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x64: simplify saving registers to stack in prologue

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This commit is contained in:
Jakub Konka 2022-06-07 11:16:08 +02:00
parent e9fc58eab7
commit 117f9f69e7
4 changed files with 154 additions and 105 deletions
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144
src/arch/x86_64/CodeGen.zig
View File

@ -409,13 +409,11 @@ fn gen(self: *Self) InnerError!void {
// The address where to store the return value for the caller is in `.rdi`
// register which the callee is free to clobber. Therefore, we purposely
// spill it to stack immediately.
const ptr_ty = Type.usize;
const abi_size = @intCast(u32, ptr_ty.abiSize(self.target.*));
const abi_align = ptr_ty.abiAlignment(self.target.*);
const stack_offset = mem.alignForwardGeneric(u32, self.next_stack_offset + abi_size, abi_align);
const stack_offset = mem.alignForwardGeneric(u32, self.next_stack_offset + 8, 8);
self.next_stack_offset = stack_offset;
self.max_end_stack = @maximum(self.max_end_stack, self.next_stack_offset);
try self.genSetStack(ptr_ty, @intCast(i32, stack_offset), MCValue{ .register = .rdi }, .{});
try self.genSetStack(Type.usize, @intCast(i32, stack_offset), MCValue{ .register = .rdi }, .{});
self.ret_mcv = MCValue{ .stack_offset = @intCast(i32, stack_offset) };
log.debug("gen: spilling .rdi to stack at offset {}", .{stack_offset});
}
@ -426,11 +424,11 @@ fn gen(self: *Self) InnerError!void {
.data = undefined,
});
// push the callee_preserved_regs that were used
const backpatch_push_callee_preserved_regs_i = try self.addInst(.{
.tag = .push_regs_from_callee_preserved_regs,
.ops = Mir.Inst.Ops.encode(.{ .reg1 = .rbp }),
.data = .{ .payload = undefined }, // to be backpatched
// Push callee-preserved regs that were used actually in use.
const backpatch_push_callee_preserved_regs = try self.addInst(.{
.tag = .nop,
.ops = undefined,
.data = undefined,
});
try self.genBody(self.air.getMainBody());
@ -446,31 +444,21 @@ fn gen(self: *Self) InnerError!void {
self.mir_instructions.items(.data)[jmp_reloc].inst = @intCast(u32, self.mir_instructions.len);
}
// calculate the data for callee_preserved_regs to be pushed and popped
const callee_preserved_regs_payload = blk: {
var data = Mir.RegsToPushOrPop{
.regs = 0,
.disp = mem.alignForwardGeneric(u32, self.next_stack_offset, 8),
};
var disp = data.disp + 8;
inline for (callee_preserved_regs) |reg, i| {
if (self.register_manager.isRegAllocated(reg)) {
data.regs |= 1 << @intCast(u5, i);
self.max_end_stack += 8;
disp += 8;
}
// Create list of registers to save in the prologue.
// TODO handle register classes
var reg_list: Mir.RegisterList(Register, &callee_preserved_regs) = .{};
inline for (callee_preserved_regs) |reg| {
if (self.register_manager.isRegAllocated(reg)) {
reg_list.push(reg);
}
break :blk try self.addExtra(data);
};
}
const saved_regs_stack_space: u32 = reg_list.count() * 8;
const data = self.mir_instructions.items(.data);
// backpatch the push instruction
data[backpatch_push_callee_preserved_regs_i].payload = callee_preserved_regs_payload;
// pop the callee_preserved_regs
_ = try self.addInst(.{
.tag = .pop_regs_from_callee_preserved_regs,
.ops = Mir.Inst.Ops.encode(.{ .reg1 = .rbp }),
.data = .{ .payload = callee_preserved_regs_payload },
// Pop saved callee-preserved regs.
const backpatch_pop_callee_preserved_regs = try self.addInst(.{
.tag = .nop,
.ops = undefined,
.data = undefined,
});
_ = try self.addInst(.{
@ -502,9 +490,11 @@ fn gen(self: *Self) InnerError!void {
if (self.max_end_stack > math.maxInt(i32)) {
return self.failSymbol("too much stack used in call parameters", .{});
}
// TODO we should reuse this mechanism to align the stack when calling any function even if
// we do not pass any args on the stack BUT we still push regs to stack with `push` inst.
const aligned_stack_end = @intCast(u32, mem.alignForward(self.max_end_stack, self.stack_align));
const aligned_stack_end = @intCast(
u32,
mem.alignForward(self.max_end_stack + saved_regs_stack_space, self.stack_align),
);
if (aligned_stack_end > 0) {
self.mir_instructions.set(backpatch_stack_sub, .{
.tag = .sub,
