[llvm] [InstCombine] Simplify the pattern `a ne/eq (zext/sext (a ne/eq c))` (PR #65852)

[via llvm-commits]

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@@ -6380,7 +6380,74 @@ Instruction *InstCombinerImpl::foldICmpUsingBoolRange(ICmpInst &I) {
       Y->getType()->isIntOrIntVectorTy(1) && Pred == ICmpInst::ICMP_ULE)
     return BinaryOperator::CreateOr(Builder.CreateIsNull(X), Y);
 
+  // icmp eq/ne X, (zext/sext (icmp eq/ne X, C))
+  ICmpInst::Predicate Pred1, Pred2;
   const APInt *C;
+  Instruction *ExtI;
+  if (match(&I, m_c_ICmp(Pred1, m_Value(X),
+                         m_CombineAnd(m_Instruction(ExtI),
+                                      m_ZExtOrSExt(m_ICmp(Pred2, m_Deferred(X),
+                                                          m_APInt(C))))))) {
+    bool IsSExt = ExtI->getOpcode() == Instruction::SExt;
+    bool HasOneUse = ExtI->hasOneUse() && ExtI->getOperand(0)->hasOneUse();
+    if (C->isZero()) {
+      if (Pred2 == ICmpInst::ICMP_EQ) {
+        // icmp eq X, (zext/sext (icmp eq X, 0)) --> false
+        // icmp ne X, (zext/sext (icmp eq X, 0)) --> true
+        return replaceInstUsesWith(
+            I, ConstantInt::getBool(I.getType(), Pred1 == ICmpInst::ICMP_NE));
+      } else if (!IsSExt || HasOneUse) {
+        // icmp eq X, (zext (icmp ne X, 0)) --> icmp ult X, 2
+        // icmp ne X, (zext (icmp ne X, 0)) --> icmp ugt X, 1
+        // icmp eq X, (sext (icmp ne X, 0)) --> icmp ult (X + 1), 2
+        // icmp ne X, (sext (icmp ne X, 0)) --> icmp ugt (X + 1), 1
+        return ICmpInst::Create(
+            Instruction::ICmp,
+            Pred1 == ICmpInst::ICMP_NE ? ICmpInst::ICMP_UGT
+                                       : ICmpInst::ICMP_ULT,
+            IsSExt ? Builder.CreateAdd(X, ConstantInt::get(X->getType(), 1))
+                   : X,
+            ConstantInt::get(X->getType(), Pred1 == ICmpInst::ICMP_NE ? 1 : 2));
+      }
+    } else if (IsSExt ? C->isAllOnes() : C->isOne()) {
+      if (Pred2 == ICmpInst::ICMP_NE) {
+        // icmp eq X, (zext (icmp ne X, 1)) --> false
+        // icmp ne X, (zext (icmp ne X, 1)) --> true
+        // icmp eq X, (sext (icmp ne X, -1)) --> false
+        // icmp ne X, (sext (icmp ne X, -1)) --> true
+        return replaceInstUsesWith(
+            I, ConstantInt::getBool(I.getType(), Pred1 == ICmpInst::ICMP_NE));
+      } else if (!IsSExt || HasOneUse) {
+        // icmp eq X, (zext (icmp eq X, 1)) --> icmp ult X, 2
+        // icmp ne X, (zext (icmp eq X, 1)) --> icmp ugt X, 1
+        // icmp eq X, (sext (icmp eq X, -1)) --> icmp ult (X + 1), 2
+        // icmp ne X, (sext (icmp eq X, -1)) --> icmp ugt (X + 1), 1
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goldsteinn wrote:

@nikic, just wondering is there a reason we don't embed alive2 proofs in codes? I know a few occasions I've wanted to for non-trivially obvious comments and would be useful for something like this.

https://github.com/llvm/llvm-project/pull/65852