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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/MCObjectWriter.h"
     18 #include "llvm/MC/MCSymbol.h"
     19 #include "llvm/MC/MCValue.h"
     20 #include "llvm/Support/Debug.h"
     21 #include "llvm/Support/ErrorHandling.h"
     22 #include "llvm/Support/raw_ostream.h"
     23 using namespace llvm;
     24 
     25 namespace {
     26 namespace stats {
     27 STATISTIC(MCExprEvaluate, "Number of MCExpr evaluations");
     28 }
     29 }
     30 
     31 void MCExpr::print(raw_ostream &OS) const {
     32   switch (getKind()) {
     33   case MCExpr::Target:
     34     return cast<MCTargetExpr>(this)->PrintImpl(OS);
     35   case MCExpr::Constant:
     36     OS << cast<MCConstantExpr>(*this).getValue();
     37     return;
     38 
     39   case MCExpr::SymbolRef: {
     40     const MCSymbolRefExpr &SRE = cast<MCSymbolRefExpr>(*this);
     41     const MCSymbol &Sym = SRE.getSymbol();
     42     // Parenthesize names that start with $ so that they don't look like
     43     // absolute names.
     44     bool UseParens = Sym.getName()[0] == '$';
     45 
     46     if (SRE.getKind() == MCSymbolRefExpr::VK_PPC_DARWIN_HA16 ||
     47         SRE.getKind() == MCSymbolRefExpr::VK_PPC_DARWIN_LO16) {
     48       OS << MCSymbolRefExpr::getVariantKindName(SRE.getKind());
     49       UseParens = true;
     50     }
     51 
     52     if (UseParens)
     53       OS << '(' << Sym << ')';
     54     else
     55       OS << Sym;
     56 
     57     if (SRE.getKind() == MCSymbolRefExpr::VK_ARM_PLT ||
     58         SRE.getKind() == MCSymbolRefExpr::VK_ARM_TLSGD ||
     59         SRE.getKind() == MCSymbolRefExpr::VK_ARM_GOT ||
     60         SRE.getKind() == MCSymbolRefExpr::VK_ARM_GOTOFF ||
     61         SRE.getKind() == MCSymbolRefExpr::VK_ARM_TPOFF ||
     62         SRE.getKind() == MCSymbolRefExpr::VK_ARM_GOTTPOFF ||
     63         SRE.getKind() == MCSymbolRefExpr::VK_ARM_TARGET1)
     64       OS << MCSymbolRefExpr::getVariantKindName(SRE.getKind());
     65     else if (SRE.getKind() != MCSymbolRefExpr::VK_None &&
     66              SRE.getKind() != MCSymbolRefExpr::VK_PPC_DARWIN_HA16 &&
     67              SRE.getKind() != MCSymbolRefExpr::VK_PPC_DARWIN_LO16)
     68       OS << '@' << MCSymbolRefExpr::getVariantKindName(SRE.getKind());
     69 
     70     return;
     71   }
     72 
     73   case MCExpr::Unary: {
     74     const MCUnaryExpr &UE = cast<MCUnaryExpr>(*this);
     75     switch (UE.getOpcode()) {
     76     case MCUnaryExpr::LNot:  OS << '!'; break;
     77     case MCUnaryExpr::Minus: OS << '-'; break;
     78     case MCUnaryExpr::Not:   OS << '~'; break;
     79     case MCUnaryExpr::Plus:  OS << '+'; break;
     80     }
     81     OS << *UE.getSubExpr();
     82     return;
     83   }
     84 
     85   case MCExpr::Binary: {
     86     const MCBinaryExpr &BE = cast<MCBinaryExpr>(*this);
     87 
     88     // Only print parens around the LHS if it is non-trivial.
     89     if (isa<MCConstantExpr>(BE.getLHS()) || isa<MCSymbolRefExpr>(BE.getLHS())) {
     90       OS << *BE.getLHS();
     91     } else {
     92       OS << '(' << *BE.getLHS() << ')';
     93     }
     94 
     95     switch (BE.getOpcode()) {
     96     case MCBinaryExpr::Add:
     97       // Print "X-42" instead of "X+-42".
