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LE Manh Cuong c5f142fa9f cmd/compile: optimize bitset tests
The assembly output for x & c == c, where c is power of 2:

	MOVQ	"".set+8(SP), AX
	ANDQ	$8, AX
	CMPQ	AX, $8
	SETEQ	"".~r2+24(SP)

With optimization using bitset:

	MOVQ	"".set+8(SP), AX
	BTL	$3, AX
	SETCS	"".~r2+24(SP)

output less than 1 instruction.

However, there is no speed improvement:

name         old time/op  new time/op  delta
AllBitSet-8  0.35ns ± 0%  0.35ns ± 0%   ~     (all equal)

Fixes #31904

Change-Id: I5dca4e410bf45716ed2145e3473979ec997e35d4
Reviewed-on: https://go-review.googlesource.com/c/go/+/175957
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
2019-08-27 18:01:16 +00:00
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api api/go1.13: add debug/elf.Symbol fields added in CL 184099 2019-08-08 18:44:16 +00:00
doc doc: align documents link 2019-08-26 17:33:52 +00:00
lib/time lib/time: update tz data to 2019b 2019-07-03 23:08:27 +00:00
misc cmd/go: include GOEXPERIMENT flags in tool id for cache key 2019-07-17 22:57:03 +00:00
src cmd/compile: optimize bitset tests 2019-08-27 18:01:16 +00:00
test cmd/compile: optimize bitset tests 2019-08-27 18:01:16 +00:00
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