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Fix PostRA antidependence breaker.

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Avoid using the same register for two def operands or and earlyclobber
def and use operand. This fixes PR8986 and improves on the prior fix
for rdar://problem/8959122.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@125089 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick 2011-02-08 17:39:46 +00:00
parent 75396a9988
commit bc4bd92d52
2 changed files with 49 additions and 11 deletions
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54
lib/CodeGen/CriticalAntiDepBreaker.cpp
View File

@ -325,17 +325,55 @@ void CriticalAntiDepBreaker::ScanInstruction(MachineInstr *MI,
}
}
// Check all machine instructions that define the antidependent register.
// Return true if any of these instructions define the new register.
// Check all machine operands that reference the antidependent register and must
// be replaced by NewReg. Return true if any of their parent instructions may
// clobber the new register.
//
// Note: AntiDepReg may be referenced by a two-address instruction such that
// it's use operand is tied to a def operand. We guard against the case in which
// the two-address instruction also defines NewReg, as may happen with
// pre/postincrement loads. In this case, both the use and def operands are in
// RegRefs because the def is inserted by PrescanInstruction and not erased
// during ScanInstruction. So checking for an instructions with definitions of
// both NewReg and AntiDepReg covers it.
bool
CriticalAntiDepBreaker::isNewRegModifiedByRefs(RegRefIter RegRefBegin,
RegRefIter RegRefEnd,
unsigned NewReg)
CriticalAntiDepBreaker::isNewRegClobberedByRefs(RegRefIter RegRefBegin,
RegRefIter RegRefEnd,
unsigned NewReg)
{
for (RegRefIter I = RegRefBegin; I != RegRefEnd; ++I ) {
MachineOperand *MO = I->second;
if (MO->getParent()->modifiesRegister(NewReg, TRI))
MachineOperand *RefOper = I->second;
// Don't allow the instruction defining AntiDepReg to earlyclobber its
// operands, in case they may be assigned to NewReg. In this case antidep
// breaking must fail, but it's too rare to bother optimizing.
if (RefOper->isDef() && RefOper->isEarlyClobber())
return true;
// Handle cases in which this instructions defines NewReg.
MachineInstr *MI = RefOper->getParent();
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &CheckOper = MI->getOperand(i);
if (!CheckOper.isReg() || !CheckOper.isDef() ||
CheckOper.getReg() != NewReg)
continue;
// Don't allow the instruction to define NewReg and AntiDepReg.
// When AntiDepReg is renamed it will be an illegal op.
if (RefOper->isDef())
return true;
// Don't allow an instruction using AntiDepReg to be earlyclobbered by
// NewReg
if (CheckOper.isEarlyClobber())
return true;
// Don't allow inline asm to define NewReg at all. Who know what it's
// doing with it.
if (MI->isInlineAsm())
return true;
}
}
return false;
}
@ -361,7 +399,7 @@ CriticalAntiDepBreaker::findSuitableFreeRegister(RegRefIter RegRefBegin,
// If any instructions that define AntiDepReg also define the NewReg, it's
// not suitable. For example, Instruction with multiple definitions can
// result in this condition.
if (isNewRegModifiedByRefs(RegRefBegin, RegRefEnd, NewReg)) continue;
if (isNewRegClobberedByRefs(RegRefBegin, RegRefEnd, NewReg)) continue;
// If NewReg is dead and NewReg's most recent def is not before
// AntiDepReg's kill, it's safe to replace AntiDepReg with NewReg.
assert(((KillIndices[AntiDepReg] == ~0u) != (DefIndices[AntiDepReg] == ~0u))

6
lib/CodeGen/CriticalAntiDepBreaker.h
View File

@ -92,9 +92,9 @@ class TargetRegisterInfo;
private:
void PrescanInstruction(MachineInstr *MI);
void ScanInstruction(MachineInstr *MI, unsigned Count);
bool isNewRegModifiedByRefs(RegRefIter RegRefBegin,
RegRefIter RegRefEnd,
unsigned NewReg);
bool isNewRegClobberedByRefs(RegRefIter RegRefBegin,
RegRefIter RegRefEnd,
unsigned NewReg);
unsigned findSuitableFreeRegister(RegRefIter RegRefBegin,
RegRefIter RegRefEnd,
unsigned AntiDepReg,