[llvm] r329027 - [InstCombine] Don't strip function type casts from musttail calls

[Reid Kleckner via llvm-commits]

Author: rnk
Date: Mon Apr  2 15:49:44 2018
New Revision: 329027

URL: http://llvm.org/viewvc/llvm-project?rev=329027&view=rev
Log:
[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

Added:
    llvm/trunk/test/Transforms/InstCombine/musttail-thunk.ll
Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp?rev=329027&r1=329026&r2=329027&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp Mon Apr  2 15:49:44 2018
@@ -3996,10 +3996,19 @@ bool InstCombiner::transformConstExprCas
   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();
 

Added: llvm/trunk/test/Transforms/InstCombine/musttail-thunk.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/musttail-thunk.ll?rev=329027&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/musttail-thunk.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/musttail-thunk.ll Mon Apr  2 15:49:44 2018
@@ -0,0 +1,32 @@
+; RUN: opt -instcombine -S < %s | FileCheck %s
+
+; These are both direct calls, but make sure instcombine leaves the casts
+; alone.
+
+define i32 @call_thunk(i32 %x, i32 %y) {
+  %r = call i32 bitcast (void (i32, ...)* @inc_first_arg_thunk to i32 (i32, i32)*)(i32 %x, i32 %y)
+  ret i32 %r
+}
+
+; CHECK-LABEL: define i32 @call_thunk(i32 %x, i32 %y)
+; CHECK:   %r = call i32 bitcast (void (i32, ...)* @inc_first_arg_thunk to i32 (i32, i32)*)(i32 %x, i32 %y)
+; CHECK:   ret i32 %r
+
+define internal void @inc_first_arg_thunk(i32 %arg1, ...) #0 {
+entry:
+  %inc = add i32 %arg1, 1
+  musttail call void (i32, ...) bitcast (i32 (i32, i32)* @plus to void (i32, ...)*)(i32 %inc, ...)
+  ret void
+}
+
+; CHECK-LABEL: define internal void @inc_first_arg_thunk(i32 %arg1, ...) #0
+; CHECK:   %inc = add i32 %arg1, 1
+; CHECK:   musttail call void (i32, ...) bitcast (i32 (i32, i32)* @plus to void (i32, ...)*)(i32 %inc, ...)
+; CHECK:   ret void
+
+define internal i32 @plus(i32 %x, i32 %y) {
+  %r = add i32 %x, %y
+  ret i32 %r
+}
+
+attributes #0 = { "thunk" }