benchmark                           old ns/op    new ns/op    delta
strconv_test.BenchmarkFormatInt         12198        12031   -1.37%
strconv_test.BenchmarkAppendInt          9268         9153   -1.24%
strconv_test.BenchmarkFormatUint         3538         3429   -3.08%
strconv_test.BenchmarkAppendUint         3133         3062   -2.27%

No performance difference for GOARCH=amd64.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5488089