https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71395
Bug ID: 71395
Summary: PowerPC vec_init of 4 SFmode values could be improved
on Power8
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: meissner at gcc dot gnu.org
Target Milestone: ---
The code for combining 4 SFmode values into a V4SFmode could be improved in
GCC.
For example:
#include <altivec.h>
vector combine (float a, float b, float c, float d)
{
return (vector float) { a, b, c, d };
}
Generates:
.file "foo.c"
.section ".text"
.align 2
.p2align 4,,15
.globl merge
.section ".opd","aw"
.align 3
merge:
.quad .L.merge,.TOC.@tocbase,0
.previous
.type merge, @function
.L.merge:
addis 9,2,.LC0@toc@ha
xxpermdi 34,2,1,0
xxpermdi 32,4,3,0
addi 9,9,.LC0@toc@l
xvcvdpsp 32,32
xvcvdpsp 34,34
lxvd2x 33,0,9
xxpermdi 33,33,33,2
vperm 2,0,2,1
blr
.long 0
.byte 0,0,0,0,0,0,0,0
.size merge,.-.L.merge
.section .rodata.cst16,"aM",@progbits,16
.align 4
.LC0:
.byte 31
.byte 30
.byte 29
.byte 28
.byte 23
.byte 22
.byte 21
.byte 20
.byte 15
.byte 14
.byte 13
.byte 12
.byte 7
.byte 6
.byte 5
.byte 4
If you build the 2 V2DF temporaries differently, you could use the VMRGEW and
VMRGOW instructions to do the final combination instead of loading up a permute
mask and doing a VPERM instruction.
