X86 lowers SELECT to a cmp / test followed by a conditional move.

llvm-svn: 24754

lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

@@ -1325,6 +1325,16 @@ SDOperand SelectionDAGLegalize::LegalizeOp(SDOperand Op) {
                                  Tmp2, Tmp3, ISD::SETNE);
       }
       break;
+    case TargetLowering::Custom: {
+      SDOperand Tmp =
+        TLI.LowerOperation(DAG.getNode(ISD::SELECT, Node->getValueType(0),
+                                       Tmp1, Tmp2, Tmp3), DAG);
+      if (Tmp.Val) {
+        Result = LegalizeOp(Tmp);
+        break;
+      }
+      // FALLTHROUGH if the target thinks it is legal.
+    }
     case TargetLowering::Legal:
       if (Tmp1 != Node->getOperand(0) || Tmp2 != Node->getOperand(1) ||
           Tmp3 != Node->getOperand(2))

lib/Target/X86/X86ISelLowering.cpp

@@ -113,6 +113,11 @@ X86TargetLowering::X86TargetLowering(TargetMachine &TM)
   // These should be promoted to a larger select which is supported.
   setOperationAction(ISD::SELECT           , MVT::i1   , Promote);
   setOperationAction(ISD::SELECT           , MVT::i8   , Promote);
+  // X86 wants to expand cmov itself.
+  if (X86DAGIsel) {
+    setOperationAction(ISD::SELECT         , MVT::i16  , Custom);
+    setOperationAction(ISD::SELECT         , MVT::i32  , Custom);
+  }
 
   // We don't have line number support yet.
   setOperationAction(ISD::LOCATION, MVT::Other, Expand);
@@ -930,5 +935,22 @@ SDOperand X86TargetLowering::LowerOperation(SDOperand Op, SelectionDAG &DAG) {
     Tys.push_back(MVT::Other);
     return DAG.getNode(ISD::MERGE_VALUES, Tys, Ops);
   }
+  case ISD::SELECT: {
+    unsigned Opc;
+    SDOperand Cond  = Op.getOperand(0);
+    SDOperand True  = Op.getOperand(1);
+    SDOperand False = Op.getOperand(2);
+    SDOperand CC;
+    if (Cond.getOpcode() == ISD::SETCC) {
+      CC = Cond.getOperand(2);
+      Cond = DAG.getNode(X86ISD::CMP, MVT::Flag,
+                         Cond.getOperand(0), Cond.getOperand(1));
+    } else {
+      CC = DAG.getCondCode(ISD::SETEQ);
+      Cond = DAG.getNode(X86ISD::TEST, MVT::Flag, Cond, Cond);
+    }
+    return DAG.getNode(X86ISD::CMOV, Op.getValueType(),
+                       Op.getOperand(1), Op.getOperand(2), CC, Cond);
+  }
   }
 }

lib/Target/X86/X86ISelLowering.h

@@ -23,7 +23,7 @@ namespace llvm {
   namespace X86ISD {
     enum NodeType {
       // Start the numbering where the builtin ops leave off.
-      FIRST_NUMBER = ISD::BUILTIN_OP_END,
+      FIRST_NUMBER = ISD::BUILTIN_OP_END+X86::INSTRUCTION_LIST_END,
 
       /// FILD64m - This instruction implements SINT_TO_FP with a
       /// 64-bit source in memory and a FP reg result.  This corresponds to
@@ -66,6 +66,12 @@ namespace llvm {
       /// RDTSC_DAG - This operation implements the lowering for 
       /// readcyclecounter
       RDTSC_DAG,
+
+      /// X86 compare and logical compare instructions.
+      CMP, TEST,
+
+      /// X86 conditional moves.
+      CMOV,
     };
   }