lib/MC/MCExpr.cpp

   1 //===- MCExpr.cpp - Assembly Level Expression Implementation --------------===//
   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 "llvm/MC/MCExpr.h"
  11 #include "llvm/MC/MCContext.h"
  12 #include "llvm/MC/MCSymbol.h"
  13 #include "llvm/MC/MCValue.h"
  14 #include "llvm/Support/raw_ostream.h"
  15 using namespace llvm;
  16
  17 void MCExpr::print(raw_ostream &OS, const MCAsmInfo *MAI) const {
  18   switch (getKind()) {
  19   case MCExpr::Constant:
  20     OS << cast<MCConstantExpr>(*this).getValue();
  21     return;
  22
  23   case MCExpr::SymbolRef: {
  24     const MCSymbol &Sym = cast<MCSymbolRefExpr>(*this).getSymbol();
  25
  26     // Parenthesize names that start with $ so that they don't look like
  27     // absolute names.
  28     if (Sym.getName()[0] == '$') {
  29       OS << '(';
  30       Sym.print(OS, MAI);
  31       OS << ')';
  32     } else {
  33       Sym.print(OS, MAI);
  34     }
  35     return;
  36   }
  37
  38   case MCExpr::Unary: {
  39     const MCUnaryExpr &UE = cast<MCUnaryExpr>(*this);
  40     switch (UE.getOpcode()) {
  41     default: assert(0 && "Invalid opcode!");
  42     case MCUnaryExpr::LNot:  OS << '!'; break;
  43     case MCUnaryExpr::Minus: OS << '-'; break;
  44     case MCUnaryExpr::Not:   OS << '~'; break;
  45     case MCUnaryExpr::Plus:  OS << '+'; break;
  46     }
  47     UE.getSubExpr()->print(OS, MAI);
  48     return;
  49   }
  50
  51   case MCExpr::Binary: {
  52     const MCBinaryExpr &BE = cast<MCBinaryExpr>(*this);
  53
  54     // Only print parens around the LHS if it is non-trivial.
  55     if (isa<MCConstantExpr>(BE.getLHS()) || isa<MCSymbolRefExpr>(BE.getLHS())) {
  56       BE.getLHS()->print(OS, MAI);
  57     } else {
  58       OS << '(';
  59       BE.getLHS()->print(OS, MAI);
  60       OS << ')';
  61     }
  62
  63     switch (BE.getOpcode()) {
  64     default: assert(0 && "Invalid opcode!");
  65     case MCBinaryExpr::Add:
  66       // Print "X-42" instead of "X+-42".
  67       if (const MCConstantExpr *RHSC = dyn_cast<MCConstantExpr>(BE.getRHS())) {
  68         if (RHSC->getValue() < 0) {
  69           OS << RHSC->getValue();
  70           return;
  71         }
  72       }
  73
  74       OS <<  '+';
  75       break;
  76     case MCBinaryExpr::And:  OS <<  '&'; break;
  77     case MCBinaryExpr::Div:  OS <<  '/'; break;
  78     case MCBinaryExpr::EQ:   OS << "=="; break;
  79     case MCBinaryExpr::GT:   OS <<  '>'; break;
  80     case MCBinaryExpr::GTE:  OS << ">="; break;
  81     case MCBinaryExpr::LAnd: OS << "&&"; break;
  82     case MCBinaryExpr::LOr:  OS << "||"; break;
  83     case MCBinaryExpr::LT:   OS <<  '<'; break;
  84     case MCBinaryExpr::LTE:  OS << "<="; break;
  85     case MCBinaryExpr::Mod:  OS <<  '%'; break;
  86     case MCBinaryExpr::Mul:  OS <<  '*'; break;
  87     case MCBinaryExpr::NE:   OS << "!="; break;
  88     case MCBinaryExpr::Or:   OS <<  '|'; break;
  89     case MCBinaryExpr::Shl:  OS << "<<"; break;
  90     case MCBinaryExpr::Shr:  OS << ">>"; break;
  91     case MCBinaryExpr::Sub:  OS <<  '-'; break;
  92     case MCBinaryExpr::Xor:  OS <<  '^'; break;
  93     }
  94
  95     // Only print parens around the LHS if it is non-trivial.
