all: remove 'extern register M *m' from runtime
The runtime has historically held two dedicated values g (current goroutine)
and m (current thread) in 'extern register' slots (TLS on x86, real registers
backed by TLS on ARM).
This CL removes the extern register m; code now uses g->m.
On ARM, this frees up the register that formerly held m (R9).
This is important for NaCl, because NaCl ARM code cannot use R9 at all.
The Go 1 macrobenchmarks (those with per-op times >= 10 µs) are unaffected:
BenchmarkBinaryTree17
5491374955 5471024381 -0.37%
BenchmarkFannkuch11
4357101311 4275174828 -1.88%
BenchmarkGobDecode
11029957 11364184 +3.03%
BenchmarkGobEncode
6852205 6784822 -0.98%
BenchmarkGzip
650795967 650152275 -0.10%
BenchmarkGunzip
140962363 141041670 +0.06%
BenchmarkHTTPClientServer 71581 73081 +2.10%
BenchmarkJSONEncode
31928079 31913356 -0.05%
BenchmarkJSONDecode
117470065 113689916 -3.22%
BenchmarkMandelbrot200
6008923 5998712 -0.17%
BenchmarkGoParse
6310917 6327487 +0.26%
BenchmarkRegexpMatchMedium_1K 114568 114763 +0.17%
BenchmarkRegexpMatchHard_1K 168977 169244 +0.16%
BenchmarkRevcomp
935294971 914060918 -2.27%
BenchmarkTemplate
145917123 148186096 +1.55%
Minux previous reported larger variations, but these were caused by
run-to-run noise, not repeatable slowdowns.
Actual code changes by Minux.
I only did the docs and the benchmarking.
LGTM=dvyukov, iant, minux
R=minux, josharian, iant, dave, bradfitz, dvyukov
CC=golang-codereviews
https://golang.org/cl/
109050043