[Sema][ObjC] Treat unknown selector messages as unrecoverable errors under ARC

[ahatanak]

Fixes a CodeGen crash observed when C++ auto variable types remained non-deduced due to a message being sent with an unknown selector under ARC.

By treating these instances as an unrecoverable error, we prevent the compiler from proceeding to CodeGen with fundamentally incorrect code.

rdar://144394403

[llvmbot]

@llvm/pr-subscribers-clang

Author: Akira Hatanaka (ahatanak)

Changes

Fixes a CodeGen crash observed when C++ auto variable types remained non-deduced due to a message being sent with an unknown selector under ARC.

By treating these instances as an unrecoverable error, we prevent the compiler from proceeding to CodeGen with fundamentally incorrect code.

rdar://144394403

---

Full diff: https://github.com/llvm/llvm-project/pull/146803.diff

2 Files Affected:

• (modified) clang/lib/Basic/DiagnosticIDs.cpp (+5-1)
• (modified) clang/test/SemaObjCXX/arc-0x.mm (+6-1)

diff --git a/clang/lib/Basic/DiagnosticIDs.cpp b/clang/lib/Basic/DiagnosticIDs.cpp
index dcf0c6cb54282..04a7f7732429d 100644
--- a/clang/lib/Basic/DiagnosticIDs.cpp
+++ b/clang/lib/Basic/DiagnosticIDs.cpp
@@ -832,7 +832,11 @@ bool DiagnosticIDs::isUnrecoverable(unsigned DiagID) const {
       DiagID == diag::err_unavailable_message)
     return false;
 
-  // Currently we consider all ARC errors as recoverable.
+  // Currently we consider all ARC errors except err_arc_may_not_respond as
+  // recoverable.
+  if (DiagID == diag::err_arc_may_not_respond)
+    return true;
+
   if (isARCDiagnostic(DiagID))
     return false;
 
diff --git a/clang/test/SemaObjCXX/arc-0x.mm b/clang/test/SemaObjCXX/arc-0x.mm
index ac788686a7374..bcaa5da6b9283 100644
--- a/clang/test/SemaObjCXX/arc-0x.mm
+++ b/clang/test/SemaObjCXX/arc-0x.mm
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -std=c++11 -fsyntax-only -fobjc-arc -fobjc-runtime-has-weak -fobjc-weak -verify -fblocks -fobjc-exceptions %s
+// RUN: %clang_cc1 -std=c++11 -fobjc-arc -fobjc-runtime-has-weak -fobjc-weak -verify -fblocks -fobjc-exceptions -emit-llvm -o - %s
 
 // "Move" semantics, trivial version.
 void move_it(__strong id &&from) {
@@ -14,6 +14,11 @@ @interface A
 // don't warn about this
 extern "C" A* MakeA();
 
+void test_nonexistent_method(A *a) {
+  // This used to crash in codegen.
+  auto a1 = [a foo]; // expected-error {{no visible @interface for 'A' declares the selector 'foo'}}
+}
+
 // Ensure that deduction works with lifetime qualifiers.
 void deduction(id obj) {
   auto a = [[A alloc] init];

[rjmccall]

Code LGTM. Please elaborate in the comment to explain why this particular error needs to be considered unrecoverable.