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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 #include "llvm/MC/MCExpr.h"
     11 #include "llvm/ADT/Statistic.h"
     12 #include "llvm/ADT/StringSwitch.h"
     13 #include "llvm/MC/MCAsmInfo.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 #define DEBUG_TYPE "mcexpr"
     26 
     27 namespace {
     28 namespace stats {
     29 STATISTIC(MCExprEvaluate, "Number of MCExpr evaluations");
     30 }
     31 }
     32 
     33 void MCExpr::print(raw_ostream &OS, const MCAsmInfo *MAI) const {
     34   switch (getKind()) {
     35   case MCExpr::Target:
     36     return cast<MCTargetExpr>(this)->printImpl(OS, MAI);
     37   case MCExpr::Constant:
     38     OS << cast<MCConstantExpr>(*this).getValue();
     39     return;
     40 
     41   case MCExpr::SymbolRef: {
     42     const MCSymbolRefExpr &SRE = cast<MCSymbolRefExpr>(*this);
     43     const MCSymbol &Sym = SRE.getSymbol();
     44     // Parenthesize names that start with $ so that they don't look like
     45     // absolute names.
     46     bool UseParens = Sym.getName().size() && Sym.getName()[0] == '$';
     47     if (UseParens) {
     48       OS << '(';
     49       Sym.print(OS, MAI);
     50       OS << ')';
     51     } else
     52       Sym.print(OS, MAI);
     53 
     54     if (SRE.getKind() != MCSymbolRefExpr::VK_None)
     55       SRE.printVariantKind(OS);
     56 
     57     return;
     58   }
     59 
     60   case MCExpr::Unary: {
     61     const MCUnaryExpr &UE = cast<MCUnaryExpr>(*this);
     62     switch (UE.getOpcode()) {
     63     case MCUnaryExpr::LNot:  OS << '!'; break;
     64     case MCUnaryExpr::Minus: OS << '-'; break;
     65     case MCUnaryExpr::Not:   OS << '~'; break;
     66     case MCUnaryExpr::Plus:  OS << '+'; break;
     67     }
     68     UE.getSubExpr()->print(OS, MAI);
     69     return;
     70   }
     71 
     72   case MCExpr::Binary: {
     73     const MCBinaryExpr &BE = cast<MCBinaryExpr>(*this);
     74 
     75     // Only print parens around the LHS if it is non-trivial.
     76     if (isa<MCConstantExpr>(BE.getLHS()) || isa<MCSymbolRefExpr>(BE.getLHS())) {
     77       BE.getLHS()->print(OS, MAI);
     78     } else {
     79       OS << '(';
     80       BE.getLHS()->print(OS, MAI);
     81       OS << ')';
     82     }
     83 
     84     switch (BE.getOpcode()) {
     85     case MCBinaryExpr::Add:
     86       // Print "X-42" instead of "X+-42".
     87       if (const MCConstantExpr *RHSC = dyn_cast<MCConstantExpr>(BE.getRHS())) {
     88         if (RHSC->getValue() < 0) {
     89           OS << RHSC->getValue();
     90           return;
     91         }
     92       }
     93 
     94       OS <<  '+';
     95       break;
     96     case MCBinaryExpr::AShr: OS << ">>"; break;
     97     case MCBinaryExpr::And:  OS <<  '&'; break;
     98     case MCBinaryExpr::Div:  OS <<  '/'; break;
     99     case MCBinaryExpr::EQ:   OS << "=="; break;
    100     case MCBinaryExpr::GT:   OS <<  '>'; break;
    101     case MCBinaryExpr::GTE:  OS << ">="; break;
    102     case MCBinaryExpr::LAnd: OS << "&&"; break;
    103     case MCBinaryExpr::LOr:  OS << "||"; break;
    104     case MCBinaryExpr::LShr: OS << ">>"; break;
    105     case MCBinaryExpr::LT:   OS <<  '<'; break;
    106     case MCBinaryExpr::LTE:  OS << "<="; break;
    107     case MCBinaryExpr::Mod:  OS <<  '%'; break;
    108     case MCBinaryExpr::Mul:  OS <<  '*'; break;
    109     case MCBinaryExpr::NE:   OS << "!="; break;
    110     case MCBinaryExpr::Or:   OS <<  '|'; break;
    111     case MCBinaryExpr::Shl:  OS << "<<"; break;
    112     case MCBinaryExpr::Sub:  OS <<  '-'; break;
    113     case MCBinaryExpr::Xor:  OS <<  '^'; break;
    114     }
    115 
    116     // Only print parens around the LHS if it is non-trivial.
