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author | Dimitry Andric <dim@FreeBSD.org> | 2021-04-09 23:07:54 +0000 |
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committer | Dimitry Andric <dim@FreeBSD.org> | 2021-04-10 11:59:57 +0000 |
commit | 3b00222f156dca5700c839d73e36daf479fa640c (patch) | |
tree | 3a8f3b991ac518c06b8b8ac808883b791cbad677 /lib/msun | |
parent | 44faff9f4a0f25588df8b217e7c94af8bd84d113 (diff) | |
download | src-3b00222f156dca5700c839d73e36daf479fa640c.tar.gz src-3b00222f156dca5700c839d73e36daf479fa640c.zip |
Avoid raising unexpected floating point exceptions in libm
When using clang with x86_64 CPUs that support AVX, some floating point
transformations may raise exceptions that would not have been raised by
the original code. To avoid this, use the -fp-exception-behavior=maytrap
flag, introduced in clang 10.0.0.
In particular, this fixes a number of test failures with ctanhf(3) and
ctanf(3), when libm is compiled with -mavx. An unexpected FE_INVALID
exception is then raised, because clang emits vdivps instructions to
perform certain divides. (The vdivps instruction operates on multiple
single-precision float operands simultaneously, but the exceptions may
be influenced by unused parts of the XMM registers. In this particular
case, it was calculating 0 / 0, which results in FE_INVALID.)
If -fp-exception-behavior=maytrap is specified however, clang uses
vdivss instructions instead, which work on one operand, and should not
raise unexpected exceptions.
Reported by: olivier
Reviewed by: arichardson
PR: 254911
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D29686
Diffstat (limited to 'lib/msun')
-rw-r--r-- | lib/msun/Makefile | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/lib/msun/Makefile b/lib/msun/Makefile index 4491bc216a4c..959dbd113ec1 100644 --- a/lib/msun/Makefile +++ b/lib/msun/Makefile @@ -34,6 +34,16 @@ CFLAGS+= -I${.CURDIR}/ld128 CFLAGS+= -I${.CURDIR}/${ARCH_SUBDIR} +.include <bsd.compiler.mk> +.if ${COMPILER_TYPE} == "clang" && ${COMPILER_VERSION} >= 100000 +# When using clang with x86_64 CPUs that support AVX, some floating point +# transformations may raise exceptions that would not have been raised by the +# original code. To avoid this, use the -fp-exception-behavior=maytrap flag, +# introduced in clang 10.0.0. +# See also: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=254911 +CFLAGS+= -ffp-exception-behavior=maytrap +.endif + .PATH: ${.CURDIR}/bsdsrc .PATH: ${.CURDIR}/src .PATH: ${.CURDIR}/man @@ -113,7 +123,6 @@ COMMON_SRCS+= catrigl.c \ # 'long double' [-Werror=overflow] # if( y >= LDBL_MAX ) # See also: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=130067 -.include <bsd.compiler.mk> .if ${COMPILER_TYPE} == "gcc" CFLAGS.e_powl.c+= -Wno-error=overflow .endif |