[llvm] [InstCombine] Preserve flags for abs(X) * abs(X) and nabs(X) * nabs(X) (PR #88662)

[via llvm-commits]

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@@ -323,11 +323,20 @@ Instruction *InstCombinerImpl::visitMul(BinaryOperator &I) {
   if (Op0 == Op1) {
     Value *X, *Y;
     SelectPatternFlavor SPF = matchSelectPattern(Op0, X, Y).Flavor;
-    if (SPF == SPF_ABS || SPF == SPF_NABS)
-      return BinaryOperator::CreateMul(X, X);
+    if (SPF == SPF_NABS ||
+        match(Op0, m_Neg(m_Intrinsic<Intrinsic::abs>(m_Value(X))))) {
+      if (I.hasNoUnsignedWrap()) {
+        Instruction *NewMul = BinaryOperator::CreateNUWMul(X, X);
+        NewMul->setHasNoSignedWrap(true);
+        return NewMul;
+      }
+      return I.hasNoSignedWrap() ? BinaryOperator::CreateNSWMul(X, X)
+                                 : BinaryOperator::CreateMul(X, X);
+    }
 
-    if (match(Op0, m_Intrinsic<Intrinsic::abs>(m_Value(X))))
-      return BinaryOperator::CreateMul(X, X);
+    if (SPF == SPF_ABS || match(Op0, m_Intrinsic<Intrinsic::abs>(m_Value(X))))
+      return I.hasNoSignedWrap() ? BinaryOperator::CreateNSWMul(X, X)
+                                 : BinaryOperator::CreateMul(X, X);
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goldsteinn wrote:

imo all one case and but `SPF !=SPF_ABS` in the `nuw` case.

https://github.com/llvm/llvm-project/pull/88662