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| author | Brian Kessler <brian.m.kessler@gmail.com> | 2019-04-23 22:04:38 -0600 |
|---|---|---|
| committer | Brad Fitzpatrick <bradfitz@golang.org> | 2019-04-25 03:00:32 +0000 |
| commit | 44343c777ca8c02262d1d381a2cc24866b3c5414 (patch) | |
| tree | 164dd1fe0618bda48496ef9b504747020fcc8ed0 /test/codegen/arithmetic.go | |
| parent | 2693b424662580c3f4fc65e43474e4db0f9c5cf5 (diff) | |
| download | go-git-44343c777ca8c02262d1d381a2cc24866b3c5414.tar.gz | |
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>
Diffstat (limited to 'test/codegen/arithmetic.go')
| -rw-r--r-- | test/codegen/arithmetic.go | 21 |
1 files changed, 17 insertions, 4 deletions
diff --git a/test/codegen/arithmetic.go b/test/codegen/arithmetic.go index b5976be9d2..a937be7fe5 100644 --- a/test/codegen/arithmetic.go +++ b/test/codegen/arithmetic.go @@ -176,15 +176,28 @@ func Pow2Mods(n1 uint, n2 int) (uint, int) { // ppc64le:"ANDCC\t[$]31" a := n1 % 32 // unsigned - // 386:-"IDIVL" - // amd64:-"IDIVQ" - // arm:-".*udiv" - // arm64:-"REM" + // 386:"SHRL",-"IDIVL" + // amd64:"SHRQ",-"IDIVQ" + // arm:"SRA",-".*udiv" + // arm64:"ASR",-"REM" + // ppc64:"SRAD" + // ppc64le:"SRAD" b := n2 % 64 // signed return a, b } +// Check that signed divisibility checks get converted to AND on low bits +func Pow2DivisibleSigned(n int) bool { + // 386:"TESTL\t[$]63",-"DIVL",-"SHRL" + // amd64:"TESTQ\t[$]63",-"DIVQ",-"SHRQ" + // arm:"AND\t[$]63",-".*udiv",-"SRA" + // arm64:"AND\t[$]63",-"UDIV",-"ASR" + // ppc64:"ANDCC\t[$]63",-"SRAD" + // ppc64le:"ANDCC\t[$]63",-"SRAD" + return n%64 == 0 // signed +} + // Check that constant modulo divs get turned into MULs func ConstMods(n1 uint, n2 int) (uint, int) { // amd64:"MOVQ\t[$]-1085102592571150095","MULQ",-"DIVQ" |