,
        outer_scope: *Scope,
        gen_kind: Scope.Defer.Kind,
    ) !bool {
        var scope = inner_scope;
        var is_noreturn = false;
        while (true) {
            switch (scope.id) {
                Scope.Id.Defer => {
                    const defer_scope = @fieldParentPtr(Scope.Defer, "base", scope);
                    const generate = switch (defer_scope.kind) {
                        Scope.Defer.Kind.ScopeExit => true,
                        Scope.Defer.Kind.ErrorExit => gen_kind == Scope.Defer.Kind.ErrorExit,
                    };
                    if (generate) {
                        const defer_expr_scope = defer_scope.defer_expr_scope;
                        const instruction = try await (async irb.genNode(
                            defer_expr_scope.expr_node,
                            &defer_expr_scope.base,
                            LVal.None,
                        ) catch unreachable);
                        if (instruction.isNoReturn()) {
                            is_noreturn = true;
                        } else {
                            _ = try irb.build(
                                Inst.CheckVoidStmt,
                                &defer_expr_scope.base,
                                Span.token(defer_expr_scope.expr_node.lastToken()),
                                Inst.CheckVoidStmt.Params{ .target = instruction },
                            );
                        }
                    }
                },
                Scope.Id.FnDef,
                Scope.Id.Decls,
                Scope.Id.Root,
                => return is_noreturn,

                Scope.Id.CompTime,
                Scope.Id.Block,
                Scope.Id.Var,
                => scope = scope.parent orelse return is_noreturn,

                Scope.Id.DeferExpr => unreachable,
                Scope.Id.AstTree => unreachable,
            }
        }
    }

    pub fn lvalWrap(irb: *Builder, scope: *Scope, instruction: *Inst, lval: LVal) !*Inst {
        switch (lval) {
            LVal.None => return instruction,
            LVal.Ptr => {
                // We needed a pointer to a value, but we got a value. So we create
                // an instruction which just makes a const pointer of it.
                return irb.build(Inst.Ref, scope, instruction.span, Inst.Ref.Params{
                    .target = instruction,
                    .mut = Type.Pointer.Mut.Const,
                    .volatility = Type.Pointer.Vol.Non,
                });
            },
        }
    }

    fn arena(self: *Builder) *Allocator {
        return &self.code.arena.allocator;
    }

    fn buildExtra(
        self: *Builder,
        comptime I: type,
        scope: *Scope,
        span: Span,
        params: I.Params,
        is_generated: bool,
    ) !*Inst {
        const inst = try self.arena().create(I);
        inst.* = I{
            .base = Inst{
                .id = Inst.typeToId(I),
                .is_generated = is_generated,
                .scope = scope,
                .debug_id = self.next_debug_id,
                .val = switch (I.ir_val_init) {
                    IrVal.Init.Unknown => IrVal.Unknown,
                    IrVal.Init.NoReturn => IrVal{ .KnownValue = &Value.NoReturn.get(self.comp).base },
                    IrVal.Init.Void => IrVal{ .KnownValue = &Value.Void.get(self.comp).base },
                },
                .ref_count = 0,
                .span = span,
                .child = null,
                .parent = null,
                .llvm_value = undefined,
                .owner_bb = self.current_basic_block,
            },
            .params = params,
        };

        // Look at the params and ref() other instructions
        comptime var i = 0;
        inline while (i < @memberCount(I.Params)) : (i += 1) {
            const FieldType = comptime @typeOf(@field(I.Params(undefined), @memberName(I.Params, i)));
            switch (FieldType) {
                *Inst => @field(inst.params, @memberName(I.Params, i)).ref(self),
                *BasicBlock => @field(inst.params, @memberName(I.Params, i)).ref(self),
                ?*Inst => if (@field(inst.params, @memberName(I.Params, i))) |other| other.ref(self),
                []*Inst => {
                    // TODO https://github.com/ziglang/zig/issues/1269
                    for (@field(inst.params, @memberName(I.Params, i))) |other|
                        other.ref(self);
                },
                []*BasicBlock => {
                    // TODO https://github.com/ziglang/zig/issues/1269
                    for (@field(inst.params, @memberName(I.Params, i))) |other|
                        other.ref(self);
                },
                Type.Pointer.Mut,
                Type.Pointer.Vol,
                Type.Pointer.Size,
                LVal,
                *Decl,
                *Scope.Var,
                => {},
                // it's ok to add more types here, just make sure that
                // any instructions and basic blocks are ref'd appropriately
                else => @compileError("unrecognized type in Params: " ++ @typeName(FieldType)),
            }
        }

        self.next_debug_id += 1;
        try self.current_basic_block.instruction_list.append(&inst.base);
        return &inst.base;
    }

    fn build(
        self: *Builder,
        comptime I: type,
        scope: *Scope,
        span: Span,
        params: I.Params,
    ) !*Inst {
        return self.buildExtra(I, scope, span, params, false);
    }

