[llvm] [InstCombine]: Eliminate redundant modulus for urem (PR #157644)

[Nikita Popov via llvm-commits]

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@@ -2473,6 +2473,16 @@ Instruction *InstCombinerImpl::visitURem(BinaryOperator &I) {
     }
   }
 
+  Value *A;
+  const APInt *Op1Cst, *BCst;
+  // urem(urem(A, BCst), Op1Cst) -> urem(A, Op1Cst)
+  // iff urem(BCst, Op1Cst) == 0
+  if (match(Op0, m_URem(m_Value(A), m_APInt(BCst))) &&
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nikic wrote:

Looks like we need a one-use check on the inner urem. Otherwise we often end up breaking up div+rem patterns, and also performing the urem on a wider type.

https://github.com/llvm/llvm-project/pull/157644