[PATCH] D107994: Making the code compliant to the documentation about Floating Point support default values for C/C++. FPP-MODEL=PRECISE enables FFP-CONTRACT (FMA is enabled).

[Zahira Ammarguellat via Phabricator via cfe-commits]

zahiraam added a comment.

In D107994#3130494 <https://reviews.llvm.org/D107994#3130494>, @wristow wrote:

> The Release Note change here says:
>
>   Floating Point Support in Clang
>   -------------------------------
>   - The -ffp-model=precise now implies -ffp-contract=on rather than
>     -ffp-contract=fast, and the documentation of these features has been
>     clarified. Previously, the documentation claimed that -ffp-model=precise was
>     the default, but this was incorrect because the precise model implied
>     -ffp-contract=fast, whereas the default behavior is -ffp-contract=on.
>     -ffp-model=precise is now exactly the default mode of the compiler.
>
> Unless I'm missing something, there is a related change here that I think should be more overtly noted (given the discussions in this review, I //think// this additional change is understood/expected, but I'm surprised it's not pointed out explicitly -- so maybe I'm misunderstanding).
>
> Specifically, this commit explicitly sets `-ffp-contract=on` in the default mode (which is what the documentation said, and continues to say).  But previously, there wasn't //any// explicit setting of `-ffp-contract` by default (and I think that lack of an explicit setting, was equivalent to `-ffp-contract=off`).
>
> So with this commit, we now enable FMA by default (even at `-O0`). Noting the semantic change that FMA is now being enabled by default seems sensible.
>
> Succinctly, in terms of the Release Note, the documentation claims that `-ffp-contract=on` is the default, but in fact the behavior //was// as though `-ffp-contract=off` was the default.  The default now really is `-ffp-contract=on`.
>
> __________________
>
> Also, I see a relatively minor point about `-ffp-contract` in the Users Manual.  It says that setting `-ffast-math` implies `-ffp-contract=fast`, and it says that setting `-ffp-model=fast` "Behaves identically to specifying both `-ffast-math` and `ffp-contract=fast`".  But that's redundant, since `-ffast-math` already implies  `-ffp-contract=fast`.  That is, `-ffast-math` and `-ffp-model=fast` are equivalent.

@wristow Are you suggesting a change of wording in the ReleaseNotes?


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https://reviews.llvm.org/D107994