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cmd/6g: avoid MOVSD between registers 

MOVSD only copies the low half of the packed register pair,
while MOVAPD copies both halves.  I assume the internal
register renaming works better with the latter, since it makes
our code run 25% faster.

Before:
mandelbrot 16000
        gcc -O2 mandelbrot.c	28.44u 0.00s 28.45r
        gc mandelbrot	44.12u 0.00s 44.13r
        gc_B mandelbrot	44.17u 0.01s 44.19r

After:
mandelbrot 16000
        gcc -O2 mandelbrot.c	28.22u 0.00s 28.23r
        gc mandelbrot	32.81u 0.00s 32.82r
        gc_B mandelbrot	32.82u 0.00s 32.83r

R=ken2
CC=golang-dev
https://golang.org/cl/6248068
This commit is contained in:
Russ Cox 2012-05-30 14:41:19 -04:00
parent eb056dbea7
commit a768de8347
1 changed files with 11 additions and 0 deletions
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11
src/cmd/6g/peep.c
View File

@ -283,6 +283,12 @@ loop1:
// copyprop. Now that copyprop is done, remov MOVLQZX R1, R2
// if it is dominated by an earlier ADDL/MOVL/etc into R1 that
// will have already cleared the high bits.
//
// MOVSD removal.
// We never use packed registers, so a MOVSD between registers
// can be replaced by MOVAPD, which moves the pair of float64s
// instead of just the lower one. We only use the lower one, but
// the processor can do better if we do moves using both.
for(r=firstr; r!=R; r=r->link) {
p = r->prog;
if(p->as == AMOVLQZX)
@ -290,6 +296,11 @@ loop1:
if(p->from.type == p->to.type)
if(prevl(r, p->from.type))
excise(r);
if(p->as == AMOVSD)
if(regtyp(&p->from))
if(regtyp(&p->to))
p->as = AMOVAPD;
}
// load pipelining