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? Thanks, Severin
