[Bug driver/115990] New: Consider deprecating -Ofast

[aaron at aaronballman dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115990

            Bug ID: 115990
           Summary: Consider deprecating -Ofast
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: driver
          Assignee: unassigned at gcc dot gnu.org
          Reporter: aaron at aaronballman dot com
  Target Milestone: ---

Clang 19 is expected to deprecate the -Ofast compiler option, with hopes to
remove the option sometime in the future (currently targeting 2026, but there's
flexibility in timeline and approach, including deprecating the option but
never removing it). The rationale why the Clang community is deprecating the
option may also apply to GCC, and can be summarized as:

* Users typically do not expect optimization levels to impact the correctness
of valid, correct code, but -Ofast enables -ffast-math which enables
non-conforming extensions that can impact the correctness of results.

* The name itself leads to people enabling it without realizing what those
impacts are. Deprecation ensures that users know about the behavior and it
guides users towards being more explicit about their intent with the command
line arguments.

* The original motivation for adding -Ofast (for compliance with SPEC benchmark
rules) no longer applies.

Does GCC have an appetite for deprecation with an eye towards eventual removal
for -Ofast?

Related:
https://discourse.llvm.org/t/rfc-deprecate-ofast/78687/
https://github.com/llvm/llvm-project/pull/98736