commit | 44343c777ca8c02262d1d381a2cc24866b3c5414 | [log] [tgz] |
---|---|---|
author | Brian Kessler <brian.m.kessler@gmail.com> | Tue Apr 23 22:04:38 2019 -0600 |
committer | Brad Fitzpatrick <bradfitz@golang.org> | Thu Apr 25 03:00:32 2019 +0000 |
tree | 164dd1fe0618bda48496ef9b504747020fcc8ed0 | |
parent | 2693b424662580c3f4fc65e43474e4db0f9c5cf5 [diff] |
cmd/compile: add signed divisibility by power of 2 rules For powers of two (c=1<<k), the divisibility check x%c == 0 can be made just by checking the trailing zeroes via a mask x&(c-1) == 0 even for signed integers. This avoids division fix-ups when just divisibility check is needed. To apply this rule, we match on the fixed-up version of the division. This is neccessary because the mod and division rewrite rules are already applied during the initial opt pass. The speed up on amd64 due to elimination of unneccessary fix-up code is ~55%: name old time/op new time/op delta DivconstI64-4 2.08ns ± 0% 2.09ns ± 1% ~ (p=0.730 n=5+5) DivisiblePow2constI64-4 1.78ns ± 1% 0.81ns ± 1% -54.66% (p=0.008 n=5+5) DivconstU64-4 2.08ns ± 0% 2.08ns ± 0% ~ (p=0.683 n=5+5) DivconstI32-4 1.53ns ± 0% 1.53ns ± 1% ~ (p=0.968 n=4+5) DivisiblePow2constI32-4 1.79ns ± 1% 0.81ns ± 1% -54.97% (p=0.008 n=5+5) DivconstU32-4 1.78ns ± 1% 1.80ns ± 2% ~ (p=0.206 n=5+5) DivconstI16-4 1.54ns ± 2% 1.54ns ± 0% ~ (p=0.238 n=5+4) DivisiblePow2constI16-4 1.78ns ± 0% 0.81ns ± 1% -54.72% (p=0.000 n=4+5) DivconstU16-4 1.00ns ± 5% 1.01ns ± 1% ~ (p=0.119 n=5+5) DivconstI8-4 1.54ns ± 0% 1.54ns ± 2% ~ (p=0.571 n=4+5) DivisiblePow2constI8-4 1.78ns ± 0% 0.82ns ± 8% -53.71% (p=0.008 n=5+5) DivconstU8-4 0.93ns ± 1% 0.93ns ± 1% ~ (p=0.643 n=5+5) A follow-up CL will address the general case of x%c == 0 for signed integers. Updates #15806 Change-Id: Iabadbbe369b6e0998c8ce85d038ebc236142e42a Reviewed-on: https://go-review.googlesource.com/c/go/+/173557 Run-TryBot: Brian Kessler <brian.m.kessler@gmail.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Keith Randall <khr@golang.org>
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