     98       if (const MCConstantExpr *RHSC = dyn_cast<MCConstantExpr>(BE.getRHS())) {
     99         if (RHSC->getValue() < 0) {
    100           OS << RHSC->getValue();
    101           return;
    102         }
    103       }
    104 
    105       OS <<  '+';
    106       break;
    107     case MCBinaryExpr::And:  OS <<  '&'; break;
    108     case MCBinaryExpr::Div:  OS <<  '/'; break;
    109     case MCBinaryExpr::EQ:   OS << "=="; break;
    110     case MCBinaryExpr::GT:   OS <<  '>'; break;
    111     case MCBinaryExpr::GTE:  OS << ">="; break;
    112     case MCBinaryExpr::LAnd: OS << "&&"; break;
    113     case MCBinaryExpr::LOr:  OS << "||"; break;
    114     case MCBinaryExpr::LT:   OS <<  '<'; break;
    115     case MCBinaryExpr::LTE:  OS << "<="; break;
    116     case MCBinaryExpr::Mod:  OS <<  '%'; break;
    117     case MCBinaryExpr::Mul:  OS <<  '*'; break;
    118     case MCBinaryExpr::NE:   OS << "!="; break;
    119     case MCBinaryExpr::Or:   OS <<  '|'; break;
    120     case MCBinaryExpr::Shl:  OS << "<<"; break;
    121     case MCBinaryExpr::Shr:  OS << ">>"; break;
    122     case MCBinaryExpr::Sub:  OS <<  '-'; break;
    123     case MCBinaryExpr::Xor:  OS <<  '^'; break;
    124     }
    125 
    126     // Only print parens around the LHS if it is non-trivial.
    127     if (isa<MCConstantExpr>(BE.getRHS()) || isa<MCSymbolRefExpr>(BE.getRHS())) {
    128       OS << *BE.getRHS();
    129     } else {
    130       OS << '(' << *BE.getRHS() << ')';
    131     }
    132     return;
    133   }
    134   }
    135 
    136   llvm_unreachable("Invalid expression kind!");
    137 }
    138 
    139 #ifndef NDEBUG
    140 void MCExpr::dump() const {
    141   print(dbgs());
    142   dbgs() << '\n';
    143 }
    144 #endif
    145 
    146 /* *** */
    147 
    148 const MCBinaryExpr *MCBinaryExpr::Create(Opcode Opc, const MCExpr *LHS,
    149                                          const MCExpr *RHS, MCContext &Ctx) {
    150   return new (Ctx) MCBinaryExpr(Opc, LHS, RHS);
    151 }
    152 
    153 const MCUnaryExpr *MCUnaryExpr::Create(Opcode Opc, const MCExpr *Expr,
    154                                        MCContext &Ctx) {
    155   return new (Ctx) MCUnaryExpr(Opc, Expr);
    156 }
    157 
    158 const MCConstantExpr *MCConstantExpr::Create(int64_t Value, MCContext &Ctx) {
    159   return new (Ctx) MCConstantExpr(Value);
    160 }
    161 
    162 /* *** */
    163 
    164 const MCSymbolRefExpr *MCSymbolRefExpr::Create(const MCSymbol *Sym,
    165                                                VariantKind Kind,
    166                                                MCContext &Ctx) {
    167   return new (Ctx) MCSymbolRefExpr(Sym, Kind);
    168 }
    169 
    170 const MCSymbolRefExpr *MCSymbolRefExpr::Create(StringRef Name, VariantKind Kind,
    171                                                MCContext &Ctx) {
    172   return Create(Ctx.GetOrCreateSymbol(Name), Kind, Ctx);
    173 }
    174 
    175 StringRef MCSymbolRefExpr::getVariantKindName(VariantKind Kind) {
    176   switch (Kind) {
    177   case VK_Invalid: return "<<invalid>>";
    178   case VK_None: return "<<none>>";
    179 
    180   case VK_GOT: return "GOT";
    181   case VK_GOTOFF: return "GOTOFF";
    182   case VK_GOTPCREL: return "GOTPCREL";
    183   case VK_GOTTPOFF: return "GOTTPOFF";
    184   case VK_INDNTPOFF: return "INDNTPOFF";
    185   case VK_NTPOFF: return "NTPOFF";
    186   case VK_GOTNTPOFF: return "GOTNTPOFF";
    187   case VK_PLT: return "PLT";
