[NFC] Change isFPPredicate comparison to ignore lower bound

[dstuttard]

Summary

Since changing the Predicate to be an unsigned enum, the lower bound check for
isFPPredicate no longer needs to check the lower bound, since
it will always evaluate to true.

Also fixed a similar issue in SIISelLowering.cpp by removing the need for
comparing to FIRST and LAST predicates

Added an assert to the isFPPredicate comparison to flag if the
FIRST_FCMP_PREDICATE is ever changed to anything other than 0, in which case the
logic will break.

Without this change warnings are generated in VS.

Change-Id: I358f0daf28c0628c7bda8ad4cab4e1757b761bab

[dstuttard]

D81662 started causing warnings for VS. This fixes those.

[gchatelet]

LGTM

llvm/include/llvm/IR/InstrTypes.h

public:
 
   /// Return the predicate for this instruction.
   Predicate getPredicate() const { return getSubclassData<PredicateField>(); }
 
   /// Set the predicate for this instruction to the specified value.
   void setPredicate(Predicate P) { setSubclassData<PredicateField>(P); }
 
   static bool isFPPredicate(Predicate P) {
-    return P >= FIRST_FCMP_PREDICATE && P <= LAST_FCMP_PREDICATE;
+    assert(FIRST_FCMP_PREDICATE == 0 &&
+           "FIRST_FCMP_PREDICATE is required to be 0");
+    return P <= LAST_FCMP_PREDICATE;
   }
 
   static bool isIntPredicate(Predicate P) {
     return P >= FIRST_ICMP_PREDICATE && P <= LAST_ICMP_PREDICATE;
   }
 
   static StringRef getPredicateName(Predicate P);
 

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

return DAG.getMergeValues(
       DL);
 }
 
 static SDValue lowerICMPIntrinsic(const SITargetLowering &TLI,
                                   SDNode *N, SelectionDAG &DAG) {
   EVT VT = N->getValueType(0);
   const auto *CD = cast<ConstantSDNode>(N->getOperand(3));
   unsigned CondCode = CD->getZExtValue();
-  if (CondCode < ICmpInst::Predicate::FIRST_ICMP_PREDICATE ||
-      CondCode > ICmpInst::Predicate::LAST_ICMP_PREDICATE)
+  if (!ICmpInst::isIntPredicate(static_cast<ICmpInst::Predicate>(CondCode)))
     return DAG.getUNDEF(VT);
 
   ICmpInst::Predicate IcInput = static_cast<ICmpInst::Predicate>(CondCode);
 
   SDValue LHS = N->getOperand(1);
   SDValue RHS = N->getOperand(2);
 
   SDLoc DL(N);

 }
 
 static SDValue lowerFCMPIntrinsic(const SITargetLowering &TLI,
                                   SDNode *N, SelectionDAG &DAG) {
   EVT VT = N->getValueType(0);
   const auto *CD = cast<ConstantSDNode>(N->getOperand(3));
 
   unsigned CondCode = CD->getZExtValue();
-  if (CondCode < FCmpInst::Predicate::FIRST_FCMP_PREDICATE ||
-      CondCode > FCmpInst::Predicate::LAST_FCMP_PREDICATE) {
+  if (!FCmpInst::isFPPredicate(static_cast<FCmpInst::Predicate>(CondCode)))
     return DAG.getUNDEF(VT);
-  }
 
   SDValue Src0 = N->getOperand(1);
   SDValue Src1 = N->getOperand(2);
   EVT CmpVT = Src0.getValueType();
   SDLoc SL(N);
 
   if (CmpVT == MVT::f16 && !TLI.isTypeLegal(CmpVT)) {
     Src0 = DAG.getNode(ISD::FP_EXTEND, SL, MVT::f32, Src0);