    fn buildGen(
        self: *Builder,
        comptime I: type,
        scope: *Scope,
        span: Span,
        params: I.Params,
    ) !*Inst {
        return self.buildExtra(I, scope, span, params, true);
    }

    fn buildConstBool(self: *Builder, scope: *Scope, span: Span, x: bool) !*Inst {
        const inst = try self.build(Inst.Const, scope, span, Inst.Const.Params{});
        inst.val = IrVal{ .KnownValue = &Value.Bool.get(self.comp, x).base };
        return inst;
    }

    fn buildConstVoid(self: *Builder, scope: *Scope, span: Span, is_generated: bool) !*Inst {
        const inst = try self.buildExtra(Inst.Const, scope, span, Inst.Const.Params{}, is_generated);
        inst.val = IrVal{ .KnownValue = &Value.Void.get(self.comp).base };
        return inst;
    }

    fn buildConstValue(self: *Builder, scope: *Scope, span: Span, v: *Value) !*Inst {
        const inst = try self.build(Inst.Const, scope, span, Inst.Const.Params{});
        inst.val = IrVal{ .KnownValue = v.getRef() };
        return inst;
    }

    /// If the code is explicitly set to be comptime, then builds a const bool,
    /// otherwise builds a TestCompTime instruction.
    fn buildTestCompTime(self: *Builder, scope: *Scope, span: Span, target: *Inst) !*Inst {
        if (self.isCompTime(scope)) {
            return self.buildConstBool(scope, span, true);
        } else {
            return self.build(
                Inst.TestCompTime,
                scope,
                span,
                Inst.TestCompTime.Params{ .target = target },
            );
        }
    }

    fn genAsyncReturn(irb: *Builder, scope: *Scope, span: Span, result: *Inst, is_gen: bool) !*Inst {
        _ = try irb.buildGen(
            Inst.AddImplicitReturnType,
            scope,
            span,
            Inst.AddImplicitReturnType.Params{ .target = result },
        );

        if (!irb.is_async) {
            return irb.buildExtra(
                Inst.Return,
                scope,
                span,
                Inst.Return.Params{ .return_value = result },
                is_gen,
            );
        }
        return error.Unimplemented;

    }

    const Ident = union(enum) {
        NotFound,
        Decl: *Decl,
        VarScope: *Scope.Var,
    };

    async fn findIdent(irb: *Builder, scope: *Scope, name: []const u8) Ident {
        var s = scope;
        while (true) {
            switch (s.id) {
                Scope.Id.Root => return Ident.NotFound,
                Scope.Id.Decls => {
                    const decls = @fieldParentPtr(Scope.Decls, "base", s);
                    const locked_table = await (async decls.table.acquireRead() catch unreachable);
                    defer locked_table.release();
                    if (locked_table.value.get(name)) |entry| {
                        return Ident{ .Decl = entry.value };
                    }
                },
                Scope.Id.Var => {
                    const var_scope = @fieldParentPtr(Scope.Var, "base", s);
                    if (mem.eql(u8, var_scope.name, name)) {
                        return Ident{ .VarScope = var_scope };
                    }
                },
                else => {},
            }
            s = s.parent.?;
        }
    }
};

const Analyze = struct {
    irb: Builder,
    old_bb_index: usize,
    const_predecessor_bb: ?*BasicBlock,
    parent_basic_block: *BasicBlock,
    instruction_index: usize,
    src_implicit_return_type_list: std.ArrayList(*Inst),
    explicit_return_type: ?*Type,

    pub const Error = error{
        /// This is only for when we have already reported a compile error. It is the poison value.
        SemanticAnalysisFailed,

        /// This is a placeholder - it is useful to use instead of panicking but once the compiler is
        /// done this error code will be removed.
        Unimplemented,

        OutOfMemory,
    };

    pub fn init(comp: *Compilation, tree_scope: *Scope.AstTree, explicit_return_type: ?*Type) !Analyze {
        var irb = try Builder.init(comp, tree_scope, null);
        errdefer irb.abort();

        return Analyze{
            .irb = irb,
            .old_bb_index = 0,
            .const_predecessor_bb = null,
            .parent_basic_block = undefined, // initialized with startBasicBlock
            .instruction_index = undefined, // initialized with startBasicBlock
            .src_implicit_return_type_list = std.ArrayList(*Inst).init(irb.arena()),
            .explicit_return_type = explicit_return_type,
        };
    }

    pub fn abort(self: *Analyze) void {
        self.irb.abort();
    }

    pub fn getNewBasicBlock(self: *Analyze, old_bb: *BasicBlock, ref_old_instruction: ?*Inst) !*BasicBlock {
        if (old_bb.child) |child| {
            if (ref_old_instruction == null or child.ref_instruction != ref_old_instruction)
                return child;
        }

