| commit | 68819fb6d2bab59e4eadcdf62aa4a2a54417d640 | [log] [tgz] |
|---|---|---|
| author | Brian Kessler <brian.m.kessler@gmail.com> | Sun Mar 17 23:11:00 2019 -0600 |
| committer | Keith Randall <khr@golang.org> | Tue Apr 23 20:35:54 2019 +0000 |
| tree | fc00096c4b319d0a1df2d262889dbc697eaae940 | |
| parent | 8515d9cf656dedce3dbcb09ac7dc00f036e454d3 [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 fixups when just divisibility check is needed. To apply this rule the generic divisibility rule for A%B = A-(A/B*B) is disabled on the "opt" pass, but this does not affect generated code as this rule is applied later. The speed up on amd64 due to elimination of unneccessary fixup code is ~55%: name old time/op new time/op delta DivconstI64-4 2.08ns ± 0% 2.07ns ± 0% ~ (p=0.079 n=5+5) DivisiblePow2constI64-4 1.78ns ± 1% 0.81ns ± 1% -54.55% (p=0.008 n=5+5) DivconstU64-4 2.08ns ± 0% 2.08ns ± 0% ~ (p=1.000 n=5+5) DivconstI32-4 1.53ns ± 0% 1.53ns ± 0% ~ (all equal) DivisiblePow2constI32-4 1.79ns ± 1% 0.81ns ± 4% -54.75% (p=0.008 n=5+5) DivconstU32-4 1.78ns ± 1% 1.78ns ± 1% ~ (p=1.000 n=5+5) DivconstI16-4 1.54ns ± 2% 1.53ns ± 0% ~ (p=0.333 n=5+4) DivisiblePow2constI16-4 1.78ns ± 0% 0.79ns ± 1% -55.39% (p=0.000 n=4+5) DivconstU16-4 1.00ns ± 5% 0.99ns ± 1% ~ (p=0.730 n=5+5) DivconstI8-4 1.54ns ± 0% 1.53ns ± 0% ~ (p=0.714 n=4+5) DivisiblePow2constI8-4 1.78ns ± 0% 0.80ns ± 0% -55.06% (p=0.000 n=5+4) DivconstU8-4 0.93ns ± 1% 0.95ns ± 1% +1.72% (p=0.024 n=5+5) A follow-up CL will address the general case of x%c == 0 for signed integers. Updates #15806 Change-Id: I0d284863774b1bc8c4ce87443bbaec6103e14ef4 Reviewed-on: https://go-review.googlesource.com/c/go/+/168038 Reviewed-by: Keith Randall <khr@golang.org>
Go is an open source programming language that makes it easy to build simple, reliable, and efficient software.
Gopher image by Renee French, licensed under Creative Commons 3.0 Attributions license.
Our canonical Git repository is located at https://go.googlesource.com/go. There is a mirror of the repository at https://github.com/golang/go.
Unless otherwise noted, the Go source files are distributed under the BSD-style license found in the LICENSE file.
Official binary distributions are available at https://golang.org/dl/.
After downloading a binary release, visit https://golang.org/doc/install or load doc/install.html in your web browser for installation instructions.
If a binary distribution is not available for your combination of operating system and architecture, visit https://golang.org/doc/install/source or load doc/install-source.html in your web browser for source installation instructions.
Go is the work of thousands of contributors. We appreciate your help!
To contribute, please read the contribution guidelines: https://golang.org/doc/contribute.html
Note that the Go project uses the issue tracker for bug reports and proposals only. See https://golang.org/wiki/Questions for a list of places to ask questions about the Go language.