On Thu, 2018-09-13 at 11:00 +1000, David Holmes wrote: > Correction ... > > On 13/09/2018 8:31 AM, David Holmes wrote: > > On 12/09/2018 6:16 PM, Severin Gehwolf wrote: > > > On Wed, 2018-09-12 at 17:58 +1000, David Holmes wrote: > > > > But I don't understand why the optimization setting is being tied to the > > > > availability of the -ffp-contract flag? > > > > > > In configure we perform a check for gcc or clang whether that flag is > > > supported. If it is, it would be non-empty exactly having -ffp-contract > > > as value. It could be another set of flags for other arches if somebody > > > wanted to do the same, fwiw. In JDK 8, for example, it's "-mno-fused- > > > madd -fno-strict-aliasing" for ppc64: > > > http://hg.openjdk.java.net/jdk8u/jdk8u-dev/jdk/file/2660b127b407/make/lib/CoreLibraries.gmk#l63 > > > > > > > > > > > > We need support for that flag (or a set of flags) when we optimize > > > fdlibm since otherwise we would lose precision. If the flag is empty > > > we'd not optimize as we can't guarantee precision. That's why we tie > > > optimization to the availability of that flag. The expectation is for > > > this flag to be available on gcc/clang arches only at this point. Does > > > that make sense? > > > > Yes that makes sense - thanks. I didn't quite glean that from the comment: > > > > 42 # If FDLIBM_CFLAGS is non-empty we know that we can optimize > > 43 # fdlibm by adding those extra C flags. Currently GCC, > > I think this should say "when adding" not "by adding".
OK. Thanks, David. I'll change that before pushing. Cheers, Severin > Thanks, > David > > > 44 # and clang only. > > 45 ifneq ($(FDLIBM_CFLAGS), ) > > 46 BUILD_LIBFDLIBM_OPTIMIZATION := LOW > > > > But now I can read it and understand. > > > > Thanks, > > David > > > > > Thanks, > > > Severin > > >
