add ucmp and scmp support to SelectionDAG

llvm/include/llvm/CodeGen/ISDOpcodes.h

@@ -676,6 +676,11 @@ enum NodeType {
   UMIN,
   UMAX,
 
+  /// [US]CMP - Three way integer comparison - returns -1, 0, or 1 if
+  /// Op1 < Op2, Op1 == Op2, Op1 > Op2, respectively.
+  SCMP,
+  UCMP,
+
   /// Bitwise operators - logical and, logical or, logical xor.
   AND,
   OR,

llvm/include/llvm/CodeGen/TargetLowering.h

@@ -5314,6 +5314,10 @@ class TargetLowering : public TargetLoweringBase {
   /// method accepts integers as its arguments.
   SDValue expandIntMINMAX(SDNode *Node, SelectionDAG &DAG) const;
 
+  /// Method for building the DAG expansion of ISD::[US]CMP. This
+  /// method accepts integers as its arguments.
+  SDValue expandCMP(SDNode *Node, SelectionDAG &DAG) const;
+
   /// Method for building the DAG expansion of ISD::[US][ADD|SUB]SAT. This
   /// method accepts integers as its arguments.
   SDValue expandAddSubSat(SDNode *Node, SelectionDAG &DAG) const;

llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

@@ -3582,6 +3582,10 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
     Results.push_back(Tmp1);
     break;
   }
+  case ISD::UCMP:
+  case ISD::SCMP:
+  // FIX: add logic here
+    break;
   case ISD::FMINNUM:
   case ISD::FMAXNUM: {
     if (SDValue Expanded = TLI.expandFMINNUM_FMAXNUM(Node, DAG))
@@ -5134,6 +5138,10 @@ void SelectionDAGLegalize::PromoteNode(SDNode *Node) {
     Results.push_back(DAG.getNode(TruncOp, dl, OVT, Tmp1));
     break;
   }
+  case ISD::UCMP:
+  case ISD::SCMP:
+    // FIX: add logic here
+    break;
   case ISD::UMUL_LOHI:
   case ISD::SMUL_LOHI: {
     // Promote to a multiply in a wider integer type.

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -6704,6 +6704,25 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
         VT.getVectorElementType() == MVT::i1)
       return getNode(ISD::XOR, DL, VT, N1, N2);
     break;
+  case ISD::UCMP:
+  case ISD::SCMP:
+    // FIX: This cast is clearly wrong
+    assert(cast<SignedInt>(N1.getValueType) && "This operator should have signed types");
+    assert(VT.isInteger() && "This operator does not apply to FP types!");
+    assert(N1.getValueType() == N2.getValueType() && N1.getValueType() == VT &&
+	       "Binary operator types must match");
+    // FIX: This logic should probably go in a separate function to deduplicate it from ucmp. Suggestions?
+    if (N1C > N2C) {
+      // FIX: All of these casts are horrible, I couldn't find the proper way to fold the constants in
+      return cast<ConstantInt>(1);
+    }
+    if (N1C == N2C) {
+      return cast<ConstantInt>(0);
+    }
+    if (N1C < N2C) {
+      return cast<ConstantInt>(-1);
+    }
+      break;
   case ISD::MUL:
     assert(VT.isInteger() && "This operator does not apply to FP types!");
     assert(N1.getValueType() == N2.getValueType() &&

llvm/unittests/Analysis/ValueTrackingTest.cpp

@@ -891,6 +891,8 @@ TEST(ValueTracking, propagatesPoison) {
       {true, "call i32 @llvm.smin.i32(i32 %x, i32 %y)", 0},
       {true, "call i32 @llvm.umax.i32(i32 %x, i32 %y)", 0},
       {true, "call i32 @llvm.umin.i32(i32 %x, i32 %y)", 0},
+      {true, "call i32 @llvm.scmp.i32.i32(i32 %x, i32 %y)", 0},
+      {true, "call i32 @llvm.ucmp.i32.i32(i32 %x, i32 %y)", 0},
       {true, "call i32 @llvm.bitreverse.i32(i32 %x)", 0},
       {true, "call i32 @llvm.bswap.i32(i32 %x)", 0},
       {false, "call i32 @llvm.fshl.i32(i32 %x, i32 %y, i32 %shamt)", 0},