1 files changed, 20 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 06e3b9a3840..4adf2405d30 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -9084,6 +9084,26 @@ SDValue DAGCombiner::visitAssertExt(SDNode *N) {
     return DAG.getNode(ISD::TRUNCATE, DL, N->getValueType(0), NewAssert);
   }
 
+  // If we have (AssertZext (truncate (AssertSext X, iX)), iY) and Y is smaller
+  // than X. Just move the AssertZext in front of the truncate and drop the
+  // AssertSExt.
+  if (N0.getOpcode() == ISD::TRUNCATE && N0.hasOneUse() &&
+      N0.getOperand(0).getOpcode() == ISD::AssertSext &&
+      Opcode == ISD::AssertZext) {
+    SDValue BigA = N0.getOperand(0);
+    EVT BigA_AssertVT = cast<VTSDNode>(BigA.getOperand(1))->getVT();
+    assert(BigA_AssertVT.bitsLE(N0.getValueType()) &&
+           "Asserting zero/sign-extended bits to a type larger than the "
+           "truncated destination does not provide information");
+
+    if (AssertVT.bitsLT(BigA_AssertVT)) {
+      SDLoc DL(N);
+      SDValue NewAssert = DAG.getNode(Opcode, DL, BigA.getValueType(),
+                                      BigA.getOperand(0), N1);
+      return DAG.getNode(ISD::TRUNCATE, DL, N->getValueType(0), NewAssert);
+    }
+  }
+
   return SDValue();
 }