68819fb6d2
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> |
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