zig/src/Air.zig

//! Analyzed Intermediate Representation.
//! This data is produced by Sema and consumed by codegen.
//! Unlike ZIR where there is one instance for an entire source file, each function
//! gets its own `Air` instance.

const std = @import("std");
const builtin = @import("builtin");
const Value = @import("value.zig").Value;
const Type = @import("type.zig").Type;
const Module = @import("Module.zig");
const assert = std.debug.assert;
const Air = @This();

instructions: std.MultiArrayList(Inst).Slice,
/// The meaning of this data is determined by `Inst.Tag` value.
/// The first few indexes are reserved. See `ExtraIndex` for the values.
extra: []const u32,
values: []const Value,

pub const ExtraIndex = enum(u32) {
    /// Payload index of the main `Block` in the `extra` array.
    main_block,

    _,
};

pub const Inst = struct {
    tag: Tag,
    data: Data,

    pub const Tag = enum(u8) {
        /// The first N instructions in the main block must be one arg instruction per
        /// function parameter. This makes function parameters participate in
        /// liveness analysis without any special handling.
        /// Uses the `ty_str` field.
        /// The string is the parameter name.
        arg,
        /// Float or integer addition. For integers, wrapping is undefined behavior.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        add,
        /// Integer addition. Wrapping is defined to be twos complement wrapping.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        addwrap,
        /// Saturating integer addition.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        add_sat,
        /// Float or integer subtraction. For integers, wrapping is undefined behavior.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        sub,
        /// Integer subtraction. Wrapping is defined to be twos complement wrapping.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        subwrap,
        /// Saturating integer subtraction.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        sub_sat,
        /// Float or integer multiplication. For integers, wrapping is undefined behavior.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        mul,
        /// Integer multiplication. Wrapping is defined to be twos complement wrapping.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        mulwrap,
        /// Saturating integer multiplication.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        mul_sat,
        /// Float division.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        div_float,
        /// Truncating integer or float division. For integers, wrapping is undefined behavior.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        div_trunc,
        /// Flooring integer or float division. For integers, wrapping is undefined behavior.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        div_floor,
        /// Integer or float division. Guaranteed no remainder.
        /// For integers, wrapping is undefined behavior.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        div_exact,
        /// Integer or float remainder division.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        rem,
        /// Integer or float modulus division.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        mod,
        /// Add an offset to a pointer, returning a new pointer.
        /// The offset is in element type units, not bytes.
        /// Wrapping is undefined behavior.
        /// The lhs is the pointer, rhs is the offset. Result type is the same as lhs.
        /// Uses the `bin_op` field.
        ptr_add,
        /// Subtract an offset from a pointer, returning a new pointer.
        /// The offset is in element type units, not bytes.
        /// Wrapping is undefined behavior.
        /// The lhs is the pointer, rhs is the offset. Result type is the same as lhs.
        /// Uses the `bin_op` field.
        ptr_sub,
        /// Given two operands which can be floats, integers, or vectors, returns the
        /// greater of the operands. For vectors it operates element-wise.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        max,
        /// Given two operands which can be floats, integers, or vectors, returns the
        /// lesser of the operands. For vectors it operates element-wise.
        /// Both operands are guaranteed to be the same type, and the result type
        /// is the same as both operands.
        /// Uses the `bin_op` field.
        min,
        /// Integer addition with overflow. Both operands are guaranteed to be the same type,
        /// and the result is bool. The wrapped value is written to the pointer given by the in
