MCExpr.cpp revision 207e06ea0446c51cb1d89f6400ec7becc46487f8 
1//===- MCExpr.cpp - Assembly Level Expression Implementation --------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9
10#define DEBUG_TYPE "mcexpr"
11#include "llvm/MC/MCExpr.h"
12#include "llvm/ADT/Statistic.h"
13#include "llvm/ADT/StringSwitch.h"
14#include "llvm/MC/MCAsmLayout.h"
15#include "llvm/MC/MCAssembler.h"
16#include "llvm/MC/MCContext.h"
17#include "llvm/MC/MCSymbol.h"
18#include "llvm/MC/MCValue.h"
19#include "llvm/Support/Debug.h"
20#include "llvm/Support/raw_ostream.h"
21#include "llvm/Target/TargetAsmBackend.h"
22using namespace llvm;
23
24namespace {
25namespace stats {
26STATISTIC(MCExprEvaluate, "Number of MCExpr evaluations");
27}
28}
29
30void MCExpr::print(raw_ostream &OS) const {
31  switch (getKind()) {
32  case MCExpr::Target:
33    return cast<MCTargetExpr>(this)->PrintImpl(OS);
34  case MCExpr::Constant:
35    OS << cast<MCConstantExpr>(*this).getValue();
36    return;
37
38  case MCExpr::SymbolRef: {
39    const MCSymbolRefExpr &SRE = cast<MCSymbolRefExpr>(*this);
40    const MCSymbol &Sym = SRE.getSymbol();
41
42    // Parenthesize names that start with $ so that they don't look like
43    // absolute names.
44    if (Sym.getName()[0] == '$')
45      OS << '(' << Sym << ')';
46    else
47      OS << Sym;
48
49    if (SRE.getKind() != MCSymbolRefExpr::VK_None)
50      OS << '@' << MCSymbolRefExpr::getVariantKindName(SRE.getKind());
51
52    return;
53  }
54
55  case MCExpr::Unary: {
56    const MCUnaryExpr &UE = cast<MCUnaryExpr>(*this);
57    switch (UE.getOpcode()) {
58    default: assert(0 && "Invalid opcode!");
59    case MCUnaryExpr::LNot:  OS << '!'; break;
60    case MCUnaryExpr::Minus: OS << '-'; break;
61    case MCUnaryExpr::Not:   OS << '~'; break;
62    case MCUnaryExpr::Plus:  OS << '+'; break;
63    }
64    OS << *UE.getSubExpr();
65    return;
66  }
67
68  case MCExpr::Binary: {
69    const MCBinaryExpr &BE = cast<MCBinaryExpr>(*this);
70
71    // Only print parens around the LHS if it is non-trivial.
72    if (isa<MCConstantExpr>(BE.getLHS()) || isa<MCSymbolRefExpr>(BE.getLHS())) {
73      OS << *BE.getLHS();
74    } else {
75      OS << '(' << *BE.getLHS() << ')';
76    }
77
78    switch (BE.getOpcode()) {
79    default: assert(0 && "Invalid opcode!");
80    case MCBinaryExpr::Add:
81      // Print "X-42" instead of "X+-42".
82      if (const MCConstantExpr *RHSC = dyn_cast<MCConstantExpr>(BE.getRHS())) {
83        if (RHSC->getValue() < 0) {
84          OS << RHSC->getValue();
85          return;
86        }
87      }
88
89      OS <<  '+';
90      break;
91    case MCBinaryExpr::And:  OS <<  '&'; break;
92    case MCBinaryExpr::Div:  OS <<  '/'; break;
93    case MCBinaryExpr::EQ:   OS << "=="; break;
94    case MCBinaryExpr::GT:   OS <<  '>'; break;
95    case MCBinaryExpr::GTE:  OS << ">="; break;
96    case MCBinaryExpr::LAnd: OS << "&&"; break;
97    case MCBinaryExpr::LOr:  OS << "||"; break;
98    case MCBinaryExpr::LT:   OS <<  '<'; break;
99    case MCBinaryExpr::LTE:  OS << "<="; break;
100    case MCBinaryExpr::Mod:  OS <<  '%'; break;
101    case MCBinaryExpr::Mul:  OS <<  '*'; break;
102    case MCBinaryExpr::NE:   OS << "!="; break;
103    case MCBinaryExpr::Or:   OS <<  '|'; break;
104    case MCBinaryExpr::Shl:  OS << "<<"; break;
105    case MCBinaryExpr::Shr:  OS << ">>"; break;
106    case MCBinaryExpr::Sub:  OS <<  '-'; break;
107    case MCBinaryExpr::Xor:  OS <<  '^'; break;
108    }
109
110    // Only print parens around the LHS if it is non-trivial.