@ -516,6 +506,21 @@ fn gen(self: *Self) InnerError!void {
.ops = Mir.Inst.Ops.encode(.{ .reg1 = .rsp }),
.data = .{ .imm = aligned_stack_end },
});
const save_reg_list = try self.addExtra(Mir.SaveRegisterList{
.register_list = reg_list.asInt(),
.stack_end = aligned_stack_end,
});
self.mir_instructions.set(backpatch_push_callee_preserved_regs, .{
.tag = .push_regs,
.ops = Mir.Inst.Ops.encode(.{ .reg1 = .rbp }),
.data = .{ .payload = save_reg_list },
});
self.mir_instructions.set(backpatch_pop_callee_preserved_regs, .{
.tag = .pop_regs,
.ops = Mir.Inst.Ops.encode(.{ .reg1 = .rbp }),
.data = .{ .payload = save_reg_list },
});
}
} else {
_ = try self.addInst(.{
@ -907,6 +912,39 @@ fn allocRegOrMem(self: *Self, inst: Air.Inst.Index, reg_ok: bool) !MCValue {
return MCValue{ .stack_offset = @intCast(i32, stack_offset) };
}
const State = struct {
next_stack_offset: u32,
registers: abi.RegisterManager.TrackedRegisters,
free_registers: abi.RegisterManager.RegisterBitSet,
eflags_inst: ?Air.Inst.Index,
stack: std.AutoHashMapUnmanaged(u32, StackAllocation),
fn deinit(state: *State, gpa: Allocator) void {
state.stack.deinit(gpa);
}
};
fn captureState(self: *Self) !State {
return State{
.next_stack_offset = self.next_stack_offset,
.registers = self.register_manager.registers,
.free_registers = self.register_manager.free_registers,
.eflags_inst = self.eflags_inst,
.stack = try self.stack.clone(self.gpa),
};
}
fn revertState(self: *Self, state: State) void {
self.register_manager.registers = state.registers;
self.eflags_inst = state.eflags_inst;
self.stack.deinit(self.gpa);
self.stack = state.stack;
self.next_stack_offset = state.next_stack_offset;
self.register_manager.free_registers = state.free_registers;
}
pub fn spillInstruction(self: *Self, reg: Register, inst: Air.Inst.Index) !void {
const stack_mcv = try self.allocRegOrMem(inst, false);
log.debug("spilling {d} to stack mcv {any}", .{ inst, stack_mcv });
@ -4503,12 +4541,7 @@ fn airCondBr(self: *Self, inst: Air.Inst.Index) !void {
}
// Capture the state of register and stack allocation state so that we can revert to it.
const parent_next_stack_offset = self.next_stack_offset;
const parent_free_registers = self.register_manager.free_registers;
const parent_eflags_inst = self.eflags_inst;
var parent_stack = try self.stack.clone(self.gpa);
defer parent_stack.deinit(self.gpa);
const parent_registers = self.register_manager.registers;
const saved_state = try self.captureState();
try self.branch_stack.append(.{});
errdefer {
@ -4526,17 +4559,10 @@ fn airCondBr(self: *Self, inst: Air.Inst.Index) !void {
var saved_then_branch = self.branch_stack.pop();
defer saved_then_branch.deinit(self.gpa);
self.register_manager.registers = parent_registers;
self.eflags_inst = parent_eflags_inst;
self.stack.deinit(self.gpa);
self.stack = parent_stack;
parent_stack = .{};
self.next_stack_offset = parent_next_stack_offset;
self.register_manager.free_registers = parent_free_registers;
self.revertState(saved_state);
try self.performReloc(reloc);
const else_branch = self.branch_stack.addOneAssumeCapacity();
else_branch.* = .{};
@ -5021,12 +5047,7 @@ fn airSwitch(self: *Self, inst: Air.Inst.Index) !void {
}
// Capture the state of register and stack allocation state so that we can revert to it.
const parent_next_stack_offset = self.next_stack_offset;
const parent_free_registers = self.register_manager.free_registers;
const parent_eflags_inst = self.eflags_inst;
var parent_stack = try self.stack.clone(self.gpa);
defer parent_stack.deinit(self.gpa);
const parent_registers = self.register_manager.registers;
const saved_state = try self.captureState();
try self.branch_stack.append(.{});
errdefer {
@ -5044,14 +5065,7 @@ fn airSwitch(self: *Self, inst: Air.Inst.Index) !void {
var saved_case_branch = self.branch_stack.pop();
defer saved_case_branch.deinit(self.gpa);
self.register_manager.registers = parent_registers;
self.eflags_inst = parent_eflags_inst;
self.stack.deinit(self.gpa);
self.stack = parent_stack;
parent_stack = .{};
self.next_stack_offset = parent_next_stack_offset;
self.register_manager.free_registers = parent_free_registers;
self.revertState(saved_state);
for (relocs) |reloc| {
try self.performReloc(reloc);