  96     if (isa<MCConstantExpr>(BE.getRHS()) || isa<MCSymbolRefExpr>(BE.getRHS())) {
  97       BE.getRHS()->print(OS, MAI);
  98     } else {
  99       OS << '(';
 100       BE.getRHS()->print(OS, MAI);
 101       OS << ')';
 102     }
 103     return;
 104   }
 105   }
 106
 107   assert(0 && "Invalid expression kind!");
 108 }
 109
 110 void MCExpr::dump() const {
 111   print(errs(), 0);
 112   errs() << '\n';
 113 }
 114
 115 /* *** */
 116
 117 const MCBinaryExpr *MCBinaryExpr::Create(Opcode Opc, const MCExpr *LHS,
 118                                          const MCExpr *RHS, MCContext &Ctx) {
 119   return new (Ctx) MCBinaryExpr(Opc, LHS, RHS);
 120 }
 121
 122 const MCUnaryExpr *MCUnaryExpr::Create(Opcode Opc, const MCExpr *Expr,
 123                                        MCContext &Ctx) {
 124   return new (Ctx) MCUnaryExpr(Opc, Expr);
 125 }
 126
 127 const MCConstantExpr *MCConstantExpr::Create(int64_t Value, MCContext &Ctx) {
 128   return new (Ctx) MCConstantExpr(Value);
 129 }
 130
 131 const MCSymbolRefExpr *MCSymbolRefExpr::Create(const MCSymbol *Sym,
 132                                                MCContext &Ctx) {
 133   return new (Ctx) MCSymbolRefExpr(Sym);
 134 }
 135
 136 /* *** */
 137
 138 bool MCExpr::EvaluateAsAbsolute(MCContext &Ctx, int64_t &Res) const {
 139   MCValue Value;
 140
 141   if (!EvaluateAsRelocatable(Ctx, Value) || !Value.isAbsolute())
 142     return false;
 143
 144   Res = Value.getConstant();
 145   return true;
 146 }
 147
 148 static bool EvaluateSymbolicAdd(const MCValue &LHS, const MCSymbol *RHS_A,
 149                                 const MCSymbol *RHS_B, int64_t RHS_Cst,
 150                                 MCValue &Res) {
 151   // We can't add or subtract two symbols.
 152   if ((LHS.getSymA() && RHS_A) ||
 153       (LHS.getSymB() && RHS_B))
 154     return false;
 155
 156   const MCSymbol *A = LHS.getSymA() ? LHS.getSymA() : RHS_A;
 157   const MCSymbol *B = LHS.getSymB() ? LHS.getSymB() : RHS_B;
 158   if (B) {
 159     // If we have a negated symbol, then we must have also have a non-negated
 160     // symbol in order to encode the expression. We can do this check later to
 161     // permit expressions which eventually fold to a representable form -- such
 162     // as (a + (0 - b)) -- if necessary.
