MCExpr.cpp revision df9c4380ee7e60c1de5cae32685b113170b1faa2 
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/MC/MCContext.h"
12#include "llvm/MC/MCSymbol.h"
13#include "llvm/MC/MCValue.h"
14#include "llvm/Support/Debug.h"
15#include "llvm/Support/raw_ostream.h"
16using namespace llvm;
17
18void MCExpr::print(raw_ostream &OS) const {
19  switch (getKind()) {
20  case MCExpr::Target:
21    return cast<MCTargetExpr>(this)->PrintImpl(OS);
22  case MCExpr::Constant:
23    OS << cast<MCConstantExpr>(*this).getValue();
24    return;
25
26  case MCExpr::SymbolRef: {
27    const MCSymbol &Sym = cast<MCSymbolRefExpr>(*this).getSymbol();
28
29    // Parenthesize names that start with $ so that they don't look like
30    // absolute names.
31    if (Sym.getName()[0] == '$')
32      OS << '(' << Sym << ')';
33    else
34      OS << Sym;
35    return;
36  }
37
38  case MCExpr::Unary: {
39    const MCUnaryExpr &UE = cast<MCUnaryExpr>(*this);
40    switch (UE.getOpcode()) {
41    default: assert(0 && "Invalid opcode!");
42    case MCUnaryExpr::LNot:  OS << '!'; break;
43    case MCUnaryExpr::Minus: OS << '-'; break;
44    case MCUnaryExpr::Not:   OS << '~'; break;
45    case MCUnaryExpr::Plus:  OS << '+'; break;
46    }
47    OS << *UE.getSubExpr();
48    return;
49  }
50
51  case MCExpr::Binary: {
52    const MCBinaryExpr &BE = cast<MCBinaryExpr>(*this);
53
54    // Only print parens around the LHS if it is non-trivial.
55    if (isa<MCConstantExpr>(BE.getLHS()) || isa<MCSymbolRefExpr>(BE.getLHS())) {
56      OS << *BE.getLHS();
57    } else {
58      OS << '(' << *BE.getLHS() << ')';
59    }
60
61    switch (BE.getOpcode()) {
62    default: assert(0 && "Invalid opcode!");
63    case MCBinaryExpr::Add:
64      // Print "X-42" instead of "X+-42".
65      if (const MCConstantExpr *RHSC = dyn_cast<MCConstantExpr>(BE.getRHS())) {
66        if (RHSC->getValue() < 0) {
67          OS << RHSC->getValue();
68          return;
69        }
70      }
71
72      OS <<  '+';
73      break;
74    case MCBinaryExpr::And:  OS <<  '&'; break;
75    case MCBinaryExpr::Div:  OS <<  '/'; break;
76    case MCBinaryExpr::EQ:   OS << "=="; break;
77    case MCBinaryExpr::GT:   OS <<  '>'; break;
78    case MCBinaryExpr::GTE:  OS << ">="; break;
79    case MCBinaryExpr::LAnd: OS << "&&"; break;
80    case MCBinaryExpr::LOr:  OS << "||"; break;
81    case MCBinaryExpr::LT:   OS <<  '<'; break;
82    case MCBinaryExpr::LTE:  OS << "<="; break;
83    case MCBinaryExpr::Mod:  OS <<  '%'; break;
84    case MCBinaryExpr::Mul:  OS <<  '*'; break;
85    case MCBinaryExpr::NE:   OS << "!="; break;
86    case MCBinaryExpr::Or:   OS <<  '|'; break;
87    case MCBinaryExpr::Shl:  OS << "<<"; break;
88    case MCBinaryExpr::Shr:  OS << ">>"; break;
89    case MCBinaryExpr::Sub:  OS <<  '-'; break;
90    case MCBinaryExpr::Xor:  OS <<  '^'; break;
91    }
92
93    // Only print parens around the LHS if it is non-trivial.