    117     if (isa<MCConstantExpr>(BE.getRHS()) || isa<MCSymbolRefExpr>(BE.getRHS())) {
    118       BE.getRHS()->print(OS, MAI);
    119     } else {
    120       OS << '(';
    121       BE.getRHS()->print(OS, MAI);
    122       OS << ')';
    123     }
    124     return;
    125   }
    126   }
    127 
    128   llvm_unreachable("Invalid expression kind!");
    129 }
    130 
    131 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
    132 void MCExpr::dump() const {
    133   dbgs() << *this;
    134   dbgs() << '\n';
    135 }
    136 #endif
    137 
    138 /* *** */
    139 
    140 const MCBinaryExpr *MCBinaryExpr::create(Opcode Opc, const MCExpr *LHS,
    141                                          const MCExpr *RHS, MCContext &Ctx) {
    142   return new (Ctx) MCBinaryExpr(Opc, LHS, RHS);
    143 }
    144 
    145 const MCUnaryExpr *MCUnaryExpr::create(Opcode Opc, const MCExpr *Expr,
    146                                        MCContext &Ctx) {
    147   return new (Ctx) MCUnaryExpr(Opc, Expr);
    148 }
    149 
    150 const MCConstantExpr *MCConstantExpr::create(int64_t Value, MCContext &Ctx) {
    151   return new (Ctx) MCConstantExpr(Value);
    152 }
    153 
    154 /* *** */
    155 
    156 MCSymbolRefExpr::MCSymbolRefExpr(const MCSymbol *Symbol, VariantKind Kind,
    157                                  const MCAsmInfo *MAI)
    158     : MCExpr(MCExpr::SymbolRef), Kind(Kind),
    159       UseParensForSymbolVariant(MAI->useParensForSymbolVariant()),
    160       HasSubsectionsViaSymbols(MAI->hasSubsectionsViaSymbols()),
    161       Symbol(Symbol) {
    162   assert(Symbol);
    163 }
    164 
    165 const MCSymbolRefExpr *MCSymbolRefExpr::create(const MCSymbol *Sym,
    166                                                VariantKind Kind,
    167                                                MCContext &Ctx) {
    168   return new (Ctx) MCSymbolRefExpr(Sym, Kind, Ctx.getAsmInfo());
    169 }
    170 
    171 const MCSymbolRefExpr *MCSymbolRefExpr::create(StringRef Name, VariantKind Kind,
    172                                                MCContext &Ctx) {
    173   return create(Ctx.getOrCreateSymbol(Name), Kind, Ctx);
    174 }
    175 
    176 StringRef MCSymbolRefExpr::getVariantKindName(VariantKind Kind) {
    177   switch (Kind) {
    178   case VK_Invalid: return "<<invalid>>";
    179   case VK_None: return "<<none>>";
    180 
    181   case VK_GOT: return "GOT";
    182   case VK_GOTOFF: return "GOTOFF";
    183   case VK_GOTPCREL: return "GOTPCREL";
    184   case VK_GOTTPOFF: return "GOTTPOFF";
    185   case VK_INDNTPOFF: return "INDNTPOFF";
    186   case VK_NTPOFF: return "NTPOFF";
    187   case VK_GOTNTPOFF: return "GOTNTPOFF";
    188   case VK_PLT: return "PLT";
    189   case VK_TLSGD: return "TLSGD";
    190   case VK_TLSLD: return "TLSLD";
    191   case VK_TLSLDM: return "TLSLDM";
    192   case VK_TPOFF: return "TPOFF";
    193   case VK_DTPOFF: return "DTPOFF";
    194   case VK_TLVP: return "TLVP";
    195   case VK_TLVPPAGE: return "TLVPPAGE";
    196   case VK_TLVPPAGEOFF: return "TLVPPAGEOFF";
    197   case VK_PAGE: return "PAGE";
    198   case VK_PAGEOFF: return "PAGEOFF";
    199   case VK_GOTPAGE: return "GOTPAGE";
    200   case VK_GOTPAGEOFF: return "GOTPAGEOFF";
    201   case VK_SECREL: return "SECREL32";
    202   case VK_SIZE: return "SIZE";
    203   case VK_WEAKREF: return "WEAKREF";
    204   case VK_ARM_NONE: return "none";
    205   case VK_ARM_GOT_PREL: return "GOT_PREL";
    206   case VK_ARM_TARGET1: return "target1";
    207   case VK_ARM_TARGET2: return "target2";
    208   case VK_ARM_PREL31: return "prel31";
    209   case VK_ARM_SBREL: return "sbrel";
    210   case VK_ARM_TLSLDO: return "tlsldo";
    211   case VK_ARM_TLSCALL: return "tlscall";
    212   case VK_ARM_TLSDESC: return "tlsdesc";
    213   case VK_ARM_TLSDESCSEQ: return "tlsdescseq";
    214   case VK_PPC_LO: return "l";
