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

[Nikita Popov via flang-commits]

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@@ -6380,7 +6380,71 @@ 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();
+    auto CreateRangeCheck = [&] {
+      Value *CmpV1 =
+          Builder.CreateICmp(Pred1, X, Constant::getNullValue(X->getType()));
+      Value *CmpV2 = Builder.CreateICmp(
+          Pred1, X, ConstantInt::get(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::get(X->getType(),
+                           Pred2 == ICmpInst::ICMP_NE ? (IsSExt ? -1 : 1) : 0));
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nikic wrote:

This looks like something that will break with 128 bit integers.

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