    188   case VK_TLSGD: return "TLSGD";
    189   case VK_TLSLD: return "TLSLD";
    190   case VK_TLSLDM: return "TLSLDM";
    191   case VK_TPOFF: return "TPOFF";
    192   case VK_DTPOFF: return "DTPOFF";
    193   case VK_TLVP: return "TLVP";
    194   case VK_SECREL: return "SECREL";
    195   case VK_ARM_PLT: return "(PLT)";
    196   case VK_ARM_GOT: return "(GOT)";
    197   case VK_ARM_GOTOFF: return "(GOTOFF)";
    198   case VK_ARM_TPOFF: return "(tpoff)";
    199   case VK_ARM_GOTTPOFF: return "(gottpoff)";
    200   case VK_ARM_TLSGD: return "(tlsgd)";
    201   case VK_ARM_TARGET1: return "(target1)";
    202   case VK_PPC_TOC: return "tocbase";
    203   case VK_PPC_TOC_ENTRY: return "toc";
    204   case VK_PPC_DARWIN_HA16: return "ha16";
    205   case VK_PPC_DARWIN_LO16: return "lo16";
    206   case VK_PPC_GAS_HA16: return "ha";
    207   case VK_PPC_GAS_LO16: return "l";
    208   case VK_PPC_TPREL16_HA: return "tprel@ha";
    209   case VK_PPC_TPREL16_LO: return "tprel@l";
    210   case VK_Mips_GPREL: return "GPREL";
    211   case VK_Mips_GOT_CALL: return "GOT_CALL";
    212   case VK_Mips_GOT16: return "GOT16";
    213   case VK_Mips_GOT: return "GOT";
    214   case VK_Mips_ABS_HI: return "ABS_HI";
    215   case VK_Mips_ABS_LO: return "ABS_LO";
    216   case VK_Mips_TLSGD: return "TLSGD";
    217   case VK_Mips_TLSLDM: return "TLSLDM";
    218   case VK_Mips_DTPREL_HI: return "DTPREL_HI";
    219   case VK_Mips_DTPREL_LO: return "DTPREL_LO";
    220   case VK_Mips_GOTTPREL: return "GOTTPREL";
    221   case VK_Mips_TPREL_HI: return "TPREL_HI";
    222   case VK_Mips_TPREL_LO: return "TPREL_LO";
    223   case VK_Mips_GPOFF_HI: return "GPOFF_HI";
    224   case VK_Mips_GPOFF_LO: return "GPOFF_LO";
    225   case VK_Mips_GOT_DISP: return "GOT_DISP";
    226   case VK_Mips_GOT_PAGE: return "GOT_PAGE";
    227   case VK_Mips_GOT_OFST: return "GOT_OFST";
    228   case VK_Mips_HIGHER:   return "HIGHER";
    229   case VK_Mips_HIGHEST:  return "HIGHEST";
    230   }
    231   llvm_unreachable("Invalid variant kind");
    232 }
    233 
    234 MCSymbolRefExpr::VariantKind
    235 MCSymbolRefExpr::getVariantKindForName(StringRef Name) {
    236   return StringSwitch<VariantKind>(Name)
    237     .Case("GOT", VK_GOT)
    238     .Case("got", VK_GOT)
    239     .Case("GOTOFF", VK_GOTOFF)
    240     .Case("gotoff", VK_GOTOFF)
    241     .Case("GOTPCREL", VK_GOTPCREL)
    242     .Case("gotpcrel", VK_GOTPCREL)
    243     .Case("GOTTPOFF", VK_GOTTPOFF)
    244     .Case("gottpoff", VK_GOTTPOFF)
    245     .Case("INDNTPOFF", VK_INDNTPOFF)
    246     .Case("indntpoff", VK_INDNTPOFF)
    247     .Case("NTPOFF", VK_NTPOFF)
    248     .Case("ntpoff", VK_NTPOFF)
    249     .Case("GOTNTPOFF", VK_GOTNTPOFF)
    250     .Case("gotntpoff", VK_GOTNTPOFF)
    251     .Case("PLT", VK_PLT)
    252     .Case("plt", VK_PLT)
    253     .Case("TLSGD", VK_TLSGD)
    254     .Case("tlsgd", VK_TLSGD)
    255     .Case("TLSLD", VK_TLSLD)
    256     .Case("tlsld", VK_TLSLD)
    257     .Case("TLSLDM", VK_TLSLDM)
    258     .Case("tlsldm", VK_TLSLDM)
    259     .Case("TPOFF", VK_TPOFF)
    260     .Case("tpoff", VK_TPOFF)
    261     .Case("DTPOFF", VK_DTPOFF)
    262     .Case("dtpoff", VK_DTPOFF)
    263     .Case("TLVP", VK_TLVP)
    264     .Case("tlvp", VK_TLVP)
    265     .Default(VK_Invalid);
    266 }
    267 
    268 /* *** */
    269 
    270 void MCTargetExpr::Anchor() {}
    271 
    272 /* *** */
    273 
    274 bool MCExpr::EvaluateAsAbsolute(int64_t &Res) const {
