cmd/5g: peep.c: reactivate some optimisations
Thanks to Minux and Remy for their advice.
The EOR optimisation is applied to a few places in the stdlib.
// hash/crc32/crc32.go
func update(crc uint32, tab *Table, p []byte) uint32 {
crc = ^crc
for _, v := range p {
crc = tab[byte(crc)^v] ^ (crc >> 8)
}
return ^crc
}
before:
--- prog list "update" ---
0164 (/home/dfc/go/src/pkg/hash/crc32/crc32.go:101) TEXT update+0(SB),$12-24
0165 (/home/dfc/go/src/pkg/hash/crc32/crc32.go:101) MOVW tab+4(FP),R8
0166 (/home/dfc/go/src/pkg/hash/crc32/crc32.go:102) MOVW crc+0(FP),R0
0167 (/home/dfc/go/src/pkg/hash/crc32/crc32.go:102) EOR $-1,R0,R5
0168 (/home/dfc/go/src/pkg/hash/crc32/crc32.go:103) MOVW p+8(FP),R0
0169 (/home/dfc/go/src/pkg/hash/crc32/crc32.go:103) MOVW R0,autotmp_0019+-12(SP)
after:
--- prog list "update" ---
0164 (/home/dfc/go/src/pkg/hash/crc32/crc32.go:101) TEXT update+0(SB),$12-24
0165 (/home/dfc/go/src/pkg/hash/crc32/crc32.go:101) MOVW tab+4(FP),R8
0166 (/home/dfc/go/src/pkg/hash/crc32/crc32.go:102) MOVW crc+0(FP),R0
0167 (/home/dfc/go/src/pkg/hash/crc32/crc32.go:102) MVN R0,R5
0168 (/home/dfc/go/src/pkg/hash/crc32/crc32.go:103) MOVW p+8(FP),R0
0169 (/home/dfc/go/src/pkg/hash/crc32/crc32.go:103) MOVW R0,autotmp_0019+-12(SP)
After 5l has done its work,
crc = ^crc
3d710:
e59d0014 ldr r0, [sp, #20]
3d714:
e3e0b000 mvn fp, #0
3d718:
e020500b eor r5, r0, fp
becomes
crc = ^crc
3d710:
e59d0014 ldr r0, [sp, #20]
3d714:
e1e05000 mvn r5, r0
The MOVB optimisation has a small impact on the stdlib, in strconv
and gzip.
// GZIP (RFC 1952) is little-endian, unlike ZLIB (RFC 1950).
func put2(p []byte, v uint16) {
p[0] = uint8(v >> 0)
p[1] = uint8(v >> 8)
}
before:
--- prog list "put2" ---
1369 (/home/dfc/go/src/pkg/compress/gzip/gzip.go:76) TEXT put2+0(SB),$0-16
1370 (/home/dfc/go/src/pkg/compress/gzip/gzip.go:76) MOVHU v+12(FP),R4
1371 (/home/dfc/go/src/pkg/compress/gzip/gzip.go:77) MOVHU R4,R0
1372 (/home/dfc/go/src/pkg/compress/gzip/gzip.go:77) MOVHU R0,R0
1373 (/home/dfc/go/src/pkg/compress/gzip/gzip.go:77) MOVBU R0,R1
1374 (/home/dfc/go/src/pkg/compress/gzip/gzip.go:77) MOVBU R1,R3
1375 (/home/dfc/go/src/pkg/compress/gzip/gzip.go:77) MOVW $p+0(FP),R1
after:
--- prog list "put2" ---
1369 (/home/dfc/go/src/pkg/compress/gzip/gzip.go:76) TEXT put2+0(SB),$0-16
1370 (/home/dfc/go/src/pkg/compress/gzip/gzip.go:76) MOVHU v+12(FP),R4
1371 (/home/dfc/go/src/pkg/compress/gzip/gzip.go:77) MOVHU R4,R0
1372 (/home/dfc/go/src/pkg/compress/gzip/gzip.go:77) MOVBU R0,R1
1373 (/home/dfc/go/src/pkg/compress/gzip/gzip.go:77) MOVBU R1,R3
1374 (/home/dfc/go/src/pkg/compress/gzip/gzip.go:77) MOVW $p+0(FP),R1
R=remyoudompheng, rsc, minux.ma
CC=golang-dev
https://golang.org/cl/
6674048