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JIT/x86: Fix reported kill regs for varargs prologs #113793

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Merged
merged 2 commits into from
Mar 22, 2025
Merged

JIT/x86: Fix reported kill regs for varargs prologs #113793

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d79301e
x86: Fix reported kill regs for varargs prologs
filipnavara Mar 22, 2025
88138f0
Address PR feedback
filipnavara Mar 22, 2025
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12 changes: 6 additions & 6 deletions src/coreclr/jit/codegencommon.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5924,11 +5924,11 @@ void CodeGen::genFnProlog()

// MOV EAX, <VARARGS HANDLE>
assert(compiler->lvaVarargsHandleArg == compiler->info.compArgsCount - 1);
GetEmitter()->emitIns_R_S(ins_Load(TYP_I_IMPL), EA_PTRSIZE, REG_EAX, compiler->lvaVarargsHandleArg, 0);
regSet.verifyRegUsed(REG_EAX);
GetEmitter()->emitIns_R_S(ins_Load(TYP_I_IMPL), EA_PTRSIZE, REG_SCRATCH, compiler->lvaVarargsHandleArg, 0);
regSet.verifyRegUsed(REG_SCRATCH);

// MOV EAX, [EAX]
GetEmitter()->emitIns_R_AR(ins_Load(TYP_I_IMPL), EA_PTRSIZE, REG_EAX, REG_EAX, 0);
GetEmitter()->emitIns_R_AR(ins_Load(TYP_I_IMPL), EA_PTRSIZE, REG_SCRATCH, REG_SCRATCH, 0);

// EDX might actually be holding something here. So make sure to only use EAX for this code
// sequence.
Expand All @@ -5940,16 +5940,16 @@ void CodeGen::genFnProlog()
noway_assert(lastArg->lvFramePointerBased);

// LEA EAX, &<VARARGS HANDLE> + EAX
GetEmitter()->emitIns_R_ARR(INS_lea, EA_PTRSIZE, REG_EAX, genFramePointerReg(), REG_EAX, offset);
GetEmitter()->emitIns_R_ARR(INS_lea, EA_PTRSIZE, REG_SCRATCH, genFramePointerReg(), REG_SCRATCH, offset);

if (varDsc->lvIsInReg())
{
GetEmitter()->emitIns_Mov(INS_mov, EA_PTRSIZE, varDsc->GetRegNum(), REG_EAX, /* canSkip */ true);
GetEmitter()->emitIns_Mov(INS_mov, EA_PTRSIZE, varDsc->GetRegNum(), REG_SCRATCH, /* canSkip */ true);
regSet.verifyRegUsed(varDsc->GetRegNum());
}
else
{
GetEmitter()->emitIns_S_R(ins_Store(TYP_I_IMPL), EA_PTRSIZE, REG_EAX, argsStartVar, 0);
GetEmitter()->emitIns_S_R(ins_Store(TYP_I_IMPL), EA_PTRSIZE, REG_SCRATCH, argsStartVar, 0);
}
}

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8 changes: 7 additions & 1 deletion src/coreclr/jit/lsrabuild.cpp
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Expand Up @@ -2448,7 +2448,13 @@ void LinearScan::buildIntervals()
// do that in the prolog. We handle registers in the prolog and the
// stack args in the scratch BB that we have ensured exists. The
// handling clobbers REG_SCRATCH, so kill it here.
if ((block == compiler->fgFirstBB) && compiler->lvaHasAnySwiftStackParamToReassemble())
bool prologUsesScratchReg = compiler->lvaHasAnySwiftStackParamToReassemble();
#ifdef TARGET_X86
// On x86, CodeGen::genFnProlog does a varargs preprocessing that uses
// the scratch register.
prologUsesScratchReg |= compiler->info.compIsVarArgs;
#endif
if ((block == compiler->fgFirstBB) && prologUsesScratchReg)
{
addKillForRegs(genRegMask(REG_SCRATCH), currentLoc + 1);
currentLoc += 2;
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