    215   case VK_PPC_HI: return "h";
    216   case VK_PPC_HA: return "ha";
    217   case VK_PPC_HIGHER: return "higher";
    218   case VK_PPC_HIGHERA: return "highera";
    219   case VK_PPC_HIGHEST: return "highest";
    220   case VK_PPC_HIGHESTA: return "highesta";
    221   case VK_PPC_GOT_LO: return "got@l";
    222   case VK_PPC_GOT_HI: return "got@h";
    223   case VK_PPC_GOT_HA: return "got@ha";
    224   case VK_PPC_TOCBASE: return "tocbase";
    225   case VK_PPC_TOC: return "toc";
    226   case VK_PPC_TOC_LO: return "toc@l";
    227   case VK_PPC_TOC_HI: return "toc@h";
    228   case VK_PPC_TOC_HA: return "toc@ha";
    229   case VK_PPC_DTPMOD: return "dtpmod";
    230   case VK_PPC_TPREL: return "tprel";
    231   case VK_PPC_TPREL_LO: return "tprel@l";
    232   case VK_PPC_TPREL_HI: return "tprel@h";
    233   case VK_PPC_TPREL_HA: return "tprel@ha";
    234   case VK_PPC_TPREL_HIGHER: return "tprel@higher";
    235   case VK_PPC_TPREL_HIGHERA: return "tprel@highera";
    236   case VK_PPC_TPREL_HIGHEST: return "tprel@highest";
    237   case VK_PPC_TPREL_HIGHESTA: return "tprel@highesta";
    238   case VK_PPC_DTPREL: return "dtprel";
    239   case VK_PPC_DTPREL_LO: return "dtprel@l";
    240   case VK_PPC_DTPREL_HI: return "dtprel@h";
    241   case VK_PPC_DTPREL_HA: return "dtprel@ha";
    242   case VK_PPC_DTPREL_HIGHER: return "dtprel@higher";
    243   case VK_PPC_DTPREL_HIGHERA: return "dtprel@highera";
    244   case VK_PPC_DTPREL_HIGHEST: return "dtprel@highest";
    245   case VK_PPC_DTPREL_HIGHESTA: return "dtprel@highesta";
    246   case VK_PPC_GOT_TPREL: return "got@tprel";
    247   case VK_PPC_GOT_TPREL_LO: return "got@tprel@l";
    248   case VK_PPC_GOT_TPREL_HI: return "got@tprel@h";
    249   case VK_PPC_GOT_TPREL_HA: return "got@tprel@ha";
    250   case VK_PPC_GOT_DTPREL: return "got@dtprel";
    251   case VK_PPC_GOT_DTPREL_LO: return "got@dtprel@l";
    252   case VK_PPC_GOT_DTPREL_HI: return "got@dtprel@h";
    253   case VK_PPC_GOT_DTPREL_HA: return "got@dtprel@ha";
    254   case VK_PPC_TLS: return "tls";
    255   case VK_PPC_GOT_TLSGD: return "got@tlsgd";
    256   case VK_PPC_GOT_TLSGD_LO: return "got@tlsgd@l";
    257   case VK_PPC_GOT_TLSGD_HI: return "got@tlsgd@h";
    258   case VK_PPC_GOT_TLSGD_HA: return "got@tlsgd@ha";
    259   case VK_PPC_TLSGD: return "tlsgd";
    260   case VK_PPC_GOT_TLSLD: return "got@tlsld";
    261   case VK_PPC_GOT_TLSLD_LO: return "got@tlsld@l";
    262   case VK_PPC_GOT_TLSLD_HI: return "got@tlsld@h";
    263   case VK_PPC_GOT_TLSLD_HA: return "got@tlsld@ha";
    264   case VK_PPC_TLSLD: return "tlsld";
    265   case VK_PPC_LOCAL: return "local";
    266   case VK_Mips_GPREL: return "GPREL";
    267   case VK_Mips_GOT_CALL: return "GOT_CALL";
    268   case VK_Mips_GOT16: return "GOT16";
    269   case VK_Mips_GOT: return "GOT";
    270   case VK_Mips_ABS_HI: return "ABS_HI";
    271   case VK_Mips_ABS_LO: return "ABS_LO";
    272   case VK_Mips_TLSGD: return "TLSGD";
    273   case VK_Mips_TLSLDM: return "TLSLDM";
    274   case VK_Mips_DTPREL_HI: return "DTPREL_HI";
    275   case VK_Mips_DTPREL_LO: return "DTPREL_LO";
    276   case VK_Mips_GOTTPREL: return "GOTTPREL";
    277   case VK_Mips_TPREL_HI: return "TPREL_HI";
    278   case VK_Mips_TPREL_LO: return "TPREL_LO";
    279   case VK_Mips_GPOFF_HI: return "GPOFF_HI";
    280   case VK_Mips_GPOFF_LO: return "GPOFF_LO";
    281   case VK_Mips_GOT_DISP: return "GOT_DISP";
    282   case VK_Mips_GOT_PAGE: return "GOT_PAGE";
    283   case VK_Mips_GOT_OFST: return "GOT_OFST";
    284   case VK_Mips_HIGHER:   return "HIGHER";
    285   case VK_Mips_HIGHEST:  return "HIGHEST";
    286   case VK_Mips_GOT_HI16: return "GOT_HI16";
    287   case VK_Mips_GOT_LO16: return "GOT_LO16";
    288   case VK_Mips_CALL_HI16: return "CALL_HI16";
    289   case VK_Mips_CALL_LO16: return "CALL_LO16";
    290   case VK_Mips_PCREL_HI16: return "PCREL_HI16";