45
src/arch/x86_64/Emit.zig
View File

@ -169,7 +169,7 @@ pub fn lowerMir(emit: *Emit) InnerError!void {
.@"test" => try emit.mirTest(inst),
.interrupt => try emit.mirInterrupt(inst),
.nop => try emit.mirNop(),
.nop => {}, // just skip it
// SSE instructions
.mov_f64_sse => try emit.mirMovFloatSse(.movsd, inst),
@ -198,8 +198,8 @@ pub fn lowerMir(emit: *Emit) InnerError!void {
.dbg_prologue_end => try emit.mirDbgPrologueEnd(inst),
.dbg_epilogue_begin => try emit.mirDbgEpilogueBegin(inst),
.push_regs_from_callee_preserved_regs => try emit.mirPushPopRegsFromCalleePreservedRegs(.push, inst),
.pop_regs_from_callee_preserved_regs => try emit.mirPushPopRegsFromCalleePreservedRegs(.pop, inst),
.push_regs => try emit.mirPushPopRegisterList(.push, inst),
.pop_regs => try emit.mirPushPopRegisterList(.pop, inst),
else => {
return emit.fail("Implement MIR->Emit lowering for x86_64 for pseudo-inst: {s}", .{tag});
@ -246,10 +246,6 @@ fn mirInterrupt(emit: *Emit, inst: Mir.Inst.Index) InnerError!void {
}
}
fn mirNop(emit: *Emit) InnerError!void {
return lowerToZoEnc(.nop, emit.code);
}
fn mirSyscall(emit: *Emit) InnerError!void {
return lowerToZoEnc(.syscall, emit.code);
}
@ -283,26 +279,27 @@ fn mirPushPop(emit: *Emit, tag: Tag, inst: Mir.Inst.Index) InnerError!void {
}
}
fn mirPushPopRegsFromCalleePreservedRegs(emit: *Emit, tag: Tag, inst: Mir.Inst.Index) InnerError!void {
fn mirPushPopRegisterList(emit: *Emit, tag: Tag, inst: Mir.Inst.Index) InnerError!void {
const ops = emit.mir.instructions.items(.ops)[inst].decode();
const payload = emit.mir.instructions.items(.data)[inst].payload;
const data = emit.mir.extraData(Mir.RegsToPushOrPop, payload).data;
const regs = data.regs;
var disp: u32 = data.disp + 8;
for (abi.callee_preserved_regs) |reg, i| {
if ((regs >> @intCast(u5, i)) & 1 == 0) continue;
if (tag == .push) {
try lowerToMrEnc(.mov, RegisterOrMemory.mem(.qword_ptr, .{
.disp = @bitCast(u32, -@intCast(i32, disp)),
.base = ops.reg1,
}), reg.to64(), emit.code);
} else {
try lowerToRmEnc(.mov, reg.to64(), RegisterOrMemory.mem(.qword_ptr, .{
.disp = @bitCast(u32, -@intCast(i32, disp)),
.base = ops.reg1,
}), emit.code);
const save_reg_list = emit.mir.extraData(Mir.SaveRegisterList, payload).data;
const reg_list = Mir.RegisterList(Register, &abi.callee_preserved_regs).fromInt(save_reg_list.register_list);
var disp: i32 = -@intCast(i32, save_reg_list.stack_end);
inline for (abi.callee_preserved_regs) |reg| {
if (reg_list.isSet(reg)) {
switch (tag) {
.push => try lowerToMrEnc(.mov, RegisterOrMemory.mem(.qword_ptr, .{
.disp = @bitCast(u32, disp),
.base = ops.reg1,
}), reg, emit.code),
.pop => try lowerToRmEnc(.mov, reg, RegisterOrMemory.mem(.qword_ptr, .{
.disp = @bitCast(u32, disp),
.base = ops.reg1,
}), emit.code),
else => unreachable,
}
disp += 8;
}
disp += 8;
}
}

