aarch64: Fix f{max,min}{f} build for GCC 4.9 and 5
Commit Message
GCC 4.9 and 5 do not generate a correct f{max,min}nm instruction for
__builtin_{fmax,fmin}{f} without -ffinite-math-only. It is clear a
compiler issue since the instruction can handle NaN and Inf correctly
and GCC6+ does not show this issue.
We backport a fix to GCC 5, raise the minimum required GCC version
for aarch64 (since GCC 4.9 branch is now closed) and/or add configure
check to check for this issue. However I think -ffinit-math-only
should be safe for these specific implementation and it is a much
simpler solution.
Checked on aarch64-linux-gnu with GCC 5.3.1.
* sysdeps/aarch64/fpu/Makefile (CFLAGS-s_fmax.c, CFLAGS-s_fmaxf.c,
CFLAGS-s_fmin.c, CFLAGS-s_fminf.c): New rule: add -ffinite-math-only.
[1] https://gcc.gnu.org/ml/gcc/2016-08/msg00010.html
Signed-off-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
---
ChangeLog | 5 +++++
sysdeps/aarch64/fpu/Makefile | 6 ++++++
2 files changed, 11 insertions(+)
Comments
On 17/11/17 10:32, Adhemerval Zanella wrote:
> GCC 4.9 and 5 do not generate a correct f{max,min}nm instruction for
> __builtin_{fmax,fmin}{f} without -ffinite-math-only. It is clear a
> compiler issue since the instruction can handle NaN and Inf correctly
> and GCC6+ does not show this issue.
>
> We backport a fix to GCC 5, raise the minimum required GCC version
> for aarch64 (since GCC 4.9 branch is now closed) and/or add configure
> check to check for this issue. However I think -ffinit-math-only
> should be safe for these specific implementation and it is a much
> simpler solution.
>
> Checked on aarch64-linux-gnu with GCC 5.3.1.
>
> * sysdeps/aarch64/fpu/Makefile (CFLAGS-s_fmax.c, CFLAGS-s_fmaxf.c,
> CFLAGS-s_fmin.c, CFLAGS-s_fminf.c): New rule: add -ffinite-math-only.
>
OK.
@@ -5,4 +5,10 @@ CFLAGS-s_lroundf.c += -fno-math-errno
CFLAGS-s_lround.c += -fno-math-errno
CFLAGS-s_llroundf.c += -fno-math-errno
CFLAGS-s_llround.c += -fno-math-errno
+# GCC 4.9 and 5 requires the flag to correct emits a f{max,min}nm
+# for a __builtin_{fmax,fmin}{f}.
+CFLAGS-s_fmax.c += -ffinite-math-only
+CFLAGS-s_fmaxf.c += -ffinite-math-only
+CFLAGS-s_fmin.c += -ffinite-math-only
+CFLAGS-s_fminf.c += -ffinite-math-only
endif