ExprClassification.cpp revision 016a4a90c8e75d59de731fa3aa98f0a55656e66c
1//===--- ExprClassification.cpp - Expression AST Node 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// This file implements Expr::classify. 11// 12//===----------------------------------------------------------------------===// 13 14#include "llvm/Support/ErrorHandling.h" 15#include "clang/AST/Expr.h" 16#include "clang/AST/ExprCXX.h" 17#include "clang/AST/ExprObjC.h" 18#include "clang/AST/ASTContext.h" 19#include "clang/AST/DeclObjC.h" 20#include "clang/AST/DeclCXX.h" 21#include "clang/AST/DeclTemplate.h" 22using namespace clang; 23 24typedef Expr::Classification Cl; 25 26static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E); 27static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D); 28static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T); 29static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E); 30static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E); 31static Cl::Kinds ClassifyConditional(ASTContext &Ctx, 32 const ConditionalOperator *E); 33static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E, 34 Cl::Kinds Kind, SourceLocation &Loc); 35 36Cl Expr::ClassifyImpl(ASTContext &Ctx, SourceLocation *Loc) const { 37 assert(!TR->isReferenceType() && "Expressions can't have reference type."); 38 39 Cl::Kinds kind = ClassifyInternal(Ctx, this); 40 // C99 6.3.2.1: An lvalue is an expression with an object type or an 41 // incomplete type other than void. 42 if (!Ctx.getLangOptions().CPlusPlus) { 43 // Thus, no functions. 44 if (TR->isFunctionType() || TR == Ctx.OverloadTy) 45 kind = Cl::CL_Function; 46 // No void either, but qualified void is OK because it is "other than void". 47 else if (TR->isVoidType() && !Ctx.getCanonicalType(TR).hasQualifiers()) 48 kind = Cl::CL_Void; 49 } 50 51 Cl::ModifiableType modifiable = Cl::CM_Untested; 52 if (Loc) 53 modifiable = IsModifiable(Ctx, this, kind, *Loc); 54 return Classification(kind, modifiable); 55} 56 57static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) { 58 // This function takes the first stab at classifying expressions. 59 const LangOptions &Lang = Ctx.getLangOptions(); 60 61 switch (E->getStmtClass()) { 62 // First come the expressions that are always lvalues, unconditionally. 63 64 case Expr::ObjCIsaExprClass: 65 // C++ [expr.prim.general]p1: A string literal is an lvalue. 66 case Expr::StringLiteralClass: 67 // @encode is equivalent to its string 68 case Expr::ObjCEncodeExprClass: 69 // __func__ and friends are too. 70 case Expr::PredefinedExprClass: 71 // Property references are lvalues 72 case Expr::ObjCPropertyRefExprClass: 73 case Expr::ObjCImplicitSetterGetterRefExprClass: 74 // C++ [expr.typeid]p1: The result of a typeid expression is an lvalue of... 75 case Expr::CXXTypeidExprClass: 76 // Unresolved lookups get classified as lvalues. 77 // FIXME: Is this wise? Should they get their own kind? 78 case Expr::UnresolvedLookupExprClass: 79 case Expr::UnresolvedMemberExprClass: 80 // ObjC instance variables are lvalues 81 // FIXME: ObjC++0x might have different rules 82 case Expr::ObjCIvarRefExprClass: 83 // C99 6.5.2.5p5 says that compound literals are lvalues. 84 // FIXME: C++ might have a different opinion. 85 case Expr::CompoundLiteralExprClass: 86 return Cl::CL_LValue; 87 88 // Next come the complicated cases. 89 90 // C++ [expr.sub]p1: The result is an lvalue of type "T". 91 // However, subscripting vector types is more like member access. 92 case Expr::ArraySubscriptExprClass: 93 if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType()) 94 return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase()); 95 return Cl::CL_LValue; 96 97 // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a 98 // function or variable and a prvalue otherwise. 