        /// operand of the `pl_op` field. Payload is `Bin` with `lhs` and `rhs` the relevant types
        /// of the operation.
        /// Uses the `pl_op` field with payload `Bin`.
        add_with_overflow,
        /// Integer subtraction with overflow. Both operands are guaranteed to be the same type,
        /// and the result is bool. The wrapped value is written to the pointer given by the in
        /// operand of the `pl_op` field. Payload is `Bin` with `lhs` and `rhs` the relevant types
        /// of the operation.
        /// Uses the `pl_op` field with payload `Bin`.
        sub_with_overflow,
        /// Integer multiplication with overflow. Both operands are guaranteed to be the same type,
        /// and the result is bool. The wrapped value is written to the pointer given by the in
        /// operand of the `pl_op` field. Payload is `Bin` with `lhs` and `rhs` the relevant types
        /// of the operation.
        /// Uses the `pl_op` field with payload `Bin`.
        mul_with_overflow,
        /// Integer left-shift with overflow. Both operands are guaranteed to be the same type,
        /// and the result is bool. The wrapped value is written to the pointer given by the in
        /// operand of the `pl_op` field. Payload is `Bin` with `lhs` and `rhs` the relevant types
        /// of the operation.
        /// Uses the `pl_op` field with payload `Bin`.
        shl_with_overflow,
        /// Allocates stack local memory.
        /// Uses the `ty` field.
        alloc,
        /// If the function will pass the result by-ref, this instruction returns the
        /// result pointer. Otherwise it is equivalent to `alloc`.
        /// Uses the `ty` field.
        ret_ptr,
        /// Inline assembly. Uses the `ty_pl` field. Payload is `Asm`.
        assembly,
        /// Bitwise AND. `&`.
        /// Result type is the same as both operands.
        /// Uses the `bin_op` field.
        bit_and,
        /// Bitwise OR. `|`.
        /// Result type is the same as both operands.
        /// Uses the `bin_op` field.
        bit_or,
        /// Shift right. `>>`
        /// Uses the `bin_op` field.
        shr,
        /// Shift left. `<<`
        /// Uses the `bin_op` field.
        shl,
        /// Shift left; For unsigned integers, the shift produces a poison value if it shifts
        /// out any non-zero bits. For signed integers, the shift produces a poison value if
        /// it shifts out any bits that disagree with the resultant sign bit.
        /// Uses the `bin_op` field.
        shl_exact,
        /// Saturating integer shift left. `<<|`
        /// Uses the `bin_op` field.
        shl_sat,
        /// Bitwise XOR. `^`
        /// Uses the `bin_op` field.
        xor,
        /// Boolean or binary NOT.
        /// Uses the `ty_op` field.
        not,
        /// Reinterpret the memory representation of a value as a different type.
        /// Uses the `ty_op` field.
        bitcast,
        /// Uses the `ty_pl` field with payload `Block`.
        block,
        /// A labeled block of code that loops forever. At the end of the body it is implied
        /// to repeat; no explicit "repeat" instruction terminates loop bodies.
        /// Result type is always noreturn; no instructions in a block follow this one.
        /// Uses the `ty_pl` field. Payload is `Block`.
        loop,
        /// Return from a block with a result.
        /// Result type is always noreturn; no instructions in a block follow this one.
        /// Uses the `br` field.
        br,
        /// Lowers to a hardware trap instruction, or the next best thing.
        /// Result type is always void.
        breakpoint,
        /// Yields the return address of the current function.
        /// Uses the `no_op` field.
        ret_addr,
        /// Function call.
        /// Result type is the return type of the function being called.
        /// Uses the `pl_op` field with the `Call` payload. operand is the callee.
        /// Triggers `resolveTypeLayout` on the return type of the callee.
        call,
        /// Count leading zeroes of an integer according to its representation in twos complement.
        /// Result type will always be an unsigned integer big enough to fit the answer.
        /// Uses the `ty_op` field.
        clz,
        /// Count trailing zeroes of an integer according to its representation in twos complement.
        /// Result type will always be an unsigned integer big enough to fit the answer.
        /// Uses the `ty_op` field.
        ctz,
        /// Count number of 1 bits in an integer according to its representation in twos complement.
        /// Result type will always be an unsigned integer big enough to fit the answer.
        /// Uses the `ty_op` field.
        popcount,

