cmd/internal/dwarf: remove global encbuf
The global encbuf helped avoid allocations. It is incompatible with a concurrent backend. To avoid a performance regression while removing it, introduce two optimizations. First, re-use a buffer in dwarf.PutFunc. Second, avoid a buffer entirely when the int being encoded fits in seven bits, which is about 75% of the time. Passes toolstash-check. Updates #15756 name old alloc/op new alloc/op delta Template 40.6MB ± 0% 40.6MB ± 0% -0.08% (p=0.001 n=8+9) Unicode 29.9MB ± 0% 29.9MB ± 0% ~ (p=0.068 n=8+10) GoTypes 116MB ± 0% 116MB ± 0% +0.05% (p=0.043 n=10+9) SSA 864MB ± 0% 864MB ± 0% +0.01% (p=0.010 n=10+9) Flate 25.8MB ± 0% 25.8MB ± 0% ~ (p=0.353 n=10+10) GoParser 32.2MB ± 0% 32.2MB ± 0% ~ (p=0.353 n=10+10) Reflect 80.2MB ± 0% 80.2MB ± 0% ~ (p=0.165 n=10+10) Tar 27.0MB ± 0% 26.9MB ± 0% ~ (p=0.143 n=10+10) XML 42.8MB ± 0% 42.8MB ± 0% ~ (p=0.400 n=10+9) name old allocs/op new allocs/op delta Template 398k ± 0% 397k ± 0% -0.20% (p=0.002 n=8+9) Unicode 320k ± 0% 321k ± 1% ~ (p=0.122 n=8+10) GoTypes 1.16M ± 0% 1.17M ± 0% ~ (p=0.053 n=10+9) SSA 7.65M ± 0% 7.65M ± 0% ~ (p=0.122 n=10+8) Flate 240k ± 1% 240k ± 1% ~ (p=0.243 n=10+9) GoParser 322k ± 1% 322k ± 1% ~ (p=0.481 n=10+10) Reflect 1.00M ± 0% 1.00M ± 0% ~ (p=0.211 n=9+10) Tar 256k ± 0% 255k ± 1% ~ (p=0.052 n=10+10) XML 400k ± 1% 400k ± 0% ~ (p=0.631 n=10+10) Change-Id: Ia39d9de09232fdbfc9c9cec14587bbf6939c9492 Reviewed-on: https://go-review.googlesource.com/38713 Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com> Reviewed-by:Brad Fitzpatrick <bradfitz@golang.org>
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