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[DAG] MatchRotate - support rotate-by-constant of illegal types

Authored by RKSimon on Thu, Nov 4, 8:09 AM.



This is a WIP patch to fix some of the regressions in D77804.

By folding to rotate/funnel-shift by constant amounts for illegal types, we prevent SimplifyDemandedBits from destroying the patterns prematurely, allowing us to use the rotate/funnel-shift legalization that was added in D112443.

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RKSimon created this revision.Thu, Nov 4, 8:09 AM
RKSimon requested review of this revision.Thu, Nov 4, 8:09 AM
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RKSimon added inline comments.Thu, Nov 11, 4:19 AM

This seems to be the last regression - we fold (and (shift x, c1), c2) but fail to do the same for (and (rotate x, c1), c2)

RKSimon added inline comments.Sat, Nov 13, 8:50 AM

This can be better handled with improved VPTERNLOG generation: D113827

RKSimon updated this revision to Diff 387074.Sun, Nov 14, 6:10 AM
RKSimon retitled this revision from [DAG] MatchRotate - support rotate-by-constant of illegal types (WIP) to [DAG] MatchRotate - support rotate-by-constant of illegal types.
RKSimon edited the summary of this revision. (Show Details)

Rebase - ready for review

I think i can't spot any more regressions.
Looks good to me, but one more review would be best.


So we exchanged this or + and-by-folded-load for constant pool load + vpternlogq ?

RKSimon added inline comments.Sun, Nov 14, 7:35 AM

Yes, that was what we went with for D113827 as a base implementation - D113845 will improve broadcast folds for ternlog

RKSimon added inline comments.Mon, Nov 15, 8:33 AM

@craig.topper Is this change OK? The test is called grev16_32 and neither target generates a grev op.

craig.topper added inline comments.Mon, Nov 15, 11:48 AM

I think it is ok. It's now matches grev16_i32_fshl and grev16_i32_fshr which are the same as this using intrinsics instead of shifts and or.

Our assumption was that a rotate would be at least as good as a grev instruction.

lebedev.ri accepted this revision.Fri, Nov 19, 1:50 AM

LG, anyone else?

This revision is now accepted and ready to land.Fri, Nov 19, 1:50 AM