wristow added a comment. In D107994#3131268 <https://reviews.llvm.org/D107994#3131268>, @zahiraam wrote:
> 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`). >> ... > > @wristow Are you suggesting a change of wording in the ReleaseNotes? Yes @zahiraam, either a modification to what was written, or an additional separate point. The critical user-visible change from this commit (AFAICS) is that previously the default behavior was `-ffp-contract=off`, whereas now the default behavior is `-ffp-contract=on`. The ReleaseNote as written implies that the FMA situation //was// `-ffp-contract=fast`, and it has been changed to `-ffp-contract=on`, and either of those modes would result in FMA being done for cases like: float foo(float a, float b, float c) { return a * b + c; } In short, the current ReleaseNote implies that FMA would be used by default, for cases like the above (because `-ffp-contract=on` was the default) -- but this isn't true. (The current ReleaseNote also clarifies that if `-ffp-model=precise` were explicitly specified, then it previously would set `-ffp-contract=fast` (which was not what the documentation said) and now it sets `-ffp-contract=on` (which //is// what the documentation says) -- this aspect is correct.) I think the ReleaseNote should clarify that the result of this change is that previously, the default behavior was equivalent to `-ffp-contract=off` (and so no FMA would be done by default), but this commit makes the default behavior `-ffp-contract=on` (so FMA is enabled by default, even at `-O0`). The documentation indicates that the default is `-ffp-contract=on`, so this change makes the compiler behavior consistent with the documentation, with respect to the `-ffp-contact` switch. It also makes it consistent with the documentation for the `-ffp-model` switch. A possible new wording is below (maybe this is too verbose, so making it more concise is fine too, from my POV): Floating Point Support in Clang ------------------------------- - The default setting of FP contraction (FMA) is now -ffp-contract=on (for languages other than CUDA/HIP). This is consistent with the documentation. Previously, the default behavior was equivalent to -ffp-contract=off, so the old behavior was that FMA would not be used by default for code like: float foo(float a, float b, float c) { return a * b + c; } Whereas now, FMA will be used in the above code, even when optimization is off. Related to this, the switch -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 (now corrected) default behavior is -ffp-contract=on. -ffp-model=precise is now exactly the default mode of the compiler. CHANGES SINCE LAST ACTION https://reviews.llvm.org/D107994/new/ https://reviews.llvm.org/D107994 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
