[llvm] [InstCombine] Fold `min(X+1, Y) - min(X, Y) --> zext X < Y` (PR #157782)

[Yingwei Zheng via llvm-commits]

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@@ -2719,6 +2719,24 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) {
     return BinaryOperator::CreateSub(X, Not);
   }
 
+  // min(X+1, Y) - min(X, Y) --> zext X < Y
+  // Replacing a sub and at least one min with an icmp
+  // and a zext is a potential improvement.
+  if (match(Op0, m_c_SMin(m_c_NSWAdd(m_Value(X), m_One()), m_Value(Y))) &&
+      match(Op1, m_c_SMin(m_Value(X), m_Value(Y))) &&
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dtcxzyw wrote:

> Is it possible that I misunderstood, and you meant a test to swap the min arguments? 

No. Just a negative test for `min(X+1, Y) - min(X, Z)`.


https://github.com/llvm/llvm-project/pull/157782