99 case Expr::DeclRefExprClass: 100 return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl()); 101 // We deal with names referenced from blocks the same way. 102 case Expr::BlockDeclRefExprClass: 103 return ClassifyDecl(Ctx, cast<BlockDeclRefExpr>(E)->getDecl()); 104 105 // Member access is complex. 106 case Expr::MemberExprClass: 107 return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E)); 108 109 case Expr::UnaryOperatorClass: 110 switch (cast<UnaryOperator>(E)->getOpcode()) { 111 // C++ [expr.unary.op]p1: The unary * operator performs indirection: 112 // [...] the result is an lvalue referring to the object or function 113 // to which the expression points. 114 case UnaryOperator::Deref: 115 return Cl::CL_LValue; 116 117 // GNU extensions, simply look through them. 118 case UnaryOperator::Real: 119 case UnaryOperator::Imag: 120 case UnaryOperator::Extension: 121 return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr()); 122 123 // C++ [expr.pre.incr]p1: The result is the updated operand; it is an 124 // lvalue, [...] 125 // Not so in C. 126 case UnaryOperator::PreInc: 127 case UnaryOperator::PreDec: 128 return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue; 129 130 default: 131 return Cl::CL_PRValue; 132 } 133 134 // Implicit casts are lvalues if they're lvalue casts. Other than that, we 135 // only specifically record class temporaries. 136 case Expr::ImplicitCastExprClass: 137 if (cast<ImplicitCastExpr>(E)->isLvalueCast()) 138 return Cl::CL_LValue; 139 return Lang.CPlusPlus && E->getType()->isRecordType() ? 140 Cl::CL_ClassTemporary : Cl::CL_PRValue; 141 142 // C++ [expr.prim.general]p4: The presence of parentheses does not affect 143 // whether the expression is an lvalue. 144 case Expr::ParenExprClass: 145 return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr()); 146 147 case Expr::BinaryOperatorClass: 148 case Expr::CompoundAssignOperatorClass: 149 // C doesn't have any binary expressions that are lvalues. 150 if (Lang.CPlusPlus) 151 return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E)); 152 return Cl::CL_PRValue; 153 154 case Expr::CallExprClass: 155 case Expr::CXXOperatorCallExprClass: 156 case Expr::CXXMemberCallExprClass: 157 return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType()); 158 159 // __builtin_choose_expr is equivalent to the chosen expression. 160 case Expr::ChooseExprClass: 161 return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr(Ctx)); 162 163 // Extended vector element access is an lvalue unless there are duplicates 164 // in the shuffle expression. 165 case Expr::ExtVectorElementExprClass: 166 return cast<ExtVectorElementExpr>(E)->containsDuplicateElements() ? 167 Cl::CL_DuplicateVectorComponents : Cl::CL_LValue; 168 169 // Simply look at the actual default argument. 170 case Expr::CXXDefaultArgExprClass: 171 return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr()); 172 173 // Same idea for temporary binding. 174 case Expr::CXXBindTemporaryExprClass: 175 return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr()); 176 177 // And the temporary lifetime guard. 178 case Expr::CXXExprWithTemporariesClass: 179 return ClassifyInternal(Ctx, cast<CXXExprWithTemporaries>(E)->getSubExpr()); 180 181 // Casts depend completely on the target type. All casts work the same. 182 case Expr::CStyleCastExprClass: 183 case Expr::CXXFunctionalCastExprClass: 184 case Expr::CXXStaticCastExprClass: 185 case Expr::CXXDynamicCastExprClass: 186 case Expr::CXXReinterpretCastExprClass: 187 case Expr::CXXConstCastExprClass: 188 // Only in C++ can casts be interesting at all. 189 if (!Lang.CPlusPlus) return Cl::CL_PRValue; 190 return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten()); 191 192 case Expr::ConditionalOperatorClass: 193 // Once again, only C++ is interesting. 