RFC: Deprecate -Ofast

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Discussion on this topic seems to be winding down, so I think now may be a good time to determine next steps for the proposal.

My reading of the comments on the thread is:

  • We have consensus against aliasing -Ofast to -O3
  • We have consensus for leaving the current behavior of -Ofast alone, but deprecating the flag and recommending users switch to either -O3 or -O3 -ffast-math as appropriate
    • The -Ofast will eventually be removed.
    • The deprecation period should be lengthy enough for users to migrate before we remove the flag; two years seems to be a suggestion with support
  • We would like to see improved documentation for this flag
  • Coordination with GCC would be appreciated but is not a requirement; if they have strong technical arguments to retain the flag, that might warrant re-opening the RFC

If you have a strong opinion to the contrary, please voice it ASAP, but otherwise I believe this RFC is accepted.

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