By definition, 'tail' calls cannot access the stack frame of their caller.
Expose this as a simple form of mod/ref information. This implements
BasicAA/tailcall-modref.ll
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21796 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 334ef4a..1110a01 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -239,6 +239,12 @@
// because it simply can't get its address.
if (!AddressMightEscape(AI))
return NoModRef;
+
+ // If this is a tail call and P points to a stack location, we know that
+ // the tail call cannot access or modify the local stack.
+ if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
+ if (CI->isTailCall() && isa<AllocaInst>(AI))
+ return NoModRef;
}
// The AliasAnalysis base class has some smarts, lets use them.