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      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 #define DEBUG_TYPE "mcexpr"
     11 #include "llvm/MC/MCExpr.h"
     12 #include "llvm/ADT/Statistic.h"
     13 #include "llvm/ADT/StringSwitch.h"
     14 #include "llvm/MC/MCAsmLayout.h"
     15 #include "llvm/MC/MCAssembler.h"
     16 #include "llvm/MC/MCContext.h"
     17 #include "llvm/MC/MCSymbol.h"
     18 #include "llvm/MC/MCValue.h"
     19 #include "llvm/Support/Debug.h"
     20 #include "llvm/Support/raw_ostream.h"
     21 using namespace llvm;
     22 
     23 namespace {
     24 namespace stats {
     25 STATISTIC(MCExprEvaluate, "Number of MCExpr evaluations");
     26 }
     27 }
     28 
     29 void MCExpr::print(raw_ostream &OS) const {
     30   switch (getKind()) {
     31   case MCExpr::Target:
     32     return cast<MCTargetExpr>(this)->PrintImpl(OS);
     33   case MCExpr::Constant:
     34     OS << cast<MCConstantExpr>(*this).getValue();
     35     return;
     36 
     37   case MCExpr::SymbolRef: {
     38     const MCSymbolRefExpr &SRE = cast<MCSymbolRefExpr>(*this);
     39     const MCSymbol &Sym = SRE.getSymbol();
     40     // Parenthesize names that start with $ so that they don't look like
     41     // absolute names.
     42     bool UseParens = Sym.getName()[0] == '$';
     43 
     44     if (SRE.getKind() == MCSymbolRefExpr::VK_PPC_DARWIN_HA16 ||
     45         SRE.getKind() == MCSymbolRefExpr::VK_PPC_DARWIN_LO16) {
     46       OS << MCSymbolRefExpr::getVariantKindName(SRE.getKind());
     47       UseParens = true;
     48     }
     49 
     50     if (UseParens)
     51       OS << '(' << Sym << ')';
     52     else
     53       OS << Sym;
     54 
     55     if (SRE.getKind() == MCSymbolRefExpr::VK_ARM_PLT ||
     56         SRE.getKind() == MCSymbolRefExpr::VK_ARM_TLSGD ||
     57         SRE.getKind() == MCSymbolRefExpr::VK_ARM_GOT ||
     58         SRE.getKind() == MCSymbolRefExpr::VK_ARM_GOTOFF ||
     59         SRE.getKind() == MCSymbolRefExpr::VK_ARM_TPOFF ||
     60         SRE.getKind() == MCSymbolRefExpr::VK_ARM_GOTTPOFF)
     61       OS << MCSymbolRefExpr::getVariantKindName(SRE.getKind());
     62     else if (SRE.getKind() != MCSymbolRefExpr::VK_None &&
     63              SRE.getKind() != MCSymbolRefExpr::VK_PPC_DARWIN_HA16 &&
     64              SRE.getKind() != MCSymbolRefExpr::VK_PPC_DARWIN_LO16)
     65       OS << '@' << MCSymbolRefExpr::getVariantKindName(SRE.getKind());
     66 
     67     return;
     68   }
     69 
     70   case MCExpr::Unary: {
     71     const MCUnaryExpr &UE = cast<MCUnaryExpr>(*this);
     72     switch (UE.getOpcode()) {
     73     default: assert(0 && "Invalid opcode!");
     74     case MCUnaryExpr::LNot:  OS << '!'; break;
     75     case MCUnaryExpr::Minus: OS << '-'; break;
     76     case MCUnaryExpr::Not:   OS << '~'; break;
     77     case MCUnaryExpr::Plus:  OS << '+'; break;
     78     }
     79     OS << *UE.getSubExpr();
     80     return;
     81   }
     82 
     83   case MCExpr::Binary: {
     84     const MCBinaryExpr &BE = cast<MCBinaryExpr>(*this);
     85 
     86     // Only print parens around the LHS if it is non-trivial.