111    if (isa<MCConstantExpr>(BE.getRHS()) || isa<MCSymbolRefExpr>(BE.getRHS())) {
112      OS << *BE.getRHS();
113    } else {
114      OS << '(' << *BE.getRHS() << ')';
115    }
116    return;
117  }
118  }
119
120  assert(0 && "Invalid expression kind!");
121}
122
123void MCExpr::dump() const {
124  print(dbgs());
125  dbgs() << '\n';
126}
127
128/* *** */
129
130const MCBinaryExpr *MCBinaryExpr::Create(Opcode Opc, const MCExpr *LHS,
131                                         const MCExpr *RHS, MCContext &Ctx) {
132  return new (Ctx) MCBinaryExpr(Opc, LHS, RHS);
133}
134
135const MCUnaryExpr *MCUnaryExpr::Create(Opcode Opc, const MCExpr *Expr,
136                                       MCContext &Ctx) {
137  return new (Ctx) MCUnaryExpr(Opc, Expr);
138}
139
140const MCConstantExpr *MCConstantExpr::Create(int64_t Value, MCContext &Ctx) {
141  return new (Ctx) MCConstantExpr(Value);
142}
143
144/* *** */
145
146const MCSymbolRefExpr *MCSymbolRefExpr::Create(const MCSymbol *Sym,
147                                               VariantKind Kind,
148                                               MCContext &Ctx) {
149  return new (Ctx) MCSymbolRefExpr(Sym, Kind);
150}
151
152const MCSymbolRefExpr *MCSymbolRefExpr::Create(StringRef Name, VariantKind Kind,
153                                               MCContext &Ctx) {
154  return Create(Ctx.GetOrCreateSymbol(Name), Kind, Ctx);
155}
156
157const MCSymbolRefExpr *MCSymbolRefExpr::CreateTemp(StringRef Name,
158                                                   VariantKind Kind,
159                                                   MCContext &Ctx) {
160  return Create(Ctx.GetOrCreateTemporarySymbol(Name), Kind, Ctx);
161}
162
163StringRef MCSymbolRefExpr::getVariantKindName(VariantKind Kind) {
164  switch (Kind) {
165  default:
166  case VK_Invalid: return "<<invalid>>";
167  case VK_None: return "<<none>>";
168
169  case VK_GOT: return "GOT";
170  case VK_GOTOFF: return "GOTOFF";
171  case VK_GOTPCREL: return "GOTPCREL";
172  case VK_GOTTPOFF: return "GOTTPOFF";
173  case VK_INDNTPOFF: return "INDNTPOFF";
174  case VK_NTPOFF: return "NTPOFF";
175  case VK_PLT: return "PLT";
176  case VK_TLSGD: return "TLSGD";
177  case VK_TPOFF: return "TPOFF";
178  }
179}
180
181MCSymbolRefExpr::VariantKind
182MCSymbolRefExpr::getVariantKindForName(StringRef Name) {
183  return StringSwitch<VariantKind>(Name)
184    .Case("GOT", VK_GOT)
185    .Case("GOTOFF", VK_GOTOFF)
186    .Case("GOTPCREL", VK_GOTPCREL)
187    .Case("GOTTPOFF", VK_GOTTPOFF)
188    .Case("INDNTPOFF", VK_INDNTPOFF)
189    .Case("NTPOFF", VK_NTPOFF)
190    .Case("PLT", VK_PLT)
191    .Case("TLSGD", VK_TLSGD)
192    .Case("TPOFF", VK_TPOFF)
193    .Default(VK_Invalid);
194}
195
196/* *** */
197
198void MCTargetExpr::Anchor() {}
199
200/* *** */
201
202bool MCExpr::EvaluateAsAbsolute(int64_t &Res, const MCAsmLayout *Layout) const {
203  MCValue Value;
204
205  // Fast path constants.
