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Check for EFLAGS live-out before clobbering it.

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It is only allowed to clobber EFLAGS at the end of a block if it isn't
live-in to any successor.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@139056 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen 2011-09-02 23:52:52 +00:00
parent 4a1b9d82a4
commit b8e052e123
1 changed files with 10 additions and 8 deletions
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18
lib/Target/X86/X86InstrInfo.cpp
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@ -975,15 +975,11 @@ static bool isSafeToClobberEFLAGS(MachineBasicBlock &MBB,
MachineBasicBlock::iterator I) {
MachineBasicBlock::iterator E = MBB.end();
// It's always safe to clobber EFLAGS at the end of a block.
if (I == E)
return true;
// For compile time consideration, if we are not able to determine the
// safety after visiting 4 instructions in each direction, we will assume
// it's not safe.
MachineBasicBlock::iterator Iter = I;
for (unsigned i = 0; i < 4; ++i) {
for (unsigned i = 0; Iter != E && i < 4; ++i) {
bool SeenDef = false;
for (unsigned j = 0, e = Iter->getNumOperands(); j != e; ++j) {
MachineOperand &MO = Iter->getOperand(j);
@ -1003,10 +999,16 @@ static bool isSafeToClobberEFLAGS(MachineBasicBlock &MBB,
// Skip over DBG_VALUE.
while (Iter != E && Iter->isDebugValue())
++Iter;
}
// If we make it to the end of the block, it's safe to clobber EFLAGS.
if (Iter == E)
return true;
// It is safe to clobber EFLAGS at the end of a block of no successor has it
// live in.
if (Iter == E) {
for (MachineBasicBlock::succ_iterator SI = MBB.succ_begin(),
SE = MBB.succ_end(); SI != SE; ++SI)
if ((*SI)->isLiveIn(X86::EFLAGS))
return false;
return true;
}
MachineBasicBlock::iterator B = MBB.begin();