        const new_bb = try self.irb.createBasicBlock(old_bb.scope, old_bb.name_hint);
        new_bb.linkToParent(old_bb);
        new_bb.ref_instruction = ref_old_instruction;
        return new_bb;
    }

    pub fn startBasicBlock(self: *Analyze, old_bb: *BasicBlock, const_predecessor_bb: ?*BasicBlock) void {
        self.instruction_index = 0;
        self.parent_basic_block = old_bb;
        self.const_predecessor_bb = const_predecessor_bb;
    }

    pub fn finishBasicBlock(ira: *Analyze, old_code: *Code) !void {
        try ira.irb.code.basic_block_list.append(ira.irb.current_basic_block);
        ira.instruction_index += 1;

        while (ira.instruction_index < ira.parent_basic_block.instruction_list.len) {
            const next_instruction = ira.parent_basic_block.instruction_list.at(ira.instruction_index);

            if (!next_instruction.is_generated) {
                try ira.addCompileError(next_instruction.span, "unreachable code");
                break;
            }
            ira.instruction_index += 1;
        }

        ira.old_bb_index += 1;

        var need_repeat = true;
        while (true) {
            while (ira.old_bb_index < old_code.basic_block_list.len) {
                const old_bb = old_code.basic_block_list.at(ira.old_bb_index);
                const new_bb = old_bb.child orelse {
                    ira.old_bb_index += 1;
                    continue;
                };
                if (new_bb.instruction_list.len != 0) {
                    ira.old_bb_index += 1;
                    continue;
                }
                ira.irb.current_basic_block = new_bb;

                ira.startBasicBlock(old_bb, null);
                return;
            }
            if (!need_repeat)
                return;
            need_repeat = false;
            ira.old_bb_index = 0;
            continue;
        }
    }

    fn addCompileError(self: *Analyze, span: Span, comptime fmt: []const u8, args: ...) !void {
        return self.irb.comp.addCompileError(self.irb.code.tree_scope, span, fmt, args);
    }

    fn resolvePeerTypes(self: *Analyze, expected_type: ?*Type, peers: []const *Inst) Analyze.Error!*Type {
        // TODO actual implementation
        return &Type.Void.get(self.irb.comp).base;
    }

    fn implicitCast(self: *Analyze, target: *Inst, optional_dest_type: ?*Type) Analyze.Error!*Inst {
        const dest_type = optional_dest_type orelse return target;
        const from_type = target.getKnownType();
        if (from_type == dest_type or from_type.id == Type.Id.NoReturn) return target;
        return self.analyzeCast(target, target, dest_type);
    }

    fn analyzeCast(ira: *Analyze, source_instr: *Inst, target: *Inst, dest_type: *Type) !*Inst {
        const from_type = target.getKnownType();

        //if (type_is_invalid(wanted_type) || type_is_invalid(actual_type)) {
        //    return ira->codegen->invalid_instruction;
        //}

        //// perfect match or non-const to const
        //ConstCastOnly const_cast_result = types_match_const_cast_only(ira, wanted_type, actual_type,
        //        source_node, false);
        //if (const_cast_result.id == ConstCastResultIdOk) {
        //    return ir_resolve_cast(ira, source_instr, value, wanted_type, CastOpNoop, false);
        //}

        //// widening conversion
        //if (wanted_type->id == TypeTableEntryIdInt &&
        //    actual_type->id == TypeTableEntryIdInt &&
        //    wanted_type->data.integral.is_signed == actual_type->data.integral.is_signed &&
        //    wanted_type->data.integral.bit_count >= actual_type->data.integral.bit_count)
        //{
        //    return ir_analyze_widen_or_shorten(ira, source_instr, value, wanted_type);
        //}

        //// small enough unsigned ints can get casted to large enough signed ints
        //if (wanted_type->id == TypeTableEntryIdInt && wanted_type->data.integral.is_signed &&
        //    actual_type->id == TypeTableEntryIdInt && !actual_type->data.integral.is_signed &&
        //    wanted_type->data.integral.bit_count > actual_type->data.integral.bit_count)
        //{
        //    return ir_analyze_widen_or_shorten(ira, source_instr, value, wanted_type);
        //}

        //// float widening conversion
        //if (wanted_type->id == TypeTableEntryIdFloat &&
        //    actual_type->id == TypeTableEntryIdFloat &&
        //    wanted_type->data.floating.bit_count >= actual_type->data.floating.bit_count)
        //{
        //    return ir_analyze_widen_or_shorten(ira, source_instr, value, wanted_type);
        //}