        /// `<`. Result type is always bool.
        /// Uses the `bin_op` field.
        cmp_lt,
        /// `<=`. Result type is always bool.
        /// Uses the `bin_op` field.
        cmp_lte,
        /// `==`. Result type is always bool.
        /// Uses the `bin_op` field.
        cmp_eq,
        /// `>=`. Result type is always bool.
        /// Uses the `bin_op` field.
        cmp_gte,
        /// `>`. Result type is always bool.
        /// Uses the `bin_op` field.
        cmp_gt,
        /// `!=`. Result type is always bool.
        /// Uses the `bin_op` field.
        cmp_neq,

        /// Conditional branch.
        /// Result type is always noreturn; no instructions in a block follow this one.
        /// Uses the `pl_op` field. Operand is the condition. Payload is `CondBr`.
        cond_br,
        /// Switch branch.
        /// Result type is always noreturn; no instructions in a block follow this one.
        /// Uses the `pl_op` field. Operand is the condition. Payload is `SwitchBr`.
        switch_br,
        /// A comptime-known value. Uses the `ty_pl` field, payload is index of
        /// `values` array.
        constant,
        /// A comptime-known type. Uses the `ty` field.
        const_ty,
        /// Notes the beginning of a source code statement and marks the line and column.
        /// Result type is always void.
        /// Uses the `dbg_stmt` field.
        dbg_stmt,
        /// ?T => bool
        /// Result type is always bool.
        /// Uses the `un_op` field.
        is_null,
        /// ?T => bool (inverted logic)
        /// Result type is always bool.
        /// Uses the `un_op` field.
        is_non_null,
        /// *?T => bool
        /// Result type is always bool.
        /// Uses the `un_op` field.
        is_null_ptr,
        /// *?T => bool (inverted logic)
        /// Result type is always bool.
        /// Uses the `un_op` field.
        is_non_null_ptr,
        /// E!T => bool
        /// Result type is always bool.
        /// Uses the `un_op` field.
        is_err,
        /// E!T => bool (inverted logic)
        /// Result type is always bool.
        /// Uses the `un_op` field.
        is_non_err,
        /// *E!T => bool
        /// Result type is always bool.
        /// Uses the `un_op` field.
        is_err_ptr,
        /// *E!T => bool (inverted logic)
        /// Result type is always bool.
        /// Uses the `un_op` field.
        is_non_err_ptr,
        /// Result type is always bool.
        /// Uses the `bin_op` field.
        bool_and,
        /// Result type is always bool.
        /// Uses the `bin_op` field.
        bool_or,
        /// Read a value from a pointer.
        /// Uses the `ty_op` field.
        load,
        /// Converts a pointer to its address. Result type is always `usize`.
        /// Uses the `un_op` field.
        ptrtoint,
        /// Given a boolean, returns 0 or 1.
        /// Result type is always `u1`.
        /// Uses the `un_op` field.
        bool_to_int,
        /// Return a value from a function.
        /// Result type is always noreturn; no instructions in a block follow this one.
        /// Uses the `un_op` field.
        /// Triggers `resolveTypeLayout` on the return type.
        ret,
        /// This instruction communicates that the function's result value is pointed to by
        /// the operand. If the function will pass the result by-ref, the operand is a
        /// `ret_ptr` instruction. Otherwise, this instruction is equivalent to a `load`
        /// on the operand, followed by a `ret` on the loaded value.
        /// Result type is always noreturn; no instructions in a block follow this one.
        /// Uses the `un_op` field.
        /// Triggers `resolveTypeLayout` on the return type.
        ret_load,
        /// Write a value to a pointer. LHS is pointer, RHS is value.
        /// Result type is always void.
        /// Uses the `bin_op` field.
        store,
        /// Indicates the program counter will never get to this instruction.
        /// Result type is always noreturn; no instructions in a block follow this one.
        unreach,
        /// Convert from a float type to a smaller one.
        /// Uses the `ty_op` field.
        fptrunc,
        /// Convert from a float type to a wider one.
        /// Uses the `ty_op` field.
        fpext,
        /// Returns an integer with a different type than the operand. The new type may have
        /// fewer, the same, or more bits than the operand type. The new type may also
        /// differ in signedness from the operand type. However, the instruction
        /// guarantees that the same integer value fits in both types.
        /// The new type may also be an enum type, in which case the integer cast operates on
        /// the integer tag type of the enum.
        /// See `trunc` for integer truncation.
        /// Uses the `ty_op` field.
        intcast,
        /// Truncate higher bits from an integer, resulting in an integer with the same
        /// sign but an equal or smaller number of bits.
