From: Duncan P. N. Exon Smith <dexonsmith@apple.com>
Date: Sat, 24 Sep 2016 19:39:47 +0000 (+0000)
Subject: Analysis: Return early in isKnownNonNullAt for ConstantData
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=e31ddb432936642e8c992a420ab6e8afb3965dde;p=llvm

Analysis: Return early in isKnownNonNullAt for ConstantData

Check and return early for ConstantPointerNull and UndefValue
specifically in isKnownNonNullAt, and assert that ConstantData never
make it to isKnownNonNullFromDominatingCondition.

This confirms that isKnownNonNullFromDominatingCondition never walks
through the use-list of an instance of ConstantData.  Given that such
use-lists cross module boundaries, it never really made sense to do so,
and was potentially very expensive.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@282333 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index df86a015569..827e2524915 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -3297,6 +3297,7 @@ static bool isKnownNonNullFromDominatingCondition(const Value *V,
                                                   const Instruction *CtxI,
                                                   const DominatorTree *DT) {
   assert(V->getType()->isPointerTy() && "V must be pointer type");
+  assert(!isa<ConstantData>(V) && "Did not expect ConstantPointerNull");
 
   unsigned NumUsesExplored = 0;
   for (auto *U : V->users()) {
@@ -3333,6 +3334,9 @@ static bool isKnownNonNullFromDominatingCondition(const Value *V,
 
 bool llvm::isKnownNonNullAt(const Value *V, const Instruction *CtxI,
                             const DominatorTree *DT) {
+  if (isa<ConstantPointerNull>(V) || isa<UndefValue>(V))
+    return false;
+
   if (isKnownNonNull(V))
     return true;