67
src/arch/x86_64/Mir.zig
View File

@ -14,6 +14,7 @@ const assert = std.debug.assert;
const bits = @import("bits.zig");
const Air = @import("../../Air.zig");
const CodeGen = @import("CodeGen.zig");
const IntegerBitSet = std.bit_set.IntegerBitSet;
const Register = bits.Register;
instructions: std.MultiArrayList(Inst).Slice,
@ -379,19 +380,13 @@ pub const Inst = struct {
/// update debug line
dbg_line,
/// push registers from the callee_preserved_regs
/// data is the bitfield of which regs to push
/// for example on x86_64, the callee_preserved_regs are [_]Register{ .rcx, .rsi, .rdi, .r8, .r9, .r10, .r11 }; };
/// so to push rcx and r8 one would make data 0b00000000_00000000_00000000_00001001 (the first and fourth bits are set)
/// ops is unused
push_regs_from_callee_preserved_regs,
/// push registers
/// Uses `payload` field with `SaveRegisterList` as payload.
push_regs,
/// pop registers from the callee_preserved_regs
/// data is the bitfield of which regs to pop
/// for example on x86_64, the callee_preserved_regs are [_]Register{ .rcx, .rsi, .rdi, .r8, .r9, .r10, .r11 }; };
/// so to pop rcx and r8 one would make data 0b00000000_00000000_00000000_00001001 (the first and fourth bits are set)
/// ops is unused
pop_regs_from_callee_preserved_regs,
/// pop registers
/// Uses `payload` field with `SaveRegisterList` as payload.
pop_regs,
};
/// The position of an MIR instruction within the `Mir` instructions array.
pub const Index = u32;
@ -471,9 +466,51 @@ pub const Inst = struct {
}
};
pub const RegsToPushOrPop = struct {
regs: u32,
disp: u32,
pub fn RegisterList(comptime Reg: type, comptime registers: []const Reg) type {
assert(registers.len <= @bitSizeOf(u32));
return struct {
bitset: RegBitSet = RegBitSet.initEmpty(),
const RegBitSet = IntegerBitSet(registers.len);
const Self = @This();
fn getIndexForReg(reg: Reg) RegBitSet.MaskInt {
inline for (registers) |cpreg, i| {
if (reg.id() == cpreg.id()) return i;
}
unreachable; // register not in input register list!
}
pub fn push(self: *Self, reg: Reg) void {
const index = getIndexForReg(reg);
self.bitset.set(index);
}
pub fn isSet(self: Self, reg: Reg) bool {
const index = getIndexForReg(reg);
return self.bitset.isSet(index);
}
pub fn asInt(self: Self) u32 {
return self.bitset.mask;
}
pub fn fromInt(mask: u32) Self {
return .{
.bitset = RegBitSet{ .mask = @intCast(RegBitSet.MaskInt, mask) },
};
}
pub fn count(self: Self) u32 {
return @intCast(u32, self.bitset.count());
}
};
}
pub const SaveRegisterList = struct {
/// Use `RegisterList` to populate.
register_list: u32,
stack_end: u32,
};
pub const ImmPair = struct {

3
src/register_manager.zig
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@ -39,7 +39,7 @@ pub fn RegisterManager(
/// register is free), the value in that slot is undefined.
///
/// The key must be canonical register.
registers: [tracked_registers.len]Air.Inst.Index = undefined,
registers: TrackedRegisters = undefined,
/// Tracks which registers are free (in which case the
/// corresponding bit is set to 1)
free_registers: RegisterBitSet = RegisterBitSet.initFull(),
@ -51,6 +51,7 @@ pub fn RegisterManager(
const Self = @This();
pub const TrackedRegisters = [tracked_registers.len]Air.Inst.Index;
pub const RegisterBitSet = StaticBitSet(tracked_registers.len);
fn getFunction(self: *Self) *Function {