    291   case VK_Mips_PCREL_LO16: return "PCREL_LO16";
    292   case VK_COFF_IMGREL32: return "IMGREL";
    293   case VK_Hexagon_PCREL: return "PCREL";
    294   case VK_Hexagon_LO16: return "LO16";
    295   case VK_Hexagon_HI16: return "HI16";
    296   case VK_Hexagon_GPREL: return "GPREL";
    297   case VK_Hexagon_GD_GOT: return "GDGOT";
    298   case VK_Hexagon_LD_GOT: return "LDGOT";
    299   case VK_Hexagon_GD_PLT: return "GDPLT";
    300   case VK_Hexagon_LD_PLT: return "LDPLT";
    301   case VK_Hexagon_IE: return "IE";
    302   case VK_Hexagon_IE_GOT: return "IEGOT";
    303   case VK_TPREL: return "tprel";
    304   case VK_DTPREL: return "dtprel";
    305   }
    306   llvm_unreachable("Invalid variant kind");
    307 }
    308 
    309 MCSymbolRefExpr::VariantKind
    310 MCSymbolRefExpr::getVariantKindForName(StringRef Name) {
    311   return StringSwitch<VariantKind>(Name.lower())
    312     .Case("got", VK_GOT)
    313     .Case("gotoff", VK_GOTOFF)
    314     .Case("gotpcrel", VK_GOTPCREL)
    315     .Case("gottpoff", VK_GOTTPOFF)
    316     .Case("indntpoff", VK_INDNTPOFF)
    317     .Case("ntpoff", VK_NTPOFF)
    318     .Case("gotntpoff", VK_GOTNTPOFF)
    319     .Case("plt", VK_PLT)
    320     .Case("tlsgd", VK_TLSGD)
    321     .Case("tlsld", VK_TLSLD)
    322     .Case("tlsldm", VK_TLSLDM)
    323     .Case("tpoff", VK_TPOFF)
    324     .Case("dtpoff", VK_DTPOFF)
    325     .Case("tlvp", VK_TLVP)
    326     .Case("tlvppage", VK_TLVPPAGE)
    327     .Case("tlvppageoff", VK_TLVPPAGEOFF)
    328     .Case("page", VK_PAGE)
    329     .Case("pageoff", VK_PAGEOFF)
    330     .Case("gotpage", VK_GOTPAGE)
    331     .Case("gotpageoff", VK_GOTPAGEOFF)
    332     .Case("imgrel", VK_COFF_IMGREL32)
    333     .Case("secrel32", VK_SECREL)
    334     .Case("size", VK_SIZE)
    335     .Case("l", VK_PPC_LO)
    336     .Case("h", VK_PPC_HI)
    337     .Case("ha", VK_PPC_HA)
    338     .Case("higher", VK_PPC_HIGHER)
    339     .Case("highera", VK_PPC_HIGHERA)
    340     .Case("highest", VK_PPC_HIGHEST)
    341     .Case("highesta", VK_PPC_HIGHESTA)
    342     .Case("got@l", VK_PPC_GOT_LO)
    343     .Case("got@h", VK_PPC_GOT_HI)
    344     .Case("got@ha", VK_PPC_GOT_HA)
    345     .Case("local", VK_PPC_LOCAL)
    346     .Case("tocbase", VK_PPC_TOCBASE)
    347     .Case("toc", VK_PPC_TOC)
    348     .Case("toc@l", VK_PPC_TOC_LO)
    349     .Case("toc@h", VK_PPC_TOC_HI)
    350     .Case("toc@ha", VK_PPC_TOC_HA)
    351     .Case("tls", VK_PPC_TLS)
    352     .Case("dtpmod", VK_PPC_DTPMOD)
    353     .Case("tprel", VK_PPC_TPREL)
    354     .Case("tprel@l", VK_PPC_TPREL_LO)
    355     .Case("tprel@h", VK_PPC_TPREL_HI)
    356     .Case("tprel@ha", VK_PPC_TPREL_HA)
    357     .Case("tprel@higher", VK_PPC_TPREL_HIGHER)
    358     .Case("tprel@highera", VK_PPC_TPREL_HIGHERA)
    359     .Case("tprel@highest", VK_PPC_TPREL_HIGHEST)
    360     .Case("tprel@highesta", VK_PPC_TPREL_HIGHESTA)
    361     .Case("dtprel", VK_PPC_DTPREL)
    362     .Case("dtprel@l", VK_PPC_DTPREL_LO)
    363     .Case("dtprel@h", VK_PPC_DTPREL_HI)
    364     .Case("dtprel@ha", VK_PPC_DTPREL_HA)
    365     .Case("dtprel@higher", VK_PPC_DTPREL_HIGHER)
    366     .Case("dtprel@highera", VK_PPC_DTPREL_HIGHERA)
    367     .Case("dtprel@highest", VK_PPC_DTPREL_HIGHEST)
    368     .Case("dtprel@highesta", VK_PPC_DTPREL_HIGHESTA)
    369     .Case("got@tprel", VK_PPC_GOT_TPREL)
    370     .Case("got@tprel@l", VK_PPC_GOT_TPREL_LO)
    371     .Case("got@tprel@h", VK_PPC_GOT_TPREL_HI)
    372     .Case("got@tprel@ha", VK_PPC_GOT_TPREL_HA)
    373     .Case("got@dtprel", VK_PPC_GOT_DTPREL)
    374     .Case("got@dtprel@l", VK_PPC_GOT_DTPREL_LO)
    375     .Case("got@dtprel@h", VK_PPC_GOT_DTPREL_HI)
    376     .Case("got@dtprel@ha", VK_PPC_GOT_DTPREL_HA)
    377     .Case("got@tlsgd", VK_PPC_GOT_TLSGD)
    378     .Case("got@tlsgd@l", VK_PPC_GOT_TLSGD_LO)
