[MSVC Compat] Correctly handle finallys nested within finallys

[majnemer]

Summary

We'd lose track of the parent CodeGenFunction, leading us to get
confused with regard to which function a nested finally belonged to.

[rnk]

lib/CodeGen/CGException.cpp

1680–1682

Let's have a new field for this. We don't want most of the behavior controlled by CurCodeDecl in the rest of CodeGen.

[majnemer]

• Address Reid's review comments

[rnk]

lgtm

lib/CodeGen/CGException.cpp

if (llvm::Comdat *C = ParentFn->getComdat()) {
     ParentFn->setComdat(C);
     Fn->setComdat(C);
   } else {
     Fn->setLinkage(llvm::GlobalValue::InternalLinkage);
   }
 
   IsOutlinedSEHHelper = true;
 
   StartFunction(GlobalDecl(), RetTy, Fn, FnInfo, Args,
                 OutlinedStmt->getLocStart(), OutlinedStmt->getLocStart());
+  CurCodeDecl = ParentCGF.CurCodeDecl;
 
   CGM.SetLLVMFunctionAttributes(nullptr, FnInfo, CurFn);
   EmitCapturedLocals(ParentCGF, OutlinedStmt, IsFilter);
 }
 
 /// Create a stub filter function that will ultimately hold the code of the
 /// filter expression. The EH preparation passes in LLVM will outline the code
 /// from the main function body into this stub.

test/CodeGen/exceptions-seh-finally.c

 // CHECK: call void @"\01?fin$0@0@nested___finally___finally_with_eh_edge@@"({{.*}})
 // CHECK-NEXT: cleanupret from %[[outerpad]] unwind to caller
 
 // CHECK-LABEL: define internal void @"\01?fin$0@0@nested___finally___finally_with_eh_edge@@"({{.*}})
 // CHECK: ret void
 
 // CHECK-LABEL: define internal void @"\01?fin$1@0@nested___finally___finally_with_eh_edge@@"({{.*}})
 // CHECK: unreachable
+
+void finally_within_finally() {
+  __try {
+    might_crash();
+  } __finally {
+    __try {
+      might_crash();
+    } __finally {
+    }
+  }
+}
+
+// CHECK-LABEL: define void @finally_within_finally(
+// CHECK: invoke void @might_crash(
+
+// CHECK: call void @"\01?fin$0@0@finally_within_finally@@"(
+// CHECK: call void @"\01?fin$0@0@finally_within_finally@@"({{.*}}) [ "funclet"(
+
+// CHECK-LABEL: define internal void @"\01?fin$0@0@finally_within_finally@@"(
+// CHECK: invoke void @might_crash(
+
+// CHECK: call void @"\01?fin$1@0@finally_within_finally@@"(
+// CHECK: call void @"\01?fin$1@0@finally_within_finally@@"({{.*}}) [ "funclet"(
+
+// CHECK-LABEL: define internal void @"\01?fin$1@0@finally_within_finally@@"(