MCExpr.cpp revision 199481 
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(StringRef Name, MCContext &Ctx) {
137  return Create(Ctx.GetOrCreateSymbol(Name), Ctx);
138}
139
140
141/* *** */
142
143bool MCExpr::EvaluateAsAbsolute(int64_t &Res) const {
144  MCValue Value;
145
146  if (!EvaluateAsRelocatable(Value) || !Value.isAbsolute())
147    return false;
148
149  Res = Value.getConstant();
150  return true;
151}
152
153static bool EvaluateSymbolicAdd(const MCValue &LHS, const MCSymbol *RHS_A,
154                                const MCSymbol *RHS_B, int64_t RHS_Cst,
155                                MCValue &Res) {
156  // We can't add or subtract two symbols.
157  if ((LHS.getSymA() && RHS_A) ||
158      (LHS.getSymB() && RHS_B))
159    return false;
160
161  const MCSymbol *A = LHS.getSymA() ? LHS.getSymA() : RHS_A;
162  const MCSymbol *B = LHS.getSymB() ? LHS.getSymB() : RHS_B;
163  if (B) {
164    // If we have a negated symbol, then we must have also have a non-negated
165    // symbol in order to encode the expression. We can do this check later to
166    // permit expressions which eventually fold to a representable form -- such
167    // as (a + (0 - b)) -- if necessary.
168    if (!A)
169      return false;
170  }
171  Res = MCValue::get(A, B, LHS.getConstant() + RHS_Cst);
172  return true;
173}
174
175bool MCExpr::EvaluateAsRelocatable(MCValue &Res) const {
176  switch (getKind()) {
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