    379     .Case("got@tlsgd@h", VK_PPC_GOT_TLSGD_HI)
    380     .Case("got@tlsgd@ha", VK_PPC_GOT_TLSGD_HA)
    381     .Case("got@tlsld", VK_PPC_GOT_TLSLD)
    382     .Case("got@tlsld@l", VK_PPC_GOT_TLSLD_LO)
    383     .Case("got@tlsld@h", VK_PPC_GOT_TLSLD_HI)
    384     .Case("got@tlsld@ha", VK_PPC_GOT_TLSLD_HA)
    385     .Case("gdgot", VK_Hexagon_GD_GOT)
    386     .Case("gdplt", VK_Hexagon_GD_PLT)
    387     .Case("iegot", VK_Hexagon_IE_GOT)
    388     .Case("ie", VK_Hexagon_IE)
    389     .Case("ldgot", VK_Hexagon_LD_GOT)
    390     .Case("ldplt", VK_Hexagon_LD_PLT)
    391     .Case("pcrel", VK_Hexagon_PCREL)
    392     .Case("none", VK_ARM_NONE)
    393     .Case("got_prel", VK_ARM_GOT_PREL)
    394     .Case("target1", VK_ARM_TARGET1)
    395     .Case("target2", VK_ARM_TARGET2)
    396     .Case("prel31", VK_ARM_PREL31)
    397     .Case("sbrel", VK_ARM_SBREL)
    398     .Case("tlsldo", VK_ARM_TLSLDO)
    399     .Case("tlscall", VK_ARM_TLSCALL)
    400     .Case("tlsdesc", VK_ARM_TLSDESC)
    401     .Default(VK_Invalid);
    402 }
    403 
    404 void MCSymbolRefExpr::printVariantKind(raw_ostream &OS) const {
    405   if (UseParensForSymbolVariant)
    406     OS << '(' << MCSymbolRefExpr::getVariantKindName(getKind()) << ')';
    407   else
    408     OS << '@' << MCSymbolRefExpr::getVariantKindName(getKind());
    409 }
    410 
    411 /* *** */
    412 
    413 void MCTargetExpr::anchor() {}
    414 
    415 /* *** */
    416 
    417 bool MCExpr::evaluateAsAbsolute(int64_t &Res) const {
    418   return evaluateAsAbsolute(Res, nullptr, nullptr, nullptr);
    419 }
    420 
    421 bool MCExpr::evaluateAsAbsolute(int64_t &Res,
    422                                 const MCAsmLayout &Layout) const {
    423   return evaluateAsAbsolute(Res, &Layout.getAssembler(), &Layout, nullptr);
    424 }
    425 
    426 bool MCExpr::evaluateAsAbsolute(int64_t &Res,
    427                                 const MCAsmLayout &Layout,
    428                                 const SectionAddrMap &Addrs) const {
    429   return evaluateAsAbsolute(Res, &Layout.getAssembler(), &Layout, &Addrs);
    430 }
    431 
    432 bool MCExpr::evaluateAsAbsolute(int64_t &Res, const MCAssembler &Asm) const {
    433   return evaluateAsAbsolute(Res, &Asm, nullptr, nullptr);
    434 }
    435 
    436 bool MCExpr::evaluateKnownAbsolute(int64_t &Res,
    437                                    const MCAsmLayout &Layout) const {
    438   return evaluateAsAbsolute(Res, &Layout.getAssembler(), &Layout, nullptr,
    439                             true);
    440 }
    441 
    442 bool MCExpr::evaluateAsAbsolute(int64_t &Res, const MCAssembler *Asm,
    443                                 const MCAsmLayout *Layout,
    444                                 const SectionAddrMap *Addrs) const {
    445   // FIXME: The use if InSet = Addrs is a hack. Setting InSet causes us
    446   // absolutize differences across sections and that is what the MachO writer
    447   // uses Addrs for.
    448   return evaluateAsAbsolute(Res, Asm, Layout, Addrs, Addrs);
    449 }
    450 
    451 bool MCExpr::evaluateAsAbsolute(int64_t &Res, const MCAssembler *Asm,
    452                                 const MCAsmLayout *Layout,
    453                                 const SectionAddrMap *Addrs, bool InSet) const {
    454   MCValue Value;
    455 
    456   // Fast path constants.
    457   if (const MCConstantExpr *CE = dyn_cast<MCConstantExpr>(this)) {
    458     Res = CE->getValue();
    459     return true;
    460   }
    461 
    462   bool IsRelocatable =
    463       evaluateAsRelocatableImpl(Value, Asm, Layout, nullptr, Addrs, InSet);
    464 
    465   // Record the current value.
    466   Res = Value.getConstant();
    467 
    468   return IsRelocatable && Value.isAbsolute();
    469 }
    470 
    471 /// \brief Helper method for \see EvaluateSymbolAdd().
