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".
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
