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[AArch64] Adjust the cost of integer vector division
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Authored by evandro on Mar 1 2018, 2:29 PM.

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Summary

Since there is no legal instruction for integer vector division, factor in the cost of singling out each element to be used with the scalar division instruction.

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rL LLVM

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evandro created this revision.Mar 1 2018, 2:29 PM

This patch results in some image processing benchmarks to improve by over 1% on big Cortex and Exynos cores.

Makes sense to me. I tested this patch on Falkor and didn't notice any significant performance differences on the benchmarks I ran. Can we add a test case, though? Maybe in test/Analysis/CostModel?

evandro updated this revision to Diff 137458.Mar 7 2018, 12:38 PM

Added a test case.

For the test case, why not just run "-cost-model -analyze" like we do for the other tests instead of running the vectorizer? Am I missing something?

The test case has scalar types and it seems more interesting to see the cost rising proportionally with the vector factor.

The test case has scalar types and it seems more interesting to see the cost rising proportionally with the vector factor.

You can't really see the costs of the divisions increasing, though. Why not follow the example in bswap.ll with something like:

define <2 x i32> @sdiv_v2i32(<2 x i32> %a, <2 x i32> %b) {
; CHECK: Found an estimated cost of 8 for instruction:   %tmp = sdiv <2 x i32> %a, %b
  %tmp = sdiv <2 x i32> %a, %b
  ret <2 x i32> %tmp
}

define <4 x i32> @sdiv_v4i32(<4 x i32> %a, <4 x i32> %b) {
; CHECK: Found an estimated cost of 22 for instruction:   %tmp = sdiv <4 x i32> %a, %b
  %tmp = sdiv <4 x i32> %a, %b
  ret <4 x i32> %tmp
}

...

That's a sensible alternative.

evandro updated this revision to Diff 137467.Mar 7 2018, 1:45 PM

Updated the test case.

mssimpso added inline comments.Mar 7 2018, 1:58 PM
llvm/test/Analysis/CostModel/AArch64/div.ll
7 โ†—(On Diff #137467)

Show the actual numbers instead of a regex?

evandro marked an inline comment as done.Mar 7 2018, 2:10 PM
evandro added inline comments.
llvm/test/Analysis/CostModel/AArch64/div.ll
7 โ†—(On Diff #137467)

I was afraid you were going to say that... ๐Ÿ™‚

evandro updated this revision to Diff 137476.Mar 7 2018, 2:10 PM
evandro marked an inline comment as done.
evandro marked an inline comment as done.
mssimpso accepted this revision.Mar 7 2018, 2:14 PM

LGTM, thanks!

This revision is now accepted and ready to land.Mar 7 2018, 2:14 PM
This revision was automatically updated to reflect the committed changes.