    472 static void AttemptToFoldSymbolOffsetDifference(
    473     const MCAssembler *Asm, const MCAsmLayout *Layout,
    474     const SectionAddrMap *Addrs, bool InSet, const MCSymbolRefExpr *&A,
    475     const MCSymbolRefExpr *&B, int64_t &Addend) {
    476   if (!A || !B)
    477     return;
    478 
    479   const MCSymbol &SA = A->getSymbol();
    480   const MCSymbol &SB = B->getSymbol();
    481 
    482   if (SA.isUndefined() || SB.isUndefined())
    483     return;
    484 
    485   if (!Asm->getWriter().isSymbolRefDifferenceFullyResolved(*Asm, A, B, InSet))
    486     return;
    487 
    488   if (SA.getFragment() == SB.getFragment() && !SA.isVariable() &&
    489       !SB.isVariable()) {
    490     Addend += (SA.getOffset() - SB.getOffset());
    491 
    492     // Pointers to Thumb symbols need to have their low-bit set to allow
    493     // for interworking.
    494     if (Asm->isThumbFunc(&SA))
    495       Addend |= 1;
    496 
    497     // Clear the symbol expr pointers to indicate we have folded these
    498     // operands.
    499     A = B = nullptr;
    500     return;
    501   }
    502 
    503   if (!Layout)
    504     return;
    505 
    506   const MCSection &SecA = *SA.getFragment()->getParent();
    507   const MCSection &SecB = *SB.getFragment()->getParent();
    508 
    509   if ((&SecA != &SecB) && !Addrs)
    510     return;
    511 
    512   // Eagerly evaluate.
    513   Addend += Layout->getSymbolOffset(A->getSymbol()) -
    514             Layout->getSymbolOffset(B->getSymbol());
    515   if (Addrs && (&SecA != &SecB))
    516     Addend += (Addrs->lookup(&SecA) - Addrs->lookup(&SecB));
    517 
    518   // Pointers to Thumb symbols need to have their low-bit set to allow
    519   // for interworking.
    520   if (Asm->isThumbFunc(&SA))
    521     Addend |= 1;
    522 
    523   // Clear the symbol expr pointers to indicate we have folded these
    524   // operands.
    525   A = B = nullptr;
    526 }
    527 
    528 /// \brief Evaluate the result of an add between (conceptually) two MCValues.
    529 ///
    530 /// This routine conceptually attempts to construct an MCValue:
    531 ///   Result = (Result_A - Result_B + Result_Cst)
    532 /// from two MCValue's LHS and RHS where
    533 ///   Result = LHS + RHS
    534 /// and
    535 ///   Result = (LHS_A - LHS_B + LHS_Cst) + (RHS_A - RHS_B + RHS_Cst).
    536 ///
    537 /// This routine attempts to aggresively fold the operands such that the result
    538 /// is representable in an MCValue, but may not always succeed.
    539 ///
    540 /// \returns True on success, false if the result is not representable in an
    541 /// MCValue.
    542 
    543 /// NOTE: It is really important to have both the Asm and Layout arguments.
    544 /// They might look redundant, but this function can be used before layout
    545 /// is done (see the object streamer for example) and having the Asm argument
    546 /// lets us avoid relaxations early.
    547 static bool
    548 EvaluateSymbolicAdd(const MCAssembler *Asm, const MCAsmLayout *Layout,
    549                     const SectionAddrMap *Addrs, bool InSet, const MCValue &LHS,
    550                     const MCSymbolRefExpr *RHS_A, const MCSymbolRefExpr *RHS_B,
    551                     int64_t RHS_Cst, MCValue &Res) {
    552   // FIXME: This routine (and other evaluation parts) are *incredibly* sloppy
    553   // about dealing with modifiers. This will ultimately bite us, one day.
    554   const MCSymbolRefExpr *LHS_A = LHS.getSymA();
    555   const MCSymbolRefExpr *LHS_B = LHS.getSymB();
    556   int64_t LHS_Cst = LHS.getConstant();
    557 
    558   // Fold the result constant immediately.
    559   int64_t Result_Cst = LHS_Cst + RHS_Cst;
    560 
    561   assert((!Layout || Asm) &&
    562          "Must have an assembler object if layout is given!");
    563 
    564   // If we have a layout, we can fold resolved differences.
    565   if (Asm) {
    566     // First, fold out any differences which are fully resolved. By
    567     // reassociating terms in
    568     //   Result = (LHS_A - LHS_B + LHS_Cst) + (RHS_A - RHS_B + RHS_Cst).
    569     // we have the four possible differences:
    570     //   (LHS_A - LHS_B),
    571     //   (LHS_A - RHS_B),
    572     //   (RHS_A - LHS_B),
    573     //   (RHS_A - RHS_B).
    574     // Since we are attempting to be as aggressive as possible about folding, we
    575     // attempt to evaluate each possible alternative.
    576     AttemptToFoldSymbolOffsetDifference(Asm, Layout, Addrs, InSet, LHS_A, LHS_B,
    577                                         Result_Cst);
    578     AttemptToFoldSymbolOffsetDifference(Asm, Layout, Addrs, InSet, LHS_A, RHS_B,
    579                                         Result_Cst);
    580     AttemptToFoldSymbolOffsetDifference(Asm, Layout, Addrs, InSet, RHS_A, LHS_B,
    581                                         Result_Cst);
    582     AttemptToFoldSymbolOffsetDifference(Asm, Layout, Addrs, InSet, RHS_A, RHS_B,
    583                                         Result_Cst);
    584   }
    585 
    586   // We can't represent the addition or subtraction of two symbols.
