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

[Ramkumar Ramachandra via llvm-commits]

================
@@ -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())) {
+          auto *R = cast<VPSingleDefRecipe>(U);
+          // not (icmp eq) -> icmp ne
+          if (match(R, m_Not(m_Specific(WideCmp))))
+            R->replaceAllUsesWith(WideCmp);
+          // select (icmp eq), x, y -> select (icmp ne), y, x
+          else if (match(R, m_Select(m_Specific(WideCmp), m_VPValue(X),
+                                     m_VPValue(Y)))) {
+            R->setOperand(1, Y);
+            R->setOperand(2, X);
+          } else
----------------
artagnon wrote:

I'd probably have two separate matches `m_Not(m_Cmp(...))` and `m_Select(m_Cmp(...), ...)`, stripping the all_of, the llvm_unreachable, and the ugly opcode matching.

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