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authorDimitry Andric <dim@FreeBSD.org>2021-04-09 23:07:54 +0000
committerDimitry Andric <dim@FreeBSD.org>2021-04-10 11:59:57 +0000
commit3b00222f156dca5700c839d73e36daf479fa640c (patch)
tree3a8f3b991ac518c06b8b8ac808883b791cbad677
parent44faff9f4a0f25588df8b217e7c94af8bd84d113 (diff)
downloadsrc-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
-rw-r--r--lib/msun/Makefile11
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