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When folding addressing modes in CodeGenPrepare, attempt to look through PHI nodes 

if all the operands of the PHI are equivalent.  This allows CodeGenPrepare to undo
unprofitable PRE transforms.

llvm-svn: 119853
This commit is contained in:
Owen Anderson 2010-11-19 22:15:03 +00:00
parent 09d7bfd886
commit dfb8c3bbfc
1 changed files with 29 additions and 3 deletions
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32
llvm/lib/Transforms/Scalar/CodeGenPrepare.cpp
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@ -618,6 +618,32 @@ static bool IsNonLocalValue(Value *V, BasicBlock *BB) {
bool CodeGenPrepare::OptimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
const Type *AccessTy,
DenseMap<Value*,Value*> &SunkAddrs) {
// Try to collapse single-value PHI nodes. This is necessary to undo
// unprofitable PRE transformations.
Value *Repl = Addr;
if (isa<PHINode>(Addr) && MemoryInst->hasOneUse()) {
PHINode *P = cast<PHINode>(Addr);
Instruction *Consensus = 0;
unsigned NumUses = 0;
for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) {
Instruction *Incoming = dyn_cast<Instruction>(P->getIncomingValue(i));
if (!Incoming || (Consensus && !Incoming->isIdenticalTo(Consensus))) {
Consensus = 0;
break;
}
if (!Consensus || Incoming->isIdenticalTo(Consensus)) {
if (Incoming->getNumUses() > NumUses) {
Consensus = Incoming;
NumUses = Incoming->getNumUses();
}
continue;
}
}
if (Consensus) Addr = Consensus;
}
// Figure out what addressing mode will be built up for this operation.
SmallVector<Instruction*, 16> AddrModeInsts;
ExtAddrMode AddrMode = AddressingModeMatcher::Match(Addr, AccessTy,MemoryInst,
@ -725,10 +751,10 @@ bool CodeGenPrepare::OptimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
SunkAddr = new IntToPtrInst(Result, Addr->getType(), "sunkaddr",InsertPt);
}
MemoryInst->replaceUsesOfWith(Addr, SunkAddr);
MemoryInst->replaceUsesOfWith(Repl, SunkAddr);
if (Addr->use_empty()) {
RecursivelyDeleteTriviallyDeadInstructions(Addr);
if (Repl->use_empty()) {
RecursivelyDeleteTriviallyDeadInstructions(Repl);
// This address is now available for reassignment, so erase the table entry;
// we don't want to match some completely different instruction.
SunkAddrs[Addr] = 0;