[llvm] [InstCombine] Fold square into comparison with constant (reopened) (PR #197665)

[Macsen Casaus via llvm-commits]

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@@ -2188,12 +2188,49 @@ Instruction *InstCombinerImpl::foldICmpMulConstant(ICmpInst &Cmp,
   Type *MulTy = Mul->getType();
   Value *X = Mul->getOperand(0);
 
-  // If there's no overflow:
-  // X * X == 0 --> X == 0
-  // X * X != 0 --> X != 0
-  if (Cmp.isEquality() && C.isZero() && X == Mul->getOperand(1) &&
-      (Mul->hasNoUnsignedWrap() || Mul->hasNoSignedWrap()))
-    return new ICmpInst(Pred, X, ConstantInt::getNullValue(MulTy));
+  // If comparing a square with a constant, try simplifying to comparing square
+  // roots
+  if (X == Mul->getOperand(1) && !Cmp.isSigned()) {
+    APInt R = C.sqrtFloor();
+    APInt R2 = R * R;
+    bool IsSqr = C == R2;
+
+    // X * X eq/ne C
+    if (Cmp.isEquality() &&
+        (Mul->hasNoUnsignedWrap() || (Mul->hasNoSignedWrap() && C.isZero()))) {
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macsencasaus wrote:

This optimization was already present and tested for
https://github.com/llvm/llvm-project/blob/b6501be5448273989e28210b4befd3b862568aff/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp#L2191-L2196

https://github.com/llvm/llvm-project/blob/b6501be5448273989e28210b4befd3b862568aff/llvm/test/Transforms/InstCombine/icmp-mul.ll#L9-L17

https://github.com/llvm/llvm-project/pull/197665