        /// Uses the `ty_op` field.
        trunc,
        /// ?T => T. If the value is null, undefined behavior.
        /// Uses the `ty_op` field.
        optional_payload,
        /// *?T => *T. If the value is null, undefined behavior.
        /// Uses the `ty_op` field.
        optional_payload_ptr,
        /// *?T => *T. Sets the value to non-null with an undefined payload value.
        /// Uses the `ty_op` field.
        optional_payload_ptr_set,
        /// Given a payload value, wraps it in an optional type.
        /// Uses the `ty_op` field.
        wrap_optional,
        /// E!T -> T. If the value is an error, undefined behavior.
        /// Uses the `ty_op` field.
        unwrap_errunion_payload,
        /// E!T -> E. If the value is not an error, undefined behavior.
        /// Uses the `ty_op` field.
        unwrap_errunion_err,
        /// *(E!T) -> *T. If the value is an error, undefined behavior.
        /// Uses the `ty_op` field.
        unwrap_errunion_payload_ptr,
        /// *(E!T) -> E. If the value is not an error, undefined behavior.
        /// Uses the `ty_op` field.
        unwrap_errunion_err_ptr,
        /// wrap from T to E!T
        /// Uses the `ty_op` field.
        wrap_errunion_payload,
        /// wrap from E to E!T
        /// Uses the `ty_op` field.
        wrap_errunion_err,
        /// Given a pointer to a struct or union and a field index, returns a pointer to the field.
        /// Uses the `ty_pl` field, payload is `StructField`.
        /// TODO rename to `agg_field_ptr`.
        struct_field_ptr,
        /// Given a pointer to a struct or union, returns a pointer to the field.
        /// The field index is the number at the end of the name.
        /// Uses `ty_op` field.
        /// TODO rename to `agg_field_ptr_index_X`
        struct_field_ptr_index_0,
        struct_field_ptr_index_1,
        struct_field_ptr_index_2,
        struct_field_ptr_index_3,
        /// Given a byval struct or union and a field index, returns the field byval.
        /// Uses the `ty_pl` field, payload is `StructField`.
        /// TODO rename to `agg_field_val`
        struct_field_val,
        /// Given a pointer to a tagged union, set its tag to the provided value.
        /// Result type is always void.
        /// Uses the `bin_op` field. LHS is union pointer, RHS is new tag value.
        set_union_tag,
        /// Given a tagged union value, get its tag value.
        /// Uses the `ty_op` field.
        get_union_tag,
        /// Constructs a slice from a pointer and a length.
        /// Uses the `ty_pl` field, payload is `Bin`. lhs is ptr, rhs is len.
        slice,
        /// Given a slice value, return the length.
        /// Result type is always usize.
        /// Uses the `ty_op` field.
        slice_len,
        /// Given a slice value, return the pointer.
        /// Uses the `ty_op` field.
        slice_ptr,
        /// Given a pointer to a slice, return a pointer to the length of the slice.
        /// Uses the `ty_op` field.
        ptr_slice_len_ptr,
        /// Given a pointer to a slice, return a pointer to the pointer of the slice.
        /// Uses the `ty_op` field.
        ptr_slice_ptr_ptr,
        /// Given an (array value or vector value) and element index,
        /// return the element value at that index.
        /// Result type is the element type of the array operand.
        /// Uses the `bin_op` field.
        array_elem_val,
        /// Given a slice value, and element index, return the element value at that index.
        /// Result type is the element type of the slice operand.
        /// Uses the `bin_op` field.
        slice_elem_val,
        /// Given a slice value and element index, return a pointer to the element value at that index.
        /// Result type is a pointer to the element type of the slice operand.
        /// Uses the `ty_pl` field with payload `Bin`.
        slice_elem_ptr,
        /// Given a pointer value, and element index, return the element value at that index.
        /// Result type is the element type of the pointer operand.
        /// Uses the `bin_op` field.
        ptr_elem_val,
        /// Given a pointer value, and element index, return the element pointer at that index.
        /// Result type is pointer to the element type of the pointer operand.
        /// Uses the `ty_pl` field with payload `Bin`.
        ptr_elem_ptr,
        /// Given a pointer to an array, return a slice.
        /// Uses the `ty_op` field.
        array_to_slice,
        /// Given a float operand, return the integer with the closest mathematical meaning.
        /// Uses the `ty_op` field.
        float_to_int,
        /// Given an integer operand, return the float with the closest mathematical meaning.
        /// Uses the `ty_op` field.
        int_to_float,
        /// Given an integer, bool, float, or pointer operand, return a vector with all elements
        /// equal to the scalar value.
        /// Uses the `ty_op` field.
        splat,

