[PATCH] D59973: [SLP] Refactoring of the operand reordering code.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev added inline comments.


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Comment at: lib/Transforms/Vectorize/SLPVectorizer.cpp:991
+              // 'Failed'.
+              ReorderingModes[OpIdx] = ReorderingMode::Failed;
+          }
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vporpo wrote:
> ABataev wrote:
> > Shall we undo previously performed swaps in this case, if we could do some reordering earlier?
> I don't think undoing the swaps would help much.  Following the reordering strategy for as long as we can without undoing on failure may actually help sometimes. For example, if our strategy is to look for the same opcode and half-way through the lanes we can no longer match it, we should still keep the order for the ones found so far, because we could potentially still vectorize these operands with a smaller vector length. If we undo them, that will not be possible.
> 
> Revisiting the failed operands and trying again with a different strategy could help. But I think we should try implement such back-tracking approaches in a separate optimization patch.
Then, maybe, you should continue trying to reorder other elements in the same lane, and should not mark it as Failed too early? You can save the value somewhere in the temp array and update the original element to Failed state after the loop.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D59973/new/

https://reviews.llvm.org/D59973