diff options
Diffstat (limited to 'llvm/lib')
| -rw-r--r-- | llvm/lib/Analysis/BasicAliasAnalysis.cpp | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp index 89ae3d0ecce..84affa1caca 100644 --- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp +++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp @@ -781,6 +781,32 @@ ModRefInfo BasicAAResult::getModRefInfo(ImmutableCallSite CS, if (isIntrinsicCall(CS, Intrinsic::experimental_guard)) return MRI_Ref; + // Like assumes, invariant.start intrinsics were also marked as arbitrarily + // writing so that proper control dependencies are maintained but they never + // mod any particular memory location visible to the IR. + // *Unlike* assumes (which are now modeled as NoModRef), invariant.start + // intrinsic is now modeled as reading memory. This prevents hoisting the + // invariant.start intrinsic over stores. Consider: + // *ptr = 40; + // *ptr = 50; + // invariant_start(ptr) + // int val = *ptr; + // print(val); + // + // This cannot be transformed to: + // + // *ptr = 40; + // invariant_start(ptr) + // *ptr = 50; + // int val = *ptr; + // print(val); + // + // The transformation will cause the second store to be ignored (based on + // rules of invariant.start) and print 40, while the first program always + // prints 50. + if (isIntrinsicCall(CS, Intrinsic::invariant_start)) + return MRI_Ref; + // The AAResultBase base class has some smarts, lets use them. return AAResultBase::getModRefInfo(CS, Loc); } |