     87     if (isa<MCConstantExpr>(BE.getLHS()) || isa<MCSymbolRefExpr>(BE.getLHS())) {
     88       OS << *BE.getLHS();
     89     } else {
     90       OS << '(' << *BE.getLHS() << ')';
     91     }
     92 
     93     switch (BE.getOpcode()) {
     94     default: assert(0 && "Invalid opcode!");
     95     case MCBinaryExpr::Add:
     96       // Print "X-42" instead of "X+-42".
     97       if (const MCConstantExpr *RHSC = dyn_cast<MCConstantExpr>(BE.getRHS())) {
     98         if (RHSC->getValue() < 0) {
     99           OS << RHSC->getValue();
    100           return;
    101         }
    102       }
    103 
    104       OS <<  '+';
    105       break;
    106     case MCBinaryExpr::And:  OS <<  '&'; break;
    107     case MCBinaryExpr::Div:  OS <<  '/'; break;
    108     case MCBinaryExpr::EQ:   OS << "=="; break;
    109     case MCBinaryExpr::GT:   OS <<  '>'; break;
    110     case MCBinaryExpr::GTE:  OS << ">="; break;
    111     case MCBinaryExpr::LAnd: OS << "&&"; break;
    112     case MCBinaryExpr::LOr:  OS << "||"; break;
    113     case MCBinaryExpr::LT:   OS <<  '<'; break;
    114     case MCBinaryExpr::LTE:  OS << "<="; break;
    115     case MCBinaryExpr::Mod:  OS <<  '%'; break;
    116     case MCBinaryExpr::Mul:  OS <<  '*'; break;
    117     case MCBinaryExpr::NE:   OS << "!="; break;
    118     case MCBinaryExpr::Or:   OS <<  '|'; break;
    119     case MCBinaryExpr::Shl:  OS << "<<"; break;
    120     case MCBinaryExpr::Shr:  OS << ">>"; break;
    121     case MCBinaryExpr::Sub:  OS <<  '-'; break;
    122     case MCBinaryExpr::Xor:  OS <<  '^'; break;
    123     }
    124 
    125     // Only print parens around the LHS if it is non-trivial.
    126     if (isa<MCConstantExpr>(BE.getRHS()) || isa<MCSymbolRefExpr>(BE.getRHS())) {
    127       OS << *BE.getRHS();
    128     } else {
    129       OS << '(' << *BE.getRHS() << ')';
    130     }
    131     return;
    132   }
    133   }
    134 
    135   assert(0 && "Invalid expression kind!");
    136 }
    137 
    138 void MCExpr::dump() const {
    139   print(dbgs());
    140   dbgs() << '\n';
    141 }
    142 
    143 /* *** */
    144 
    145 const MCBinaryExpr *MCBinaryExpr::Create(Opcode Opc, const MCExpr *LHS,
    146                                          const MCExpr *RHS, MCContext &Ctx) {
    147   return new (Ctx) MCBinaryExpr(Opc, LHS, RHS);
    148 }
    149 
    150 const MCUnaryExpr *MCUnaryExpr::Create(Opcode Opc, const MCExpr *Expr,
    151                                        MCContext &Ctx) {
    152   return new (Ctx) MCUnaryExpr(Opc, Expr);
    153 }
    154 
    155 const MCConstantExpr *MCConstantExpr::Create(int64_t Value, MCContext &Ctx) {
    156   return new (Ctx) MCConstantExpr(Value);
    157 }
    158 
    159 /* *** */
    160 
    161 const MCSymbolRefExpr *MCSymbolRefExpr::Create(const MCSymbol *Sym,
    162                                                VariantKind Kind,
    163                                                MCContext &Ctx) {
    164   return new (Ctx) MCSymbolRefExpr(Sym, Kind);
    165 }
    166 
    167 const MCSymbolRefExpr *MCSymbolRefExpr::Create(StringRef Name, VariantKind Kind,
    168                                                MCContext &Ctx) {
    169   return Create(Ctx.GetOrCreateSymbol(Name), Kind, Ctx);
    170 }
    171 
    172 StringRef MCSymbolRefExpr::getVariantKindName(VariantKind Kind) {
    173   switch (Kind) {
    174   default:
    175   case VK_Invalid: return "<<invalid>>";
    176   case VK_None: return "<<none>>";
    177 
    178   case VK_GOT: return "GOT";
