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[Bug target/46209] New: pmovmskb, useless sign extension
- From: "tbptbp at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 28 Oct 2010 08:30:31 +0000
- Subject: [Bug target/46209] New: pmovmskb, useless sign extension
- Auto-submitted: auto-generated
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46209
Summary: pmovmskb, useless sign extension
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: tbptbp@gmail.com
Host: x86_64-pc-linux-gnu
Target: x86_64-pc-linux-gnu
Hello,
$ cat movemsk.c
#include <xmmintrin.h>
typedef long unsigned int uint64_t;
uint64_t foo128(__m128i x) { return _mm_movemask_epi8(x); }
uint64_t foo64(__m64 x) { return _mm_movemask_pi8(x); }
$ /usr/local/gcc-4.6-20101026/bin/gcc -O3 -march=native movemsk.c -S -o -
foo128:
.LFB516:
.cfi_startproc
pmovmskb %xmm0, %eax
cltq
ret
foo64:
.LFB517:
.cfi_startproc
movdq2q %xmm0, %mm0
movq %xmm0, -8(%rsp)
pmovmskb %mm0, %eax
cltq
ret
I won't discuss the interesting mmx code generation but to point that in both
cases, as per Intel doc, there's no need to extend the result; a sign extension
is even slightly more wrong.
$ /usr/local/gcc-4.6-20101026/bin/gcc -v
Using built-in specs.
COLLECT_GCC=/usr/local/gcc-4.6-20101026/bin/gcc
COLLECT_LTO_WRAPPER=/usr/local/gcc-4.6-20101026/bin/../libexec/gcc/x86_64-unknown-linux-gnu/4.6.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --prefix=/usr/local/gcc-4.6.0
--enable-languages=c,c++ --enable-threads=posix --disable-nls
--with-system-zlib --disable-bootstrap --enable-mpfr --enable-gold --enable-lto
--with-ppl --with-cloog --with-arch=native --enable-checking=release
Thread model: posix
gcc version 4.6.0 20101026 (experimental) (GCC)