        //// cast from [N]T to []const T
        //if (is_slice(wanted_type) && actual_type->id == TypeTableEntryIdArray) {
        //    TypeTableEntry *ptr_type = wanted_type->data.structure.fields[slice_ptr_index].type_entry;
        //    assert(ptr_type->id == TypeTableEntryIdPointer);
        //    if ((ptr_type->data.pointer.is_const || actual_type->data.array.len == 0) &&
        //        types_match_const_cast_only(ira, ptr_type->data.pointer.child_type, actual_type->data.array.child_type,
        //            source_node, false).id == ConstCastResultIdOk)
        //    {
        //        return ir_analyze_array_to_slice(ira, source_instr, value, wanted_type);
        //    }
        //}

        //// cast from *const [N]T to []const T
        //if (is_slice(wanted_type) &&
        //    actual_type->id == TypeTableEntryIdPointer &&
        //    actual_type->data.pointer.is_const &&
        //    actual_type->data.pointer.child_type->id == TypeTableEntryIdArray)
        //{
        //    TypeTableEntry *ptr_type = wanted_type->data.structure.fields[slice_ptr_index].type_entry;
        //    assert(ptr_type->id == TypeTableEntryIdPointer);

        //    TypeTableEntry *array_type = actual_type->data.pointer.child_type;

        //    if ((ptr_type->data.pointer.is_const || array_type->data.array.len == 0) &&
        //        types_match_const_cast_only(ira, ptr_type->data.pointer.child_type, array_type->data.array.child_type,
        //            source_node, false).id == ConstCastResultIdOk)
        //    {
        //        return ir_analyze_array_to_slice(ira, source_instr, value, wanted_type);
        //    }
        //}

        //// cast from [N]T to *const []const T
        //if (wanted_type->id == TypeTableEntryIdPointer &&
        //    wanted_type->data.pointer.is_const &&
        //    is_slice(wanted_type->data.pointer.child_type) &&
        //    actual_type->id == TypeTableEntryIdArray)
        //{
        //    TypeTableEntry *ptr_type =
        //        wanted_type->data.pointer.child_type->data.structure.fields[slice_ptr_index].type_entry;
        //    assert(ptr_type->id == TypeTableEntryIdPointer);
        //    if ((ptr_type->data.pointer.is_const || actual_type->data.array.len == 0) &&
        //        types_match_const_cast_only(ira, ptr_type->data.pointer.child_type, actual_type->data.array.child_type,
        //            source_node, false).id == ConstCastResultIdOk)
        //    {
        //        IrInstruction *cast1 = ir_analyze_cast(ira, source_instr, wanted_type->data.pointer.child_type, value);
        //        if (type_is_invalid(cast1->value.type))
        //            return ira->codegen->invalid_instruction;

        //        IrInstruction *cast2 = ir_analyze_cast(ira, source_instr, wanted_type, cast1);
        //        if (type_is_invalid(cast2->value.type))
        //            return ira->codegen->invalid_instruction;

        //        return cast2;
        //    }
        //}

        //// cast from [N]T to ?[]const T
        //if (wanted_type->id == TypeTableEntryIdOptional &&
        //    is_slice(wanted_type->data.maybe.child_type) &&
        //    actual_type->id == TypeTableEntryIdArray)
        //{
        //    TypeTableEntry *ptr_type =
        //        wanted_type->data.maybe.child_type->data.structure.fields[slice_ptr_index].type_entry;
        //    assert(ptr_type->id == TypeTableEntryIdPointer);
        //    if ((ptr_type->data.pointer.is_const || actual_type->data.array.len == 0) &&
        //        types_match_const_cast_only(ira, ptr_type->data.pointer.child_type, actual_type->data.array.child_type,
        //            source_node, false).id == ConstCastResultIdOk)
        //    {
        //        IrInstruction *cast1 = ir_analyze_cast(ira, source_instr, wanted_type->data.maybe.child_type, value);
        //        if (type_is_invalid(cast1->value.type))
        //            return ira->codegen->invalid_instruction;

        //        IrInstruction *cast2 = ir_analyze_cast(ira, source_instr, wanted_type, cast1);
        //        if (type_is_invalid(cast2->value.type))
        //            return ira->codegen->invalid_instruction;

        //        return cast2;
        //    }
        //}

        //// *[N]T to [*]T
        //if (wanted_type->id == TypeTableEntryIdPointer &&
        //    wanted_type->data.pointer.ptr_len == PtrLenUnknown &&
        //    actual_type->id == TypeTableEntryIdPointer &&
        //    actual_type->data.pointer.ptr_len == PtrLenSingle &&
        //    actual_type->data.pointer.child_type->id == TypeTableEntryIdArray &&
        //    actual_type->data.pointer.alignment >= wanted_type->data.pointer.alignment &&
        //    types_match_const_cast_only(ira, wanted_type->data.pointer.child_type,
        //        actual_type->data.pointer.child_type->data.array.child_type, source_node,
        //        !wanted_type->data.pointer.is_const).id == ConstCastResultIdOk)
        //{
        //    return ir_resolve_ptr_of_array_to_unknown_len_ptr(ira, source_instr, value, wanted_type);
        //}

