[clang] Allow class with anonymous union member to be const-default-constructible even if a union member has a default member initializer (#95854) #96301

Rajveer100 · 2024-06-21T13:01:51Z

Resolves #95854

-- As per https://eel.is/c++draft/dcl.init#general-8.3

llvmbot · 2024-06-21T13:02:25Z

@llvm/pr-subscribers-clang

Author: Rajveer Singh Bharadwaj (Rajveer100)

Changes

Resolves #95854

-- As per https://eel.is/c++draft/dcl.init#general-8.3

Full diff: https://github.com/llvm/llvm-project/pull/96301.diff

2 Files Affected:

(modified) clang/include/clang/AST/DeclCXX.h (+2-1)
(added) clang/test/Sema/debug-95854.cpp (+11)

diff --git a/clang/include/clang/AST/DeclCXX.h b/clang/include/clang/AST/DeclCXX.h
index fb52ac804849d..1d1083a5d6205 100644
--- a/clang/include/clang/AST/DeclCXX.h
+++ b/clang/include/clang/AST/DeclCXX.h
@@ -1392,7 +1392,8 @@ class CXXRecordDecl : public RecordDecl {
   bool allowConstDefaultInit() const {
     return !data().HasUninitializedFields ||
            !(data().HasDefaultedDefaultConstructor ||
-             needsImplicitDefaultConstructor());
+             needsImplicitDefaultConstructor()) ||
+           hasInClassInitializer();
   }
 
   /// Determine whether this class has a destructor which has no
diff --git a/clang/test/Sema/debug-95854.cpp b/clang/test/Sema/debug-95854.cpp
new file mode 100644
index 0000000000000..1fb976558650d
--- /dev/null
+++ b/clang/test/Sema/debug-95854.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -std=c++23 -fsyntax-only -verify %s
+//
+// expected-no-diagnostics
+
+struct A {
+  union {
+    int n = 0;
+    int m;
+  };
+};
+const A a;

Rajveer100 · 2024-06-21T13:05:27Z

@zygoloid

shafik

Thank you for this fix. It needs a release note and your summary should have some more details on what the cause of the bug is and how your PR fixes it. efriedma-quic's comment provides a good framework for explaining the cause.

It also looks like your change broke some tests:

Clang :: AST/Interp/records.cpp
Clang :: SemaCXX/cxx0x-cursory-default-delete.cpp

Are these expected breaks? If so then please update these tests

clang/include/clang/AST/DeclCXX.h

clang/test/Sema/debug-95854.cpp

Rajveer100 · 2024-07-05T11:14:52Z

@zygoloid
Let me know if the new changes work well.

Rajveer100 · 2024-08-10T11:30:08Z

@zygoloid
Could you review this?

clang/test/SemaCXX/GH95854.cpp

Sirraide

I think the changes generally make sense.

clang/docs/ReleaseNotes.rst

clang/include/clang/AST/DeclCXX.h

Rajveer100 · 2024-08-13T17:09:13Z

@Sirraide The tests pass, not sure about the failure though.

shafik

I don't think the test failures look related to the changes can you push and empty change to see if rerunning the tests comes up clean?

Rajveer100 · 2024-08-27T07:56:29Z

Only windows failed.

PS: Pushed again to resolve merge conflict.

cor3ntin

Here are more tests to consider https://godbolt.org/z/M6fj5zTfq
Thanks!

clang/lib/AST/DeclCXX.cpp

clang/docs/ReleaseNotes.rst

Rajveer100 · 2024-08-27T10:44:23Z

@cor3ntin
CI looks good.

cor3ntin · 2024-08-27T12:53:09Z

Neither GCC, EDG nor MSVC agree with us https://godbolt.org/z/Wqrhnz63a
The behavior of GCC is a bit weird but I am pretty sure the last two tests should pass
@hubert-reinterpretcast

clang/test/SemaCXX/GH95854.cpp

Rajveer100 · 2024-10-01T11:04:58Z

@shafik
Anything else that's needed?

cor3ntin

LGTM, Thanks!
Give a couple of days to @shafik before merging

Rajveer100 · 2024-10-08T06:08:11Z

Thanks for the approval @cor3ntin, could you land this for me?!