206  if (const MCConstantExpr *CE = dyn_cast<MCConstantExpr>(this)) {
207    Res = CE->getValue();
208    return true;
209  }
210
211  if (!EvaluateAsRelocatable(Value, Layout) || !Value.isAbsolute())
212    return false;
213
214  Res = Value.getConstant();
215  return true;
216}
217
218static bool EvaluateSymbolicAdd(const MCValue &LHS,const MCSymbolRefExpr *RHS_A,
219                                const MCSymbolRefExpr *RHS_B, int64_t RHS_Cst,
220                                MCValue &Res) {
221  // We can't add or subtract two symbols.
222  if ((LHS.getSymA() && RHS_A) ||
223      (LHS.getSymB() && RHS_B))
224    return false;
225
226  const MCSymbolRefExpr *A = LHS.getSymA() ? LHS.getSymA() : RHS_A;
227  const MCSymbolRefExpr *B = LHS.getSymB() ? LHS.getSymB() : RHS_B;
228  if (B) {
229    // If we have a negated symbol, then we must have also have a non-negated
230    // symbol in order to encode the expression. We can do this check later to
231    // permit expressions which eventually fold to a representable form -- such
232    // as (a + (0 - b)) -- if necessary.
233    if (!A)
234      return false;
235  }
236  Res = MCValue::get(A, B, LHS.getConstant() + RHS_Cst);
237  return true;
238}
239
240bool MCExpr::EvaluateAsRelocatable(MCValue &Res,
241                                   const MCAsmLayout *Layout) const {
242  ++stats::MCExprEvaluate;
243
244  switch (getKind()) {
245  case Target:
246    return cast<MCTargetExpr>(this)->EvaluateAsRelocatableImpl(Res, Layout);
247
248  case Constant:
249    Res = MCValue::get(cast<MCConstantExpr>(this)->getValue());
250    return true;
251
252  case SymbolRef: {
253    const MCSymbolRefExpr *SRE = cast<MCSymbolRefExpr>(this);
254    const MCSymbol &Sym = SRE->getSymbol();
255
256    // Evaluate recursively if this is a variable.
257    if (Sym.isVariable()) {
258      if (!Sym.getValue()->EvaluateAsRelocatable(Res, Layout))
259        return false;
260
261      // Absolutize symbol differences between defined symbols when we have a
262      // layout object and the target requests it.
