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| author | Brian Kessler <brian.m.kessler@gmail.com> | 2019-03-17 23:11:00 -0600 |
|---|---|---|
| committer | Keith Randall <khr@golang.org> | 2019-04-23 20:35:54 +0000 |
| commit | 68819fb6d2bab59e4eadcdf62aa4a2a54417d640 (patch) | |
| tree | fc00096c4b319d0a1df2d262889dbc697eaae940 /test/codegen/arithmetic.go | |
| parent | 8515d9cf656dedce3dbcb09ac7dc00f036e454d3 (diff) | |
| download | go-git-68819fb6d2bab59e4eadcdf62aa4a2a54417d640.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 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>
Diffstat (limited to 'test/codegen/arithmetic.go')
| -rw-r--r-- | test/codegen/arithmetic.go | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/test/codegen/arithmetic.go b/test/codegen/arithmetic.go index b5976be9d2..535e3349fc 100644 --- a/test/codegen/arithmetic.go +++ b/test/codegen/arithmetic.go @@ -185,6 +185,17 @@ func Pow2Mods(n1 uint, n2 int) (uint, int) { return a, b } +// Check that signed divisibility checks get converted to AND on low bits +func Pow2DivisibleSigned(n int) bool { + // 386:"TESTL\t[$]63",-"DIVL" + // amd64:"TESTQ\t[$]63",-"DIVQ" + // arm:"AND\t[$]63",-".*udiv" + // arm64:"AND\t[$]63",-"UDIV" + // ppc64:"ANDCC\t[$]63" + // ppc64le:"ANDCC\t[$]63" + 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" |