xiongji90 added a comment. In D144454#4162129 <https://reviews.llvm.org/D144454#4162129>, @rjmccall wrote:
> In D144454#4157717 <https://reviews.llvm.org/D144454#4157717>, @xiongji90 > wrote: > >> In D144454#4142253 <https://reviews.llvm.org/D144454#4142253>, @rjmccall >> wrote: >> >>> New builtins should be documented in the user manual. >>> >>> There are standard pragmas for changing the rounding mode, right? What's >>> the interaction between the ability to set this dynamically with a builtin >>> call and those pragmas? >> >> Hi, @rjmccall >> Current status is LLVM has added llvm.get.rounding and llvm.set.rounding >> intrinsic and has also added "__builtin_flt_rounds" for llvm.get.rounding >> but there is no corresponding for llvm.set.rounding intrinisc. According to >> original patch to add llvm.set.rounding: https://reviews.llvm.org/D74729 and >> LLVM document for this intrinsic: https://llvm.org/docs/LangRef.html#id1506 >> The introduction of llvm.set.rounding intrinsic can provide same >> functionality as C library function "fesetround" and avoid unnecessary >> dependency on C library. Currently, this intrinsic can't benefit C/C++ >> developers since we don't have a corresponding builtin and we even can't add >> a C/C++ test for this intrinsic. > > If this builtin is defined to have the same behavior as `fesetround`, the > obvious name would be `__builtin_fesetround`. You seem to have patterned it > off of `__builtin_flt_rounds`, but that is not an arbitrarily-chosen name, > it's taken from the standard `FLT_ROUNDS` macro and is expected to work as an > implementation of it. > > We already understand how `fesetround` is supposed to interact with the > standard pragmas about the FP environment, so that indirectly answers that > part of my question. I assume you've modeled your intrinsic correctly in > LLVM so that the optimizer understands it can't reorder the > environment-sensitive math intrinsics around calls to the new intrinsic? > > If this builtin is just an intrinsic implementation of `fesetround`, I don't > think we need further documentation of it. > > I assume the intrinsic is only implemented on certain targets? If so, we > might need to restrict uses of the builtin as well (and make sure that > `__has_builtin` only returns true on those targets). Hi, @rjmccall "llvm.set.rounding" intrinsic will change default floating-point environment, so as same as explicit C library call to "fesetround", this intrinsic should work with "pragma std fenv_access on", then "strictfp" attr will be added and optimizer will honor it. "llvm.set.rounding" shouldn't be a target-sepcific intrinsic and target backend should be responsible for supporting it. I didn't my local tests on x86/x86_64 hardware and I also searched tests related to "llvm.set.rounding", arm, aarch64, risc-v all include such tests, so this builtin should work for these targets too. Thanks very much. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D144454/new/ https://reviews.llvm.org/D144454 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
