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

1 files changed, 6 insertions, 0 deletions

diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 334ef4a7d5..1110a017de 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -239,6 +239,12 @@ BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
       // 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.