cmd/compile: allocate less in regalloc's liveValues
Instrumenting the compiler shows that, at the end of liveValues, the
values of the workList's cap are distributed as:
cap freq
1 0.006
2 0.002
4 0.237
8 0.272
16 0.254
32 0.141
64 0.062
128 0.02
256 0.005
512 0.001
1024 0.0
Since the initial workList slice allocation is always on the stack
(as the variable does not escape), we can aggressively pre-allocate a
big backing array at (almost) no cost. This will save several
allocations in liveValues calls that end up having a large workList,
with no performance penalties for calls that have a small workList.
name old time/op new time/op delta
Template 284ms ± 3% 282ms ± 3% ~ (p=0.201 n=20+20)
Unicode 138ms ± 7% 138ms ± 7% ~ (p=0.718 n=20+20)
GoTypes 905ms ± 2% 895ms ± 1% -1.10% (p=0.003 n=19+18)
Compiler 4.26s ± 1% 4.25s ± 1% -0.38% (p=0.038 n=20+19)
SSA 9.85s ± 2% 9.80s ± 1% ~ (p=0.061 n=20+19)
Flate 187ms ± 6% 186ms ± 5% ~ (p=0.289 n=20+20)
GoParser 227ms ± 3% 225ms ± 3% ~ (p=0.072 n=20+20)
Reflect 578ms ± 2% 575ms ± 2% ~ (p=0.059 n=18+20)
Tar 263ms ± 2% 265ms ± 3% ~ (p=0.224 n=19+20)
XML 323ms ± 3% 325ms ± 2% ~ (p=0.127 n=20+20)
name old user-time/op new user-time/op delta
Template 406ms ± 6% 404ms ± 4% ~ (p=0.314 n=20+20)
Unicode 220ms ± 6% 215ms ±11% ~ (p=0.077 n=18+20)
GoTypes 1.25s ± 3% 1.24s ± 4% ~ (p=0.461 n=20+20)
Compiler 5.95s ± 2% 5.84s ± 5% -1.93% (p=0.007 n=20+20)
SSA 14.4s ± 4% 14.2s ± 4% ~ (p=0.108 n=20+20)
Flate 257ms ± 6% 252ms ± 9% ~ (p=0.063 n=20+20)
GoParser 317ms ± 5% 312ms ± 6% -1.85% (p=0.049 n=20+20)
Reflect 779ms ± 2% 774ms ± 3% ~ (p=0.253 n=20+20)
Tar 371ms ± 4% 374ms ± 4% ~ (p=0.327 n=20+20)
XML 440ms ± 5% 442ms ± 5% ~ (p=0.678 n=20+20)
name old alloc/op new alloc/op delta
Template 39.4MB ± 0% 39.0MB ± 0% -0.96% (p=0.000 n=20+20)
Unicode 29.1MB ± 0% 29.0MB ± 0% -0.13% (p=0.000 n=20+20)
GoTypes 117MB ± 0% 116MB ± 0% -0.88% (p=0.000 n=20+20)
Compiler 502MB ± 0% 498MB ± 0% -0.77% (p=0.000 n=19+20)
SSA 1.42GB ± 0% 1.40GB ± 0% -0.80% (p=0.000 n=20+20)
Flate 25.3MB ± 0% 25.0MB ± 0% -1.10% (p=0.000 n=20+19)
GoParser 31.3MB ± 0% 31.0MB ± 0% -1.05% (p=0.000 n=20+20)
Reflect 77.9MB ± 0% 77.1MB ± 0% -1.03% (p=0.000 n=20+20)
Tar 40.0MB ± 0% 39.7MB ± 0% -0.80% (p=0.000 n=20+20)
XML 45.2MB ± 0% 44.9MB ± 0% -0.72% (p=0.000 n=20+20)
name old allocs/op new allocs/op delta
Template 392k ± 0% 386k ± 0% -1.44% (p=0.000 n=20+20)
Unicode 337k ± 0% 337k ± 0% -0.22% (p=0.000 n=20+20)
GoTypes 1.22M ± 0% 1.20M ± 0% -1.33% (p=0.000 n=20+20)
Compiler 4.76M ± 0% 4.71M ± 0% -1.12% (p=0.000 n=20+20)
SSA 11.8M ± 0% 11.7M ± 0% -1.00% (p=0.000 n=20+20)
Flate 241k ± 0% 238k ± 0% -1.49% (p=0.000 n=20+20)
GoParser 324k ± 0% 320k ± 0% -1.17% (p=0.000 n=20+20)
Reflect 981k ± 0% 961k ± 0% -2.11% (p=0.000 n=20+20)
Tar 402k ± 0% 397k ± 0% -1.29% (p=0.000 n=20+20)
XML 424k ± 0% 419k ± 0% -1.10% (p=0.000 n=19+20)
Change-Id: If46667ae98eee2d47a615cad05e18df0629d8388
Reviewed-on: https://go-review.googlesource.com/102495
Run-TryBot: Alberto Donizetti <alb.donizetti@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>