    275   return EvaluateAsAbsolute(Res, 0, 0, 0);
    276 }
    277 
    278 bool MCExpr::EvaluateAsAbsolute(int64_t &Res,
    279                                 const MCAsmLayout &Layout) const {
    280   return EvaluateAsAbsolute(Res, &Layout.getAssembler(), &Layout, 0);
    281 }
    282 
    283 bool MCExpr::EvaluateAsAbsolute(int64_t &Res,
    284                                 const MCAsmLayout &Layout,
    285                                 const SectionAddrMap &Addrs) const {
    286   return EvaluateAsAbsolute(Res, &Layout.getAssembler(), &Layout, &Addrs);
    287 }
    288 
    289 bool MCExpr::EvaluateAsAbsolute(int64_t &Res, const MCAssembler &Asm) const {
    290   return EvaluateAsAbsolute(Res, &Asm, 0, 0);
    291 }
    292 
    293 bool MCExpr::EvaluateAsAbsolute(int64_t &Res, const MCAssembler *Asm,
    294                                 const MCAsmLayout *Layout,
    295                                 const SectionAddrMap *Addrs) const {
    296   MCValue Value;
    297 
    298   // Fast path constants.
    299   if (const MCConstantExpr *CE = dyn_cast<MCConstantExpr>(this)) {
    300     Res = CE->getValue();
    301     return true;
    302   }
    303 
    304   // FIXME: The use if InSet = Addrs is a hack. Setting InSet causes us
    305   // absolutize differences across sections and that is what the MachO writer
    306   // uses Addrs for.
    307   bool IsRelocatable =
    308     EvaluateAsRelocatableImpl(Value, Asm, Layout, Addrs, /*InSet*/ Addrs);
    309 
    310   // Record the current value.
    311   Res = Value.getConstant();
    312 
    313   return IsRelocatable && Value.isAbsolute();
    314 }
    315 
    316 /// \brief Helper method for \see EvaluateSymbolAdd().
    317 static void AttemptToFoldSymbolOffsetDifference(const MCAssembler *Asm,
    318                                                 const MCAsmLayout *Layout,
    319                                                 const SectionAddrMap *Addrs,
    320                                                 bool InSet,
    321                                                 const MCSymbolRefExpr *&A,
    322                                                 const MCSymbolRefExpr *&B,
    323                                                 int64_t &Addend) {
    324   if (!A || !B)
    325     return;
    326 
    327   const MCSymbol &SA = A->getSymbol();
    328   const MCSymbol &SB = B->getSymbol();
    329 
    330   if (SA.isUndefined() || SB.isUndefined())
    331     return;
    332 
    333   if (!Asm->getWriter().IsSymbolRefDifferenceFullyResolved(*Asm, A, B, InSet))
    334     return;
    335 
    336   MCSymbolData &AD = Asm->getSymbolData(SA);
    337   MCSymbolData &BD = Asm->getSymbolData(SB);
    338 
    339   if (AD.getFragment() == BD.getFragment()) {
    340     Addend += (AD.getOffset() - BD.getOffset());
    341 
    342     // Pointers to Thumb symbols need to have their low-bit set to allow
    343     // for interworking.
    344     if (Asm->isThumbFunc(&SA))
    345       Addend |= 1;
    346 
    347     // Clear the symbol expr pointers to indicate we have folded these
    348     // operands.
    349     A = B = 0;
    350     return;
    351   }
    352 
    353   if (!Layout)
    354     return;
    355 
    356   const MCSectionData &SecA = *AD.getFragment()->getParent();
    357   const MCSectionData &SecB = *BD.getFragment()->getParent();
    358 
    359   if ((&SecA != &SecB) && !Addrs)
    360     return;
    361 
    362   // Eagerly evaluate.
