Fix a layering violation: hasConstantValue, which is part of the PHINode
class, uses DominatorTree which is an analysis. This change moves all of
the tricky hasConstantValue logic to SimplifyInstruction, and replaces it
with a very simple literal implementation. I already taught users of
hasConstantValue that need tricky stuff to use SimplifyInstruction instead.
I didn't update InlineFunction because the IR looks like it might be in a
funky state at the point it calls hasConstantValue, which makes calling
SimplifyInstruction dangerous since it can in theory do a lot of tricky
reasoning. This may be a pessimization, for example in the case where
all phi node operands are either undef or a fixed constant.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119459 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index cf1548e..c540d6f 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -173,7 +173,7 @@
Value *CommonValue = 0;
for (unsigned i = 0, e = PI->getNumIncomingValues(); i != e; ++i) {
Value *Incoming = PI->getIncomingValue(i);
- // If the incoming value is the phi node itself, it can be safely skipped.
+ // If the incoming value is the phi node itself, it can safely be skipped.
if (Incoming == PI) continue;
Value *V = PI == LHS ?
SimplifyBinOp(Opcode, Incoming, RHS, TD, DT, MaxRecurse) :
@@ -211,7 +211,7 @@
Value *CommonValue = 0;
for (unsigned i = 0, e = PI->getNumIncomingValues(); i != e; ++i) {
Value *Incoming = PI->getIncomingValue(i);
- // If the incoming value is the phi node itself, it can be safely skipped.
+ // If the incoming value is the phi node itself, it can safely be skipped.
if (Incoming == PI) continue;
Value *V = SimplifyCmpInst(Pred, Incoming, RHS, TD, DT, MaxRecurse);
// If the operation failed to simplify, or simplified to a different value
@@ -663,6 +663,40 @@
(Constant *const*)Ops+1, NumOps-1);
}
+/// SimplifyPHINode - See if we can fold the given phi. If not, returns null.
+static Value *SimplifyPHINode(PHINode *PN, const DominatorTree *DT) {
+ // If all of the PHI's incoming values are the same then replace the PHI node
+ // with the common value.
+ Value *CommonValue = 0;
+ bool HasUndefInput = false;
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ Value *Incoming = PN->getIncomingValue(i);
+ // If the incoming value is the phi node itself, it can safely be skipped.
+ if (Incoming == PN) continue;
+ if (isa<UndefValue>(Incoming)) {
+ // Remember that we saw an undef value, but otherwise ignore them.
+ HasUndefInput = true;
+ continue;
+ }
+ if (CommonValue && Incoming != CommonValue)
+ return 0; // Not the same, bail out.
+ CommonValue = Incoming;
+ }
+
+ // If CommonValue is null then all of the incoming values were either undef or
+ // equal to the phi node itself.
+ if (!CommonValue)
+ return UndefValue::get(PN->getType());
+
+ // If we have a PHI node like phi(X, undef, X), where X is defined by some
+ // instruction, we cannot return X as the result of the PHI node unless it
+ // dominates the PHI block.
+ if (HasUndefInput)
+ return ValueDominatesPHI(CommonValue, PN, DT) ? CommonValue : 0;
+
+ return CommonValue;
+}
+
//=== Helper functions for higher up the class hierarchy.
@@ -748,7 +782,7 @@
return SimplifyGEPInst(&Ops[0], Ops.size(), TD, DT);
}
case Instruction::PHI:
- return cast<PHINode>(I)->hasConstantValue(DT);
+ return SimplifyPHINode(cast<PHINode>(I), DT);
}
}
diff --git a/lib/Analysis/Lint.cpp b/lib/Analysis/Lint.cpp
index 4318a30..8b76b87 100644
--- a/lib/Analysis/Lint.cpp
+++ b/lib/Analysis/Lint.cpp
@@ -582,7 +582,7 @@
BBI = BB->end();
}
} else if (PHINode *PN = dyn_cast<PHINode>(V)) {
- if (Value *W = PN->hasConstantValue(DT))
+ if (Value *W = PN->hasConstantValue())
return findValueImpl(W, OffsetOk, Visited);
} else if (CastInst *CI = dyn_cast<CastInst>(V)) {
if (CI->isNoopCast(TD ? TD->getIntPtrType(V->getContext()) :
@@ -615,7 +615,7 @@
// As a last resort, try SimplifyInstruction or constant folding.
if (Instruction *Inst = dyn_cast<Instruction>(V)) {
- if (Value *W = SimplifyInstruction(Inst, TD))
+ if (Value *W = SimplifyInstruction(Inst, TD, DT))
if (W != Inst)
return findValueImpl(W, OffsetOk, Visited);
} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {