Implement and_sext.ll:test3, generating:

_test4:
        srawi r3, r3, 16
        blr

instead of:

_test4:
        srwi r2, r3, 16
        extsh r3, r2
        blr

for:

short test4(unsigned X) {
  return (X >> 16);
}

llvm-svn: 28174

1 files changed, 8 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index e90f902736f..1515df5fd4e 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1936,7 +1936,7 @@ SDOperand DAGCombiner::visitSIGN_EXTEND_INREG(SDNode *N) {
   unsigned EVTBits = MVT::getSizeInBits(EVT);
   
   // fold (sext_in_reg c1) -> c1
-  if (isa<ConstantSDNode>(N0))
+  if (isa<ConstantSDNode>(N0) || N0.getOpcode() == ISD::UNDEF)
     return DAG.getNode(ISD::SIGN_EXTEND_INREG, VT, N0, N1);
   
   // If the input is already sign extended, just drop the extension.
@@ -1949,6 +1949,13 @@ SDOperand DAGCombiner::visitSIGN_EXTEND_INREG(SDNode *N) {
     return DAG.getNode(ISD::SIGN_EXTEND_INREG, VT, N0.getOperand(0), N1);
   }
   
+  // fold (sext_in_reg (srl X, 24), i8) -> sra X, 24
+  if (N0.getOpcode() == ISD::SRL) {
+    if (ConstantSDNode *ShAmt = dyn_cast<ConstantSDNode>(N0.getOperand(1)))
+      if (ShAmt->getValue()+EVTBits == MVT::getSizeInBits(VT))
+        return DAG.getNode(ISD::SRA, VT, N0.getOperand(0), N0.getOperand(1));
+  }
+  
   // fold (sext_in_reg x) -> (zext_in_reg x) if the sign bit is zero
   if (TLI.MaskedValueIsZero(N0, 1ULL << (EVTBits-1)))
     return DAG.getZeroExtendInReg(N0, EVT);