[BasicAA] Fix AA bug on dynamic allocas and stackrestore
Summary:
BasicAA has special logic for unescaped allocas, which normally applies
equally well to dynamic and static allocas. However, llvm.stackrestore
has the power to end the lifetime of dynamic allocas, without referring
to them directly.
stackrestore is already marked with the most conservative memory
modification attributes, but because the alloca is not escaped, the
normal logic produces incorrect results. I think BasicAA needs a special
case here to teach it about the relationship between dynamic allocas and
stackrestore.
Fixes PR40118
Reviewers: gbiv, efriedma, george.burgess.iv
Subscribers: hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D55969
llvm-svn: 349945
diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index b7aa395..5bb85b4 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -812,6 +812,12 @@
!CI->getAttributes().hasAttrSomewhere(Attribute::ByVal))
return ModRefInfo::NoModRef;
+ // Stack restore is able to modify unescaped dynamic allocas. Assume it may
+ // modify them even though the alloca is not escaped.
+ if (auto *AI = dyn_cast<AllocaInst>(Object))
+ if (!AI->isStaticAlloca() && isIntrinsicCall(CS, Intrinsic::stackrestore))
+ return ModRefInfo::Mod;
+
// If the pointer is to a locally allocated object that does not escape,
// then the call can not mod/ref the pointer unless the call takes the pointer
// as an argument, and itself doesn't capture it.