[PATCH] D83605: [SelectionDAG][WebAssembly] Recognize splat value ABS operations

[Heejin Ahn via Phabricator via llvm-commits]

aheejin added a comment.

Wouldn't we want to add `ISD::ABS` to `scalarizeSplatValue` method in DAGCombiner.cpp too? WebAssembly wouldn't benefit from it, but it can benefit other targets that have a scalar `abs` instruction, and it is also consistent.



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Comment at: llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp:1749
+  if (VecOp.getOpcode() == ISD::ABS && VecOp.hasOneUse() &&
+      !DCI.isAfterLegalizeDAG() &&
+      DAG.isSplatValue(VecOp, /*AllowUndefs=*/true)) {
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Why is this?


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Comment at: llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp:1758
+  return SDValue();
+}
+
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Does this function run before `DAGCombiner::visitEXTRACT_VECTOR_ELT` or after it? Or does this replace it? If this runs once before or after it, we wouldn't be able to optimize patterns that mixes `abs` with `add` or `sub`, such as `abs(add(abs(v1) + abs(v2)))`, right?


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https://reviews.llvm.org/D83605