gcc seems allergic to movq in the context of mmx:
% cat movq.c
#include <inttypes.h>
#include <mmintrin.h>
__m64 x;
__m64 y;
uint64_t foo(__m64 m) {
return _mm_cvtm64_si64(_mm_add_pi32(x, y));
}
% gcc -g -O3 -Wall -std=gnu99 -c -o movq.o movq.c
% objdump -dr movq.o
movq.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <foo>:
0: 48 8b 05 00 00 00 00 mov 0(%rip),%rax # 7 <foo+0x7>
3: R_X86_64_PC32 x+0xfffffffffffffffc
7: 48 89 44 24 f8 mov %rax,0xfffffffffffffff8(%rsp)
c: 0f 6f 44 24 f8 movq 0xfffffffffffffff8(%rsp),%mm0
11: 0f fe 05 00 00 00 00 paddd 0(%rip),%mm0 # 18 <foo+0x18>
14: R_X86_64_PC32 y+0xfffffffffffffffc
18: 0f 7f 44 24 f8 movq %mm0,0xfffffffffffffff8(%rsp)
1d: 48 8b 44 24 f8 mov 0xfffffffffffffff8(%rsp),%rax
22: c3 retq
the load of x should use "movq m64,mm". this is true in i386 targets as well.
the transfer of %mm0 to %rax has the option of "movq %mm0,%rax" on x86_64, but
should possibly be passed through memory depending on -mtune= settings:
for intel core2 always use movq directly between the registers, no matter which
direction.
for AMD k8 family 15 always pass through mem
for AMD k8 family 16+, for gpr->xmm/mmx pass through memory and for xmm/mmx ->
gpr always use movd/movq direct between the registers.
-dean
p.s. gcc -v
Using built-in specs.
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc/configure --prefix=/home/odo/gcc --disable-multilib
--disable-biarch x86_64-unknown-linux-gnu --enable-languages=c
Thread model: posix
gcc version 4.3.0 20071128 (experimental) (GCC)
--
Summary: mmx and movd/movq on x86_64
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: dean at arctic dot org
GCC build triplet: x86_64-unknown-linux-gnu
GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34256