    587   if ((LHS_A && RHS_A) || (LHS_B && RHS_B))
    588     return false;
    589 
    590   // At this point, we have at most one additive symbol and one subtractive
    591   // symbol -- find them.
    592   const MCSymbolRefExpr *A = LHS_A ? LHS_A : RHS_A;
    593   const MCSymbolRefExpr *B = LHS_B ? LHS_B : RHS_B;
    594 
    595   Res = MCValue::get(A, B, Result_Cst);
    596   return true;
    597 }
    598 
    599 bool MCExpr::evaluateAsRelocatable(MCValue &Res,
    600                                    const MCAsmLayout *Layout,
    601                                    const MCFixup *Fixup) const {
    602   MCAssembler *Assembler = Layout ? &Layout->getAssembler() : nullptr;
    603   return evaluateAsRelocatableImpl(Res, Assembler, Layout, Fixup, nullptr,
    604                                    false);
    605 }
    606 
    607 bool MCExpr::evaluateAsValue(MCValue &Res, const MCAsmLayout &Layout) const {
    608   MCAssembler *Assembler = &Layout.getAssembler();
    609   return evaluateAsRelocatableImpl(Res, Assembler, &Layout, nullptr, nullptr,
    610                                    true);
    611 }
    612 
    613 static bool canExpand(const MCSymbol &Sym, bool InSet) {
    614   const MCExpr *Expr = Sym.getVariableValue();
    615   const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
    616   if (Inner) {
    617     if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
    618       return false;
    619   }
    620 
    621   if (InSet)
    622     return true;
    623   return !Sym.isInSection();
    624 }
    625 
    626 bool MCExpr::evaluateAsRelocatableImpl(MCValue &Res, const MCAssembler *Asm,
    627                                        const MCAsmLayout *Layout,
    628                                        const MCFixup *Fixup,
    629                                        const SectionAddrMap *Addrs,
    630                                        bool InSet) const {
    631   ++stats::MCExprEvaluate;
    632 
    633   switch (getKind()) {
    634   case Target:
    635     return cast<MCTargetExpr>(this)->evaluateAsRelocatableImpl(Res, Layout,
    636                                                                Fixup);
    637 
    638   case Constant:
    639     Res = MCValue::get(cast<MCConstantExpr>(this)->getValue());
    640     return true;
    641 
    642   case SymbolRef: {
    643     const MCSymbolRefExpr *SRE = cast<MCSymbolRefExpr>(this);
    644     const MCSymbol &Sym = SRE->getSymbol();
    645 
    646     // Evaluate recursively if this is a variable.
    647     if (Sym.isVariable() && SRE->getKind() == MCSymbolRefExpr::VK_None &&
    648         canExpand(Sym, InSet)) {
    649       bool IsMachO = SRE->hasSubsectionsViaSymbols();
    650       if (Sym.getVariableValue()->evaluateAsRelocatableImpl(
    651               Res, Asm, Layout, Fixup, Addrs, InSet || IsMachO)) {
    652         if (!IsMachO)
    653           return true;
    654 
    655         const MCSymbolRefExpr *A = Res.getSymA();
    656         const MCSymbolRefExpr *B = Res.getSymB();
    657         // FIXME: This is small hack. Given
    658         // a = b + 4
    659         // .long a
    660         // the OS X assembler will completely drop the 4. We should probably
    661         // include it in the relocation or produce an error if that is not
    662         // possible.
    663         if (!A && !B)
    664           return true;
    665       }
    666     }
    667 
    668     Res = MCValue::get(SRE, nullptr, 0);
    669     return true;
    670   }
    671 
    672   case Unary: {
    673     const MCUnaryExpr *AUE = cast<MCUnaryExpr>(this);
    674     MCValue Value;
    675 
    676     if (!AUE->getSubExpr()->evaluateAsRelocatableImpl(Value, Asm, Layout, Fixup,
    677                                                       Addrs, InSet))
    678       return false;
    679 
    680     switch (AUE->getOpcode()) {
    681     case MCUnaryExpr::LNot:
    682       if (!Value.isAbsolute())
    683         return false;
    684       Res = MCValue::get(!Value.getConstant());
    685       break;
    686     case MCUnaryExpr::Minus:
    687       /// -(a - b + const) ==> (b - a - const)
    688       if (Value.getSymA() && !Value.getSymB())
    689         return false;
    690       Res = MCValue::get(Value.getSymB(), Value.getSymA(),
    691                          -Value.getConstant());
    692       break;
    693     case MCUnaryExpr::Not:
    694       if (!Value.isAbsolute())
    695         return false;
    696       Res = MCValue::get(~Value.getConstant());
    697       break;
    698     case MCUnaryExpr::Plus:
    699       Res = Value;
    700       break;
    701     }
    702 
    703     return true;
    704   }
    705 
    706   case Binary: {
    707     const MCBinaryExpr *ABE = cast<MCBinaryExpr>(this);
    708     MCValue LHSValue, RHSValue;
    709 
    710     if (!ABE->getLHS()->evaluateAsRelocatableImpl(LHSValue, Asm, Layout, Fixup,
    711                                                   Addrs, InSet) ||
    712         !ABE->getRHS()->evaluateAsRelocatableImpl(RHSValue, Asm, Layout, Fixup,
    713                                                   Addrs, InSet))
    714       return false;
    715 
    716     // We only support a few operations on non-constant expressions, handle
    717     // those first.
