[llvm] [LoopVectorizer] Allow partial reductions to be made in predicated loops (PR #124268)

[James Chesterman via llvm-commits]

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@@ -8904,6 +8897,12 @@ VPRecipeBuilder::tryToCreatePartialReduction(Instruction *Reduction,
       isa<VPPartialReductionRecipe>(BinOpRecipe))
     std::swap(BinOp, Accumulator);
 
+  VPValue *Mask = getBlockInMask(Reduction->getParent());
+  if (Mask) {
+    VPValue *Zero =
+        Plan.getOrAddLiveIn(ConstantInt::get(Reduction->getType(), 0));
+    BinOp = Builder.createSelect(Mask, BinOp, Zero, Reduction->getDebugLoc());
+  }
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JamesChesterman wrote:

Done.
The assert wasn't getting hit for the non-predicated tests, as they would return a mask of 0 rather than no mask at all. But I've added the extra condition for more safety. It needed to be a slightly different function inside the condition as this one was not working as required.

https://github.com/llvm/llvm-project/pull/124268