cmd/gc, runtime: inline append in frontend.
A new transformation during walk turns append calls
into a combination of growslice and memmove.
benchmark old ns/op new ns/op delta
BenchmarkAppend 141 141 +0.00%
BenchmarkAppend1Byte 18 11 -39.56%
BenchmarkAppend4Bytes 19 10 -42.63%
BenchmarkAppend7Bytes 18 10 -42.16%
BenchmarkAppend8Bytes 18 10 -40.44%
BenchmarkAppend15Bytes 19 11 -41.67%
BenchmarkAppend16Bytes 19 11 -41.97%
BenchmarkAppend32Bytes 23 14 -38.82%
BenchmarkAppendStr1Byte 14 10 -23.78%
BenchmarkAppendStr4Bytes 14 11 -21.13%
BenchmarkAppendStr8Bytes 14 10 -25.17%
BenchmarkAppendStr16Bytes 19 11 -41.45%
BenchmarkAppendStr32Bytes 18 14 -19.44%
BenchmarkAppendSpecialCase 62 63 +1.77%
R=golang-dev, khr, cshapiro, rsc, dave
CC=golang-dev
https://golang.org/cl/
12815046