MCExpr.cpp revision e579849652f2ba062e6c91a3af4d9a3843411b44 
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/raw_ostream.h"
15using namespace llvm;
16
17void MCExpr::print(raw_ostream &OS, const MCAsmInfo *MAI) const {
18  switch (getKind()) {
19  case MCExpr::Constant:
20    OS << cast<MCConstantExpr>(*this).getValue();
21    return;
22
23  case MCExpr::SymbolRef: {
24    const MCSymbol &Sym = cast<MCSymbolRefExpr>(*this).getSymbol();
25
26    // Parenthesize names that start with $ so that they don't look like
27    // absolute names.
28    if (Sym.getName()[0] == '$') {
29      OS << '(';
30      Sym.print(OS, MAI);
31      OS << ')';
32    } else {
33      Sym.print(OS, MAI);
34    }
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    UE.getSubExpr()->print(OS, MAI);
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      BE.getLHS()->print(OS, MAI);
57    } else {
58      OS << '(';
59      BE.getLHS()->print(OS, MAI);
60      OS << ')';
61    }
62
63    switch (BE.getOpcode()) {
64    default: assert(0 && "Invalid opcode!");
65    case MCBinaryExpr::Add:
66      // Print "X-42" instead of "X+-42".
67      if (const MCConstantExpr *RHSC = dyn_cast<MCConstantExpr>(BE.getRHS())) {
68        if (RHSC->getValue() < 0) {
69          OS << RHSC->getValue();
70          return;
71        }
72      }
73
74      OS <<  '+';
75      break;
76    case MCBinaryExpr::And:  OS <<  '&'; break;
77    case MCBinaryExpr::Div:  OS <<  '/'; break;
78    case MCBinaryExpr::EQ:   OS << "=="; break;
79    case MCBinaryExpr::GT:   OS <<  '>'; break;
80    case MCBinaryExpr::GTE:  OS << ">="; break;
81    case MCBinaryExpr::LAnd: OS << "&&"; break;
82    case MCBinaryExpr::LOr:  OS << "||"; break;
83    case MCBinaryExpr::LT:   OS <<  '<'; break;
84    case MCBinaryExpr::LTE:  OS << "<="; break;
85    case MCBinaryExpr::Mod:  OS <<  '%'; break;
86    case MCBinaryExpr::Mul:  OS <<  '*'; break;
87    case MCBinaryExpr::NE:   OS << "!="; break;
88    case MCBinaryExpr::Or:   OS <<  '|'; break;
89    case MCBinaryExpr::Shl:  OS << "<<"; break;
90    case MCBinaryExpr::Shr:  OS << ">>"; break;
91    case MCBinaryExpr::Sub:  OS <<  '-'; break;
92    case MCBinaryExpr::Xor:  OS <<  '^'; break;
93    }
94
95    // Only print parens around the LHS if it is non-trivial.
96    if (isa<MCConstantExpr>(BE.getRHS()) || isa<MCSymbolRefExpr>(BE.getRHS())) {
97      BE.getRHS()->print(OS, MAI);
98    } else {
99      OS << '(';
100      BE.getRHS()->print(OS, MAI);
101      OS << ')';
102    }
103    return;
104  }
105  }
106
107  assert(0 && "Invalid expression kind!");
108}
109
110void MCExpr::dump() const {
111  print(errs(), 0);
112  errs() << '\n';
113}
114
115/* *** */
116
117const MCBinaryExpr *MCBinaryExpr::Create(Opcode Opc, const MCExpr *LHS,
118                                         const MCExpr *RHS, MCContext &Ctx) {
119  return new (Ctx) MCBinaryExpr(Opc, LHS, RHS);
120}
121
122const MCUnaryExpr *MCUnaryExpr::Create(Opcode Opc, const MCExpr *Expr,
123                                       MCContext &Ctx) {
124  return new (Ctx) MCUnaryExpr(Opc, Expr);
125}
126
127const MCConstantExpr *MCConstantExpr::Create(int64_t Value, MCContext &Ctx) {
128  return new (Ctx) MCConstantExpr(Value);
129}
130
131const MCSymbolRefExpr *MCSymbolRefExpr::Create(const MCSymbol *Sym,
132                                               MCContext &Ctx) {
133  return new (Ctx) MCSymbolRefExpr(Sym);
134}
135
136const MCSymbolRefExpr *MCSymbolRefExpr::Create(const StringRef &Name,
137                                               MCContext &Ctx) {
138  return Create(Ctx.GetOrCreateSymbol(Name), Ctx);
139}
140
141
142/* *** */
143
144bool MCExpr::EvaluateAsAbsolute(MCContext &Ctx, int64_t &Res) const {
145  MCValue Value;
146
147  if (!EvaluateAsRelocatable(Ctx, Value) || !Value.isAbsolute())
148    return false;
149
150  Res = Value.getConstant();
151  return true;
152}
153
154static bool EvaluateSymbolicAdd(const MCValue &LHS, const MCSymbol *RHS_A,
155                                const MCSymbol *RHS_B, int64_t RHS_Cst,
156                                MCValue &Res) {
157  // We can't add or subtract two symbols.
