From ea4e321d4daef32f4cd8df8ec799122ff3c6b9f0 Mon Sep 17 00:00:00 2001 From: Dave Cheney Date: Sat, 12 Sep 2015 00:10:42 +1000 Subject: [PATCH] cmd/compile/internal/gc: avoid allocation in bnum 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 Run-TryBot: Brad Fitzpatrick TryBot-Result: Gobot Gobot --- src/cmd/compile/internal/gc/reg.go | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/src/cmd/compile/internal/gc/reg.go b/src/cmd/compile/internal/gc/reg.go index b3e96216bd..ff6ec321a1 100644 --- a/src/cmd/compile/internal/gc/reg.go +++ b/src/cmd/compile/internal/gc/reg.go @@ -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] -- 2.48.1