X-Bugzilla-Reason: CC
+++ This bug was initially created as a clone of Bug #24073 +++
Take the following example:
#define vector __attribute__((vector_size(16)))
float a; float b;
vector float f(void) { return (vector float){ a, b, 0.0, 0.0}; }
---
Currently we get:
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)
xorps %xmm1, %xmm1
movlhps %xmm1, %xmm0
addl $12, %esp
------
We should be able to produce:
movss _b, %xmm0
movss _a, %xmm1
shufps 60, /*[0, 3, 3, 0]*/, %xmm1, %xmm0 // _a, 0, 0, _b
shufps 201, /*[3, 0, 2, 1]*/, %xmm0, %xmm0 // _a, _b, 0, 0
This is from Nathan Begeman.
================================================================
------- Comment #4 From Uros Bizjak 2005-09-27 11:41 -------
I think that following example wins the contest:
vector float f(void) { return (vector float){ a, a, b, b}; }
gcc -O2 -msse -fomit-frame-pointer
subl $28, %esp
movss a, %xmm0
movss %xmm0, 4(%esp)
movss b, %xmm0
movd 4(%esp), %mm0
punpckldq %mm0, %mm0
movss %xmm0, 4(%esp)
movq %mm0, 16(%esp)
movd 4(%esp), %mm0
punpckldq %mm0, %mm0
movq %mm0, 8(%esp)
movlps 16(%esp), %xmm1
movhps 8(%esp), %xmm1
addl $28, %esp
movaps %xmm1, %xmm0
ret
Note the usage of MMX registers.
------- Comment #5 From Andrew Pinski 2005-09-27 14:33 -------
(In reply to comment #4)
> I think that following example wins the contest:
>
> vector float f(void) { return (vector float){ a, a, b, b}; }
For this, it is a different bug. The issue with the above is that
ix86_expand_vector_init_duplicate check
for mmx_okay is bad.
Currently, we have
if (!mmx_ok && !TARGET_SSE)
but I if I change it to:
if (!mmx_ok)
we get:
movss _a, %xmm0
movss _b, %xmm1
unpcklps %xmm0, %xmm0
unpcklps %xmm1, %xmm1
movlhps %xmm1, %xmm0
Which looks ok to me. That testcase should be opened into another bug as it is
obviously wrong.
=====================================================================
Cloned from 24073 to track the MMX insn issue; the original 24073 problem is a
performance issue.
--
Summary: return (vector float) { a, a, b, b } generates unwanted
MMX insns
Product: gcc
Version: 4.2.0
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: stuart at apple dot com
GCC target triplet: i786-*-*
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28825