        /// Given dest ptr, value, and len, set all elements at dest to value.
        /// Result type is always void.
        /// Uses the `pl_op` field. Operand is the dest ptr. Payload is `Bin`. `lhs` is the
        /// value, `rhs` is the length.
        /// The element type may be any type, not just u8.
        memset,
        /// Given dest ptr, src ptr, and len, copy len elements from src to dest.
        /// Result type is always void.
        /// Uses the `pl_op` field. Operand is the dest ptr. Payload is `Bin`. `lhs` is the
        /// src ptr, `rhs` is the length.
        /// The element type may be any type, not just u8.
        memcpy,

        /// Uses the `ty_pl` field with payload `Cmpxchg`.
        cmpxchg_weak,
        /// Uses the `ty_pl` field with payload `Cmpxchg`.
        cmpxchg_strong,
        /// Lowers to a memory fence instruction.
        /// Result type is always void.
        /// Uses the `fence` field.
        fence,
        /// Atomically load from a pointer.
        /// Result type is the element type of the pointer.
        /// Uses the `atomic_load` field.
        atomic_load,
        /// Atomically store through a pointer.
        /// Result type is always `void`.
        /// Uses the `bin_op` field. LHS is pointer, RHS is element.
        atomic_store_unordered,
        /// Same as `atomic_store_unordered` but with `AtomicOrder.Monotonic`.
        atomic_store_monotonic,
        /// Same as `atomic_store_unordered` but with `AtomicOrder.Release`.
        atomic_store_release,
        /// Same as `atomic_store_unordered` but with `AtomicOrder.SeqCst`.
        atomic_store_seq_cst,
        /// Atomically read-modify-write via a pointer.
        /// Result type is the element type of the pointer.
        /// Uses the `pl_op` field with payload `AtomicRmw`. Operand is `ptr`.
        atomic_rmw,

        /// Given an enum tag value, returns the tag name. The enum type may be non-exhaustive.
        /// Result type is always `[:0]const u8`.
        /// Uses the `un_op` field.
        tag_name,

        /// Given an error value, return the error name. Result type is always `[:0] const u8`.
        /// Uses the `un_op` field.
        error_name,

        /// Constructs a vector value out of runtime-known elements.
        /// Uses the `ty_pl` field, payload is index of an array of elements, each of which
        /// is a `Ref`. Length of the array is given by the vector type.
        vector_init,

        pub fn fromCmpOp(op: std.math.CompareOperator) Tag {
            return switch (op) {
                .lt => .cmp_lt,
                .lte => .cmp_lte,
                .eq => .cmp_eq,
                .gte => .cmp_gte,
                .gt => .cmp_gt,
                .neq => .cmp_neq,
            };
        }

        pub fn toCmpOp(tag: Tag) ?std.math.CompareOperator {
            return switch (tag) {
                .cmp_lt => .lt,
                .cmp_lte => .lte,
                .cmp_eq => .eq,
                .cmp_gte => .gte,
                .cmp_gt => .gt,
                .cmp_neq => .neq,
                else => null,
            };
        }
    };

