[llvm] [VPlan] Allow folding not (cmp eq) -> icmp ne with other select users (PR #154497)

[David Sherwood via llvm-commits]

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@@ -1107,13 +1107,30 @@ static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
       return Def->replaceAllUsesWith(A);
 
     // Try to fold Not into compares by adjusting the predicate in-place.
-    if (isa<VPWidenRecipe>(A) && A->getNumUsers() == 1) {
+    auto CanFold = [&A](VPUser *U) {
+      return match(
+          U, m_CombineOr(m_Not(m_Specific(A)),
+                         m_Select(m_Specific(A), m_VPValue(), m_VPValue())));
+    };
+    if (isa<VPWidenRecipe>(A) && all_of(A->users(), CanFold)) {
       auto *WideCmp = cast<VPWidenRecipe>(A);
       if (WideCmp->getOpcode() == Instruction::ICmp ||
           WideCmp->getOpcode() == Instruction::FCmp) {
         WideCmp->setPredicate(
             CmpInst::getInversePredicate(WideCmp->getPredicate()));
-        Def->replaceAllUsesWith(WideCmp);
+        for (VPUser *U : to_vector(WideCmp->users())) {
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david-arm wrote:

Isn't there a problem here with `R->replaceAllUsesWith(WideCmp);` further down? The list of users of `WideCmp` can grow part-way through the loop. I imagine we have to take a snapshot of the users prior to entering the loop.

https://github.com/llvm/llvm-project/pull/154497