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

This patch folds the pattern `a ne/eq (zext/sext (a ne/eq c))` into a boolean constant or a compare.
Clang vs GCC: https://godbolt.org/z/4ro817WE8
Proof for `zext`: https://alive2.llvm.org/ce/z/6z9NRF
Proof for `sext`: https://alive2.llvm.org/ce/z/tv5wuE
Fixes #65073.

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -6481,6 +6481,73 @@ 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)))))) &&
+      ICmpInst::isEquality(Pred1) && ICmpInst::isEquality(Pred2)) {
+    bool IsSExt = ExtI->getOpcode() == Instruction::SExt;
+    bool HasOneUse = ExtI->hasOneUse() && ExtI->getOperand(0)->hasOneUse();
+    auto CreateRangeCheck = [&] {
+      Value *CmpV1 =
+          Builder.CreateICmp(Pred1, X, Constant::getNullValue(X->getType()));
+      Value *CmpV2 = Builder.CreateICmp(
+          Pred1, X, ConstantInt::getSigned(X->getType(), IsSExt ? -1 : 1));
+      return BinaryOperator::Create(
+          Pred1 == ICmpInst::ICMP_EQ ? Instruction::Or : Instruction::And,
+          CmpV1, CmpV2);
+    };
+    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)) --> X == 0 || X == 1
+        // icmp ne X, (zext (icmp ne X, 0)) --> X != 0 && X != 1
+        // icmp eq X, (sext (icmp ne X, 0)) --> X == 0 || X == -1
+        // icmp ne X, (sext (icmp ne X, 0)) --> X != 0 && X == -1
+        return CreateRangeCheck();
+      }
+    } 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)) --> X == 0 || X == 1
+        // icmp ne X, (zext (icmp eq X, 1)) --> X != 0 && X != 1
+        // icmp eq X, (sext (icmp eq X, -1)) --> X == 0 || X == -1
+        // icmp ne X, (sext (icmp eq X, -1)) --> X != 0 && X == -1
+        return CreateRangeCheck();
+      }
+    } else {
+      // when C != 0 && C != 1:
+      //   icmp eq X, (zext (icmp eq X, C)) --> icmp eq X, 0
+      //   icmp eq X, (zext (icmp ne X, C)) --> icmp eq X, 1
+      //   icmp ne X, (zext (icmp eq X, C)) --> icmp ne X, 0
+      //   icmp ne X, (zext (icmp ne X, C)) --> icmp ne X, 1
+      // when C != 0 && C != -1:
+      //   icmp eq X, (sext (icmp eq X, C)) --> icmp eq X, 0
+      //   icmp eq X, (sext (icmp ne X, C)) --> icmp eq X, -1
+      //   icmp ne X, (sext (icmp eq X, C)) --> icmp ne X, 0
+      //   icmp ne X, (sext (icmp ne X, C)) --> icmp ne X, -1
+      return ICmpInst::Create(
+          Instruction::ICmp, Pred1, X,
+          ConstantInt::getSigned(X->getType(), Pred2 == ICmpInst::ICMP_NE
+                                                   ? (IsSExt ? -1 : 1)
+                                                   : 0));
+    }
+  }
+
   return nullptr;
 }