[PATCH] D148419: [clang][AST] Constexpr evaluator should treat [[gnu::weak]] member pointer comparisons as evaluation failure

[Takuya Shimizu via Phabricator via cfe-commits]

hazohelet created this revision.
hazohelet added reviewers: rsmith, tbaeder, shafik, aaron.ballman.
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hazohelet requested review of this revision.
Herald added a project: clang.

This patch fixes the wrong signal from the constexpr evaluator that `[[gnu::weak]]` member pointer comparison is valid, while it is emitting notes on them.
I found a crashing case fixed by this change and added it as a test case.
https://godbolt.org/z/8391fGjGn

I noticed this while I was working on D146358 <https://reviews.llvm.org/D146358>
CC @rsmith as the original author


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D148419

Files:
  clang/lib/AST/ExprConstant.cpp
  clang/test/SemaCXX/crash-lambda-weak-attr.cpp


Index: clang/test/SemaCXX/crash-lambda-weak-attr.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/crash-lambda-weak-attr.cpp
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++2b %s
+
+struct Weak {
+    [[gnu::weak]]void weak_method();
+};
+static_assert([](){ return &Weak::weak_method != nullptr; }()); // expected-error {{static assertion expression is not an integral constant expression}} \
+                                                                // expected-note {{comparison against pointer to weak member 'Weak::weak_method' can only be performed at runtime}} \
+                                                                // expected-note {{in call to}}
+
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -13142,12 +13142,12 @@
     if (LHSValue.getDecl() && LHSValue.getDecl()->isWeak()) {
       Info.FFDiag(E, diag::note_constexpr_mem_pointer_weak_comparison)
           << LHSValue.getDecl();
-      return true;
+      return false;
     }
     if (RHSValue.getDecl() && RHSValue.getDecl()->isWeak()) {
       Info.FFDiag(E, diag::note_constexpr_mem_pointer_weak_comparison)
           << RHSValue.getDecl();
-      return true;
+      return false;
     }
 
     // C++11 [expr.eq]p2:


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