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emit_x64: Improve code emission of FPCompare{32,64}

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Replace if-chain with table lookup
This commit is contained in:
MerryMage 2017-11-22 17:46:46 +00:00
parent 814e378249
commit c4b40909f7
1 changed files with 6 additions and 15 deletions
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21
src/backend_x64/emit_x64.cpp
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@ -2447,25 +2447,16 @@ void EmitX64::EmitFPSub64(RegAlloc& reg_alloc, IR::Block& block, IR::Inst* inst)
}
static void SetFpscrNzcvFromFlags(BlockOfCode* code, RegAlloc& reg_alloc) {
reg_alloc.ScratchGpr({HostLoc::RAX}); // lahf requires use of ah
Xbyak::Reg32 nzcv_imm = reg_alloc.ScratchGpr().cvt32();
reg_alloc.ScratchGpr({HostLoc::RCX}); // shifting requires use of cl
Xbyak::Reg32 nzcv = reg_alloc.ScratchGpr().cvt32();
using namespace Xbyak::util;
code->lahf();
code->mov(nzcv_imm, 0x30000000);
code->cmp(ah, 0b01000111);
code->cmove(nzcv, nzcv_imm);
code->mov(nzcv_imm, 0x20000000);
code->cmp(ah, 0b00000010);
code->cmove(nzcv, nzcv_imm);
code->mov(nzcv_imm, 0x80000000);
code->cmp(ah, 0b00000011);
code->cmove(nzcv, nzcv_imm);
code->mov(nzcv_imm, 0x60000000);
code->cmp(ah, 0b01000010);
code->cmove(nzcv, nzcv_imm);
code->mov(nzcv, 0x28630000);
code->sete(cl);
code->rcl(cl, 3);
code->shl(nzcv, cl);
code->and_(nzcv, 0xF0000000);
code->mov(dword[r15 + offsetof(JitState, FPSCR_nzcv)], nzcv);
}