[llvm] [VPlan] Fold NOT into predicate of wide compares. (PR #129430)

[Florian Hahn via llvm-commits]

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@@ -972,8 +972,25 @@ static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
   if (match(&R, m_c_Mul(m_VPValue(A), m_SpecificInt(1))))
     return R.getVPSingleValue()->replaceAllUsesWith(A);
 
-  if (match(&R, m_Not(m_Not(m_VPValue(A)))))
-    return R.getVPSingleValue()->replaceAllUsesWith(A);
+  if (match(&R, m_Not(m_VPValue(A)))) {
+    if (match(A, m_Not(m_VPValue(A))))
+      return R.getVPSingleValue()->replaceAllUsesWith(A);
+
+    // Try to fold Not into compares by adjusting the predicate in-place.
+    if (isa<VPWidenRecipe>(A) && A->getNumUsers() == 1) {
+      auto *WideCmp = cast<VPWidenRecipe>(A);
+      if (WideCmp->getOpcode() == Instruction::ICmp ||
+          WideCmp->getOpcode() == Instruction::FCmp) {
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fhahn wrote:

AFAIK the predicates should be symmetric, instcombine also folds the negation into the compare by adjusting the predicate for all cases: https://llvm.godbolt.org/z/a9KqeocWd

I also checked most of the changes in the tests with Alive2: https://alive2.llvm.org/ce/z/WGDz9U

https://github.com/llvm/llvm-project/pull/129430