[Hexagon] Hoist nonnull assert up.

Once a pointer is turned into a reference it cannot be nullptr, clang
rightfully warns about this assert being a tautology. Put the assert
before the reference is created.

llvm-svn: 260949

lib/Target/Hexagon/AsmParser/HexagonAsmParser.cpp

@@ -592,7 +592,6 @@ public:
 
   static std::unique_ptr<HexagonOperand> CreateImm(const MCExpr *Val, SMLoc S,
                                                    SMLoc E) {
-    assert(&HexagonMCInstrInfo::getExpr(*Val) != nullptr);
     HexagonOperand *Op = new HexagonOperand(Immediate);
     Op->Imm.Val = Val;
     Op->Imm.MustExtend = false;

lib/Target/Hexagon/MCTargetDesc/HexagonMCInstrInfo.cpp

@@ -193,6 +193,7 @@ MCInstrDesc const &HexagonMCInstrInfo::getDesc(MCInstrInfo const &MCII,
 
 MCExpr const &HexagonMCInstrInfo::getExpr(MCExpr const &Expr) {
   HexagonMCExpr const &HExpr = *llvm::cast<HexagonMCExpr>(&Expr);
+  assert(HExpr.getExpr());
   return *HExpr.getExpr();
 }