[Mlir-commits] [mlir] [MLIR][XeGPU] Use all ones as the neutral value of an AND reduction (PR #232828)

[Md Abdullah Shahneous Bari]

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mshahneo wrote:

The helper is used without a cross-subgroup reduction too. WG-to-SG starts every subgroup's local reduction from createReductionNeutralValue, and combines the original accumulator only afterwards. The cross-subgroup path also uses it for the final reduction. So the old test did fail without the fix: the local reduction started from dense<1>.

But you are right that the test was hard to read. Its accumulator was -1, the same value as the neutral. So the CHECKs could not show which constant the reduction starts from, and `andi %x, -1` folded the accumulator combine away. In the new version the accumulator is 7. The CHECKs now show the reduction starting from -1, then arith.andi with the accumulator. I also added a cross-subgroup case. Both cases fail without the fix.

https://github.com/llvm/llvm-project/pull/232828