    /// The position of an AIR instruction within the `Air` instructions array.
    pub const Index = u32;

    pub const Ref = @import("Zir.zig").Inst.Ref;

    /// All instructions have an 8-byte payload, which is contained within
    /// this union. `Tag` determines which union field is active, as well as
    /// how to interpret the data within.
    pub const Data = union {
        no_op: void,
        un_op: Ref,
        bin_op: struct {
            lhs: Ref,
            rhs: Ref,
        },
        ty: Type,
        ty_op: struct {
            ty: Ref,
            operand: Ref,
        },
        ty_pl: struct {
            ty: Ref,
            // Index into a different array.
            payload: u32,
        },
        ty_str: struct {
            ty: Ref,
            // ZIR string table index.
            str: u32,
        },
        br: struct {
            block_inst: Index,
            operand: Ref,
        },
        pl_op: struct {
            operand: Ref,
            payload: u32,
        },
        dbg_stmt: struct {
            line: u32,
            column: u32,
        },
        fence: std.builtin.AtomicOrder,
        atomic_load: struct {
            ptr: Ref,
            order: std.builtin.AtomicOrder,
        },

        // Make sure we don't accidentally add a field to make this union
        // bigger than expected. Note that in Debug builds, Zig is allowed
        // to insert a secret field for safety checks.
        comptime {
            if (builtin.mode != .Debug) {
                assert(@sizeOf(Data) == 8);
            }
        }
    };
};

/// Trailing is a list of instruction indexes for every `body_len`.
pub const Block = struct {
    body_len: u32,
};

/// Trailing is a list of `Inst.Ref` for every `args_len`.
pub const Call = struct {
    args_len: u32,
};

/// This data is stored inside extra, with two sets of trailing `Inst.Ref`:
/// * 0. the then body, according to `then_body_len`.
/// * 1. the else body, according to `else_body_len`.
pub const CondBr = struct {
    then_body_len: u32,
    else_body_len: u32,
};

/// Trailing:
/// * 0. `Case` for each `cases_len`
/// * 1. the else body, according to `else_body_len`.
pub const SwitchBr = struct {
    cases_len: u32,
    else_body_len: u32,

    /// Trailing:
    /// * item: Inst.Ref // for each `items_len`.
    /// * instruction index for each `body_len`.
    pub const Case = struct {
        items_len: u32,
        body_len: u32,
    };
};

pub const StructField = struct {
    /// Whether this is a pointer or byval is determined by the AIR tag.
    struct_operand: Inst.Ref,
    field_index: u32,
};

pub const Bin = struct {
    lhs: Inst.Ref,
    rhs: Inst.Ref,
};

/// Trailing:
/// 0. `Inst.Ref` for every outputs_len
/// 1. `Inst.Ref` for every inputs_len
pub const Asm = struct {
    /// Index to the corresponding ZIR instruction.
    /// `asm_source`, `outputs_len`, `inputs_len`, `clobbers_len`, `is_volatile`, and
    /// clobbers are found via here.
    zir_index: u32,
};

pub const Cmpxchg = struct {
    ptr: Inst.Ref,
    expected_value: Inst.Ref,
    new_value: Inst.Ref,
    /// 0b00000000000000000000000000000XXX - success_order
    /// 0b00000000000000000000000000XXX000 - failure_order
    flags: u32,

    pub fn successOrder(self: Cmpxchg) std.builtin.AtomicOrder {
        return @intToEnum(std.builtin.AtomicOrder, @truncate(u3, self.flags));
    }

    pub fn failureOrder(self: Cmpxchg) std.builtin.AtomicOrder {
        return @intToEnum(std.builtin.AtomicOrder, @truncate(u3, self.flags >> 3));
    }
};

pub const AtomicRmw = struct {
    operand: Inst.Ref,
    /// 0b00000000000000000000000000000XXX - ordering
    /// 0b0000000000000000000000000XXXX000 - op
    flags: u32,

    pub fn ordering(self: AtomicRmw) std.builtin.AtomicOrder {
        return @intToEnum(std.builtin.AtomicOrder, @truncate(u3, self.flags));
    }

