[llvm] [LoopVectorizer][AArch64] Add support for partial reduce subtraction (PR #123636)

[Florian Hahn via llvm-commits]

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@@ -8932,6 +8936,20 @@ VPRecipeBuilder::tryToCreatePartialReduction(Instruction *Reduction,
     std::swap(BinOp, Accumulator);
 
   unsigned ReductionOpcode = Reduction->getOpcode();
+  if (ReductionOpcode == Instruction::Sub) {
+    VPBasicBlock *ParentBlock = Builder.getInsertBlock();
+    if (!ParentBlock)
+      return nullptr;
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fhahn wrote:

Can the insert block ever be null?  I'd expect it to always be set at this point?

https://github.com/llvm/llvm-project/pull/123636