    179   case VK_GOTOFF: return "GOTOFF";
    180   case VK_GOTPCREL: return "GOTPCREL";
    181   case VK_GOTTPOFF: return "GOTTPOFF";
    182   case VK_INDNTPOFF: return "INDNTPOFF";
    183   case VK_NTPOFF: return "NTPOFF";
    184   case VK_GOTNTPOFF: return "GOTNTPOFF";
    185   case VK_PLT: return "PLT";
    186   case VK_TLSGD: return "TLSGD";
    187   case VK_TLSLD: return "TLSLD";
    188   case VK_TLSLDM: return "TLSLDM";
    189   case VK_TPOFF: return "TPOFF";
    190   case VK_DTPOFF: return "DTPOFF";
    191   case VK_TLVP: return "TLVP";
    192   case VK_ARM_PLT: return "(PLT)";
    193   case VK_ARM_GOT: return "(GOT)";
    194   case VK_ARM_GOTOFF: return "(GOTOFF)";
    195   case VK_ARM_TPOFF: return "(tpoff)";
    196   case VK_ARM_GOTTPOFF: return "(gottpoff)";
    197   case VK_ARM_TLSGD: return "(tlsgd)";
    198   case VK_PPC_TOC: return "toc";
    199   case VK_PPC_DARWIN_HA16: return "ha16";
    200   case VK_PPC_DARWIN_LO16: return "lo16";
    201   case VK_PPC_GAS_HA16: return "ha";
    202   case VK_PPC_GAS_LO16: return "l";
    203   }
    204 }
    205 
    206 MCSymbolRefExpr::VariantKind
    207 MCSymbolRefExpr::getVariantKindForName(StringRef Name) {
    208   return StringSwitch<VariantKind>(Name)
    209     .Case("GOT", VK_GOT)
    210     .Case("got", VK_GOT)
    211     .Case("GOTOFF", VK_GOTOFF)
    212     .Case("gotoff", VK_GOTOFF)
    213     .Case("GOTPCREL", VK_GOTPCREL)
    214     .Case("gotpcrel", VK_GOTPCREL)
    215     .Case("GOTTPOFF", VK_GOTTPOFF)
    216     .Case("gottpoff", VK_GOTTPOFF)
    217     .Case("INDNTPOFF", VK_INDNTPOFF)
    218     .Case("indntpoff", VK_INDNTPOFF)
    219     .Case("NTPOFF", VK_NTPOFF)
    220     .Case("ntpoff", VK_NTPOFF)
    221     .Case("GOTNTPOFF", VK_GOTNTPOFF)
    222     .Case("gotntpoff", VK_GOTNTPOFF)
    223     .Case("PLT", VK_PLT)
    224     .Case("plt", VK_PLT)
    225     .Case("TLSGD", VK_TLSGD)
    226     .Case("tlsgd", VK_TLSGD)
    227     .Case("TLSLD", VK_TLSLD)
    228     .Case("tlsld", VK_TLSLD)
    229     .Case("TLSLDM", VK_TLSLDM)
    230     .Case("tlsldm", VK_TLSLDM)
    231     .Case("TPOFF", VK_TPOFF)
    232     .Case("tpoff", VK_TPOFF)
    233     .Case("DTPOFF", VK_DTPOFF)
    234     .Case("dtpoff", VK_DTPOFF)
    235     .Case("TLVP", VK_TLVP)
    236     .Case("tlvp", VK_TLVP)
    237     .Default(VK_Invalid);
    238 }
    239 
    240 /* *** */
    241 
    242 void MCTargetExpr::Anchor() {}
    243 
    244 /* *** */
    245 
    246 bool MCExpr::EvaluateAsAbsolute(int64_t &Res) const {
    247   return EvaluateAsAbsolute(Res, 0, 0, 0);
    248 }
    249 
    250 bool MCExpr::EvaluateAsAbsolute(int64_t &Res,
    251                                 const MCAsmLayout &Layout) const {
    252   return EvaluateAsAbsolute(Res, &Layout.getAssembler(), &Layout, 0);
    253 }
    254 
    255 bool MCExpr::EvaluateAsAbsolute(int64_t &Res,
    256                                 const MCAsmLayout &Layout,
    257                                 const SectionAddrMap &Addrs) const {
    258   return EvaluateAsAbsolute(Res, &Layout.getAssembler(), &Layout, &Addrs);
    259 }
    260 
    261 bool MCExpr::EvaluateAsAbsolute(int64_t &Res, const MCAssembler &Asm) const {
    262   return EvaluateAsAbsolute(Res, &Asm, 0, 0);
    263 }
    264 
    265 bool MCExpr::EvaluateAsAbsolute(int64_t &Res, const MCAssembler *Asm,
    266                                 const MCAsmLayout *Layout,
    267                                 const SectionAddrMap *Addrs) const {
    268   MCValue Value;
    269 
    270   // Fast path constants.
