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[Bug target/24073] (vector float){a, b, 0, 0} code gen is not good
- From: "uros at kss-loka dot si" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 27 Sep 2005 11:19:21 -0000
- Subject: [Bug target/24073] (vector float){a, b, 0, 0} code gen is not good
- References: <20050927040602.24073.pinskia@gcc.gnu.org>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Additional Comments From uros at kss-loka dot si 2005-09-27 11:19 -------
With a couple of months old mainline gcc (20050716), following asm is produced:
(-O2 -msse2 -fomit-frame-pointer):
subl $12, %esp
movss b, %xmm0
movss a, %xmm1
unpcklps %xmm0, %xmm1
movaps %xmm1, %xmm0
xorl %eax, %eax
xorl %edx, %edx
movl %eax, (%esp)
movl %edx, 4(%esp)
>>> movlps (%esp), %xmm1
addl $12, %esp
movlhps %xmm1, %xmm0
ret
This explains where all those xor and moves come from. It looks that newer
compilers somehow fix the damage by using xorps, a bit late in the game, IMO.
This part of bug depends on PR target/22076.
Other than that, the problem is that V4SF vector initialization is decomposed
to two V2SF initializations (these are MMX insns and this further confuses
x87/MMX switching patch) that are later concated to V4SF.
--
What |Removed |Added
----------------------------------------------------------------------------
BugsThisDependsOn| |22076
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24073