https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88769
Bug ID: 88769
Summary: Call to sin() optimized away, disregarding possible
side-effect (errno)
Product: gcc
Version: 7.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: per at pz dot se
Target Milestone: ---
(This is my first GCC bug report, so please have patience with me...)
Test program:
#include <math.h>
void foo(float x)
{
sin(x);
}
When compiling with -O1 (or higher), the call to sin() is optimized away:
.file "test.c"
.text
.globl foo
.type foo, @function
foo:
.LFB0:
.cfi_startproc
rep ret
.cfi_endproc
.LFE0:
.size foo, .-foo
.ident "GCC: (Ubuntu 7.3.0-27ubuntu1~18.04) 7.3.0"
.section .note.GNU-stack,"",@progbits
However, the sin() call has possible side-effects; according to the glibc docs,
it sets errno to EDOM in case the argument is an infinity.
The math errno can be disabled with -fno-math-errno, but according to the GCC
docs it is enabled by default, and compiling with the -fmath-errno makes no
difference.
The behavior is the same with GCC 8.2 and "trunk" (via godbolt.org).
clang 6.0 does not optimize away the sin() call, except when called with
-fno-math-errno.
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
7.3.0-27ubuntu1~18.04' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr
--with-gcc-major-version-only --program-suffix=-7
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie
--with-system-zlib --with-target-system-zlib --enable-objc-gc=auto
--enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 7.3.0 (Ubuntu 7.3.0-27ubuntu1~18.04)
