tools/llvm-mc/AsmExpr.cpp

   1 //===- AsmExpr.cpp - Assembly file expressions ----------------------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #include "AsmExpr.h"
  11 #include "llvm/MC/MCContext.h"
  12 #include "llvm/MC/MCSymbol.h"
  13 #include "llvm/MC/MCValue.h"
  14 using namespace llvm;
  15
  16 AsmExpr::~AsmExpr() {
  17 }
  18
  19 bool AsmExpr::EvaluateAsAbsolute(MCContext &Ctx, int64_t &Res) const {
  20   MCValue Value;
  21
  22   if (!EvaluateAsRelocatable(Ctx, Value) || !Value.isAbsolute())
  23     return false;
  24
  25   Res = Value.getConstant();
  26   return true;
  27 }
  28
  29 static bool EvaluateSymbolicAdd(const MCValue &LHS, MCSymbol *RHS_A,
  30                                 MCSymbol *RHS_B, int64_t RHS_Cst,
  31                                 MCValue &Res) {
  32   // We can't add or subtract two symbols.
  33   if ((LHS.getSymA() && RHS_A) ||
  34       (LHS.getSymB() && RHS_B))
  35     return false;
  36
  37   MCSymbol *A = LHS.getSymA() ? LHS.getSymA() : RHS_A;
  38   MCSymbol *B = LHS.getSymB() ? LHS.getSymB() : RHS_B;
  39   if (B) {
  40     // If we have a negated symbol, then we must have also have a non-negated
  41     // symbol in order to encode the expression. We can do this check later to
  42     // permit expressions which eventually fold to a representable form -- such
  43     // as (a + (0 - b)) -- if necessary.
  44     if (!A)
  45       return false;
  46   }
  47   Res = MCValue::get(A, B, LHS.getConstant() + RHS_Cst);
  48   return true;
  49 }
  50
  51 bool AsmExpr::EvaluateAsRelocatable(MCContext &Ctx, MCValue &Res) const {
  52   switch (getKind()) {
  53   default:
  54     assert(0 && "Invalid assembly expression kind!");
  55
  56   case Constant:
  57     Res = MCValue::get(cast<AsmConstantExpr>(this)->getValue());
  58     return true;
  59
  60   case SymbolRef: {
  61     MCSymbol *Sym = cast<AsmSymbolRefExpr>(this)->getSymbol();
  62     if (const MCValue *Value = Ctx.GetSymbolValue(Sym))
  63       Res = *Value;
  64     else
  65       Res = MCValue::get(Sym, 0, 0);
  66     return true;
  67   }
  68
  69   case Unary: {
  70     const AsmUnaryExpr *AUE = cast<AsmUnaryExpr>(this);
  71     MCValue Value;
  72
  73     if (!AUE->getSubExpr()->EvaluateAsRelocatable(Ctx, Value))
  74       return false;
  75
  76     switch (AUE->getOpcode()) {
  77     case AsmUnaryExpr::LNot:
  78       if (!Value.isAbsolute())
  79         return false;
  80       Res = MCValue::get(!Value.getConstant());
  81       break;
  82     case AsmUnaryExpr::Minus:
  83       /// -(a - b + const) ==> (b - a - const)
  84       if (Value.getSymA() && !Value.getSymA())
  85         return false;
  86       Res = MCValue::get(Value.getSymB(), Value.getSymA(),
  87                          -Value.getConstant());
  88       break;
  89     case AsmUnaryExpr::Not:
  90       if (!Value.isAbsolute())
  91         return false;
  92       Res = MCValue::get(~Value.getConstant());
  93       break;
  94     case AsmUnaryExpr::Plus:
  95       Res = Value;
  96       break;
  97     }
  98
  99     return true;
 100   }
 101
 102   case Binary: {
 103     const AsmBinaryExpr *ABE = cast<AsmBinaryExpr>(this);
 104     MCValue LHSValue, RHSValue;
 105
 106     if (!ABE->getLHS()->EvaluateAsRelocatable(Ctx, LHSValue) ||
 107         !ABE->getRHS()->EvaluateAsRelocatable(Ctx, RHSValue))
 108       return false;
 109
 110     // We only support a few operations on non-constant expressions, handle
 111     // those first.
 112     if (!LHSValue.isAbsolute() || !RHSValue.isAbsolute()) {
 113       switch (ABE->getOpcode()) {
 114       default:
 115         return false;
 116       case AsmBinaryExpr::Sub:
 117         // Negate RHS and add.
 118         return EvaluateSymbolicAdd(LHSValue,
 119                                    RHSValue.getSymB(), RHSValue.getSymA(),
 120                                    -RHSValue.getConstant(),
 121                                    Res);
 122
 123       case AsmBinaryExpr::Add:
 124         return EvaluateSymbolicAdd(LHSValue,
 125                                    RHSValue.getSymA(), RHSValue.getSymB(),
 126                                    RHSValue.getConstant(),
 127                                    Res);
 128       }
 129     }
 130
 131     // FIXME: We need target hooks for the evaluation. It may be limited in
 132     // width, and gas defines the result of comparisons differently from Apple
 133     // as (the result is sign extended).
 134     int64_t LHS = LHSValue.getConstant(), RHS = RHSValue.getConstant();
 135     int64_t Result = 0;
 136     switch (ABE->getOpcode()) {
 137     case AsmBinaryExpr::Add:  Result = LHS + RHS; break;
 138     case AsmBinaryExpr::And:  Result = LHS & RHS; break;
 139     case AsmBinaryExpr::Div:  Result = LHS / RHS; break;
 140     case AsmBinaryExpr::EQ:   Result = LHS == RHS; break;
 141     case AsmBinaryExpr::GT:   Result = LHS > RHS; break;
 142     case AsmBinaryExpr::GTE:  Result = LHS >= RHS; break;
 143     case AsmBinaryExpr::LAnd: Result = LHS && RHS; break;
 144     case AsmBinaryExpr::LOr:  Result = LHS || RHS; break;
 145     case AsmBinaryExpr::LT:   Result = LHS < RHS; break;
 146     case AsmBinaryExpr::LTE:  Result = LHS <= RHS; break;
 147     case AsmBinaryExpr::Mod:  Result = LHS % RHS; break;
 148     case AsmBinaryExpr::Mul:  Result = LHS * RHS; break;
 149     case AsmBinaryExpr::NE:   Result = LHS != RHS; break;
 150     case AsmBinaryExpr::Or:   Result = LHS | RHS; break;
 151     case AsmBinaryExpr::Shl:  Result = LHS << RHS; break;
 152     case AsmBinaryExpr::Shr:  Result = LHS >> RHS; break;
 153     case AsmBinaryExpr::Sub:  Result = LHS - RHS; break;
 154     case AsmBinaryExpr::Xor:  Result = LHS ^ RHS; break;
 155     }
 156
 157     Res = MCValue::get(Result);
 158     return true;
 159   }
 160   }
 161 }
 162