https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48128
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |4.8.0
Status|NEW |RESOLVED
Known to work| |4.8.0
Keywords| |ra
Resolution|--- |FIXED
--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The problem was this RTL:
(insn 7 2 25 2 (set (reg:V4SI 65 [ MEM[(int[8] *)&baz] ])
(mem/c:V4SI (symbol_ref:SI ("baz") [flags 0x2] <var_decl
0x7fc7df4971e0 baz>) [2 MEM[(int[8] *)&baz]+0 S16 A256])) /app/example.cpp:19
1080 {*movv4si_internal}
(nil))
(insn 25 7 26 2 (set (reg:SI 72)
(subreg:SI (reg:V4SI 65 [ MEM[(int[8] *)&baz] ]) 0))
/app/example.cpp:19 -1
(nil))
Which was produced by dse.
In GCC 4.8 we produce the same except lra produces:
(insn 25 7 26 2 (set (reg:SI 0 ax [72])
(mem/c:SI (symbol_ref:SI ("baz") [flags 0x2] <var_decl 0x7ffb6912d428
baz>) [2 MEM[(int[8] *)&baz]+0 S4 A256])) /app/example.cpp:19 89
{*movsi_internal}
(nil))
So this got fixed with the new reload (LRA) :).
Note -fno-tree-loop-distribute-patterns is needed otherwise you get a memcpy
:).
With -mno-sse, the extra register push was gone in GCC 4.6.0.
GCC 8 also no longer vectorizers the code based on the cost model of pentium3,
you need to add -fno-vect-cost-model.
Starting GCC 9, GCC is able to produce for -msse2 case:
movd %xmm0, %eax
Anyways the original issue is fixed.
With the trunk -O3 -m32 -msse GCC produces:
foo2():
movdqa baz, %xmm7
movd %xmm7, %eax
movaps %xmm7, bar
movdqa baz+16, %xmm7
movaps %xmm7, bar+16
ret
With -O3 -m32 -msse2:
foo2():
movdqa baz, %xmm7
movd %xmm7, %eax
movaps %xmm7, bar
movdqa baz+16, %xmm7
movaps %xmm7, bar+16
ret
The problem is -march=pentium3 causes a loop for the memcpy (tuning).
