[llvm] a959796 - [VPlan] Assert ComputeReductionResult isn't predicated in middle block. NFC (#191767)

[via llvm-commits]

Author: Luke Lau
Date: 2026-04-13T08:20:29Z
New Revision: a95979686f532a194d9fb8a8671800f5e75e3405

URL: https://github.com/llvm/llvm-project/commit/a95979686f532a194d9fb8a8671800f5e75e3405
DIFF: https://github.com/llvm/llvm-project/commit/a95979686f532a194d9fb8a8671800f5e75e3405.diff

LOG: [VPlan] Assert ComputeReductionResult isn't predicated in middle block. NFC (#191767)

Added: 
    

Modified: 
    llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index d46f05f9ead57..b2e8b6a85a35a 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -3288,6 +3288,17 @@ static void fixupVFUsersForEVL(VPlan &Plan, VPValue &EVL) {
   if (!HeaderMask)
     return;
 
+  // Ensure that any reduction that uses a select to mask off tail lanes does so
+  // in the vector loop, not the middle block, since EVL tail folding can have
+  // tail elements in the penultimate iteration.
+  assert(all_of(*Plan.getMiddleBlock(), [&Plan, HeaderMask](VPRecipeBase &R) {
+    if (match(&R, m_ComputeReductionResult(m_Select(m_Specific(HeaderMask),
+                                                    m_VPValue(), m_VPValue()))))
+      return R.getOperand(0)->getDefiningRecipe()->getRegion() ==
+             Plan.getVectorLoopRegion();
+    return true;
+  }));
+
   // Replace header masks with a mask equivalent to predicating by EVL:
   //
   // icmp ule widen-canonical-iv backedge-taken-count