rjmccall added a comment. 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). ================ Comment at: clang/test/CodeGen/builtins.c:283 + res = __builtin_flt_rounds_set(1); + // CHECK: call void @llvm.set.rounding( } ---------------- xiongji90 wrote: > rjmccall wrote: > > Just for completeness, please test that this gets the result of the > > expression. > Hi, @rjmccall > I updated the test to check "llvm.set.rounding" string with input, does it > meet your requirement? > Thanks very much. Yes, thank you. 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
