[clang] Add debug info in MicrosoftCXXABI::EmitVirtualMemPtrThunk()

[aeubanks]

Summary

(Probably) fixes https://crbug.com/1355639

[aeubanks]

update test

[dblaikie]

clang/test/CodeGenCXX/microsoft-abi-member-pointers-debug-info.cpp

13

might be worth checking what location this is, to show it's a good one? (the code added makes some choice about what location to ascribe to this call, so the test should probably verify that)

[aeubanks]

update test

[dblaikie]

Sounds good to me.

(Ah, I see, that chrome bug actually hit the underlying problem, not even the verifier constraint - when the constraint is violated & not detected, then code gets inlined without being stitched up to the inline scope and you end up with instructions in a function where the function has one subprogram, but the scope chain of the instruction's location leads to a different subprogram - which is a problem/makes building the scope tree weird/not possible (because it's no longer a tree but a forest))

clang/lib/CodeGen/MicrosoftCXXABI.cpp

MicrosoftCXXABI::EmitVirtualMemPtrThunk(const CXXMethodDecl *MD,
   // Build FunctionArgs, but only include the implicit 'this' parameter
   // declaration.
   FunctionArgList FunctionArgs;
   buildThisParam(CGF, FunctionArgs);
 
   // Start defining the function.
   CGF.StartFunction(GlobalDecl(), FnInfo.getReturnType(), ThunkFn, FnInfo,
                     FunctionArgs, MD->getLocation(), SourceLocation());
+
+  ApplyDebugLocation AL(CGF, MD->getLocation());
   setCXXABIThisValue(CGF, loadIncomingCXXThis(CGF));
 
   // Load the vfptr and then callee from the vftable.  The callee should have
   // adjusted 'this' so that the vfptr is at offset zero.
   llvm::Type *ThunkPtrTy = ThunkTy->getPointerTo();
   llvm::Value *VTable = CGF.GetVTablePtr(
       getThisAddress(CGF), ThunkPtrTy->getPointerTo(), MD->getParent());
 

clang/test/CodeGenCXX/microsoft-abi-member-pointers-debug-info.cpp

+// RUN: %clang_cc1 -std=c++11 -debug-info-kind=line-tables-only -fno-rtti -emit-llvm %s -o - -triple=x86_64-pc-win32 -fms-extensions | FileCheck %s
+
+struct Task {
+  virtual void Run() = 0;
+};
+
+auto b = &Task::Run;
+
+// CHECK: define {{.*}}@"??_9Task@@$BA@AA"
+// CHECK-NOT: define
+// CHECK: musttail call {{.*}}, !dbg ![[DBG:[0-9]+]]
+
+// CHECK: ![[DBG]] = !DILocation(
+