    271   if (const MCConstantExpr *CE = dyn_cast<MCConstantExpr>(this)) {
    272     Res = CE->getValue();
    273     return true;
    274   }
    275 
    276   // FIXME: The use if InSet = Addrs is a hack. Setting InSet causes us
    277   // absolutize differences across sections and that is what the MachO writer
    278   // uses Addrs for.
    279   bool IsRelocatable =
    280     EvaluateAsRelocatableImpl(Value, Asm, Layout, Addrs, /*InSet*/ Addrs);
    281 
    282   // Record the current value.
    283   Res = Value.getConstant();
    284 
    285   return IsRelocatable && Value.isAbsolute();
    286 }
    287 
    288 /// \brief Helper method for \see EvaluateSymbolAdd().
    289 static void AttemptToFoldSymbolOffsetDifference(const MCAssembler *Asm,
    290                                                 const MCAsmLayout *Layout,
    291                                                 const SectionAddrMap *Addrs,
    292                                                 bool InSet,
    293                                                 const MCSymbolRefExpr *&A,
    294                                                 const MCSymbolRefExpr *&B,
    295                                                 int64_t &Addend) {
    296   if (!A || !B)
    297     return;
    298 
    299   const MCSymbol &SA = A->getSymbol();
    300   const MCSymbol &SB = B->getSymbol();
    301 
    302   if (SA.isUndefined() || SB.isUndefined())
    303     return;
    304 
    305   if (!Asm->getWriter().IsSymbolRefDifferenceFullyResolved(*Asm, A, B, InSet))
    306     return;
    307 
    308   MCSymbolData &AD = Asm->getSymbolData(SA);
    309   MCSymbolData &BD = Asm->getSymbolData(SB);
    310 
    311   if (AD.getFragment() == BD.getFragment()) {
    312     Addend += (AD.getOffset() - BD.getOffset());
    313 
    314     // Pointers to Thumb symbols need to have their low-bit set to allow
    315     // for interworking.
    316     if (Asm->isThumbFunc(&SA))
    317       Addend |= 1;
    318 
    319     // Clear the symbol expr pointers to indicate we have folded these
    320     // operands.
    321     A = B = 0;
    322     return;
    323   }
    324 
    325   if (!Layout)
    326     return;
    327 
    328   const MCSectionData &SecA = *AD.getFragment()->getParent();
    329   const MCSectionData &SecB = *BD.getFragment()->getParent();
    330 
    331   if ((&SecA != &SecB) && !Addrs)
    332     return;
    333 
    334   // Eagerly evaluate.
    335   Addend += (Layout->getSymbolOffset(&Asm->getSymbolData(A->getSymbol())) -
    336              Layout->getSymbolOffset(&Asm->getSymbolData(B->getSymbol())));
    337   if (Addrs && (&SecA != &SecB))
    338     Addend += (Addrs->lookup(&SecA) - Addrs->lookup(&SecB));
    339 
    340   // Clear the symbol expr pointers to indicate we have folded these
    341   // operands.
