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Fix SimplifyCFG/2006-10-19-UncondDiv.ll by disabling a bad xform.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31061 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-10-20 00:42:07 +00:00
parent 8a53688a13
commit b74b181630
1 changed files with 38 additions and 21 deletions
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59
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -323,7 +323,14 @@ static Value *GetIfCondition(BasicBlock *BB,
static bool DominatesMergePoint(Value *V, BasicBlock *BB,
std::set<Instruction*> *AggressiveInsts) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return true; // Non-instructions all dominate instructions.
if (!I) {
// Non-instructions all dominate instructions, but not all constantexprs
// can be executed unconditionally.
if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
if (C->canTrap())
return false;
return true;
}
BasicBlock *PBB = I->getParent();
// We don't want to allow weird loops that might have the "if condition" in
@ -1297,28 +1304,38 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
if (FVPN->getParent() == FalseSucc)
FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
TrueSucc->removePredecessor(BI->getParent());
FalseSucc->removePredecessor(BI->getParent());
// In order for this transformation to be safe, we must be able to
// unconditionally execute both operands to the return. This is
// normally the case, but we could have a potentially-trapping
// constant expression that prevents this transformation from being
// safe.
if ((!isa<ConstantExpr>(TrueValue) ||
!cast<ConstantExpr>(TrueValue)->canTrap()) &&
(!isa<ConstantExpr>(TrueValue) ||
!cast<ConstantExpr>(TrueValue)->canTrap())) {
TrueSucc->removePredecessor(BI->getParent());
FalseSucc->removePredecessor(BI->getParent());
// Insert a new select instruction.
Value *NewRetVal;
Value *BrCond = BI->getCondition();
if (TrueValue != FalseValue)
NewRetVal = new SelectInst(BrCond, TrueValue,
FalseValue, "retval", BI);
else
NewRetVal = TrueValue;
DEBUG(std::cerr << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
<< "\n " << *BI << "Select = " << *NewRetVal
<< "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
// Insert a new select instruction.
Value *NewRetVal;
Value *BrCond = BI->getCondition();
if (TrueValue != FalseValue)
NewRetVal = new SelectInst(BrCond, TrueValue,
FalseValue, "retval", BI);
else
NewRetVal = TrueValue;
DEBUG(std::cerr << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
<< "\n " << *BI << "Select = " << *NewRetVal
<< "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
new ReturnInst(NewRetVal, BI);
BI->eraseFromParent();
if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
if (isInstructionTriviallyDead(BrCondI))
BrCondI->eraseFromParent();
return true;
new ReturnInst(NewRetVal, BI);
BI->eraseFromParent();
if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
if (isInstructionTriviallyDead(BrCondI))
BrCondI->eraseFromParent();
return true;
}
}
}
}