http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54446
Bug #: 54446
Summary: Stack needlessly aligned with AVX
Classification: Unclassified
Product: gcc
Version: 4.6.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: ces...@cesarb.net
When compiling the following small function, gcc aligns the stack, even though
the function does not store any AVX values in the stack:
bool test(__m256i *p)
{
__m256i x = _mm256_load_si256(p);
return _mm256_testz_si256(x, x);
}
The generated assembly output is:
test:
pushq %rbp
movq %rsp, %rbp
andq $-32, %rsp
addq $16, %rsp
vmovdqa (%rdi), %ymm0
vptest %ymm0, %ymm0
leave
sete %al
vzeroupper
ret
The assembly output should instead be something like:
test:
vmovdqa (%rdi), %ymm0
vptest %ymm0, %ymm0
sete %al
vzeroupper
ret
The command line is "gcc -mavx -std=c99 -O3 -Wall -Wextra -Werror -save-temps".
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.6.3/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto --enable-plugin
--enable-java-awt=gtk --disable-dssi
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-ppl --with-cloog --with-tune=generic --with-arch_32=i686
--build=x86_64-redhat-linux
Thread model: posix
gcc version 4.6.3 20120306 (Red Hat 4.6.3-2) (GCC)
