add scaffolding for target-specific MCExprs.

llvm-svn: 95559

llvm/include/llvm/MC/MCExpr.h

@@ -29,7 +29,8 @@ public:
     Binary,    ///< Binary expressions.
     Constant,  ///< Constant expressions.
     SymbolRef, ///< References to labels and assigned expressions.
-    Unary      ///< Unary expressions.
+    Unary,     ///< Unary expressions.
+    Target     ///< Target specific expression.
   };
 
 private:
@@ -326,6 +327,28 @@ public:
   static bool classof(const MCBinaryExpr *) { return true; }
 };
 
+/// MCTargetExpr - This is an extension point for target-specific MCExpr
+/// subclasses to implement.
+///
+/// NOTE: All subclasses are required to have trivial destructors because
+/// MCExprs are bump pointer allocated and not destructed.
+class MCTargetExpr : public MCExpr {
+  virtual ~MCTargetExpr(); // Not accessible.
+protected:
+  MCTargetExpr() : MCExpr(Target) {}
+  
+public:
+  
+  virtual void PrintImpl(raw_ostream &OS) const = 0;
+  virtual bool EvaluateAsRelocatableImpl(MCValue &Res) const = 0;
+
+  
+  static bool classof(const MCExpr *E) {
+    return E->getKind() == MCExpr::Target;
+  }
+  static bool classof(const MCTargetExpr *) { return true; }
+};
+
 } // end namespace llvm
 
 #endif

llvm/lib/MC/MCExpr.cpp

@@ -17,6 +17,8 @@ using namespace llvm;
 
 void MCExpr::print(raw_ostream &OS) const {
   switch (getKind()) {
+  case MCExpr::Target:
+    return cast<MCTargetExpr>(this)->PrintImpl(OS);
   case MCExpr::Constant:
     OS << cast<MCConstantExpr>(*this).getValue();
     return;
@@ -131,6 +133,7 @@ const MCSymbolRefExpr *MCSymbolRefExpr::Create(StringRef Name, MCContext &Ctx) {
   return Create(Ctx.GetOrCreateSymbol(Name), Ctx);
 }
 
+MCTargetExpr::~MCTargetExpr() {}
 
 /* *** */
 
@@ -168,6 +171,9 @@ static bool EvaluateSymbolicAdd(const MCValue &LHS, const MCSymbol *RHS_A,
 
 bool MCExpr::EvaluateAsRelocatable(MCValue &Res) const {
   switch (getKind()) {
+  case Target:
+    return cast<MCTargetExpr>(this)->EvaluateAsRelocatableImpl(Res);
+      
   case Constant:
     Res = MCValue::get(cast<MCConstantExpr>(this)->getValue());
     return true;

llvm/lib/MC/MCMachOStreamer.cpp

@@ -87,6 +87,7 @@ public:
 
   const MCExpr *AddValueSymbols(const MCExpr *Value) {
     switch (Value->getKind()) {
+    case MCExpr::Target: assert(0 && "Can't handle target exprs yet!");
     case MCExpr::Constant:
       break;