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"
23using namespace llvm;
24
25namespace {
26namespace stats {
27STATISTIC(MCExprEvaluate, "Number of MCExpr evaluations");
28}
29}
30
31void 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#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
140void MCExpr::dump() const {
141  print(dbgs());
142  dbgs() << '\n';
143}
144#endif
145
146/* *** */
147
148const MCBinaryExpr *MCBinaryExpr::Create(Opcode Opc, const MCExpr *LHS,
149                                         const MCExpr *RHS, MCContext &Ctx) {
150  return new (Ctx) MCBinaryExpr(Opc, LHS, RHS);
151}
152
153const MCUnaryExpr *MCUnaryExpr::Create(Opcode Opc, const MCExpr *Expr,
154                                       MCContext &Ctx) {
155  return new (Ctx) MCUnaryExpr(Opc, Expr);
156}
157
158const MCConstantExpr *MCConstantExpr::Create(int64_t Value, MCContext &Ctx) {
159  return new (Ctx) MCConstantExpr(Value);
160}
161
162/* *** */
163
164const MCSymbolRefExpr *MCSymbolRefExpr::Create(const MCSymbol *Sym,
165                                               VariantKind Kind,
166                                               MCContext &Ctx) {
167  return new (Ctx) MCSymbolRefExpr(Sym, Kind);
168}
169
170const MCSymbolRefExpr *MCSymbolRefExpr::Create(StringRef Name, VariantKind Kind,
171                                               MCContext &Ctx) {
172  return Create(Ctx.GetOrCreateSymbol(Name), Kind, Ctx);
173}
174
175StringRef 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
234MCSymbolRefExpr::VariantKind
235MCSymbolRefExpr::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
270void MCTargetExpr::anchor() {}
271
272/* *** */
273
274bool MCExpr::EvaluateAsAbsolute(int64_t &Res) const {
275  return EvaluateAsAbsolute(Res, 0, 0, 0);
276}
277
278bool MCExpr::EvaluateAsAbsolute(int64_t &Res,
279                                const MCAsmLayout &Layout) const {
280  return EvaluateAsAbsolute(Res, &Layout.getAssembler(), &Layout, 0);
281}
282
283bool MCExpr::EvaluateAsAbsolute(int64_t &Res,
284                                const MCAsmLayout &Layout,
285                                const SectionAddrMap &Addrs) const {
286  return EvaluateAsAbsolute(Res, &Layout.getAssembler(), &Layout, &Addrs);
287}
288
289bool MCExpr::EvaluateAsAbsolute(int64_t &Res, const MCAssembler &Asm) const {
290  return EvaluateAsAbsolute(Res, &Asm, 0, 0);
291}
292
293bool 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().
317static 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.
397static 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
456bool MCExpr::EvaluateAsRelocatable(MCValue &Res,
457                                   const MCAsmLayout &Layout) const {
458  return EvaluateAsRelocatableImpl(Res, &Layout.getAssembler(), &Layout,
459                                   0, false);
460}
461
462bool 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
596const 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