263      if (Layout && Res.getSymB() &&
264          Layout->getAssembler().getBackend().hasAbsolutizedSet() &&
265          Res.getSymA()->getSymbol().isDefined() &&
266          Res.getSymB()->getSymbol().isDefined()) {
267        MCSymbolData &A =
268          Layout->getAssembler().getSymbolData(Res.getSymA()->getSymbol());
269        MCSymbolData &B =
270          Layout->getAssembler().getSymbolData(Res.getSymB()->getSymbol());
271        Res = MCValue::get(+ Layout->getSymbolAddress(&A) + A.getOffset()
272                           - Layout->getSymbolAddress(&B) - B.getOffset()
273                           + Res.getConstant());
274      }
275
276      return true;
277    }
278
279    Res = MCValue::get(SRE, 0, 0);
280    return true;
281  }
282
283  case Unary: {
284    const MCUnaryExpr *AUE = cast<MCUnaryExpr>(this);
285    MCValue Value;
286
287    if (!AUE->getSubExpr()->EvaluateAsRelocatable(Value, Layout))
288      return false;
289
290    switch (AUE->getOpcode()) {
291    case MCUnaryExpr::LNot:
292      if (!Value.isAbsolute())
293        return false;
294      Res = MCValue::get(!Value.getConstant());
295      break;
296    case MCUnaryExpr::Minus:
297      /// -(a - b + const) ==> (b - a - const)
298      if (Value.getSymA() && !Value.getSymB())
299        return false;
300      Res = MCValue::get(Value.getSymB(), Value.getSymA(),
301                         -Value.getConstant());
302      break;
303    case MCUnaryExpr::Not:
304      if (!Value.isAbsolute())
305        return false;
306      Res = MCValue::get(~Value.getConstant());
307      break;
308    case MCUnaryExpr::Plus:
309      Res = Value;
310      break;
311    }
312
313    return true;
314  }
315
316  case Binary: {
317    const MCBinaryExpr *ABE = cast<MCBinaryExpr>(this);
318    MCValue LHSValue, RHSValue;
319
320    if (!ABE->getLHS()->EvaluateAsRelocatable(LHSValue, Layout) ||
321        !ABE->getRHS()->EvaluateAsRelocatable(RHSValue, Layout))
322      return false;
323
324    // We only support a few operations on non-constant expressions, handle
325    // those first.
326    if (!LHSValue.isAbsolute() || !RHSValue.isAbsolute()) {
327      switch (ABE->getOpcode()) {
328      default:
329        return false;
330      case MCBinaryExpr::Sub:
331        // Negate RHS and add.
332        return EvaluateSymbolicAdd(LHSValue,
333                                   RHSValue.getSymB(), RHSValue.getSymA(),
334                                   -RHSValue.getConstant(),
335                                   Res);
336
337      case MCBinaryExpr::Add:
338        return EvaluateSymbolicAdd(LHSValue,
339                                   RHSValue.getSymA(), RHSValue.getSymB(),
340                                   RHSValue.getConstant(),
341                                   Res);
342      }
343    }
344
345    // FIXME: We need target hooks for the evaluation. It may be limited in
346    // width, and gas defines the result of comparisons and right shifts
347    // differently from Apple as.
348    int64_t LHS = LHSValue.getConstant(), RHS = RHSValue.getConstant();
349    int64_t Result = 0;
350    switch (ABE->getOpcode()) {
351    case MCBinaryExpr::Add:  Result = LHS + RHS; break;
352    case MCBinaryExpr::And:  Result = LHS & RHS; break;
353    case MCBinaryExpr::Div:  Result = LHS / RHS; break;
354    case MCBinaryExpr::EQ:   Result = LHS == RHS; break;
355    case MCBinaryExpr::GT:   Result = LHS > RHS; break;
356    case MCBinaryExpr::GTE:  Result = LHS >= RHS; break;
357    case MCBinaryExpr::LAnd: Result = LHS && RHS; break;
358    case MCBinaryExpr::LOr:  Result = LHS || RHS; break;
359    case MCBinaryExpr::LT:   Result = LHS < RHS; break;
360    case MCBinaryExpr::LTE:  Result = LHS <= RHS; break;
361    case MCBinaryExpr::Mod:  Result = LHS % RHS; break;
362    case MCBinaryExpr::Mul:  Result = LHS * RHS; break;
363    case MCBinaryExpr::NE:   Result = LHS != RHS; break;
364    case MCBinaryExpr::Or:   Result = LHS | RHS; break;
365    case MCBinaryExpr::Shl:  Result = LHS << RHS; break;
366    case MCBinaryExpr::Shr:  Result = LHS >> RHS; break;
367    case MCBinaryExpr::Sub:  Result = LHS - RHS; break;
368    case MCBinaryExpr::Xor:  Result = LHS ^ RHS; break;
369    }
370
371    Res = MCValue::get(Result);
372    return true;
373  }
374  }
375
376  assert(0 && "Invalid assembly expression kind!");
377  return false;
378}
379