    pub fn op(self: AtomicRmw) std.builtin.AtomicRmwOp {
        return @intToEnum(std.builtin.AtomicRmwOp, @truncate(u4, self.flags >> 3));
    }
};

pub fn getMainBody(air: Air) []const Air.Inst.Index {
    const body_index = air.extra[@enumToInt(ExtraIndex.main_block)];
    const extra = air.extraData(Block, body_index);
    return air.extra[extra.end..][0..extra.data.body_len];
}

pub fn typeOf(air: Air, inst: Air.Inst.Ref) Type {
    const ref_int = @enumToInt(inst);
    if (ref_int < Air.Inst.Ref.typed_value_map.len) {
        return Air.Inst.Ref.typed_value_map[ref_int].ty;
    }
    return air.typeOfIndex(@intCast(Air.Inst.Index, ref_int - Air.Inst.Ref.typed_value_map.len));
}

pub fn typeOfIndex(air: Air, inst: Air.Inst.Index) Type {
    const datas = air.instructions.items(.data);
    switch (air.instructions.items(.tag)[inst]) {
        .arg => return air.getRefType(datas[inst].ty_str.ty),

        .add,
        .addwrap,
        .add_sat,
        .sub,
        .subwrap,
        .sub_sat,
        .mul,
        .mulwrap,
        .mul_sat,
        .div_float,
        .div_trunc,
        .div_floor,
        .div_exact,
        .rem,
        .mod,
        .bit_and,
        .bit_or,
        .xor,
        .ptr_add,
        .ptr_sub,
        .shr,
        .shl,
        .shl_exact,
        .shl_sat,
        .min,
        .max,
        => return air.typeOf(datas[inst].bin_op.lhs),

        .cmp_lt,
        .cmp_lte,
        .cmp_eq,
        .cmp_gte,
        .cmp_gt,
        .cmp_neq,
        .is_null,
        .is_non_null,
        .is_null_ptr,
        .is_non_null_ptr,
        .is_err,
        .is_non_err,
        .is_err_ptr,
        .is_non_err_ptr,
        .bool_and,
        .bool_or,
        => return Type.initTag(.bool),

        .const_ty => return Type.initTag(.type),

        .alloc,
        .ret_ptr,
        => return datas[inst].ty,

        .assembly,
        .block,
        .constant,
        .struct_field_ptr,
        .struct_field_val,
        .slice_elem_ptr,
        .ptr_elem_ptr,
        .cmpxchg_weak,
        .cmpxchg_strong,
        .slice,
        .vector_init,
        => return air.getRefType(datas[inst].ty_pl.ty),

        .not,
        .bitcast,
        .load,
        .fpext,
        .fptrunc,
        .intcast,
        .trunc,
        .optional_payload,
        .optional_payload_ptr,
        .optional_payload_ptr_set,
        .wrap_optional,
        .unwrap_errunion_payload,
        .unwrap_errunion_err,
        .unwrap_errunion_payload_ptr,
        .unwrap_errunion_err_ptr,
        .wrap_errunion_payload,
        .wrap_errunion_err,
        .slice_ptr,
        .ptr_slice_len_ptr,
        .ptr_slice_ptr_ptr,
        .struct_field_ptr_index_0,
        .struct_field_ptr_index_1,
        .struct_field_ptr_index_2,
        .struct_field_ptr_index_3,
        .array_to_slice,
        .float_to_int,
        .int_to_float,
        .splat,
        .get_union_tag,
        .clz,
        .ctz,
        .popcount,
        => return air.getRefType(datas[inst].ty_op.ty),

        .loop,
        .br,
        .cond_br,
        .switch_br,
        .ret,
        .ret_load,
        .unreach,
        => return Type.initTag(.noreturn),

        .breakpoint,
        .dbg_stmt,
        .store,
        .fence,
        .atomic_store_unordered,
        .atomic_store_monotonic,
        .atomic_store_release,
        .atomic_store_seq_cst,
        .memset,
        .memcpy,
        .set_union_tag,
        => return Type.initTag(.void),

