[InstCombine] Don't strip function type casts from musttail calls
Summary:
The cast simplifications that instcombine does here do not make any
attempt to obey the verifier rules for musttail calls. Therefore we have
to disable them.
Reviewers: efriedma, majnemer, pcc
Subscribers: hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D45186
llvm-svn: 329027
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index f5400f9..31fbaa7 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -3996,10 +3996,19 @@
if (!Callee)
return false;
- // The prototype of a thunk is a lie. Don't directly call such a function.
+ // If this is a call to a thunk function, don't remove the cast. Thunks are
+ // used to transparently forward all incoming parameters and outgoing return
+ // values, so it's important to leave the cast in place.
if (Callee->hasFnAttribute("thunk"))
return false;
+ // If this is a musttail call, the callee's prototype must match the caller's
+ // prototype with the exception of pointee types. The code below doesn't
+ // implement that, so we can't do this transform.
+ // TODO: Do the transform if it only requires adding pointer casts.
+ if (CS.isMustTailCall())
+ return false;
+
Instruction *Caller = CS.getInstruction();
const AttributeList &CallerPAL = CS.getAttributes();