        //// *[N]T to []T
        //if (is_slice(wanted_type) &&
        //    actual_type->id == TypeTableEntryIdPointer &&
        //    actual_type->data.pointer.ptr_len == PtrLenSingle &&
        //    actual_type->data.pointer.child_type->id == TypeTableEntryIdArray)
        //{
        //    TypeTableEntry *slice_ptr_type = wanted_type->data.structure.fields[slice_ptr_index].type_entry;
        //    assert(slice_ptr_type->id == TypeTableEntryIdPointer);
        //    if (types_match_const_cast_only(ira, slice_ptr_type->data.pointer.child_type,
        //        actual_type->data.pointer.child_type->data.array.child_type, source_node,
        //        !slice_ptr_type->data.pointer.is_const).id == ConstCastResultIdOk)
        //    {
        //        return ir_resolve_ptr_of_array_to_slice(ira, source_instr, value, wanted_type);
        //    }
        //}

        //// cast from T to ?T
        //// note that the *T to ?*T case is handled via the "ConstCastOnly" mechanism
        //if (wanted_type->id == TypeTableEntryIdOptional) {
        //    TypeTableEntry *wanted_child_type = wanted_type->data.maybe.child_type;
        //    if (types_match_const_cast_only(ira, wanted_child_type, actual_type, source_node,
        //        false).id == ConstCastResultIdOk)
        //    {
        //        return ir_analyze_maybe_wrap(ira, source_instr, value, wanted_type);
        //    } else if (actual_type->id == TypeTableEntryIdComptimeInt ||
        //            actual_type->id == TypeTableEntryIdComptimeFloat)
        //    {
        //        if (ir_num_lit_fits_in_other_type(ira, value, wanted_child_type, true)) {
        //            return ir_analyze_maybe_wrap(ira, source_instr, value, wanted_type);
        //        } else {
        //            return ira->codegen->invalid_instruction;
        //        }
        //    } else if (wanted_child_type->id == TypeTableEntryIdPointer &&
        //            wanted_child_type->data.pointer.is_const &&
        //            (actual_type->id == TypeTableEntryIdPointer || is_container(actual_type)))
        //    {
        //        IrInstruction *cast1 = ir_analyze_cast(ira, source_instr, wanted_child_type, value);
        //        if (type_is_invalid(cast1->value.type))
        //            return ira->codegen->invalid_instruction;

        //        IrInstruction *cast2 = ir_analyze_cast(ira, source_instr, wanted_type, cast1);
        //        if (type_is_invalid(cast2->value.type))
        //            return ira->codegen->invalid_instruction;

        //        return cast2;
        //    }
        //}

        //// cast from null literal to maybe type
        //if (wanted_type->id == TypeTableEntryIdOptional &&
        //    actual_type->id == TypeTableEntryIdNull)
        //{
        //    return ir_analyze_null_to_maybe(ira, source_instr, value, wanted_type);
        //}

        //// cast from child type of error type to error type
        //if (wanted_type->id == TypeTableEntryIdErrorUnion) {
        //    if (types_match_const_cast_only(ira, wanted_type->data.error_union.payload_type, actual_type,
        //        source_node, false).id == ConstCastResultIdOk)
        //    {
        //        return ir_analyze_err_wrap_payload(ira, source_instr, value, wanted_type);
        //    } else if (actual_type->id == TypeTableEntryIdComptimeInt ||
        //            actual_type->id == TypeTableEntryIdComptimeFloat)
        //    {
        //        if (ir_num_lit_fits_in_other_type(ira, value, wanted_type->data.error_union.payload_type, true)) {
        //            return ir_analyze_err_wrap_payload(ira, source_instr, value, wanted_type);
        //        } else {
        //            return ira->codegen->invalid_instruction;
        //        }
        //    }
        //}

        //// cast from [N]T to E![]const T
        //if (wanted_type->id == TypeTableEntryIdErrorUnion &&
        //    is_slice(wanted_type->data.error_union.payload_type) &&
        //    actual_type->id == TypeTableEntryIdArray)
        //{
        //    TypeTableEntry *ptr_type =
        //        wanted_type->data.error_union.payload_type->data.structure.fields[slice_ptr_index].type_entry;
        //    assert(ptr_type->id == TypeTableEntryIdPointer);
        //    if ((ptr_type->data.pointer.is_const || actual_type->data.array.len == 0) &&
        //        types_match_const_cast_only(ira, ptr_type->data.pointer.child_type, actual_type->data.array.child_type,
        //            source_node, false).id == ConstCastResultIdOk)
        //    {
        //        IrInstruction *cast1 = ir_analyze_cast(ira, source_instr, wanted_type->data.error_union.payload_type, value);
        //        if (type_is_invalid(cast1->value.type))
        //            return ira->codegen->invalid_instruction;

