[llvm] [LV] Don't create partial reductions if factor doesn't match accumulator (PR #158603)

[Sander de Smalen via llvm-commits]

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@@ -141,3 +141,17 @@ VPBasicBlock *vputils::getFirstLoopHeader(VPlan &Plan, VPDominatorTree &VPDT) {
   });
   return I == DepthFirst.end() ? nullptr : cast<VPBasicBlock>(*I);
 }
+
+unsigned vputils::getVFScaleFactor(VPRecipeBase *R) {
+  if (!R)
+    return 1;
+  if (auto *RR = dyn_cast<VPReductionPHIRecipe>(R))
+    return RR->getVFScaleFactor();
+  if (auto *RR = dyn_cast<VPPartialReductionRecipe>(R))
+    return RR->getVFScaleFactor();
+  assert(
+      (!isa<VPInstruction>(R) || cast<VPInstruction>(R)->getOpcode() !=
+                                     VPInstruction::ReductionStartVector) &&
+      "getting scaling factor of reduction-start-vector not implemented yet");
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sdesmalen-arm wrote:

Will this now result in the compiler (with asserts enabled) to fail on valid code when trying to vectorise it?
If so then this needs to be a FIXME instead.

https://github.com/llvm/llvm-project/pull/158603