    363   Addend += (Layout->getSymbolOffset(&Asm->getSymbolData(A->getSymbol())) -
    364              Layout->getSymbolOffset(&Asm->getSymbolData(B->getSymbol())));
    365   if (Addrs && (&SecA != &SecB))
    366     Addend += (Addrs->lookup(&SecA) - Addrs->lookup(&SecB));
    367 
    368   // Pointers to Thumb symbols need to have their low-bit set to allow
    369   // for interworking.
    370   if (Asm->isThumbFunc(&SA))
    371     Addend |= 1;
    372 
    373   // Clear the symbol expr pointers to indicate we have folded these
    374   // operands.
    375   A = B = 0;
    376 }
    377 
    378 /// \brief Evaluate the result of an add between (conceptually) two MCValues.
    379 ///
    380 /// This routine conceptually attempts to construct an MCValue:
    381 ///   Result = (Result_A - Result_B + Result_Cst)
    382 /// from two MCValue's LHS and RHS where
    383 ///   Result = LHS + RHS
    384 /// and
    385 ///   Result = (LHS_A - LHS_B + LHS_Cst) + (RHS_A - RHS_B + RHS_Cst).
    386 ///
    387 /// This routine attempts to aggresively fold the operands such that the result
    388 /// is representable in an MCValue, but may not always succeed.
    389 ///
    390 /// \returns True on success, false if the result is not representable in an
    391 /// MCValue.
    392 
    393 /// NOTE: It is really important to have both the Asm and Layout arguments.
    394 /// They might look redundant, but this function can be used before layout
    395 /// is done (see the object streamer for example) and having the Asm argument
    396 /// lets us avoid relaxations early.
    397 static bool EvaluateSymbolicAdd(const MCAssembler *Asm,
    398                                 const MCAsmLayout *Layout,
    399                                 const SectionAddrMap *Addrs,
    400                                 bool InSet,
    401                                 const MCValue &LHS,const MCSymbolRefExpr *RHS_A,
    402                                 const MCSymbolRefExpr *RHS_B, int64_t RHS_Cst,
    403                                 MCValue &Res) {
    404   // FIXME: This routine (and other evaluation parts) are *incredibly* sloppy
    405   // about dealing with modifiers. This will ultimately bite us, one day.
    406   const MCSymbolRefExpr *LHS_A = LHS.getSymA();
    407   const MCSymbolRefExpr *LHS_B = LHS.getSymB();
    408   int64_t LHS_Cst = LHS.getConstant();
    409 
    410   // Fold the result constant immediately.
    411   int64_t Result_Cst = LHS_Cst + RHS_Cst;
    412 
    413   assert((!Layout || Asm) &&
    414          "Must have an assembler object if layout is given!");
    415 
    416   // If we have a layout, we can fold resolved differences.
    417   if (Asm) {
    418     // First, fold out any differences which are fully resolved. By
    419     // reassociating terms in
    420     //   Result = (LHS_A - LHS_B + LHS_Cst) + (RHS_A - RHS_B + RHS_Cst).
    421     // we have the four possible differences:
    422     //   (LHS_A - LHS_B),
    423     //   (LHS_A - RHS_B),
    424     //   (RHS_A - LHS_B),
    425     //   (RHS_A - RHS_B).
    426     // Since we are attempting to be as aggressive as possible about folding, we
    427     // attempt to evaluate each possible alternative.
    428     AttemptToFoldSymbolOffsetDifference(Asm, Layout, Addrs, InSet, LHS_A, LHS_B,
    429                                         Result_Cst);
    430     AttemptToFoldSymbolOffsetDifference(Asm, Layout, Addrs, InSet, LHS_A, RHS_B,
    431                                         Result_Cst);
    432     AttemptToFoldSymbolOffsetDifference(Asm, Layout, Addrs, InSet, RHS_A, LHS_B,
    433                                         Result_Cst);
    434     AttemptToFoldSymbolOffsetDifference(Asm, Layout, Addrs, InSet, RHS_A, RHS_B,
    435                                         Result_Cst);
    436   }
    437 
    438   // We can't represent the addition or subtraction of two symbols.
    439   if ((LHS_A && RHS_A) || (LHS_B && RHS_B))
    440     return false;
    441 
    442   // At this point, we have at most one additive symbol and one subtractive
    443   // symbol -- find them.