        //        IrInstruction *cast2 = ir_analyze_cast(ira, source_instr, wanted_type, cast1);
        //        if (type_is_invalid(cast2->value.type))
        //            return ira->codegen->invalid_instruction;

        //        return cast2;
        //    }
        //}

        //// cast from error set to error union type
        //if (wanted_type->id == TypeTableEntryIdErrorUnion &&
        //    actual_type->id == TypeTableEntryIdErrorSet)
        //{
        //    return ir_analyze_err_wrap_code(ira, source_instr, value, wanted_type);
        //}

        //// cast from T to E!?T
        //if (wanted_type->id == TypeTableEntryIdErrorUnion &&
        //    wanted_type->data.error_union.payload_type->id == TypeTableEntryIdOptional &&
        //    actual_type->id != TypeTableEntryIdOptional)
        //{
        //    TypeTableEntry *wanted_child_type = wanted_type->data.error_union.payload_type->data.maybe.child_type;
        //    if (types_match_const_cast_only(ira, wanted_child_type, actual_type, source_node, false).id == ConstCastResultIdOk ||
        //        actual_type->id == TypeTableEntryIdNull ||
        //        actual_type->id == TypeTableEntryIdComptimeInt ||
        //        actual_type->id == TypeTableEntryIdComptimeFloat)
        //    {
        //        IrInstruction *cast1 = ir_analyze_cast(ira, source_instr, wanted_type->data.error_union.payload_type, value);
        //        if (type_is_invalid(cast1->value.type))
        //            return ira->codegen->invalid_instruction;

        //        IrInstruction *cast2 = ir_analyze_cast(ira, source_instr, wanted_type, cast1);
        //        if (type_is_invalid(cast2->value.type))
        //            return ira->codegen->invalid_instruction;

        //        return cast2;
        //    }
        //}

        // cast from comptime-known integer to another integer where the value fits
        if (target.isCompTime() and (from_type.id == Type.Id.Int or from_type.id == Type.Id.ComptimeInt)) cast: {
            const target_val = target.val.KnownValue;
            const from_int = &target_val.cast(Value.Int).?.big_int;
            const fits = fits: {
                if (dest_type.cast(Type.ComptimeInt)) |ctint| {
                    break :fits true;
                }
                if (dest_type.cast(Type.Int)) |int| {
                    break :fits from_int.fitsInTwosComp(int.key.is_signed, int.key.bit_count);
                }
                break :cast;
            };
            if (!fits) {
                try ira.addCompileError(
                    source_instr.span,
                    "integer value '{}' cannot be stored in type '{}'",
                    from_int,
                    dest_type.name,
                );
                return error.SemanticAnalysisFailed;
            }

            const new_val = try target.copyVal(ira.irb.comp);
            new_val.setType(dest_type, ira.irb.comp);
            return ira.irb.buildConstValue(source_instr.scope, source_instr.span, new_val);
        }

        // cast from number literal to another type
        // cast from number literal to *const integer
        //if (actual_type->id == TypeTableEntryIdComptimeFloat ||
        //    actual_type->id == TypeTableEntryIdComptimeInt)
        //{
        //    ensure_complete_type(ira->codegen, wanted_type);
        //    if (type_is_invalid(wanted_type))
        //        return ira->codegen->invalid_instruction;
        //    if (wanted_type->id == TypeTableEntryIdEnum) {
        //        IrInstruction *cast1 = ir_analyze_cast(ira, source_instr, wanted_type->data.enumeration.tag_int_type, value);
        //        if (type_is_invalid(cast1->value.type))
        //            return ira->codegen->invalid_instruction;

        //        IrInstruction *cast2 = ir_analyze_cast(ira, source_instr, wanted_type, cast1);
        //        if (type_is_invalid(cast2->value.type))
        //            return ira->codegen->invalid_instruction;

        //        return cast2;
        //    } else if (wanted_type->id == TypeTableEntryIdPointer &&
        //        wanted_type->data.pointer.is_const)
        //    {
        //        IrInstruction *cast1 = ir_analyze_cast(ira, source_instr, wanted_type->data.pointer.child_type, value);
        //        if (type_is_invalid(cast1->value.type))
        //            return ira->codegen->invalid_instruction;

        //        IrInstruction *cast2 = ir_analyze_cast(ira, source_instr, wanted_type, cast1);
        //        if (type_is_invalid(cast2->value.type))
        //            return ira->codegen->invalid_instruction;

        //        return cast2;
        //    } else if (ir_num_lit_fits_in_other_type(ira, value, wanted_type, true)) {
        //        CastOp op;
        //        if ((actual_type->id == TypeTableEntryIdComptimeFloat &&
        //            wanted_type->id == TypeTableEntryIdFloat) ||
        //            (actual_type->id == TypeTableEntryIdComptimeInt &&
        //            wanted_type->id == TypeTableEntryIdInt))
        //        {
        //            op = CastOpNumLitToConcrete;
        //        } else if (wanted_type->id == TypeTableEntryIdInt) {
        //            op = CastOpFloatToInt;
        //        } else if (wanted_type->id == TypeTableEntryIdFloat) {
        //            op = CastOpIntToFloat;
        //        } else {
        //            zig_unreachable();
        //        }
        //        return ir_resolve_cast(ira, source_instr, value, wanted_type, op, false);
        //    } else {
        //        return ira->codegen->invalid_instruction;
        //    }
        //}

