LegalizeTypes support for promotion of bswap.

In LegalizeDAG the value is zero-extended to
the new type before byte swapping.  It doesn't
matter how the extension is done since the new
bits are shifted off anyway after the swap, so
extend by any old rubbish bits.  This results
in the final assembler for the testcase being
one line shorter.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53604 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp

@@ -54,6 +54,7 @@ void DAGTypeLegalizer::PromoteIntegerResult(SDNode *N, unsigned ResNo) {
     assert(0 && "Do not know how to promote this operator!");
     abort();
   case ISD::BIT_CONVERT: Result = PromoteIntRes_BIT_CONVERT(N); break;
+  case ISD::BSWAP:       Result = PromoteIntRes_BSWAP(N); break;
   case ISD::BUILD_PAIR:  Result = PromoteIntRes_BUILD_PAIR(N); break;
   case ISD::Constant:    Result = PromoteIntRes_Constant(N); break;
   case ISD::CTLZ:        Result = PromoteIntRes_CTLZ(N); break;
@@ -150,6 +151,16 @@ SDOperand DAGTypeLegalizer::PromoteIntRes_BIT_CONVERT(SDNode *N) {
   return PromoteIntRes_LOAD(cast<LoadSDNode>(Op.Val));
 }
 
+SDOperand DAGTypeLegalizer::PromoteIntRes_BSWAP(SDNode *N) {
+  SDOperand Op = GetPromotedInteger(N->getOperand(0));
+  MVT OVT = N->getValueType(0);
+  MVT NVT = Op.getValueType();
+
+  unsigned DiffBits = NVT.getSizeInBits() - OVT.getSizeInBits();
+  return DAG.getNode(ISD::SRL, NVT, DAG.getNode(ISD::BSWAP, NVT, Op),
+                     DAG.getConstant(DiffBits, TLI.getShiftAmountTy()));
+}
+
 SDOperand DAGTypeLegalizer::PromoteIntRes_BUILD_PAIR(SDNode *N) {
   // The pair element type may be legal, or may not promote to the same type as
   // the result, for example i14 = BUILD_PAIR (i7, i7).  Handle all cases.

lib/CodeGen/SelectionDAG/LegalizeTypes.h

@@ -213,6 +213,7 @@ private:
   // Integer Result Promotion.
   void PromoteIntegerResult(SDNode *N, unsigned ResNo);
   SDOperand PromoteIntRes_BIT_CONVERT(SDNode *N);
+  SDOperand PromoteIntRes_BSWAP(SDNode *N);
   SDOperand PromoteIntRes_BUILD_PAIR(SDNode *N);
   SDOperand PromoteIntRes_Constant(SDNode *N);
   SDOperand PromoteIntRes_CTLZ(SDNode *N);