    342   A = B = 0;
    343 }
    344 
    345 /// \brief Evaluate the result of an add between (conceptually) two MCValues.
    346 ///
    347 /// This routine conceptually attempts to construct an MCValue:
    348 ///   Result = (Result_A - Result_B + Result_Cst)
    349 /// from two MCValue's LHS and RHS where
    350 ///   Result = LHS + RHS
    351 /// and
    352 ///   Result = (LHS_A - LHS_B + LHS_Cst) + (RHS_A - RHS_B + RHS_Cst).
    353 ///
    354 /// This routine attempts to aggresively fold the operands such that the result
    355 /// is representable in an MCValue, but may not always succeed.
    356 ///
    357 /// \returns True on success, false if the result is not representable in an
    358 /// MCValue.
    359 
    360 /// NOTE: It is really important to have both the Asm and Layout arguments.
    361 /// They might look redundant, but this function can be used before layout
    362 /// is done (see the object streamer for example) and having the Asm argument
    363 /// lets us avoid relaxations early.
    364 static bool EvaluateSymbolicAdd(const MCAssembler *Asm,
    365                                 const MCAsmLayout *Layout,
    366                                 const SectionAddrMap *Addrs,
    367                                 bool InSet,
    368                                 const MCValue &LHS,const MCSymbolRefExpr *RHS_A,
    369                                 const MCSymbolRefExpr *RHS_B, int64_t RHS_Cst,
    370                                 MCValue &Res) {
    371   // FIXME: This routine (and other evaluation parts) are *incredibly* sloppy
    372   // about dealing with modifiers. This will ultimately bite us, one day.
    373   const MCSymbolRefExpr *LHS_A = LHS.getSymA();
    374   const MCSymbolRefExpr *LHS_B = LHS.getSymB();
    375   int64_t LHS_Cst = LHS.getConstant();
    376 
    377   // Fold the result constant immediately.
    378   int64_t Result_Cst = LHS_Cst + RHS_Cst;
    379 
    380   assert((!Layout || Asm) &&
    381          "Must have an assembler object if layout is given!");
    382 
    383   // If we have a layout, we can fold resolved differences.
    384   if (Asm) {
    385     // First, fold out any differences which are fully resolved. By
    386     // reassociating terms in
    387     //   Result = (LHS_A - LHS_B + LHS_Cst) + (RHS_A - RHS_B + RHS_Cst).
    388     // we have the four possible differences:
    389     //   (LHS_A - LHS_B),
    390     //   (LHS_A - RHS_B),
    391     //   (RHS_A - LHS_B),
    392     //   (RHS_A - RHS_B).
    393     // Since we are attempting to be as aggressive as possible about folding, we
    394     // attempt to evaluate each possible alternative.
    395     AttemptToFoldSymbolOffsetDifference(Asm, Layout, Addrs, InSet, LHS_A, LHS_B,
    396                                         Result_Cst);
    397     AttemptToFoldSymbolOffsetDifference(Asm, Layout, Addrs, InSet, LHS_A, RHS_B,
    398                                         Result_Cst);
    399     AttemptToFoldSymbolOffsetDifference(Asm, Layout, Addrs, InSet, RHS_A, LHS_B,
    400                                         Result_Cst);
    401     AttemptToFoldSymbolOffsetDifference(Asm, Layout, Addrs, InSet, RHS_A, RHS_B,
    402                                         Result_Cst);
    403   }
    404 
    405   // We can't represent the addition or subtraction of two symbols.
    406   if ((LHS_A && RHS_A) || (LHS_B && RHS_B))
    407     return false;
    408 
    409   // At this point, we have at most one additive symbol and one subtractive
    410   // symbol -- find them.
    411   const MCSymbolRefExpr *A = LHS_A ? LHS_A : RHS_A;
    412   const MCSymbolRefExpr *B = LHS_B ? LHS_B : RHS_B;
    413 
    414   // If we have a negated symbol, then we must have also have a non-negated
    415   // symbol in order to encode the expression.