194 if (!Lang.CPlusPlus) return Cl::CL_PRValue; 195 return ClassifyConditional(Ctx, cast<ConditionalOperator>(E)); 196 197 // ObjC message sends are effectively function calls, if the target function 198 // is known. 199 case Expr::ObjCMessageExprClass: 200 if (const ObjCMethodDecl *Method = 201 cast<ObjCMessageExpr>(E)->getMethodDecl()) { 202 return ClassifyUnnamed(Ctx, Method->getResultType()); 203 } 204 205 // Some C++ expressions are always class temporaries. 206 case Expr::CXXConstructExprClass: 207 case Expr::CXXTemporaryObjectExprClass: 208 case Expr::CXXScalarValueInitExprClass: 209 return Cl::CL_ClassTemporary; 210 211 // Everything we haven't handled is a prvalue. 212 default: 213 return Cl::CL_PRValue; 214 } 215} 216 217/// ClassifyDecl - Return the classification of an expression referencing the 218/// given declaration. 219static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) { 220 // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a 221 // function, variable, or data member and a prvalue otherwise. 222 // In C, functions are not lvalues. 223 // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an 224 // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to 225 // special-case this. 226 bool islvalue; 227 if (const NonTypeTemplateParmDecl *NTTParm = 228 dyn_cast<NonTypeTemplateParmDecl>(D)) 229 islvalue = NTTParm->getType()->isReferenceType(); 230 else 231 islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) || 232 (Ctx.getLangOptions().CPlusPlus && 233 (isa<FunctionDecl>(D) || isa<FunctionTemplateDecl>(D))); 234 235 return islvalue ? Cl::CL_LValue : Cl::CL_PRValue; 236} 237 238/// ClassifyUnnamed - Return the classification of an expression yielding an 239/// unnamed value of the given type. This applies in particular to function 240/// calls and casts. 241static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) { 242 // In C, function calls are always rvalues. 243 if (!Ctx.getLangOptions().CPlusPlus) return Cl::CL_PRValue; 244 245 // C++ [expr.call]p10: A function call is an lvalue if the result type is an 246 // lvalue reference type or an rvalue reference to function type, an xvalue 247 // if the result type is an rvalue refernence to object type, and a prvalue 248 // otherwise. 249 if (T->isLValueReferenceType()) 250 return Cl::CL_LValue; 251 const RValueReferenceType *RV = T->getAs<RValueReferenceType>(); 252 if (!RV) // Could still be a class temporary, though. 253 return T->isRecordType() ? Cl::CL_ClassTemporary : Cl::CL_PRValue; 254 255 return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue; 256} 257 258static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) { 259 // Handle C first, it's easier. 260 if (!Ctx.getLangOptions().CPlusPlus) { 261 // C99 6.5.2.3p3 262 // For dot access, the expression is an lvalue if the first part is. For 263 // arrow access, it always is an lvalue. 264 if (E->isArrow()) 265 return Cl::CL_LValue; 266 // ObjC property accesses are not lvalues, but get special treatment. 267 Expr *Base = E->getBase(); 268 if (isa<ObjCPropertyRefExpr>(Base) || 269 isa<ObjCImplicitSetterGetterRefExpr>(Base)) 270 return Cl::CL_SubObjCPropertySetting; 271 return ClassifyInternal(Ctx, Base); 272 } 273 274 NamedDecl *Member = E->getMemberDecl(); 275 // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2. 276 // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then 277 // E1.E2 is an lvalue. 278 if (ValueDecl *Value = dyn_cast<ValueDecl>(Member)) 279 if (Value->getType()->isReferenceType()) 280 return Cl::CL_LValue; 281 282 // Otherwise, one of the following rules applies. 