…onstructible even if a union member has a default member initializer (llvm#95854) Resolves llvm#95854 Clang incorrectly considers a class with an anonymous union member to not be const-default-constructible even if a union member has a default member initializer. ``` struct A { union { int n = 0; int m; }; }; const A a; ``` -- As per https://eel.is/c++draft/dcl.init#general-8.3

llvm-ci · 2024-10-22T09:08:21Z

LLVM Buildbot has detected a new failure on builder openmp-offload-libc-amdgpu-runtime running on omp-vega20-1 while building clang at step 11 "Add check check-libc-amdgcn-amd-amdhsa".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/73/builds/7389

Here is the relevant piece of the build log for the reference

Step 11 (Add check check-libc-amdgcn-amd-amdhsa) failure: 1200 seconds without output running [b'ninja', b'-j 32', b'check-libc-amdgcn-amd-amdhsa'], attempting to kill
...
[2442/2681] Linking CXX executable libc/test/src/string/libc.test.src.string.strncat_test.__hermetic__.__build__
[2443/2681] Linking CXX executable libc/test/src/locale/libc.test.src.locale.localeconv_test.__hermetic__.__build__
[2444/2681] Linking CXX executable libc/test/src/inttypes/libc.test.src.inttypes.strtoimax_test.__hermetic__.__build__
[2445/2681] Linking CXX executable libc/test/src/inttypes/libc.test.src.inttypes.strtoumax_test.__hermetic__.__build__
[2446/2681] Linking CXX executable libc/test/src/string/libc.test.src.string.memcmp_test.__hermetic__.__build__
[2447/2681] Linking CXX executable libc/test/src/time/libc.test.src.time.clock_test.__hermetic__.__build__
[2448/2681] Linking CXX executable libc/test/src/string/libc.test.src.string.memmove_test.__hermetic__.__build__
[2449/2681] Linking CXX executable libc/test/src/time/libc.test.src.time.clock_gettime_test.__hermetic__.__build__
[2450/2681] Linking CXX executable libc/test/src/stdio/libc.test.src.stdio.asprintf_test.__hermetic__.__build__
[2451/2681] Linking CXX executable libc/test/src/stdio/libc.test.src.stdio.vasprintf_test.__hermetic__.__build__
command timed out: 1200 seconds without output running [b'ninja', b'-j 32', b'check-libc-amdgcn-amd-amdhsa'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1470.210201

llvmbot added clang Clang issues not falling into any other category clang:frontend Language frontend issues, e.g. anything involving "Sema" labels Jun 21, 2024

shafik reviewed Jun 21, 2024

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Rajveer100 force-pushed the branch-for-issue-95854 branch from c8f2496 to b964923 Compare June 22, 2024 19:06

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Rajveer100 force-pushed the branch-for-issue-95854 branch 2 times, most recently from 3fb29e5 to 751e630 Compare July 5, 2024 11:10

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Rajveer100 force-pushed the branch-for-issue-95854 branch 9 times, most recently from 49e6fb5 to 3ccb1c9 Compare August 13, 2024 13:36

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Rajveer100 force-pushed the branch-for-issue-95854 branch 2 times, most recently from d6b3358 to 1e1e446 Compare October 1, 2024 11:04

cor3ntin approved these changes Oct 3, 2024

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Rajveer100 force-pushed the branch-for-issue-95854 branch from 1e1e446 to 38ded4c Compare October 16, 2024 10:44

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Rajveer100 force-pushed the branch-for-issue-95854 branch from 38ded4c to c12be47 Compare October 19, 2024 10:44

Rajveer100 force-pushed the branch-for-issue-95854 branch from c12be47 to cbd6e83 Compare October 19, 2024 10:46

cor3ntin merged commit 7305734 into llvm:main Oct 22, 2024
7 of 9 checks passed

[clang] Allow class with anonymous union member to be const-default-constructible even if a union member has a default member initializer (#95854) #96301

[clang] Allow class with anonymous union member to be const-default-constructible even if a union member has a default member initializer (#95854) #96301

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