spatel added a comment. In https://reviews.llvm.org/D39204#904312, @efriedma wrote:
> The gcc documentation says "GCC includes built-in versions of many of the > functions in the standard C library. These functions come in two forms: one > whose names start with the `__builtin_` prefix, and the other without. Both > forms have the same type (including prototype), the same address (when their > address is taken), and the same meaning as the C library functions". And gcc > specifically preserves the stated semantics. Given that, I'm not sure it > makes sense for us to try to redefine `__builtin_sqrt()` just because it's > convenient. > > Note that this reasoning only applies if the user hasn't specified any > fast-math flags; under -ffinite-math-only, we can assume the result isn't a > NaN, and therefore we can use `llvm.sqrt.*`. (The definition of `llvm.sqrt.*` > changed in https://reviews.llvm.org/D28797; I don't think we ever updated > clang to take advantage of this). > > If we really need a name for the never-sets-errno sqrt, we should probably > use a different name, e.g. `__builtin_ieee_sqrt()`. Thanks for the explanation and link. Let me know if I've gone wrong: 1. We don't want to convert clang math builtins to llvm intrinsics because builtins are supposed to be exactly equivalent to C library functions (including setting errno). 2. LLVM intrinsics should be equivalent to C library functions except that they don't set errno (but this is currently wrong in some cases, and https://reviews.llvm.org/D28335 would fix that). 3. Therefore, the existing code in this file that is converting 'pow' and other builtin calls to intrinsics is correct for now, but only because 2 wrongs made it right? :) https://reviews.llvm.org/D39204 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
