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Teach memdep to phi translate bitcasts. This allows us to compile

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the example in GCC PR16799 to:

LBB1_2:                                                     ## %bb1
	movl	%eax, %eax
	subq	%rax, %rdi
	movq	%rdi, (%rcx)
	movl	(%rdi), %eax
	testl	%eax, %eax
	je	LBB1_2

instead of:

LBB1_2:                                                     ## %bb1
	movl	(%rdi), %ecx
	subq	%rcx, %rdi
	movq	%rdi, (%rax)
	cmpl	$0, (%rdi)
	je	LBB1_2



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89978 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2009-11-26 23:41:07 +00:00
parent 38028653a9
commit cc3d0eb483
3 changed files with 53 additions and 5 deletions
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30
lib/Analysis/MemoryDependenceAnalysis.cpp
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@@ -690,10 +690,15 @@ static bool isPHITranslatable(Instruction *Inst) {
if (isa<PHINode>(Inst))
return true;
// TODO: BITCAST, GEP.
// ...
// We can handle bitcast of a PHI, but the PHI needs to be in the same block
// as the bitcast.
if (BitCastInst *BC = dyn_cast<BitCastInst>(Inst))
if (PHINode *PN = dyn_cast<PHINode>(BC->getOperand(0)))
if (PN->getParent() == BC->getParent())
return true;
// TODO: GEP, ...
// cerr << "MEMDEP: Could not PHI translate: " << *Pointer;
// if (isa<BitCastInst>(PtrInst) || isa<GetElementPtrInst>(PtrInst))
// cerr << "OP:\t\t\t\t" << *PtrInst->getOperand(0);
@@ -708,6 +713,25 @@ static Value *PHITranslateForPred(Instruction *Inst, BasicBlock *Pred) {
if (PHINode *PN = dyn_cast<PHINode>(Inst))
return PN->getIncomingValueForBlock(Pred);
if (BitCastInst *BC = dyn_cast<BitCastInst>(Inst)) {
PHINode *BCPN = cast<PHINode>(BC->getOperand(0));
Value *PHIIn = BCPN->getIncomingValueForBlock(Pred);
// Constants are trivial to phi translate.
if (Constant *C = dyn_cast<Constant>(PHIIn))
return ConstantExpr::getBitCast(C, BC->getType());
// Otherwise we have to see if a bitcasted version of the incoming pointer
// is available. If so, we can use it, otherwise we have to fail.
for (Value::use_iterator UI = PHIIn->use_begin(), E = PHIIn->use_end();
UI != E; ++UI) {
if (BitCastInst *BCI = dyn_cast<BitCastInst>(*UI))
if (BCI->getType() == BC->getType())
return BCI;
}
return 0;
}
return 0;
}