8000 Backport fix for znver1 miscompilation by mati865 · Pull Request #28 · rust-lang/llvm-project · GitHub
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Backport fix for znver1 miscompilation #28

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Merged
merged 1 commit into from
Nov 29, 2019
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Backport fix for znver1 miscompilation #28

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Teach the regmask clobber check to check if any subregister is preser… 
…ved before considering the super register clobbered

X86 has some calling conventions where bits 127:0 of a vector register are callee saved, but the upper bits aren't. Previously we could detect that the full ymm register was clobbered when the xmm portion was really preserved. This patch checks the subregisters to make sure they aren't preserved.

Fixes PR44140

Differential Revision: https://reviews.llvm.org/D70699
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@topperc @mati865
topperc authored and mati865 committed Nov 29, 2019
commit 5d902855b136536d62c847d2b3ff73a6cd7ce603
16 changes: 13 additions & 3 deletions llvm/lib/CodeGen/CriticalAntiDepBreaker.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -261,15 +261,25 @@ void CriticalAntiDepBreaker::ScanInstruction(MachineInstr &MI, unsigned Count) {
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);

if (MO.isRegMask())
for (unsigned i = 0, e = TRI->getNumRegs(); i != e; ++i)
if (MO.clobbersPhysReg(i)) {
if (MO.isRegMask()) {
auto ClobbersPhysRegAndSubRegs = [&](unsigned PhysReg) {
for (MCSubRegIterator SRI(PhysReg, TRI, true); SRI.isValid(); ++SRI)
if (!MO.clobbersPhysReg(*SRI))
return false;

return true;
};

for (unsigned i = 0, e = TRI->getNumRegs(); i != e; ++i) {
if (ClobbersPhysRegAndSubRegs(i)) {
DefIndices[i] = Count;
KillIndices[i] = ~0u;
KeepRegs.reset(i);
Classes[i] = nullptr;
RegRefs.erase(i);
}
}
}

if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
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