tools/llvm-mc/AsmExpr.cpp

//===- AsmExpr.cpp - Assembly file expressions ----------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "AsmExpr.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCValue.h"
using namespace llvm;

AsmExpr::~AsmExpr() {
}

bool AsmExpr::EvaluateAsAbsolute(MCContext &Ctx, int64_t &Res) const {
  MCValue Value;
  
  if (!EvaluateAsRelocatable(Ctx, Value) || !Value.isConstant())
    return false;

  Res = Value.getConstant();
  return true;
}

bool AsmExpr::EvaluateAsRelocatable(MCContext &Ctx, MCValue &Res) const {
  switch (getKind()) {
  default:
    assert(0 && "Invalid assembly expression kind!");

  case Constant:
    Res = MCValue::get(cast<AsmConstantExpr>(this)->getValue());
    return true;

  case SymbolRef: {
    MCSymbol *Sym = cast<AsmSymbolRefExpr>(this)->getSymbol();
    if (const MCValue *Value = Ctx.GetSymbolValue(Sym))
      Res = *Value;
    else
      Res = MCValue::get(Sym, 0, 0);
    return true;
  }

  case Unary: {
    const AsmUnaryExpr *AUE = cast<AsmUnaryExpr>(this);
    MCValue Value;

    if (!AUE->getSubExpr()->EvaluateAsRelocatable(Ctx, Value))
      return false;

    switch (AUE->getOpcode()) {
    case AsmUnaryExpr::LNot:
      if (!Value.isConstant())
        return false;
      Res = MCValue::get(!Value.getConstant());
      break;
    case AsmUnaryExpr::Minus:
      /// -(a - b + const) ==> (b - a - const)
      if (Value.getSymA() && !Value.getSymA())
        return false;
      Res = MCValue::get(Value.getSymB(), Value.getSymA(), 
                         -Value.getConstant()); 
      break;
    case AsmUnaryExpr::Not:
      if (!Value.isConstant())
        return false;
      Res = MCValue::get(~Value.getConstant()); 
      break;
    case AsmUnaryExpr::Plus:
      Res = Value;
      break;
    }

    return true;
  }

  case Binary: {
    const AsmBinaryExpr *ABE = cast<AsmBinaryExpr>(this);
    MCValue LHSValue, RHSValue;
    
    if (!ABE->getLHS()->EvaluateAsRelocatable(Ctx, LHSValue) ||
        !ABE->getRHS()->EvaluateAsRelocatable(Ctx, RHSValue))
      return false;

    // We only support a few operations on non-constant expressions, handle
    // those first.
    if (!LHSValue.isConstant() || !RHSValue.isConstant()) {
      switch (ABE->getOpcode()) {
      default:
        return false;
      case AsmBinaryExpr::Sub:
        // Negate RHS and fall through.
        RHSValue = MCValue::get(RHSValue.getSymB(), RHSValue.getSymA(), 
                                -RHSValue.getConstant());
      case AsmBinaryExpr::Add:
        // (a_0 - b_0 + cst_0) + (a_1 - b_1 + cst_1)

        // We can't add or subtract two symbols.
        if ((LHSValue.getSymA() && RHSValue.getSymB()) ||
            (LHSValue.getSymB() && RHSValue.getSymB()))
          return false;

        MCSymbol *A = 
          LHSValue.getSymA() ? LHSValue.getSymA() : RHSValue.getSymA();
        MCSymbol *B = 
          LHSValue.getSymB() ? LHSValue.getSymB() : RHSValue.getSymB();
        if (B) {
          // If we have a negated symbol, then we must have also have a
          // non-negated symbol, and both symbols must be in the same
          // non-external section. We can do this check later to permit
          // expressions which eventually fold to a representable form -- such
          // as (a + (0 - b)) -- if necessary.
          if (!A || !A->getSection() || A->getSection() != B->getSection())
            return false;
        }
        Res = MCValue::get(A, B, 
                           LHSValue.getConstant() + RHSValue.getConstant());
        return true;
      }
    }

    // FIXME: We need target hooks for the evaluation. It may be limited in
    // width, and gas defines the result of comparisons differently from Apple
    // as (the result is sign extended).
    int64_t Result, LHS = LHSValue.getConstant(), RHS = RHSValue.getConstant();
    switch (ABE->getOpcode()) {
    case AsmBinaryExpr::Add:  Result = LHS + RHS; break;
    case AsmBinaryExpr::And:  Result = LHS & RHS; break;
    case AsmBinaryExpr::Div:  Result = LHS / RHS; break;
    case AsmBinaryExpr::EQ:   Result = LHS == RHS; break;
    case AsmBinaryExpr::GT:   Result = LHS > RHS; break;
    case AsmBinaryExpr::GTE:  Result = LHS >= RHS; break;
    case AsmBinaryExpr::LAnd: Result = LHS && RHS; break;
    case AsmBinaryExpr::LOr:  Result = LHS || RHS; break;
    case AsmBinaryExpr::LT:   Result = LHS < RHS; break;
    case AsmBinaryExpr::LTE:  Result = LHS <= RHS; break;
    case AsmBinaryExpr::Mod:  Result = LHS % RHS; break;
    case AsmBinaryExpr::Mul:  Result = LHS * RHS; break;
    case AsmBinaryExpr::NE:   Result = LHS != RHS; break;
    case AsmBinaryExpr::Or:   Result = LHS | RHS; break;
    case AsmBinaryExpr::Shl:  Result = LHS << RHS; break;
    case AsmBinaryExpr::Shr:  Result = LHS >> RHS; break;
    case AsmBinaryExpr::Sub:  Result = LHS - RHS; break;
    case AsmBinaryExpr::Xor:  Result = LHS ^ RHS; break;
    }

    Res = MCValue::get(Result);
    return true;
  }
  }
}