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cmd/compile: implement register moves for int<->float conversions on ppc64le #18922

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laboger opened this issue Feb 3, 2017 · 2 comments
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cmd/compile: implement register moves for int<->float conversions on ppc64le #18922

laboger opened this issue Feb 3, 2017 · 2 comments
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@laboger
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laboger commented Feb 3, 2017

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go tip

What operating system and processor architecture are you using (go env)?

Ubuntu 16.04

What did you do?

Code inspection and profiles on many math functions show that conversion between integer and float are done with a store to and load from memory which is not as efficient if done in registers. In power8 there are instructions to allow this conversion in registers.

This change will generate register moves for integer <-> float conversions (both to and from) on ppc64le. It won't be done on ppc64 (BE) since that currently must be compatible with power5 and the instruction to do the move is not available there.
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CL https://golang.org/cl/36725 mentions this issue.

@gopherbot
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CL https://golang.org/cl/37651 mentions this issue.

gopherbot pushed a commit that referenced this issue Mar 1, 2017
@randall77
cmd/compile: ppc64x no longer needs a scratch stack location
13c35a1 
After https://go-review.googlesource.com/c/36725/, ppc64x no longer
needs a temp stack location for int reg <-> fp reg moves.

Update #18922

Change-Id: Ib4319784f7a855f593dfa5231604ca2c24e4c882
Reviewed-on: https://go-review.googlesource.com/37651
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
ceseo pushed a commit to powertechpreview/go that referenced this issue May 17, 2017
@laboger @ceseo
cmd/compile: use reg moves for int <-> float conversions on ppc64x
c2faa8c 
This makes a change in the SSA code generated for OpPPC64Xf2i64
and OpPPC64Xi2f64 to use register based instructions to convert
between float and integer.  This will require at least power8.
Currently the conversion is done by storing to and loading
from memory, which is more expensive.

This improves some of the math functions:

BenchmarkExp-128                     74.1          66.8          -9.85%
BenchmarkExpGo-128                   87.4          66.3          -24.14%
BenchmarkExp2-128                    72.2          64.3          -10.94%
BenchmarkExp2Go-128                  74.3          65.9          -11.31%

BenchmarkLgamma-128                  51.0          39.7          -22.16%
BenchmarkLog-128                     42.9          40.6          -5.36%
BenchmarkLogb-128                    11.5          9.16          -20.35%
BenchmarkLog1p-128                   38.9          36.2          -6.94%

BenchmarkSin-128                     29.5          23.7          -19.66%
BenchmarkTan-128                     32.8          27.4          -16.46%

Fixes golang#18922

Change-Id: I8e1cf14d3880d7cd720dc5188dd174cba1f7fef7
Reviewed-on: https://go-review.googlesource.com/36725
Reviewed-by: Carlos Eduardo Seo <cseo@linux.vnet.ibm.com>
Reviewed-by: Keith Randall <khr@golang.org>
@golang golang locked and limited conversation to collaborators Mar 1, 2018
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