[llvm] [InstCombine] Fold (X << Y) / (X << Z) -> (1 << Y) / (1 << Z) (PR #68863)

[Yingwei Zheng via llvm-commits]

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@@ -980,6 +980,28 @@ static Instruction *foldIDivShl(BinaryOperator &I,
       Ret = BinaryOperator::CreateSDiv(X, Y);
   }
 
+  // If X << Y and X << Z does not overflow, then:
+  // (X << Y) / (X << Z) -> (1 << Y) / (1 << Z)
+  // Ignore it when X == 1, to avoid infinite loop.
+  if (match(Op0, m_Shl(m_Value(X), m_Value(Y))) &&
+      match(Op1, m_Shl(m_Specific(X), m_Value(Z))) && !match(X, m_One()) &&
+      (Op0->hasOneUse() || Op1->hasOneUse())) {
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dtcxzyw wrote:

Please add some comments here and add test `sdiv_shl_pair_multi_use`.


https://github.com/llvm/llvm-project/pull/68863