1 files changed, 16 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 4f2eb1e..df353c4 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -10988,6 +10988,22 @@ SDValue DAGCombiner::visitSRA(SDNode *N) {
     }
   }
 
+  // fold (sra (xor (sra x, c1), -1), c2) -> (xor (sra x, c3), -1)
+  // This allows merging two arithmetic shifts even when there's a NOT in
+  // between.
+  SDValue X;
+  APInt C1;
+  if (N1C && sd_match(N0, m_OneUse(m_Not(
+                              m_OneUse(m_Sra(m_Value(X), m_ConstInt(C1))))))) {
+    APInt C2 = N1C->getAPIntValue();
+    zeroExtendToMatch(C1, C2, 1 /* Overflow Bit */);
+    APInt Sum = C1 + C2;
+    unsigned ShiftSum = Sum.getLimitedValue(OpSizeInBits - 1);
+    SDValue NewShift = DAG.getNode(
+        ISD::SRA, DL, VT, X, DAG.getShiftAmountConstant(ShiftSum, VT, DL));
+    return DAG.getNOT(DL, NewShift, VT);
+  }
+
   // fold (sra (shl X, m), (sub result_size, n))
   // -> (sign_extend (trunc (shl X, (sub (sub result_size, n), m)))) for
   // result_size - n != m.