[CodeGen] bugfix: ApplyDebugLocation goes out of scope before intended

[usama54321]

Summary

ApplyDebugLocation goes out of scope at the end of the conditional branch which is a bug. This causes a crash in the test added in the patch.

rdar://103570533

[aprantl]

Code LGTM, it would be nice if we could further reduce the test case.

clang/test/CodeGenObjC/objc-arc-ubsan-debugging.m

3

Could you get by with just defining NSObject inline and forward-declaring NSString? Including Foundation.h is very expensive.

[usama54321]

Removing unnecessary code from test

[usama54321]

The libcxx test failure seems unrelated and seems to be failing on master
https://buildkite.com/llvm-project/libcxx-ci/builds?branch=master

clang/lib/CodeGen/CodeGenFunction.cpp

 //===--- CodeGenFunction.cpp - Emit LLVM Code from ASTs for a Function ----===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
void CodeGenFunction::FinishFunction(SourceLocation EndLoc) {
   // Pop any cleanups that might have been associated with the
   // parameters.  Do this in whatever block we're currently in; it's
   // important to do this before we enter the return block or return
   // edges will be *really* confused.
   bool HasCleanups = EHStack.stable_begin() != PrologueCleanupDepth;
   bool HasOnlyLifetimeMarkers =
       HasCleanups && EHStack.containsOnlyLifetimeMarkers(PrologueCleanupDepth);
   bool EmitRetDbgLoc = !HasCleanups || HasOnlyLifetimeMarkers;
+
+  std::optional<ApplyDebugLocation> OAL;
   if (HasCleanups) {
     // Make sure the line table doesn't jump back into the body for
     // the ret after it's been at EndLoc.
-    std::optional<ApplyDebugLocation> AL;
     if (CGDebugInfo *DI = getDebugInfo()) {
       if (OnlySimpleReturnStmts)
         DI->EmitLocation(Builder, EndLoc);
       else
         // We may not have a valid end location. Try to apply it anyway, and
         // fall back to an artificial location if needed.
-        AL = ApplyDebugLocation::CreateDefaultArtificial(*this, EndLoc);
+        OAL = ApplyDebugLocation::CreateDefaultArtificial(*this, EndLoc);
     }
 
     PopCleanupBlocks(PrologueCleanupDepth);
   }
 
   // Emit function epilog (to return).
   llvm::DebugLoc Loc = EmitReturnBlock();
 

clang/test/CodeGenObjC/objc-arc-ubsan-debugging.m

+// RUN: %clang -x objective-c -target arm64-apple-macos12.0 -fobjc-arc -std=gnu99  -O0 -fsanitize=undefined -fsanitize=nullability -c %s -v -g
+
+@interface NSString
+@end
+
+struct A {
+    NSString *a;
+};
+
+NSString* _Nonnull foo()
+{
+    struct A a;
+    return 0;
+}