94    if (isa<MCConstantExpr>(BE.getRHS()) || isa<MCSymbolRefExpr>(BE.getRHS())) {
95      OS << *BE.getRHS();
96    } else {
97      OS << '(' << *BE.getRHS() << ')';
98    }
99    return;
100  }
101  }
102
103  assert(0 && "Invalid expression kind!");
104}
105
106void MCExpr::dump() const {
107  print(dbgs());
108  dbgs() << '\n';
109}
110
111/* *** */
112
113const MCBinaryExpr *MCBinaryExpr::Create(Opcode Opc, const MCExpr *LHS,
114                                         const MCExpr *RHS, MCContext &Ctx) {
115  return new (Ctx) MCBinaryExpr(Opc, LHS, RHS);
116}
117
118const MCUnaryExpr *MCUnaryExpr::Create(Opcode Opc, const MCExpr *Expr,
119                                       MCContext &Ctx) {
120  return new (Ctx) MCUnaryExpr(Opc, Expr);
121}
122
123const MCConstantExpr *MCConstantExpr::Create(int64_t Value, MCContext &Ctx) {
124  return new (Ctx) MCConstantExpr(Value);
125}
126
127const MCSymbolRefExpr *MCSymbolRefExpr::Create(const MCSymbol *Sym,
128                                               MCContext &Ctx) {
129  return new (Ctx) MCSymbolRefExpr(Sym);
130}
131
132const MCSymbolRefExpr *MCSymbolRefExpr::Create(StringRef Name, MCContext &Ctx) {
133  return Create(Ctx.GetOrCreateSymbol(Name), Ctx);
134}
135
136void MCTargetExpr::Anchor() {}
137
138/* *** */
139
140bool MCExpr::EvaluateAsAbsolute(int64_t &Res) const {
141  MCValue Value;
142
143  if (!EvaluateAsRelocatable(Value) || !Value.isAbsolute())
144    return false;
145
146  Res = Value.getConstant();
147  return true;
148}
149
150static bool EvaluateSymbolicAdd(const MCValue &LHS, const MCSymbol *RHS_A,
151                                const MCSymbol *RHS_B, int64_t RHS_Cst,
152                                MCValue &Res) {
153  // We can't add or subtract two symbols.
154  if ((LHS.getSymA() && RHS_A) ||
155      (LHS.getSymB() && RHS_B))
156    return false;
157
158  const MCSymbol *A = LHS.getSymA() ? LHS.getSymA() : RHS_A;
159  const MCSymbol *B = LHS.getSymB() ? LHS.getSymB() : RHS_B;
160  if (B) {
161    // If we have a negated symbol, then we must have also have a non-negated
162    // symbol in order to encode the expression. We can do this check later to
163    // permit expressions which eventually fold to a representable form -- such
164    // as (a + (0 - b)) -- if necessary.
165    if (!A)
166      return false;
167  }
168  Res = MCValue::get(A, B, LHS.getConstant() + RHS_Cst);
169  return true;
170}
171
172bool MCExpr::EvaluateAsRelocatable(MCValue &Res) const {
173  switch (getKind()) {
174  case Target:
175    return cast<MCTargetExpr>(this)->EvaluateAsRelocatableImpl(Res);
176
177  case Constant:
178    Res = MCValue::get(cast<MCConstantExpr>(this)->getValue());
179    return true;
180
181  case SymbolRef: {
182    const MCSymbol &Sym = cast<MCSymbolRefExpr>(this)->getSymbol();
183
184    // Evaluate recursively if this is a variable.
