cmd/compile: optimize lookupVarOutgoing
If b has exactly one predecessor, as happens
frequently with static calls, we can make
lookupVarOutgoing generate less garbage.
Instead of generating a value that is just
going to be an OpCopy and then get eliminated,
loop. This can lead to lots of looping.
However, this loop is way cheaper than generating
lots of ssa.Values and then eliminating them.
For a subset of the code in #15537:
Before:
28.31 real 36.17 user 1.68 sys
2282450944 maximum resident set size
After:
9.63 real 11.66 user 0.51 sys
638144512 maximum resident set size
Updates #15537.
Excitingly, it appears that this also helps
regular code:
name old time/op new time/op delta
Template 288ms ± 6% 276ms ± 7% -4.13% (p=0.000 n=21+24)
Unicode 143ms ± 8% 141ms ±10% ~ (p=0.287 n=24+25)
GoTypes 932ms ± 4% 874ms ± 4% -6.20% (p=0.000 n=23+22)
Compiler 4.89s ± 4% 4.58s ± 4% -6.46% (p=0.000 n=22+23)
MakeBash 40.2s ±13% 39.8s ± 9% ~ (p=0.648 n=23+23)
name old user-ns/op new user-ns/op delta
Template 388user-ms ±10% 373user-ms ± 5% -3.80% (p=0.000 n=24+25)
Unicode 203user-ms ± 6% 202user-ms ± 7% ~ (p=0.492 n=22+24)
GoTypes 1.29user-s ± 4% 1.17user-s ± 4% -9.67% (p=0.000 n=25+23)
Compiler 6.86user-s ± 5% 6.28user-s ± 4% -8.49% (p=0.000 n=25+25)
name old alloc/op new alloc/op delta
Template 51.5MB ± 0% 47.6MB ± 0% -7.47% (p=0.000 n=22+25)
Unicode 37.2MB ± 0% 37.1MB ± 0% -0.21% (p=0.000 n=25+25)
GoTypes 166MB ± 0% 138MB ± 0% -16.83% (p=0.000 n=25+25)
Compiler 756MB ± 0% 628MB ± 0% -16.96% (p=0.000 n=25+23)
name old allocs/op new allocs/op delta
Template 450k ± 0% 445k ± 0% -1.02% (p=0.000 n=25+25)
Unicode 356k ± 0% 356k ± 0% ~ (p=0.374 n=24+25)
GoTypes 1.31M ± 0% 1.25M ± 0% -4.18% (p=0.000 n=25+25)
Compiler 5.29M ± 0% 5.02M ± 0% -5.15% (p=0.000 n=25+23)
It also seems to help in other cases in which
phi insertion is a pain point (#14774, #14934).
Change-Id: Ibd05ed7b99d262117ece7bb250dfa8c3d1cc5dd2
Reviewed-on: https://go-review.googlesource.com/22790
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>