[PATCH] D11476: Marked call instruction in thunk function with musttail attribute when applicable

[Amjad Aboud]

aaboud created this revision.
aaboud added reviewers: rnk, hans.
aaboud added a subscriber: cfe-commits.
aaboud set the repository for this revision to rL LLVM.

This patch fix PR24235.
When thunk function is being generated with a call to the original adjusted function, the thunk function will appear in the call stack of the debugger.
To solve this issue, the thunk function should try replace the call instruction with a jump instruction.

This patch mark the call function with musttail attribute, when it is applicable, to force the backend to replace the call with a jump.

Notice that marking the call with a tail might be safer, however, it is not good enough to remove the call in the 32-bit mode.

Repository:
  rL LLVM

http://reviews.llvm.org/D11476

Files:
  lib/CodeGen/CGVTables.cpp
  test/CodeGenCXX/microsoft-abi-structors.cpp

Index: lib/CodeGen/CGVTables.cpp
===================================================================
--- lib/CodeGen/CGVTables.cpp
+++ lib/CodeGen/CGVTables.cpp
@@ -312,6 +312,8 @@
   // 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_MustTail);
 
   // Emit return.
   if (!ResultType->isVoidType() && Slot.isNull())
Index: test/CodeGenCXX/microsoft-abi-structors.cpp
===================================================================
--- test/CodeGenCXX/microsoft-abi-structors.cpp
+++ test/CodeGenCXX/microsoft-abi-structors.cpp
@@ -176,7 +176,7 @@
 //      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 at dtor_in_second_nvbase@@UAEPAXI at Z"
+// DTORS2:   %[[CALL:.*]] = musttail call x86_thiscallcc i8* @"\01??_GC at dtor_in_second_nvbase@@UAEPAXI at Z"
 // DTORS2:   ret i8* %[[CALL]]
 
 }


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