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emit_x64_data_processing: Minor optimization for immediates in EmitSub

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This commit is contained in:
MerryMage 2021-01-01 13:35:01 +00:00
parent eeeafaf5fb
commit e926f0b393
1 changed files with 14 additions and 6 deletions
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16
src/backend/x64/emit_x64_data_processing.cpp
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@ -1090,19 +1090,21 @@ static void EmitSub(BlockOfCode& code, EmitContext& ctx, IR::Inst* inst, int bit
// TODO: Optimize CMP case. // TODO: Optimize CMP case.
// Note that x64 CF is inverse of what the ARM carry flag is here. // Note that x64 CF is inverse of what the ARM carry flag is here.
bool invert_output_carry = true;
if (args[1].IsImmediate() && args[1].GetType() == IR::Type::U32) { if (args[1].IsImmediate() && args[1].GetType() == IR::Type::U32) {
const u32 op_arg = args[1].GetImmediateU32(); const u32 op_arg = args[1].GetImmediateU32();
if (carry_in.IsImmediate()) { if (carry_in.IsImmediate()) {
if (carry_in.GetImmediateU1()) { if (carry_in.GetImmediateU1()) {
code.sub(result, op_arg); code.sub(result, op_arg);
} else { } else {
code.stc(); code.add(result, ~op_arg);
code.sbb(result, op_arg); invert_output_carry = false;
} }
} else { } else {
code.bt(carry.cvt32(), 0); code.bt(carry.cvt32(), 0);
code.cmc(); code.adc(result, ~op_arg);
code.sbb(result, op_arg); invert_output_carry = false;
} }
} else { } else {
OpArg op_arg = ctx.reg_alloc.UseOpArg(args[1]); OpArg op_arg = ctx.reg_alloc.UseOpArg(args[1]);
@ -1122,14 +1124,20 @@ static void EmitSub(BlockOfCode& code, EmitContext& ctx, IR::Inst* inst, int bit
} }
if (nzcv_inst) { if (nzcv_inst) {
if (invert_output_carry) {
code.cmc(); code.cmc();
}
code.lahf(); code.lahf();
code.seto(code.al); code.seto(code.al);
ctx.reg_alloc.DefineValue(nzcv_inst, nzcv); ctx.reg_alloc.DefineValue(nzcv_inst, nzcv);
ctx.EraseInstruction(nzcv_inst); ctx.EraseInstruction(nzcv_inst);
} }
if (carry_inst) { if (carry_inst) {
if (invert_output_carry) {
code.setnc(carry); code.setnc(carry);
} else {
code.setc(carry);
}
ctx.reg_alloc.DefineValue(carry_inst, carry); ctx.reg_alloc.DefineValue(carry_inst, carry);
ctx.EraseInstruction(carry_inst); ctx.EraseInstruction(carry_inst);
} }