    444   const MCSymbolRefExpr *A = LHS_A ? LHS_A : RHS_A;
    445   const MCSymbolRefExpr *B = LHS_B ? LHS_B : RHS_B;
    446 
    447   // If we have a negated symbol, then we must have also have a non-negated
    448   // symbol in order to encode the expression.
    449   if (B && !A)
    450     return false;
    451 
    452   Res = MCValue::get(A, B, Result_Cst);
    453   return true;
    454 }
    455 
    456 bool MCExpr::EvaluateAsRelocatable(MCValue &Res,
    457                                    const MCAsmLayout &Layout) const {
    458   return EvaluateAsRelocatableImpl(Res, &Layout.getAssembler(), &Layout,
    459                                    0, false);
    460 }
    461 
    462 bool MCExpr::EvaluateAsRelocatableImpl(MCValue &Res,
    463                                        const MCAssembler *Asm,
    464                                        const MCAsmLayout *Layout,
    465                                        const SectionAddrMap *Addrs,
    466                                        bool InSet) const {
    467   ++stats::MCExprEvaluate;
    468 
    469   switch (getKind()) {
    470   case Target:
    471     return cast<MCTargetExpr>(this)->EvaluateAsRelocatableImpl(Res, Layout);
    472 
    473   case Constant:
    474     Res = MCValue::get(cast<MCConstantExpr>(this)->getValue());
    475     return true;
    476 
    477   case SymbolRef: {
    478     const MCSymbolRefExpr *SRE = cast<MCSymbolRefExpr>(this);
    479     const MCSymbol &Sym = SRE->getSymbol();
    480 
    481     // Evaluate recursively if this is a variable.
    482     if (Sym.isVariable() && SRE->getKind() == MCSymbolRefExpr::VK_None) {
    483       bool Ret = Sym.getVariableValue()->EvaluateAsRelocatableImpl(Res, Asm,
    484                                                                    Layout,
    485                                                                    Addrs,
    486                                                                    true);
    487       // If we failed to simplify this to a constant, let the target
    488       // handle it.
    489       if (Ret && !Res.getSymA() && !Res.getSymB())
    490         return true;
    491     }
    492 
    493     Res = MCValue::get(SRE, 0, 0);
    494     return true;
    495   }
    496 
    497   case Unary: {
    498     const MCUnaryExpr *AUE = cast<MCUnaryExpr>(this);
    499     MCValue Value;
    500 
    501     if (!AUE->getSubExpr()->EvaluateAsRelocatableImpl(Value, Asm, Layout,
    502                                                       Addrs, InSet))
    503       return false;
    504 
    505     switch (AUE->getOpcode()) {
    506     case MCUnaryExpr::LNot:
    507       if (!Value.isAbsolute())
    508         return false;
    509       Res = MCValue::get(!Value.getConstant());
    510       break;
    511     case MCUnaryExpr::Minus:
    512       /// -(a - b + const) ==> (b - a - const)
    513       if (Value.getSymA() && !Value.getSymB())
    514         return false;
    515       Res = MCValue::get(Value.getSymB(), Value.getSymA(),
    516                          -Value.getConstant());
    517       break;
    518     case MCUnaryExpr::Not:
    519       if (!Value.isAbsolute())
    520         return false;
    521       Res = MCValue::get(~Value.getConstant());
    522       break;
    523     case MCUnaryExpr::Plus:
    524       Res = Value;
    525       break;
    526     }
    527 
    528     return true;
    529   }
    530 
    531   case Binary: {
    532     const MCBinaryExpr *ABE = cast<MCBinaryExpr>(this);
    533     MCValue LHSValue, RHSValue;
    534 
    535     if (!ABE->getLHS()->EvaluateAsRelocatableImpl(LHSValue, Asm, Layout,
    536                                                   Addrs, InSet) ||
    537         !ABE->getRHS()->EvaluateAsRelocatableImpl(RHSValue, Asm, Layout,
    538                                                   Addrs, InSet))
    539       return false;
    540 
    541     // We only support a few operations on non-constant expressions, handle
    542     // those first.
    543     if (!LHSValue.isAbsolute() || !RHSValue.isAbsolute()) {
    544       switch (ABE->getOpcode()) {
    545       default:
    546         return false;
    547       case MCBinaryExpr::Sub:
    548         // Negate RHS and add.
