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 <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>