On 13/10/17 18:28, vladimir.mezent...@oracle.com wrote: > On 10/12/2017 03:40 AM, Richard Earnshaw wrote: >> On 12/10/17 06:21, vladimir.mezent...@oracle.com wrote: >>> From: Vladimir Mezentsev <vladimir.mezent...@oracle.com> >>> >>> FMA (floating-point multiply-add) instructions are supported on aarch64. >>> These instructions can produce different result if two operations executed >>> separately. >>> -ffp-contract=off doesn't allow the FMA instructions. >>> >>> Tested on aarch64-linux-gnu. >>> No regression. Two failed tests now passed. >>> >>> ChangeLog: >>> 2017-10-11 Vladimir Mezentsev <vladimir.mezent...@oracle.com> >>> >>> PR libgcc/59714 >>> * libgcc/config/aarch64/t-aarch64 (HOST_LIBGCC2_CFLAGS): Add >>> -ffp-contract=off >>> --- >>> libgcc/config/aarch64/t-aarch64 | 1 + >>> 1 file changed, 1 insertion(+) >>> >>> diff --git a/libgcc/config/aarch64/t-aarch64 >>> b/libgcc/config/aarch64/t-aarch64 >>> index 3af933c..e33bef0 100644 >>> --- a/libgcc/config/aarch64/t-aarch64 >>> +++ b/libgcc/config/aarch64/t-aarch64 >>> @@ -18,4 +18,5 @@ >>> # along with GCC; see the file COPYING3. If not see >>> # <http://www.gnu.org/licenses/>. >>> >>> +HOST_LIBGCC2_CFLAGS += -ffp-contract=off >>> LIB2ADD += $(srcdir)/config/aarch64/sync-cache.c >>> >> Why would we want to do this on AArch64 only? If it's right for us, >> then surely it would be right for everyone and the option should be >> applied at the top level. > > It is a machine dependent option. > We don't need this option, for example, on sparc or intel machines. >
No, it's a target-independent option (it's in the -f... option space). It might be a no-op on some machines, but either it should be on globally, or it should be off globally. If it's a no-op then it won't matter whether it's on or off. R. > -Vladimir >> >> Hint: I'm not convinced on the evidence here that it is right across the >> whole of libgcc. Before moving forward on this particular PR I think we >> need to understand what behaviour we do want out of the compiler. >> >> R. >
