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ValueTracking: ComputeNumSignBits should tolerate misshapen phi nodes

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PHI nodes can have zero operands in the middle of a transform.  It is
expected that utilities in Analysis don't freak out when this happens.

Note that it is considered invalid to allow these misshapen phi nodes to
make it to another pass.

This fixes PR22086.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225126 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2015-01-04 07:06:53 +00:00
parent a46dd583d6
commit 77e22b7836
2 changed files with 33 additions and 2 deletions
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7
lib/Analysis/ValueTracking.cpp
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@ -1821,13 +1821,16 @@ unsigned ComputeNumSignBits(Value *V, const DataLayout *TD,
case Instruction::PHI: {
PHINode *PN = cast<PHINode>(U);
unsigned NumIncomingValues = PN->getNumIncomingValues();
// Don't analyze large in-degree PHIs.
if (PN->getNumIncomingValues() > 4) break;
if (NumIncomingValues > 4) break;
// Unreachable blocks may have zero-operand PHI nodes.
if (NumIncomingValues == 0) break;
// Take the minimum of all incoming values. This can't infinitely loop
// because of our depth threshold.
Tmp = ComputeNumSignBits(PN->getIncomingValue(0), TD, Depth+1, Q);
for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
for (unsigned i = 1, e = NumIncomingValues; i != e; ++i) {
if (Tmp == 1) return Tmp;
Tmp = std::min(Tmp,
ComputeNumSignBits(PN->getIncomingValue(i), TD,