185    if (Sym.isVariable())
186      return Sym.getValue()->EvaluateAsRelocatable(Res);
187
188    Res = MCValue::get(&Sym, 0, 0);
189    return true;
190  }
191
192  case Unary: {
193    const MCUnaryExpr *AUE = cast<MCUnaryExpr>(this);
194    MCValue Value;
195
196    if (!AUE->getSubExpr()->EvaluateAsRelocatable(Value))
197      return false;
198
199    switch (AUE->getOpcode()) {
200    case MCUnaryExpr::LNot:
201      if (!Value.isAbsolute())
202        return false;
203      Res = MCValue::get(!Value.getConstant());
204      break;
205    case MCUnaryExpr::Minus:
206      /// -(a - b + const) ==> (b - a - const)
207      if (Value.getSymA() && !Value.getSymB())
208        return false;
209      Res = MCValue::get(Value.getSymB(), Value.getSymA(),
210                         -Value.getConstant());
211      break;
212    case MCUnaryExpr::Not:
213      if (!Value.isAbsolute())
214        return false;
215      Res = MCValue::get(~Value.getConstant());
216      break;
217    case MCUnaryExpr::Plus:
218      Res = Value;
219      break;
220    }
221
222    return true;
223  }
224
225  case Binary: {
226    const MCBinaryExpr *ABE = cast<MCBinaryExpr>(this);
227    MCValue LHSValue, RHSValue;
228
229    if (!ABE->getLHS()->EvaluateAsRelocatable(LHSValue) ||
230        !ABE->getRHS()->EvaluateAsRelocatable(RHSValue))
231      return false;
232
233    // We only support a few operations on non-constant expressions, handle
234    // those first.
235    if (!LHSValue.isAbsolute() || !RHSValue.isAbsolute()) {
236      switch (ABE->getOpcode()) {
237      default:
238        return false;
239      case MCBinaryExpr::Sub:
240        // Negate RHS and add.
241        return EvaluateSymbolicAdd(LHSValue,
242                                   RHSValue.getSymB(), RHSValue.getSymA(),
243                                   -RHSValue.getConstant(),
244                                   Res);
245
246      case MCBinaryExpr::Add:
247        return EvaluateSymbolicAdd(LHSValue,
248                                   RHSValue.getSymA(), RHSValue.getSymB(),
249                                   RHSValue.getConstant(),
250                                   Res);
251      }
252    }
253
254    // FIXME: We need target hooks for the evaluation. It may be limited in
255    // width, and gas defines the result of comparisons differently from Apple
256    // as (the result is sign extended).
257    int64_t LHS = LHSValue.getConstant(), RHS = RHSValue.getConstant();
258    int64_t Result = 0;
259    switch (ABE->getOpcode()) {
260    case MCBinaryExpr::Add:  Result = LHS + RHS; break;
261    case MCBinaryExpr::And:  Result = LHS & RHS; break;
262    case MCBinaryExpr::Div:  Result = LHS / RHS; break;
263    case MCBinaryExpr::EQ:   Result = LHS == RHS; break;
264    case MCBinaryExpr::GT:   Result = LHS > RHS; break;
265    case MCBinaryExpr::GTE:  Result = LHS >= RHS; break;
266    case MCBinaryExpr::LAnd: Result = LHS && RHS; break;
267    case MCBinaryExpr::LOr:  Result = LHS || RHS; break;
268    case MCBinaryExpr::LT:   Result = LHS < RHS; break;
269    case MCBinaryExpr::LTE:  Result = LHS <= RHS; break;
270    case MCBinaryExpr::Mod:  Result = LHS % RHS; break;
271    case MCBinaryExpr::Mul:  Result = LHS * RHS; break;
272    case MCBinaryExpr::NE:   Result = LHS != RHS; break;
273    case MCBinaryExpr::Or:   Result = LHS | RHS; break;
274    case MCBinaryExpr::Shl:  Result = LHS << RHS; break;
275    case MCBinaryExpr::Shr:  Result = LHS >> RHS; break;
276    case MCBinaryExpr::Sub:  Result = LHS - RHS; break;
277    case MCBinaryExpr::Xor:  Result = LHS ^ RHS; break;
278    }
279
280    Res = MCValue::get(Result);
281    return true;
282  }
283  }
284
285  assert(0 && "Invalid assembly expression kind!");
286  return false;
287}
288