158  if ((LHS.getSymA() && RHS_A) ||
159      (LHS.getSymB() && RHS_B))
160    return false;
161
162  const MCSymbol *A = LHS.getSymA() ? LHS.getSymA() : RHS_A;
163  const MCSymbol *B = LHS.getSymB() ? LHS.getSymB() : RHS_B;
164  if (B) {
165    // If we have a negated symbol, then we must have also have a non-negated
166    // symbol in order to encode the expression. We can do this check later to
167    // permit expressions which eventually fold to a representable form -- such
168    // as (a + (0 - b)) -- if necessary.
169    if (!A)
170      return false;
171  }
172  Res = MCValue::get(A, B, LHS.getConstant() + RHS_Cst);
173  return true;
174}
175
176bool MCExpr::EvaluateAsRelocatable(MCContext &Ctx, MCValue &Res) const {
177  switch (getKind()) {
178  case Constant:
179    Res = MCValue::get(cast<MCConstantExpr>(this)->getValue());
180    return true;
181
182  case SymbolRef: {
183    const MCSymbol &Sym = cast<MCSymbolRefExpr>(this)->getSymbol();
184    if (const MCExpr *Value = Ctx.GetSymbolValue(&Sym))
185      return Value->EvaluateAsRelocatable(Ctx, Res);
186    Res = MCValue::get(&Sym, 0, 0);
187    return true;
188  }
189
190  case Unary: {
191    const MCUnaryExpr *AUE = cast<MCUnaryExpr>(this);
192    MCValue Value;
193
194    if (!AUE->getSubExpr()->EvaluateAsRelocatable(Ctx, Value))
195      return false;
196
197    switch (AUE->getOpcode()) {
198    case MCUnaryExpr::LNot:
199      if (!Value.isAbsolute())
200        return false;
201      Res = MCValue::get(!Value.getConstant());
202      break;
203    case MCUnaryExpr::Minus:
204      /// -(a - b + const) ==> (b - a - const)
205      if (Value.getSymA() && !Value.getSymB())
206        return false;
207      Res = MCValue::get(Value.getSymB(), Value.getSymA(),
208                         -Value.getConstant());
209      break;
210    case MCUnaryExpr::Not:
211      if (!Value.isAbsolute())
212        return false;
213      Res = MCValue::get(~Value.getConstant());
214      break;
215    case MCUnaryExpr::Plus:
216      Res = Value;
217      break;
218    }
219
220    return true;
221  }
222
223  case Binary: {
224    const MCBinaryExpr *ABE = cast<MCBinaryExpr>(this);
225    MCValue LHSValue, RHSValue;
226
227    if (!ABE->getLHS()->EvaluateAsRelocatable(Ctx, LHSValue) ||
228        !ABE->getRHS()->EvaluateAsRelocatable(Ctx, RHSValue))
229      return false;
230
231    // We only support a few operations on non-constant expressions, handle
232    // those first.
233    if (!LHSValue.isAbsolute() || !RHSValue.isAbsolute()) {
234      switch (ABE->getOpcode()) {
235      default:
236        return false;
237      case MCBinaryExpr::Sub:
238        // Negate RHS and add.
239        return EvaluateSymbolicAdd(LHSValue,
240                                   RHSValue.getSymB(), RHSValue.getSymA(),
241                                   -RHSValue.getConstant(),
242                                   Res);
243
244      case MCBinaryExpr::Add:
245        return EvaluateSymbolicAdd(LHSValue,
246                                   RHSValue.getSymA(), RHSValue.getSymB(),
247                                   RHSValue.getConstant(),
248                                   Res);
249      }
250    }
251
252    // FIXME: We need target hooks for the evaluation. It may be limited in
253    // width, and gas defines the result of comparisons differently from Apple
254    // as (the result is sign extended).
255    int64_t LHS = LHSValue.getConstant(), RHS = RHSValue.getConstant();
256    int64_t Result = 0;
257    switch (ABE->getOpcode()) {
258    case MCBinaryExpr::Add:  Result = LHS + RHS; break;
259    case MCBinaryExpr::And:  Result = LHS & RHS; break;
260    case MCBinaryExpr::Div:  Result = LHS / RHS; break;
261    case MCBinaryExpr::EQ:   Result = LHS == RHS; break;
262    case MCBinaryExpr::GT:   Result = LHS > RHS; break;
263    case MCBinaryExpr::GTE:  Result = LHS >= RHS; break;
264    case MCBinaryExpr::LAnd: Result = LHS && RHS; break;
265    case MCBinaryExpr::LOr:  Result = LHS || RHS; break;
266    case MCBinaryExpr::LT:   Result = LHS < RHS; break;
267    case MCBinaryExpr::LTE:  Result = LHS <= RHS; break;
268    case MCBinaryExpr::Mod:  Result = LHS % RHS; break;
269    case MCBinaryExpr::Mul:  Result = LHS * RHS; break;
270    case MCBinaryExpr::NE:   Result = LHS != RHS; break;
271    case MCBinaryExpr::Or:   Result = LHS | RHS; break;
272    case MCBinaryExpr::Shl:  Result = LHS << RHS; break;
273    case MCBinaryExpr::Shr:  Result = LHS >> RHS; break;
274    case MCBinaryExpr::Sub:  Result = LHS - RHS; break;
275    case MCBinaryExpr::Xor:  Result = LHS ^ RHS; break;
276    }
277
278    Res = MCValue::get(Result);
279    return true;
280  }
281  }
282
283  assert(0 && "Invalid assembly expression kind!");
284  return false;
285}
286