283 // -- If E2 is a static member [...] then E1.E2 is an lvalue. 284 if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord()) 285 return Cl::CL_LValue; 286 287 // -- If E2 is a non-static data member [...]. If E1 is an lvalue, then 288 // E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue; 289 // otherwise, it is a prvalue. 290 if (isa<FieldDecl>(Member)) { 291 // *E1 is an lvalue 292 if (E->isArrow()) 293 return Cl::CL_LValue; 294 return ClassifyInternal(Ctx, E->getBase()); 295 } 296 297 // -- If E2 is a [...] member function, [...] 298 // -- If it refers to a static member function [...], then E1.E2 is an 299 // lvalue; [...] 300 // -- Otherwise [...] E1.E2 is a prvalue. 301 if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Member)) 302 return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction; 303 304 // -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue. 305 // So is everything else we haven't handled yet. 306 return Cl::CL_PRValue; 307} 308 309static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E) { 310 assert(Ctx.getLangOptions().CPlusPlus && 311 "This is only relevant for C++."); 312 // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand. 313 if (E->isAssignmentOp()) 314 return Cl::CL_LValue; 315 316 // C++ [expr.comma]p1: the result is of the same value category as its right 317 // operand, [...]. 318 if (E->getOpcode() == BinaryOperator::Comma) 319 return ClassifyInternal(Ctx, E->getRHS()); 320 321 // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand 322 // is a pointer to a data member is of the same value category as its first 323 // operand. 324 if (E->getOpcode() == BinaryOperator::PtrMemD) 325 return E->getType()->isFunctionType() ? Cl::CL_MemberFunction : 326 ClassifyInternal(Ctx, E->getLHS()); 327 328 // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its 329 // second operand is a pointer to data member and a prvalue otherwise. 330 if (E->getOpcode() == BinaryOperator::PtrMemI) 331 return E->getType()->isFunctionType() ? 332 Cl::CL_MemberFunction : Cl::CL_LValue; 333 334 // All other binary operations are prvalues. 335 return Cl::CL_PRValue; 336} 337 338static Cl::Kinds ClassifyConditional(ASTContext &Ctx, 339 const ConditionalOperator *E) { 340 assert(Ctx.getLangOptions().CPlusPlus && 341 "This is only relevant for C++."); 342 343 Expr *True = E->getTrueExpr(); 344 Expr *False = E->getFalseExpr(); 345 // C++ [expr.cond]p2 346 // If either the second or the third operand has type (cv) void, [...] 347 // the result [...] is a prvalue. 348 if (True->getType()->isVoidType() || False->getType()->isVoidType()) 349 return Cl::CL_PRValue; 350 351 // Note that at this point, we have already performed all conversions 352 // according to [expr.cond]p3. 353 // C++ [expr.cond]p4: If the second and third operands are glvalues of the 354 // same value category [...], the result is of that [...] value category. 355 // C++ [expr.cond]p5: Otherwise, the result is a prvalue. 356 Cl::Kinds LCl = ClassifyInternal(Ctx, True), 357 RCl = ClassifyInternal(Ctx, False); 358 return LCl == RCl ? LCl : Cl::CL_PRValue; 359} 360 361static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E, 362 Cl::Kinds Kind, SourceLocation &Loc) { 363 // As a general rule, we only care about lvalues. But there are some rvalues 364 // for which we want to generate special results. 365 if (Kind == Cl::CL_PRValue) { 366 // For the sake of better diagnostics, we want to specifically recognize 367 // use of the GCC cast-as-lvalue extension. 