cmd/compile/ssa: more aggressive constant folding
Add rewrite rules that canonicalize the location of constants in expressions, and fold conststants that appear in operations that can be trivially reassociated. After this change, the compiler constant-folds expressions like "4 + x - 1" and "4 & x & 1" Benchmarks affected on darwin/amd64: name old time/op new time/op delta FmtFprintfInt-8 82.1ns ± 1% 81.7ns ± 1% -0.46% (p=0.023 n=8+9) FmtFprintfIntInt-8 122ns ± 2% 120ns ± 2% -1.48% (p=0.047 n=10+10) FmtManyArgs-8 493ns ± 0% 486ns ± 1% -1.37% (p=0.000 n=8+10) Gzip-8 230ms ± 0% 229ms ± 1% -0.46% (p=0.001 n=10+9) HTTPClientServer-8 74.5µs ± 1% 73.7µs ± 1% -1.11% (p=0.000 n=10+10) JSONDecode-8 51.7ms ± 0% 51.9ms ± 1% +0.42% (p=0.017 n=10+9) RegexpMatchEasy0_32-8 82.6ns ± 1% 81.7ns ± 0% -1.02% (p=0.000 n=9+8) RegexpMatchMedium_32-8 121ns ± 1% 120ns ± 1% -1.48% (p=0.001 n=10+10) Revcomp-8 426ms ± 1% 400ms ± 1% -6.16% (p=0.000 n=10+10) TimeFormat-8 330ns ± 1% 327ns ± 0% -0.82% (p=0.000 n=10+10) name old speed new speed delta Gzip-8 84.4MB/s ± 0% 84.8MB/s ± 1% +0.47% (p=0.001 n=10+9) JSONDecode-8 37.6MB/s ± 0% 37.4MB/s ± 1% -0.42% (p=0.016 n=10+9) RegexpMatchEasy0_32-8 387MB/s ± 1% 392MB/s ± 0% +1.06% (p=0.000 n=9+8) RegexpMatchMedium_32-8 8.21MB/s ± 1% 8.34MB/s ± 1% +1.58% (p=0.000 n=10+9) Revcomp-8 597MB/s ± 1% 636MB/s ± 1% +6.57% (p=0.000 n=10+10) Change-Id: Ie37ff91605b76a984a8400dfd1e34f50bf61c864 Reviewed-on: https://go-review.googlesource.com/37290Reviewed-by:Keith Randall <khr@golang.org> Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com> TryBot-Result: Gobot Gobot <gobot@golang.org>
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