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