Mark calls in thunk functions as tail-call optimization candidates

When a thunk is generated with a call to the original adjusted function, 
the thunk appears in the debugger call stack. We want the backend to perform
tail-call optimization on the call, to make it invisible to the debugger.

This fixes PR24235

Patch by: amjad.aboud@intel.com
Differential Revision: http://reviews.llvm.org/D11476

llvm-svn: 244207

2 files changed, 3 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
index 42cfd36e845..83f45b5da2c 100644
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -312,6 +312,8 @@ void CodeGenFunction::EmitCallAndReturnForThunk(llvm::Value *Callee,
   // Consider return adjustment if we have ThunkInfo.
   if (Thunk && !Thunk->Return.isEmpty())
     RV = PerformReturnAdjustment(*this, ResultType, RV, *Thunk);
+  else if (llvm::CallInst* Call = dyn_cast<llvm::CallInst>(CallOrInvoke))
+    Call->setTailCallKind(llvm::CallInst::TCK_Tail);
 
   // Emit return.
   if (!ResultType->isVoidType() && Slot.isNull())
diff --git a/clang/test/CodeGenCXX/microsoft-abi-structors.cpp b/clang/test/CodeGenCXX/microsoft-abi-structors.cpp
index 594dea473ef..88400e7c0bd 100644
--- a/clang/test/CodeGenCXX/microsoft-abi-structors.cpp
+++ b/clang/test/CodeGenCXX/microsoft-abi-structors.cpp
@@ -176,7 +176,7 @@ void foo() {
 //      Do an adjustment from B* to C*.
 // DTORS2:   getelementptr i8, i8* %{{.*}}, i32 -4
 // DTORS2:   bitcast i8* %{{.*}} to %"struct.dtor_in_second_nvbase::C"*
-// DTORS2:   %[[CALL:.*]] = call x86_thiscallcc i8* @"\01??_GC@dtor_in_second_nvbase@@UAEPAXI@Z"
+// DTORS2:   %[[CALL:.*]] = tail call x86_thiscallcc i8* @"\01??_GC@dtor_in_second_nvbase@@UAEPAXI@Z"
 // DTORS2:   ret i8* %[[CALL]]
 
 }