        .ptrtoint,
        .slice_len,
        .ret_addr,
        => return Type.initTag(.usize),

        .bool_to_int => return Type.initTag(.u1),

        .tag_name, .error_name => return Type.initTag(.const_slice_u8_sentinel_0),

        .call => {
            const callee_ty = air.typeOf(datas[inst].pl_op.operand);
            switch (callee_ty.zigTypeTag()) {
                .Fn => return callee_ty.fnReturnType(),
                .Pointer => return callee_ty.childType().fnReturnType(),
                else => unreachable,
            }
        },

        .slice_elem_val, .ptr_elem_val, .array_elem_val => {
            const ptr_ty = air.typeOf(datas[inst].bin_op.lhs);
            return ptr_ty.elemType();
        },
        .atomic_load => {
            const ptr_ty = air.typeOf(datas[inst].atomic_load.ptr);
            return ptr_ty.elemType();
        },
        .atomic_rmw => {
            const ptr_ty = air.typeOf(datas[inst].pl_op.operand);
            return ptr_ty.elemType();
        },

        .add_with_overflow,
        .sub_with_overflow,
        .mul_with_overflow,
        .shl_with_overflow,
        => return Type.initTag(.bool),
    }
}

pub fn getRefType(air: Air, ref: Air.Inst.Ref) Type {
    const ref_int = @enumToInt(ref);
    if (ref_int < Air.Inst.Ref.typed_value_map.len) {
        var buffer: Value.ToTypeBuffer = undefined;
        return Air.Inst.Ref.typed_value_map[ref_int].val.toType(&buffer);
    }
    const inst_index = ref_int - Air.Inst.Ref.typed_value_map.len;
    const air_tags = air.instructions.items(.tag);
    const air_datas = air.instructions.items(.data);
    assert(air_tags[inst_index] == .const_ty);
    return air_datas[inst_index].ty;
}

/// Returns the requested data, as well as the new index which is at the start of the
/// trailers for the object.
pub fn extraData(air: Air, comptime T: type, index: usize) struct { data: T, end: usize } {
    const fields = std.meta.fields(T);
    var i: usize = index;
    var result: T = undefined;
    inline for (fields) |field| {
        @field(result, field.name) = switch (field.field_type) {
            u32 => air.extra[i],
            Inst.Ref => @intToEnum(Inst.Ref, air.extra[i]),
            i32 => @bitCast(i32, air.extra[i]),
            else => @compileError("bad field type"),
        };
        i += 1;
    }
    return .{
        .data = result,
        .end = i,
    };
}

pub fn deinit(air: *Air, gpa: std.mem.Allocator) void {
    air.instructions.deinit(gpa);
    gpa.free(air.extra);
    gpa.free(air.values);
    air.* = undefined;
}

const ref_start_index: u32 = Air.Inst.Ref.typed_value_map.len;

pub fn indexToRef(inst: Air.Inst.Index) Air.Inst.Ref {
    return @intToEnum(Air.Inst.Ref, ref_start_index + inst);
}

pub fn refToIndex(inst: Air.Inst.Ref) ?Air.Inst.Index {
    const ref_int = @enumToInt(inst);
    if (ref_int >= ref_start_index) {
        return ref_int - ref_start_index;
    } else {
        return null;
    }
}

/// Returns `null` if runtime-known.
pub fn value(air: Air, inst: Air.Inst.Ref) ?Value {
    const ref_int = @enumToInt(inst);
    if (ref_int < Air.Inst.Ref.typed_value_map.len) {
        return Air.Inst.Ref.typed_value_map[ref_int].val;
    }
    const inst_index = @intCast(Air.Inst.Index, ref_int - Air.Inst.Ref.typed_value_map.len);
    const air_datas = air.instructions.items(.data);
    switch (air.instructions.items(.tag)[inst_index]) {
        .constant => return air.values[air_datas[inst_index].ty_pl.payload],
        .const_ty => unreachable,
        else => return air.typeOfIndex(inst_index).onePossibleValue(),
    }
}