        //// cast from typed number to integer or float literal.
        //// works when the number is known at compile time
        //if (instr_is_comptime(value) &&
        //    ((actual_type->id == TypeTableEntryIdInt && wanted_type->id == TypeTableEntryIdComptimeInt) ||
        //    (actual_type->id == TypeTableEntryIdFloat && wanted_type->id == TypeTableEntryIdComptimeFloat)))
        //{
        //    return ir_analyze_number_to_literal(ira, source_instr, value, wanted_type);
        //}

        //// cast from union to the enum type of the union
        //if (actual_type->id == TypeTableEntryIdUnion && wanted_type->id == TypeTableEntryIdEnum) {
        //    type_ensure_zero_bits_known(ira->codegen, actual_type);
        //    if (type_is_invalid(actual_type))
        //        return ira->codegen->invalid_instruction;

        //    if (actual_type->data.unionation.tag_type == wanted_type) {
        //        return ir_analyze_union_to_tag(ira, source_instr, value, wanted_type);
        //    }
        //}

        //// enum to union which has the enum as the tag type
        //if (wanted_type->id == TypeTableEntryIdUnion && actual_type->id == TypeTableEntryIdEnum &&
        //    (wanted_type->data.unionation.decl_node->data.container_decl.auto_enum ||
        //    wanted_type->data.unionation.decl_node->data.container_decl.init_arg_expr != nullptr))
        //{
        //    type_ensure_zero_bits_known(ira->codegen, wanted_type);
        //    if (wanted_type->data.unionation.tag_type == actual_type) {
        //        return ir_analyze_enum_to_union(ira, source_instr, value, wanted_type);
        //    }
        //}

        //// enum to &const union which has the enum as the tag type
        //if (actual_type->id == TypeTableEntryIdEnum && wanted_type->id == TypeTableEntryIdPointer) {
        //    TypeTableEntry *union_type = wanted_type->data.pointer.child_type;
        //    if (union_type->data.unionation.decl_node->data.container_decl.auto_enum ||
        //        union_type->data.unionation.decl_node->data.container_decl.init_arg_expr != nullptr)
        //    {
        //        type_ensure_zero_bits_known(ira->codegen, union_type);
        //        if (union_type->data.unionation.tag_type == actual_type) {
        //            IrInstruction *cast1 = ir_analyze_cast(ira, source_instr, union_type, value);
        //            if (type_is_invalid(cast1->value.type))
        //                return ira->codegen->invalid_instruction;

        //            IrInstruction *cast2 = ir_analyze_cast(ira, source_instr, wanted_type, cast1);
        //            if (type_is_invalid(cast2->value.type))
        //                return ira->codegen->invalid_instruction;

        //            return cast2;
        //        }
        //    }
        //}

        //// cast from *T to *[1]T
        //if (wanted_type->id == TypeTableEntryIdPointer && wanted_type->data.pointer.ptr_len == PtrLenSingle &&
        //    actual_type->id == TypeTableEntryIdPointer && actual_type->data.pointer.ptr_len == PtrLenSingle)
        //{
        //    TypeTableEntry *array_type = wanted_type->data.pointer.child_type;
        //    if (array_type->id == TypeTableEntryIdArray && array_type->data.array.len == 1 &&
        //        types_match_const_cast_only(ira, array_type->data.array.child_type,
        //        actual_type->data.pointer.child_type, source_node,
        //        !wanted_type->data.pointer.is_const).id == ConstCastResultIdOk)
        //    {
        //        if (wanted_type->data.pointer.alignment > actual_type->data.pointer.alignment) {
        //            ErrorMsg *msg = ir_add_error(ira, source_instr, buf_sprintf("cast increases pointer alignment"));
        //            add_error_note(ira->codegen, msg, value->source_node,
        //                    buf_sprintf("'%s' has alignment %" PRIu32, buf_ptr(&actual_type->name),
        //                        actual_type->data.pointer.alignment));
        //            add_error_note(ira->codegen, msg, source_instr->source_node,
        //                    buf_sprintf("'%s' has alignment %" PRIu32, buf_ptr(&wanted_type->name),
        //                        wanted_type->data.pointer.alignment));
        //            return ira->codegen->invalid_instruction;
        //        }
        //        return ir_analyze_ptr_to_array(ira, source_instr, value, wanted_type);
        //    }
        //}

