[llvm] [SLP][REVEC] Ignore UserTreeIndex if it is empty. (PR #131993)

[Alexey Bataev via llvm-commits]

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@@ -6449,9 +6449,10 @@ void BoUpSLP::reorderTopToBottom() {
             assert(SLPReVec && "Only supported by REVEC.");
             // ShuffleVectorInst does not do reorderOperands (and it should not
             // because ShuffleVectorInst supports only a limited set of
-            // patterns). Only do reorderNodeWithReuses if all of the users are
-            // not ShuffleVectorInst.
-            if (isa<ShuffleVectorInst>(TE->UserTreeIndex.UserTE->getMainOp()))
+            // patterns). Only do reorderNodeWithReuses if the user is not
+            // ShuffleVectorInst.
+            if (TE->UserTreeIndex &&
+                isa<ShuffleVectorInst>(TE->UserTreeIndex.UserTE->getMainOp()))
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alexey-bataev wrote:

Some entries might have Gather parents

https://github.com/llvm/llvm-project/pull/131993