lebedev.ri added a subscriber: hans. lebedev.ri added a comment. In D104854#2959680 <https://reviews.llvm.org/D104854#2959680>, @thopre wrote:
> In D104854#2957735 <https://reviews.llvm.org/D104854#2957735>, @kpn wrote: > >> In D104854#2957490 <https://reviews.llvm.org/D104854#2957490>, @lebedev.ri >> wrote: >> >>> In D104854#2957471 <https://reviews.llvm.org/D104854#2957471>, @sepavloff >>> wrote: >>> >>>> In D104854#2957423 <https://reviews.llvm.org/D104854#2957423>, @spatel >>>> wrote: >>>> >>>>> Is it intentional that we are not canonicalizing the intrinsic call back >>>>> to `fcmp uno` in the default FP environment? >>>> >>>> It is lowered to unordered comparison by default. Changing `llvm.isnan` to >>>> `fcmp uno` somewhere in IR would make it possible to optimize out the >>>> latter if fast-math mode is on. Preserving semantics of `isnan` when >>>> fast-math is in effect was one of the goals of this change. >>> >>> Eeek. Was there an RFC about this? >>> This does not sound good to me at all, >>> much like "let's not apply fast-math flags to x86 vector intrinsics". >> >> We can switch into and out of the default FP environment inside a single >> function. > > Really? The constrained intrinsic documentation claims the reverse > (https://llvm.org/docs/LangRef.html#constrainedfp): > >> If any FP operation in a function is constrained then they all must be >> constrained. This is required for correct LLVM IR. Optimizations that move >> code around can create miscompiles if mixing of constrained and normal >> operations is done. The correct way to mix constrained and less constrained >> operations is to use the rounding mode and exception handling metadata to >> mark constrained intrinsics as having LLVM’s default behavior. @sepavloff please can you undo the clang part of this change (+@hans) and post an RFC to further hash out the design here? Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D104854/new/ https://reviews.llvm.org/D104854 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
