commit | 6f9b94ab6658bbebe4c89791dc3e5ebe53be3d82 | [log] [tgz] |
---|---|---|
author | Michael Munday <mike.munday@ibm.com> | Fri May 25 17:54:58 2018 +0100 |
committer | Michael Munday <mike.munday@ibm.com> | Mon Sep 03 14:35:38 2018 +0000 |
tree | 4850119296318dcb26d743333d5998d2c71a5b9b | |
parent | ff468a43be1740890a0f3b64a6ab920ea92c2c17 [diff] |
cmd/compile: implement OnesCount{8,16,32,64} intrinsics on s390x This CL implements the math/bits.OnesCount{8,16,32,64} functions as intrinsics on s390x using the 'population count' (popcnt) instruction. This instruction was released as the 'population-count' facility which uses the same facility bit (45) as the 'distinct-operands' facility which is a pre-requisite for Go on s390x. We can therefore use it without a feature check. The s390x popcnt instruction treats a 64 bit register as a vector of 8 bytes, summing the number of ones in each byte individually. It then writes the results to the corresponding bytes in the output register. Therefore to implement OnesCount{16,32,64} we need to sum the individual byte counts using some extra instructions. To do this efficiently I've added some additional pseudo operations to the s390x SSA backend. Unlike other architectures the new instruction sequence is faster for OnesCount8, so that is implemented using the intrinsic. name old time/op new time/op delta OnesCount 3.21ns ± 1% 1.35ns ± 0% -58.00% (p=0.000 n=20+20) OnesCount8 0.91ns ± 1% 0.81ns ± 0% -11.43% (p=0.000 n=20+20) OnesCount16 1.51ns ± 3% 1.21ns ± 0% -19.71% (p=0.000 n=20+17) OnesCount32 1.91ns ± 0% 1.12ns ± 1% -41.60% (p=0.000 n=19+20) OnesCount64 3.18ns ± 4% 1.35ns ± 0% -57.52% (p=0.000 n=20+20) Change-Id: Id54f0bd28b6db9a887ad12c0d72fcc168ef9c4e0 Reviewed-on: https://go-review.googlesource.com/114675 Run-TryBot: Michael Munday <mike.munday@ibm.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Cherry Zhang <cherryyz@google.com>
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