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Re: Documentation for fp-contract
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: David Edelsohn <dje dot gcc at gmail dot com>
- Cc: GCC Development <gcc at gcc dot gnu dot org>
- Date: Fri, 05 Apr 2013 21:04:05 +0200
- Subject: Re: Documentation for fp-contract
- References: <CAGWvnynG9ozOjkbMdQ-gMmKuQeyMEui3mhuY4g2YF2_v3SvX0w at mail dot gmail dot com>
David Edelsohn <dje.gcc@gmail.com> wrote:
>Richi,
>
>The GCC documentation for fp-contract is a little confusing and I'm
>not sure what was intended. The last sentences says:
>
>"-ffp-contract=on enables floating-point expression contraction if
>allowed by the language standard. This is currently not implemented
>and treated equal to -ffp-contract=off."
>
>Apparently "This" refers to "on". So contraction is enabled for
>"fast" but the documentation implies that "on" is implemented as "off"
>instead of "fast", i.e., explicitly choosing "on" will disable the
>contraction.
>
>What did you intend?
Fp-contract=on should allow contraction as
Allowed by the language standard. This is not implemented, we only implement no contraction at all or contraction without restrictions. Contraction according to the language constraints is thus implemented conservatively correct by mapping to no contraction at all.
Richard.
>Thanks, David