    718     if (!LHSValue.isAbsolute() || !RHSValue.isAbsolute()) {
    719       switch (ABE->getOpcode()) {
    720       default:
    721         return false;
    722       case MCBinaryExpr::Sub:
    723         // Negate RHS and add.
    724         return EvaluateSymbolicAdd(Asm, Layout, Addrs, InSet, LHSValue,
    725                                    RHSValue.getSymB(), RHSValue.getSymA(),
    726                                    -RHSValue.getConstant(), Res);
    727 
    728       case MCBinaryExpr::Add:
    729         return EvaluateSymbolicAdd(Asm, Layout, Addrs, InSet, LHSValue,
    730                                    RHSValue.getSymA(), RHSValue.getSymB(),
    731                                    RHSValue.getConstant(), Res);
    732       }
    733     }
    734 
    735     // FIXME: We need target hooks for the evaluation. It may be limited in
    736     // width, and gas defines the result of comparisons differently from
    737     // Apple as.
    738     int64_t LHS = LHSValue.getConstant(), RHS = RHSValue.getConstant();
    739     int64_t Result = 0;
    740     switch (ABE->getOpcode()) {
    741     case MCBinaryExpr::AShr: Result = LHS >> RHS; break;
    742     case MCBinaryExpr::Add:  Result = LHS + RHS; break;
    743     case MCBinaryExpr::And:  Result = LHS & RHS; break;
    744     case MCBinaryExpr::Div:
    745       // Handle division by zero. gas just emits a warning and keeps going,
    746       // we try to be stricter.
    747       // FIXME: Currently the caller of this function has no way to understand
    748       // we're bailing out because of 'division by zero'. Therefore, it will
    749       // emit a 'expected relocatable expression' error. It would be nice to
    750       // change this code to emit a better diagnostic.
    751       if (RHS == 0)
    752         return false;
    753       Result = LHS / RHS;
    754       break;
    755     case MCBinaryExpr::EQ:   Result = LHS == RHS; break;
    756     case MCBinaryExpr::GT:   Result = LHS > RHS; break;
    757     case MCBinaryExpr::GTE:  Result = LHS >= RHS; break;
    758     case MCBinaryExpr::LAnd: Result = LHS && RHS; break;
    759     case MCBinaryExpr::LOr:  Result = LHS || RHS; break;
    760     case MCBinaryExpr::LShr: Result = uint64_t(LHS) >> uint64_t(RHS); break;
    761     case MCBinaryExpr::LT:   Result = LHS < RHS; break;
    762     case MCBinaryExpr::LTE:  Result = LHS <= RHS; break;
    763     case MCBinaryExpr::Mod:  Result = LHS % RHS; break;
    764     case MCBinaryExpr::Mul:  Result = LHS * RHS; break;
    765     case MCBinaryExpr::NE:   Result = LHS != RHS; break;
    766     case MCBinaryExpr::Or:   Result = LHS | RHS; break;
    767     case MCBinaryExpr::Shl:  Result = uint64_t(LHS) << uint64_t(RHS); break;
    768     case MCBinaryExpr::Sub:  Result = LHS - RHS; break;
    769     case MCBinaryExpr::Xor:  Result = LHS ^ RHS; break;
    770     }
    771 
    772     Res = MCValue::get(Result);
    773     return true;
    774   }
    775   }
    776 
    777   llvm_unreachable("Invalid assembly expression kind!");
    778 }
    779 
    780 MCFragment *MCExpr::findAssociatedFragment() const {
    781   switch (getKind()) {
    782   case Target:
    783     // We never look through target specific expressions.
    784     return cast<MCTargetExpr>(this)->findAssociatedFragment();
    785 
    786   case Constant:
    787     return MCSymbol::AbsolutePseudoFragment;
    788 
    789   case SymbolRef: {
    790     const MCSymbolRefExpr *SRE = cast<MCSymbolRefExpr>(this);
    791     const MCSymbol &Sym = SRE->getSymbol();
    792     return Sym.getFragment();
    793   }
    794 
    795   case Unary:
    796     return cast<MCUnaryExpr>(this)->getSubExpr()->findAssociatedFragment();
    797 
    798   case Binary: {
    799     const MCBinaryExpr *BE = cast<MCBinaryExpr>(this);
    800     MCFragment *LHS_F = BE->getLHS()->findAssociatedFragment();
    801     MCFragment *RHS_F = BE->getRHS()->findAssociatedFragment();
    802 
    803     // If either is absolute, return the other.
    804     if (LHS_F == MCSymbol::AbsolutePseudoFragment)
    805       return RHS_F;
    806     if (RHS_F == MCSymbol::AbsolutePseudoFragment)
    807       return LHS_F;
    808 
    809     // Not always correct, but probably the best we can do without more context.
    810     if (BE->getOpcode() == MCBinaryExpr::Sub)
    811       return MCSymbol::AbsolutePseudoFragment;
    812 
    813     // Otherwise, return the first non-null fragment.
    814     return LHS_F ? LHS_F : RHS_F;
    815   }
    816   }
    817 
    818   llvm_unreachable("Invalid assembly expression kind!");
    819 }
    820