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cmd/compile/internal/gc: avoid allocation in bnum

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Although bnum was being called with a Bits value, a limitation
of the escape analyser (golang/go#12588) meant that taking the
address of the Bits.b array in the range statement caused the
formal parameter to escape to the heap.

Passing the a pointer to a Bits, as with all the other Bits helper
methods avoids the allocation.

Before:
BenchmarkBnum1-4        20000000                69.6 ns/op            32 B/op          1 allocs/op

After:
BenchmarkBnum1-4        100000000               10.1 ns/op             0 B/op          0 allocs/op

Change-Id: I673bd57ddc032ee67d09474156d795fb1ba72018
Reviewed-on: https://go-review.googlesource.com/14501
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Dave Cheney 2015-09-12 00:10:42 +10:00
parent 3b0224282c
commit ea4e321d4d
1 changed files with 4 additions and 4 deletions
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8
src/cmd/compile/internal/gc/reg.go
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@ -170,7 +170,7 @@ func setaddrs(bit Bits) {
for bany(&bit) {
// convert each bit to a variable
i = bnum(bit)
i = bnum(&bit)
node = vars[i].node
n = int(vars[i].name)
@ -1321,7 +1321,7 @@ loop2:
bit.b[z] = LOAD(r, z) &^ (r.act.b[z] | addrs.b[z])
}
for bany(&bit) {
i = bnum(bit)
i = bnum(&bit)
change = 0
paint1(f, i)
biclr(&bit, uint(i))
@ -1465,7 +1465,7 @@ func bany(a *Bits) bool {
}
// bnum reports the lowest index of a 1 bit in a.
func bnum(a Bits) int {
func bnum(a *Bits) int {
for i, x := range &a.b { // & to avoid making a copy of a.b
if x != 0 {
return 64*i + Bitno(x)
@ -1541,7 +1541,7 @@ func (bits Bits) String() string {
var buf bytes.Buffer
sep := ""
for bany(&bits) {
i := bnum(bits)
i := bnum(&bits)
buf.WriteString(sep)
sep = " "
v := &vars[i]