1 files changed, 15 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 71a175d..bfa72bf 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -5630,6 +5630,7 @@ bool SelectionDAG::canCreateUndefOrPoison(SDValue Op, const APInt &DemandedElts,
   case ISD::FDIV:
   case ISD::FREM:
   case ISD::FCOPYSIGN:
+  case ISD::FP_EXTEND:
     // No poison except from flags (which is handled above)
     return false;
 
@@ -6422,6 +6423,20 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
     if (N1.isUndef())
       // sext(undef) = 0, because the top bits will all be the same.
       return getConstant(0, DL, VT);
+
+    // Skip unnecessary sext_inreg pattern:
+    // (sext (trunc x)) -> x iff the upper bits are all signbits.
+    if (OpOpcode == ISD::TRUNCATE) {
+      SDValue OpOp = N1.getOperand(0);
+      if (OpOp.getValueType() == VT) {
+        unsigned NumSignExtBits =
+            VT.getScalarSizeInBits() - N1.getScalarValueSizeInBits();
+        if (ComputeNumSignBits(OpOp) > NumSignExtBits) {
+          transferDbgValues(N1, OpOp);
+          return OpOp;
+        }
+      }
+    }
     break;
   case ISD::ZERO_EXTEND:
     assert(VT.isInteger() && N1.getValueType().isInteger() &&