Re: [PATCH v3] c-family: Enable -Wstrict-aliasing even with -fno-strict-aliasing enabled

[sammy]

On Jun 10, 2026, at 3:58 AM, Richard Biener <richard.guent...@gmail.com> wrote: +  int m_saved; +}; On Tue, Jun 9, 2026 at 9:45 PM Sammy Al Hashemi <sa...@salh.xyz> wrote: The -Wstrict-aliasing warning was gated on flag_strict_aliasing, so passing -fno-strict-aliasing silenced the warning even when explicitly requested with -Wstrict-aliasing.  The warning analysis is purely type-based and does not depend on the optimization being active, so temporarily enable flag_strict_aliasing around the alias set query calls to get meaningful results for the warning. gcc/c-family/ChangeLog:        * c-warn.cc (strict_aliasing_warning): Remove guard on        flag_strict_aliasing.  Temporarily enable it via RAII around        alias set queries so the warning fires independently. gcc/ChangeLog:        * doc/invoke.texi (-Wstrict-aliasing): Document that the        warning now works independently of -fstrict-aliasing. gcc/testsuite/ChangeLog:        * c-c++-common/Wstrict-aliasing2-with-fno.c: New test.        * c-c++-common/Wstrict-aliasing3-with-fno.c: New test. Signed-off-by: Sammy Al Hashemi <sa...@salh.xyz> --- Thanks for your feedback, I'm still new to contributing here so I appreciate it. Changes from v2:    - Added RAII class (auto_override_flag) to save/restore      flag_strict_aliasing    - Filled in ChangeLog descriptions gcc/c-family/c-warn.cc                        | 28 +++++++++++++++++-- gcc/doc/invoke.texi                           | 16 +++++++---- .../c-c++-common/Wstrict-aliasing2-with-fno.c | 12 ++++++++ .../c-c++-common/Wstrict-aliasing3-with-fno.c | 12 ++++++++ 4 files changed, 60 insertions(+), 8 deletions(-) create mode 100644 gcc/testsuite/c-c++-common/Wstrict-aliasing2-with-fno.c create mode 100644 gcc/testsuite/c-c++-common/Wstrict-aliasing3-with-fno.c diff --git a/gcc/c-family/c-warn.cc b/gcc/c-family/c-warn.cc index 1767d2dc090..072c16f9b64 100644 --- a/gcc/c-family/c-warn.cc +++ b/gcc/c-family/c-warn.cc @@ -685,6 +685,27 @@ warn_if_unused_value (const_tree exp, location_t locus, bool quiet)     } } +/* RAII guard to temporarily override an integer flag, restoring its +   original value when the guard goes out of scope.  */ +class auto_override_flag +{ +public: +  auto_override_flag (int &flag, int new_value) +    : m_flag (flag), m_saved (flag) +  { +    m_flag = new_value; +  } + +  ~auto_override_flag () +  { +    m_flag = m_saved; +  } + +private: +  int &m_flag; +  int m_saved; +}; Somehow I think we already have such class, in the C++ frontend? If it’s there I’m happy to make the switch. I’m still new to the codebase and would be curious if there is a general spot where common utilities like this belong.