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Avoid commuting a def MI in order to coalesce a copy instruction away if any use of the same val# is a copy instruction that has already been coalesced.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48833 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2008-03-26 19:03:01 +00:00
parent e326332acd
commit ed70cbb3f3
3 changed files with 62 additions and 2 deletions
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14
lib/CodeGen/SimpleRegisterCoalescing.cpp
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@ -283,6 +283,17 @@ bool SimpleRegisterCoalescing::RemoveCopyByCommutingDef(LiveInterval &IntA,
if (HasOtherReachingDefs(IntA, IntB, AValNo, BValNo))
return false;
// If some of the uses of IntA.reg is already coalesced away, return false.
// It's not possible to determine whether it's safe to perform the coalescing.
for (MachineRegisterInfo::use_iterator UI = mri_->use_begin(IntA.reg),
UE = mri_->use_end(); UI != UE; ++UI) {
MachineInstr *UseMI = &*UI;
unsigned UseIdx = li_->getInstructionIndex(UseMI);
LiveInterval::iterator ULR = IntA.FindLiveRangeContaining(UseIdx);
if (ULR->valno == AValNo && JoinedCopies.count(UseMI))
return false;
}
// At this point we have decided that it is legal to do this
// transformation. Start by commuting the instruction.
MachineBasicBlock *MBB = DefMI->getParent();
@ -323,8 +334,7 @@ bool SimpleRegisterCoalescing::RemoveCopyByCommutingDef(LiveInterval &IntA,
MachineInstr *UseMI = &*UI;
++UI;
if (JoinedCopies.count(UseMI))
// It'll no longer be "joined" after the change.
JoinedCopies.erase(UseMI);
continue;
unsigned UseIdx = li_->getInstructionIndex(UseMI);
LiveInterval::iterator ULR = IntA.FindLiveRangeContaining(UseIdx);
if (ULR->valno != AValNo)