[llvm] [LoopVectorizer] Add support for partial reductions (PR #92418)

[Graham Hunter via llvm-commits]

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@@ -8671,6 +8754,59 @@ VPRecipeBuilder::tryToCreateWidenRecipe(Instruction *Instr,
   return tryToWiden(Instr, Operands, VPBB);
 }
 
+void VPRecipeBuilder::removeInvalidScaledReductionExitInstrs() {
+  // A partial reduction is invalid if any of its extends are used by
+  // something that isn't another partial reduction. This is because the
+  // extends are intended to be lowered along with the reduction itself.
+
+  // Build up a set of partial reduction bin ops for efficient use checking
+  SmallSet<Instruction *, 4> PartialReductionBinOps;
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huntergr-arm wrote:

You can make this a SmallSet of `User *`, avoiding the cast later.

https://github.com/llvm/llvm-project/pull/92418