[llvm] [DAG] Fold urem(urem(A, BCst), Op1Cst) -> urem(A, Op1Cst) (PR #159517)

[Simon Pilgrim via llvm-commits]

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@@ -5405,6 +5406,25 @@ SDValue DAGCombiner::visitREM(SDNode *N) {
   if (SDValue DivRem = useDivRem(N))
     return DivRem.getValue(1);
 
+  // fold urem(urem(A, BCst), Op1Cst) -> urem(A, Op1Cst)
+  // iff urem(BCst, Op1Cst) == 0
+  SDValue A;
+  APInt Op1Cst, BCst;
+  if (sd_match(N, m_URem(m_URem(m_Value(A), m_ConstInt(BCst)),
+                         m_ConstInt(Op1Cst))) &&
+      BCst.urem(Op1Cst).isZero()) {
+    return DAG.getNode(ISD::UREM, DL, VT, A, DAG.getConstant(Op1Cst, DL, VT));
+  }
+
+  // fold srem(srem(A, BCst), Op1Cst) -> srem(A, Op1Cst)
+  // iff srem(BCst, Op1Cst) == 0 && Op1Cst != 1
+  if (sd_match(N, m_SRem(m_SRem(m_Value(A), m_ConstInt(BCst)),
+                         m_ConstInt(Op1Cst))) &&
+      BCst.srem(Op1Cst).isZero() &&
+      Op1Cst.ne(APInt::getAllOnes(Op1Cst.getBitWidth()))) {
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RKSimon wrote:

`!Op1Cst.isAllOnes()` ?

https://github.com/llvm/llvm-project/pull/159517