xiongji90 added a comment. In D144454#4163658 <https://reviews.llvm.org/D144454#4163658>, @sepavloff wrote:
> C standard function `fesetround` accepts rounding mode in the form of > target-specific values like `FE_TONEAREST`. They usually represent > corresponding bits in control register, so are different for different > targets. `llvm.set_rounding` in contrast accepts rounding mode as > target-independent value, the encoding is same as used in `FLT_ROUNDS`. > > The difference between `fesetround` and `llvm.set_rounding` is same as for > `fegetround` and `FLT_ROUNDS`. They differ in how rounding mode is specified, > - as target-specific or as target-independent values respectively. > > The intrinsic `llvm.set_rounding` was introduced to facilitate work on IR, > because IR is (mainly) target-agnostic and defines like `FE_TONEAREST` are > not available there. It would be nice to have a C builtin counterpart for > `FLT_ROUNDS`, I don't know why the standard does not define it. > > Implementation of `fesetround` with `set_rounding` would be very useful, but > it requires translation of target-specific values for rounding mode into > universal values and also checking availability of FPU, as `fesetround` > returns value if rounding mode cannot be set. Both these checks are likely to > require separate builtins. Hi, @sepavloff This patch only aims to add a builtin for llvm.set.rounding, llvm.set.rounding can benefit C/C++ developers then. Since llvm.set.rounding is target-independent, __builtin_fesetround should be target-independent as well and the then arguments for this builtin should align with what documented here: https://llvm.org/docs/LangRef.html#id1502 for all targets. If we want to map fesetround to llvm.set.rounding in the future, we need to take care of 2 points: 1. translate fesetround arugment to llvm.set.rounding arugment. 2. properly handle the return value. Did I correctly understand your points? 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