    416   if (B && !A)
    417     return false;
    418 
    419   Res = MCValue::get(A, B, Result_Cst);
    420   return true;
    421 }
    422 
    423 bool MCExpr::EvaluateAsRelocatable(MCValue &Res,
    424                                    const MCAsmLayout &Layout) const {
    425   return EvaluateAsRelocatableImpl(Res, &Layout.getAssembler(), &Layout,
    426                                    0, false);
    427 }
    428 
    429 bool MCExpr::EvaluateAsRelocatableImpl(MCValue &Res,
    430                                        const MCAssembler *Asm,
    431                                        const MCAsmLayout *Layout,
    432                                        const SectionAddrMap *Addrs,
    433                                        bool InSet) const {
    434   ++stats::MCExprEvaluate;
    435 
    436   switch (getKind()) {
    437   case Target:
    438     return cast<MCTargetExpr>(this)->EvaluateAsRelocatableImpl(Res, Layout);
    439 
    440   case Constant:
    441     Res = MCValue::get(cast<MCConstantExpr>(this)->getValue());
    442     return true;
    443 
    444   case SymbolRef: {
    445     const MCSymbolRefExpr *SRE = cast<MCSymbolRefExpr>(this);
    446     const MCSymbol &Sym = SRE->getSymbol();
    447 
    448     // Evaluate recursively if this is a variable.
    449     if (Sym.isVariable() && SRE->getKind() == MCSymbolRefExpr::VK_None) {
    450       bool Ret = Sym.getVariableValue()->EvaluateAsRelocatableImpl(Res, Asm,
    451                                                                    Layout,
    452                                                                    Addrs,
    453                                                                    true);
    454       // If we failed to simplify this to a constant, let the target
    455       // handle it.
    456       if (Ret && !Res.getSymA() && !Res.getSymB())
    457         return true;
    458     }
    459 
    460     Res = MCValue::get(SRE, 0, 0);
    461     return true;
    462   }
    463 
    464   case Unary: {
    465     const MCUnaryExpr *AUE = cast<MCUnaryExpr>(this);
    466     MCValue Value;
    467 
    468     if (!AUE->getSubExpr()->EvaluateAsRelocatableImpl(Value, Asm, Layout,
    469                                                       Addrs, InSet))
    470       return false;
    471 
    472     switch (AUE->getOpcode()) {
    473     case MCUnaryExpr::LNot:
    474       if (!Value.isAbsolute())
    475         return false;
    476       Res = MCValue::get(!Value.getConstant());
    477       break;
    478     case MCUnaryExpr::Minus:
    479       /// -(a - b + const) ==> (b - a - const)
    480       if (Value.getSymA() && !Value.getSymB())
    481         return false;
    482       Res = MCValue::get(Value.getSymB(), Value.getSymA(),
    483                          -Value.getConstant());
    484       break;
    485     case MCUnaryExpr::Not:
    486       if (!Value.isAbsolute())
    487         return false;
    488       Res = MCValue::get(~Value.getConstant());
    489       break;
    490     case MCUnaryExpr::Plus:
    491       Res = Value;
    492       break;
    493     }
    494 
    495     return true;
    496   }
    497 
    498   case Binary: {
    499     const MCBinaryExpr *ABE = cast<MCBinaryExpr>(this);
    500     MCValue LHSValue, RHSValue;
    501 
    502     if (!ABE->getLHS()->EvaluateAsRelocatableImpl(LHSValue, Asm, Layout,
    503                                                   Addrs, InSet) ||
    504         !ABE->getRHS()->EvaluateAsRelocatableImpl(RHSValue, Asm, Layout,
    505                                                   Addrs, InSet))
    506       return false;
    507 
    508     // We only support a few operations on non-constant expressions, handle
    509     // those first.
    510     if (!LHSValue.isAbsolute() || !RHSValue.isAbsolute()) {
    511       switch (ABE->getOpcode()) {
    512       default:
    513         return false;
    514       case MCBinaryExpr::Sub:
    515         // Negate RHS and add.
