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Fix PR5262: when folding select into PHI, make sure all operands are available

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in the PHI's Basic Block. This uses a conservative approach, because we don't
have dominator info in instcombine.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84754 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Torok Edwin
2009-10-21 10:49:00 +00:00
parent 4e4bba5c80
commit 0739bd0ab2
3 changed files with 169 additions and 6 deletions
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66
lib/Transforms/Scalar/InstructionCombining.cpp
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@@ -1985,6 +1985,42 @@ static Instruction *FoldOpIntoSelect(Instruction &Op, SelectInst *SI,
return 0;
}
// Check whether all the operands of the PHI dominate the PHI node,
// knowing that the PHI's operands either dominate BB, or are defined in the BB.
static bool checkPHI(PHINode *PN, BasicBlock *BB)
{
BasicBlock *phiBB = PN->getParent();
for (unsigned i=0;i<PN->getNumIncomingValues();i++) {
Instruction *I = dyn_cast<Instruction>(PN->getIncomingValue(i));
if (!I)
continue;
BasicBlock *pBB = I->getParent();
if (pBB == BB) {
// another PHI in same BB is always before PN (PN is last phi).
if (isa<PHINode>(I))
continue;
// An instruction in the same BB, and not a phi, this is after PN.
return false;
}
if (phiBB == BB)
continue;
// We don't have dominator info, so just check that the instruction
// is not defined in on of the BB on the unique path between BB and phiBB.
// If there is no such unique path, or pBB equals to one of the BBs on that
// path we know that this operand doesn't dominate the PHI node.
BasicBlock *B = PN->getIncomingBlock(i);
while ((B = B->getUniquePredecessor())) {
if (pBB == B)
return false;
if (B == phiBB)
break;
}
// No unique path -> doesn't dominate
if (!B)
return false;
}
return true;
}
/// FoldOpIntoPhi - Given a binary operator, cast instruction, or select which
/// has a PHI node as operand #0, see if we can fold the instruction into the
@@ -2036,9 +2072,13 @@ Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I,
// Okay, we can do the transformation: create the new PHI node.
PHINode *NewPN = PHINode::Create(I.getType(), "");
NewPN->reserveOperandSpace(PN->getNumOperands()/2);
InsertNewInstBefore(NewPN, *PN);
NewPN->takeName(PN);
// We must the PHI node as the last PHI, because it may use one of the other
// PHIs.
BasicBlock::iterator BBIt = PN;
while (isa<PHINode>(BBIt)) ++BBIt;
InsertNewInstBefore(NewPN, *BBIt);
SmallVector<Instruction*, 2> tmpWorklist;
// Next, add all of the operands to the PHI.
if (SelectInst *SI = dyn_cast<SelectInst>(&I)) {
// We only currently try to fold the condition of a select when it is a phi,
@@ -2058,7 +2098,7 @@ Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I,
InV = SelectInst::Create(PN->getIncomingValue(i), TrueVInPred,
FalseVInPred,
"phitmp", NonConstBB->getTerminator());
Worklist.Add(cast<Instruction>(InV));
tmpWorklist.push_back(cast<Instruction>(InV));
}
NewPN->addIncoming(InV, ThisBB);
}
@@ -2084,8 +2124,7 @@ Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I,
NonConstBB->getTerminator());
else
llvm_unreachable("Unknown binop!");
Worklist.Add(cast<Instruction>(InV));
tmpWorklist.push_back(cast<Instruction>(InV));
}
NewPN->addIncoming(InV, PN->getIncomingBlock(i));
}
@@ -2101,11 +2140,26 @@ Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I,
InV = CastInst::Create(CI->getOpcode(), PN->getIncomingValue(i),
I.getType(), "phitmp",
NonConstBB->getTerminator());
Worklist.Add(cast<Instruction>(InV));
tmpWorklist.push_back(cast<Instruction>(InV));
}
NewPN->addIncoming(InV, PN->getIncomingBlock(i));
}
}
// The PHI's operands must dominate the PHI, if we can't prove that
// undo this transformation.
if (!checkPHI(NewPN, I.getParent())) {
Worklist.Remove(NewPN);
NewPN->eraseFromParent();
while (!tmpWorklist.empty()) {
tmpWorklist.pop_back_val()->eraseFromParent();
}
return 0;
}
while (!tmpWorklist.empty()) {
Worklist.Add(tmpWorklist.pop_back_val());
}
NewPN->takeName(PN);
Worklist.Add(PN);
return ReplaceInstUsesWith(I, NewPN);
}