Fix SimplifyCFG/2006-10-19-UncondDiv.ll by disabling a bad xform.
llvm-svn: 31061
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 7ac9444..867455e 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -323,7 +323,14 @@
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 @@
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;
+ }
}
}
}