    549         return EvaluateSymbolicAdd(Asm, Layout, Addrs, InSet, LHSValue,
    550                                    RHSValue.getSymB(), RHSValue.getSymA(),
    551                                    -RHSValue.getConstant(),
    552                                    Res);
    553 
    554       case MCBinaryExpr::Add:
    555         return EvaluateSymbolicAdd(Asm, Layout, Addrs, InSet, LHSValue,
    556                                    RHSValue.getSymA(), RHSValue.getSymB(),
    557                                    RHSValue.getConstant(),
    558                                    Res);
    559       }
    560     }
    561 
    562     // FIXME: We need target hooks for the evaluation. It may be limited in
    563     // width, and gas defines the result of comparisons and right shifts
    564     // differently from Apple as.
    565     int64_t LHS = LHSValue.getConstant(), RHS = RHSValue.getConstant();
    566     int64_t Result = 0;
    567     switch (ABE->getOpcode()) {
    568     case MCBinaryExpr::Add:  Result = LHS + RHS; break;
    569     case MCBinaryExpr::And:  Result = LHS & RHS; break;
    570     case MCBinaryExpr::Div:  Result = LHS / RHS; break;
    571     case MCBinaryExpr::EQ:   Result = LHS == RHS; break;
    572     case MCBinaryExpr::GT:   Result = LHS > RHS; break;
    573     case MCBinaryExpr::GTE:  Result = LHS >= RHS; break;
    574     case MCBinaryExpr::LAnd: Result = LHS && RHS; break;
    575     case MCBinaryExpr::LOr:  Result = LHS || RHS; break;
    576     case MCBinaryExpr::LT:   Result = LHS < RHS; break;
    577     case MCBinaryExpr::LTE:  Result = LHS <= RHS; break;
    578     case MCBinaryExpr::Mod:  Result = LHS % RHS; break;
    579     case MCBinaryExpr::Mul:  Result = LHS * RHS; break;
    580     case MCBinaryExpr::NE:   Result = LHS != RHS; break;
    581     case MCBinaryExpr::Or:   Result = LHS | RHS; break;
    582     case MCBinaryExpr::Shl:  Result = LHS << RHS; break;
    583     case MCBinaryExpr::Shr:  Result = LHS >> RHS; break;
    584     case MCBinaryExpr::Sub:  Result = LHS - RHS; break;
    585     case MCBinaryExpr::Xor:  Result = LHS ^ RHS; break;
    586     }
    587 
    588     Res = MCValue::get(Result);
    589     return true;
    590   }
    591   }
    592 
    593   llvm_unreachable("Invalid assembly expression kind!");
    594 }
    595 
    596 const MCSection *MCExpr::FindAssociatedSection() const {
    597   switch (getKind()) {
    598   case Target:
    599     // We never look through target specific expressions.
    600     return cast<MCTargetExpr>(this)->FindAssociatedSection();
    601 
    602   case Constant:
    603     return MCSymbol::AbsolutePseudoSection;
    604 
    605   case SymbolRef: {
    606     const MCSymbolRefExpr *SRE = cast<MCSymbolRefExpr>(this);
    607     const MCSymbol &Sym = SRE->getSymbol();
    608 
    609     if (Sym.isDefined())
    610       return &Sym.getSection();
    611 
    612     return 0;
    613   }
    614 
    615   case Unary:
    616     return cast<MCUnaryExpr>(this)->getSubExpr()->FindAssociatedSection();
    617 
    618   case Binary: {
    619     const MCBinaryExpr *BE = cast<MCBinaryExpr>(this);
    620     const MCSection *LHS_S = BE->getLHS()->FindAssociatedSection();
    621     const MCSection *RHS_S = BE->getRHS()->FindAssociatedSection();
    622 
    623     // If either section is absolute, return the other.
    624     if (LHS_S == MCSymbol::AbsolutePseudoSection)
    625       return RHS_S;
    626     if (RHS_S == MCSymbol::AbsolutePseudoSection)
    627       return LHS_S;
    628 
    629     // Otherwise, return the first non-null section.
    630     return LHS_S ? LHS_S : RHS_S;
    631   }
    632   }
    633 
    634   llvm_unreachable("Invalid assembly expression kind!");
    635 }
    636