        //// cast from T to *T where T is zero bits
        //if (wanted_type->id == TypeTableEntryIdPointer && wanted_type->data.pointer.ptr_len == PtrLenSingle &&
        //    types_match_const_cast_only(ira, wanted_type->data.pointer.child_type,
        //        actual_type, source_node, !wanted_type->data.pointer.is_const).id == ConstCastResultIdOk)
        //{
        //    type_ensure_zero_bits_known(ira->codegen, actual_type);
        //    if (type_is_invalid(actual_type)) {
        //        return ira->codegen->invalid_instruction;
        //    }
        //    if (!type_has_bits(actual_type)) {
        //        return ir_get_ref(ira, source_instr, value, false, false);
        //    }
        //}

        //// cast from undefined to anything
        //if (actual_type->id == TypeTableEntryIdUndefined) {
        //    return ir_analyze_undefined_to_anything(ira, source_instr, value, wanted_type);
        //}

        //// cast from something to const pointer of it
        //if (!type_requires_comptime(actual_type)) {
        //    TypeTableEntry *const_ptr_actual = get_pointer_to_type(ira->codegen, actual_type, true);
        //    if (types_match_const_cast_only(ira, wanted_type, const_ptr_actual, source_node, false).id == ConstCastResultIdOk) {
        //        return ir_analyze_cast_ref(ira, source_instr, value, wanted_type);
        //    }
        //}

        try ira.addCompileError(
            source_instr.span,
            "expected type '{}', found '{}'",
            dest_type.name,
            from_type.name,
        );
        //ErrorMsg *parent_msg = ir_add_error_node(ira, source_instr->source_node,
        //    buf_sprintf("expected type '%s', found '%s'",
        //        buf_ptr(&wanted_type->name),
        //        buf_ptr(&actual_type->name)));
        //report_recursive_error(ira, source_instr->source_node, &const_cast_result, parent_msg);
        return error.SemanticAnalysisFailed;
    }

    fn getCompTimeValOrNullUndefOk(self: *Analyze, target: *Inst) ?*Value {
        @panic("TODO");
    }

    fn getCompTimeRef(
        self: *Analyze,
        value: *Value,
        ptr_mut: Value.Ptr.Mut,
        mut: Type.Pointer.Mut,
        volatility: Type.Pointer.Vol,
    ) Analyze.Error!*Inst {
        return error.Unimplemented;
    }
};

pub async fn gen(
    comp: *Compilation,
    body_node: *ast.Node,
    tree_scope: *Scope.AstTree,
    scope: *Scope,
) !*Code {
    var irb = try Builder.init(comp, tree_scope, scope);
    errdefer irb.abort();

    const entry_block = try irb.createBasicBlock(scope, "Entry");
    entry_block.ref(&irb); // Entry block gets a reference because we enter it to begin.
    try irb.setCursorAtEndAndAppendBlock(entry_block);

    const result = try await (async irb.genNode(body_node, scope, LVal.None) catch unreachable);
    if (!result.isNoReturn()) {
        // no need for save_err_ret_addr because this cannot return error
        _ = try irb.genAsyncReturn(scope, Span.token(body_node.lastToken()), result, true);
    }

    return irb.finish();
}

pub async fn analyze(comp: *Compilation, old_code: *Code, expected_type: ?*Type) !*Code {
    const old_entry_bb = old_code.basic_block_list.at(0);

    var ira = try Analyze.init(comp, old_code.tree_scope, expected_type);
    errdefer ira.abort();

    const new_entry_bb = try ira.getNewBasicBlock(old_entry_bb, null);
    new_entry_bb.ref(&ira.irb);

    ira.irb.current_basic_block = new_entry_bb;

    ira.startBasicBlock(old_entry_bb, null);

    while (ira.old_bb_index < old_code.basic_block_list.len) {
        const old_instruction = ira.parent_basic_block.instruction_list.at(ira.instruction_index);

        if (old_instruction.ref_count == 0 and !old_instruction.hasSideEffects()) {
            ira.instruction_index += 1;
            continue;
        }

        const return_inst = try await (async old_instruction.analyze(&ira) catch unreachable);
        assert(return_inst.val != IrVal.Unknown); // at least the type should be known at this point
        return_inst.linkToParent(old_instruction);
        // Note: if we ever modify the above to handle error.CompileError by continuing analysis,
        // then here we want to check if ira.isCompTime() and return early if true

        if (return_inst.isNoReturn()) {
            try ira.finishBasicBlock(old_code);
            continue;
        }

        ira.instruction_index += 1;
    }

    if (ira.src_implicit_return_type_list.len == 0) {
        ira.irb.code.return_type = &Type.NoReturn.get(comp).base;
        return ira.irb.finish();
    }

    ira.irb.code.return_type = try ira.resolvePeerTypes(expected_type, ira.src_implicit_return_type_list.toSliceConst());
    return ira.irb.finish();
}