 163     if (!A)
 164       return false;
 165   }
 166   Res = MCValue::get(A, B, LHS.getConstant() + RHS_Cst);
 167   return true;
 168 }
 169
 170 bool MCExpr::EvaluateAsRelocatable(MCContext &Ctx, MCValue &Res) const {
 171   switch (getKind()) {
 172   case Constant:
 173     Res = MCValue::get(cast<MCConstantExpr>(this)->getValue());
 174     return true;
 175
 176   case SymbolRef: {
 177     const MCSymbol &Sym = cast<MCSymbolRefExpr>(this)->getSymbol();
 178     if (const MCValue *Value = Ctx.GetSymbolValue(&Sym))
 179       Res = *Value;
 180     else
 181       Res = MCValue::get(&Sym, 0, 0);
 182     return true;
 183   }
 184
 185   case Unary: {
 186     const MCUnaryExpr *AUE = cast<MCUnaryExpr>(this);
 187     MCValue Value;
 188
 189     if (!AUE->getSubExpr()->EvaluateAsRelocatable(Ctx, Value))
 190       return false;
 191
 192     switch (AUE->getOpcode()) {
 193     case MCUnaryExpr::LNot:
 194       if (!Value.isAbsolute())
 195         return false;
 196       Res = MCValue::get(!Value.getConstant());
 197       break;
 198     case MCUnaryExpr::Minus:
 199       /// -(a - b + const) ==> (b - a - const)
 200       if (Value.getSymA() && !Value.getSymB())
 201         return false;
 202       Res = MCValue::get(Value.getSymB(), Value.getSymA(),
 203                          -Value.getConstant());
 204       break;
 205     case MCUnaryExpr::Not:
 206       if (!Value.isAbsolute())
 207         return false;
 208       Res = MCValue::get(~Value.getConstant());
 209       break;
 210     case MCUnaryExpr::Plus:
 211       Res = Value;
 212       break;
 213     }
 214
 215     return true;
 216   }
 217
 218   case Binary: {
 219     const MCBinaryExpr *ABE = cast<MCBinaryExpr>(this);
 220     MCValue LHSValue, RHSValue;
 221
 222     if (!ABE->getLHS()->EvaluateAsRelocatable(Ctx, LHSValue) ||
 223         !ABE->getRHS()->EvaluateAsRelocatable(Ctx, RHSValue))
 224       return false;
 225
 226     // We only support a few operations on non-constant expressions, handle
 227     // those first.
 228     if (!LHSValue.isAbsolute() || !RHSValue.isAbsolute()) {
 229       switch (ABE->getOpcode()) {
 230       default:
 231         return false;
 232       case MCBinaryExpr::Sub:
 233         // Negate RHS and add.
 234         return EvaluateSymbolicAdd(LHSValue,
 235                                    RHSValue.getSymB(), RHSValue.getSymA(),
 236                                    -RHSValue.getConstant(),
 237                                    Res);
 238
 239       case MCBinaryExpr::Add:
 240         return EvaluateSymbolicAdd(LHSValue,
 241                                    RHSValue.getSymA(), RHSValue.getSymB(),
 242                                    RHSValue.getConstant(),
 243                                    Res);
 244       }
 245     }
 246
 247     // FIXME: We need target hooks for the evaluation. It may be limited in
 248     // width, and gas defines the result of comparisons differently from Apple
 249     // as (the result is sign extended).
 250     int64_t LHS = LHSValue.getConstant(), RHS = RHSValue.getConstant();
 251     int64_t Result = 0;
 252     switch (ABE->getOpcode()) {
 253     case MCBinaryExpr::Add:  Result = LHS + RHS; break;
 254     case MCBinaryExpr::And:  Result = LHS & RHS; break;
 255     case MCBinaryExpr::Div:  Result = LHS / RHS; break;
 256     case MCBinaryExpr::EQ:   Result = LHS == RHS; break;
 257     case MCBinaryExpr::GT:   Result = LHS > RHS; break;
 258     case MCBinaryExpr::GTE:  Result = LHS >= RHS; break;
 259     case MCBinaryExpr::LAnd: Result = LHS && RHS; break;
 260     case MCBinaryExpr::LOr:  Result = LHS || RHS; break;
 261     case MCBinaryExpr::LT:   Result = LHS < RHS; break;
 262     case MCBinaryExpr::LTE:  Result = LHS <= RHS; break;
 263     case MCBinaryExpr::Mod:  Result = LHS % RHS; break;
 264     case MCBinaryExpr::Mul:  Result = LHS * RHS; break;
 265     case MCBinaryExpr::NE:   Result = LHS != RHS; break;
 266     case MCBinaryExpr::Or:   Result = LHS | RHS; break;
 267     case MCBinaryExpr::Shl:  Result = LHS << RHS; break;
 268     case MCBinaryExpr::Shr:  Result = LHS >> RHS; break;
 269     case MCBinaryExpr::Sub:  Result = LHS - RHS; break;
 270     case MCBinaryExpr::Xor:  Result = LHS ^ RHS; break;
 271     }
 272
 273     Res = MCValue::get(Result);
 274     return true;
 275   }
 276   }
 277
 278   assert(0 && "Invalid assembly expression kind!");
 279   return false;
 280 }