    516         return EvaluateSymbolicAdd(Asm, Layout, Addrs, InSet, LHSValue,
    517                                    RHSValue.getSymB(), RHSValue.getSymA(),
    518                                    -RHSValue.getConstant(),
    519                                    Res);
    520 
    521       case MCBinaryExpr::Add:
    522         return EvaluateSymbolicAdd(Asm, Layout, Addrs, InSet, LHSValue,
    523                                    RHSValue.getSymA(), RHSValue.getSymB(),
    524                                    RHSValue.getConstant(),
    525                                    Res);
    526       }
    527     }
    528 
    529     // FIXME: We need target hooks for the evaluation. It may be limited in
    530     // width, and gas defines the result of comparisons and right shifts
    531     // differently from Apple as.
    532     int64_t LHS = LHSValue.getConstant(), RHS = RHSValue.getConstant();
    533     int64_t Result = 0;
    534     switch (ABE->getOpcode()) {
    535     case MCBinaryExpr::Add:  Result = LHS + RHS; break;
    536     case MCBinaryExpr::And:  Result = LHS & RHS; break;
    537     case MCBinaryExpr::Div:  Result = LHS / RHS; break;
    538     case MCBinaryExpr::EQ:   Result = LHS == RHS; break;
    539     case MCBinaryExpr::GT:   Result = LHS > RHS; break;
    540     case MCBinaryExpr::GTE:  Result = LHS >= RHS; break;
    541     case MCBinaryExpr::LAnd: Result = LHS && RHS; break;
    542     case MCBinaryExpr::LOr:  Result = LHS || RHS; break;
    543     case MCBinaryExpr::LT:   Result = LHS < RHS; break;
    544     case MCBinaryExpr::LTE:  Result = LHS <= RHS; break;
    545     case MCBinaryExpr::Mod:  Result = LHS % RHS; break;
    546     case MCBinaryExpr::Mul:  Result = LHS * RHS; break;
    547     case MCBinaryExpr::NE:   Result = LHS != RHS; break;
    548     case MCBinaryExpr::Or:   Result = LHS | RHS; break;
    549     case MCBinaryExpr::Shl:  Result = LHS << RHS; break;
    550     case MCBinaryExpr::Shr:  Result = LHS >> RHS; break;
    551     case MCBinaryExpr::Sub:  Result = LHS - RHS; break;
    552     case MCBinaryExpr::Xor:  Result = LHS ^ RHS; break;
    553     }
    554 
    555     Res = MCValue::get(Result);
    556     return true;
    557   }
    558   }
    559 
    560   assert(0 && "Invalid assembly expression kind!");
    561   return false;
    562 }
    563 
    564 const MCSection *MCExpr::FindAssociatedSection() const {
    565   switch (getKind()) {
    566   case Target:
    567     // We never look through target specific expressions.
    568     return cast<MCTargetExpr>(this)->FindAssociatedSection();
    569 
    570   case Constant:
    571     return MCSymbol::AbsolutePseudoSection;
    572 
    573   case SymbolRef: {
    574     const MCSymbolRefExpr *SRE = cast<MCSymbolRefExpr>(this);
    575     const MCSymbol &Sym = SRE->getSymbol();
    576 
    577     if (Sym.isDefined())
    578       return &Sym.getSection();
    579 
    580     return 0;
    581   }
    582 
    583   case Unary:
    584     return cast<MCUnaryExpr>(this)->getSubExpr()->FindAssociatedSection();
    585 
    586   case Binary: {
    587     const MCBinaryExpr *BE = cast<MCBinaryExpr>(this);
    588     const MCSection *LHS_S = BE->getLHS()->FindAssociatedSection();
    589     const MCSection *RHS_S = BE->getRHS()->FindAssociatedSection();
    590 
    591     // If either section is absolute, return the other.
    592     if (LHS_S == MCSymbol::AbsolutePseudoSection)
    593       return RHS_S;
    594     if (RHS_S == MCSymbol::AbsolutePseudoSection)
    595       return LHS_S;
    596 
    597     // Otherwise, return the first non-null section.
    598     return LHS_S ? LHS_S : RHS_S;
    599   }
    600   }
    601 
    602   assert(0 && "Invalid assembly expression kind!");
    603   return 0;
    604 }
    605