[llvm] [LoopVectorize] Generate wide active lane masks (PR #147535)

[David Sherwood via llvm-commits]

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@@ -954,6 +954,9 @@ class VPInstruction : public VPRecipeWithIRFlags,
     // part if it is scalar. In the latter case, the recipe will be removed
     // during unrolling.
     ExtractPenultimateElement,
+    // Extracts a subvector from a vector (first operand) starting at a given
+    // offset (second operand).
+    ExtractSubvector,
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david-arm wrote:

It would be good to add this to VPInstruction::computeCost to make sure the cost is properly represented in the VPlan, although I know that currently the only use case is during plan execution, after the cost model.

https://github.com/llvm/llvm-project/pull/147535