368 if (const CStyleCastExpr *CE = dyn_cast<CStyleCastExpr>(E->IgnoreParens())){ 369 if (CE->getSubExpr()->Classify(Ctx).isLValue()) { 370 Loc = CE->getLParenLoc(); 371 return Cl::CM_LValueCast; 372 } 373 } 374 } 375 if (Kind != Cl::CL_LValue) 376 return Cl::CM_RValue; 377 378 // This is the lvalue case. 379 // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6) 380 if (Ctx.getLangOptions().CPlusPlus && E->getType()->isFunctionType()) 381 return Cl::CM_Function; 382 383 // You cannot assign to a variable outside a block from within the block if 384 // it is not marked __block, e.g. 385 // void takeclosure(void (^C)(void)); 386 // void func() { int x = 1; takeclosure(^{ x = 7; }); } 387 if (const BlockDeclRefExpr *BDR = dyn_cast<BlockDeclRefExpr>(E)) { 388 if (!BDR->isByRef() && isa<VarDecl>(BDR->getDecl())) 389 return Cl::CM_NotBlockQualified; 390 } 391 392 // Assignment to a property in ObjC is an implicit setter access. But a 393 // setter might not exist. 394 if (const ObjCImplicitSetterGetterRefExpr *Expr = 395 dyn_cast<ObjCImplicitSetterGetterRefExpr>(E)) { 396 if (Expr->getSetterMethod() == 0) 397 return Cl::CM_NoSetterProperty; 398 } 399 400 CanQualType CT = Ctx.getCanonicalType(E->getType()); 401 // Const stuff is obviously not modifiable. 402 if (CT.isConstQualified()) 403 return Cl::CM_ConstQualified; 404 // Arrays are not modifiable, only their elements are. 405 if (CT->isArrayType()) 406 return Cl::CM_ArrayType; 407 // Incomplete types are not modifiable. 408 if (CT->isIncompleteType()) 409 return Cl::CM_IncompleteType; 410 411 // Records with any const fields (recursively) are not modifiable. 412 if (const RecordType *R = CT->getAs<RecordType>()) { 413 assert(!Ctx.getLangOptions().CPlusPlus && 414 "C++ struct assignment should be resolved by the " 415 "copy assignment operator."); 416 if (R->hasConstFields()) 417 return Cl::CM_ConstQualified; 418 } 419 420 return Cl::CM_Modifiable; 421} 422 423Expr::isLvalueResult Expr::isLvalue(ASTContext &Ctx) const { 424 Classification VC = Classify(Ctx); 425 switch (VC.getKind()) { 426 case Cl::CL_LValue: return LV_Valid; 427 case Cl::CL_XValue: return LV_InvalidExpression; 428 case Cl::CL_Function: return LV_NotObjectType; 429 case Cl::CL_Void: return LV_IncompleteVoidType; 430 case Cl::CL_DuplicateVectorComponents: return LV_DuplicateVectorComponents; 431 case Cl::CL_MemberFunction: return LV_MemberFunction; 432 case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting; 433 case Cl::CL_ClassTemporary: return LV_ClassTemporary; 434 case Cl::CL_PRValue: return LV_InvalidExpression; 435 } 436 llvm_unreachable("Unhandled kind"); 437} 438 439Expr::isModifiableLvalueResult 440Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const { 441 SourceLocation dummy; 442 Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy); 443 switch (VC.getKind()) { 444 case Cl::CL_LValue: break; 445 case Cl::CL_XValue: return MLV_InvalidExpression; 446 case Cl::CL_Function: return MLV_NotObjectType; 447 case Cl::CL_Void: return MLV_IncompleteVoidType; 448 case Cl::CL_DuplicateVectorComponents: return MLV_DuplicateVectorComponents; 449 case Cl::CL_MemberFunction: return MLV_MemberFunction; 450 case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting; 451 case Cl::CL_ClassTemporary: return MLV_ClassTemporary; 452 case Cl::CL_PRValue: 453 return VC.getModifiable() == Cl::CM_LValueCast ? 454 MLV_LValueCast : MLV_InvalidExpression; 455 } 456 assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind"); 457 switch (VC.getModifiable()) { 458 case Cl::CM_Untested: llvm_unreachable("Did not test modifiability"); 459 case Cl::CM_Modifiable: return MLV_Valid; 460 case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match"); 461 case Cl::CM_Function: return MLV_NotObjectType; 462 case Cl::CM_LValueCast: 463 llvm_unreachable("CM_LValueCast and CL_LValue don't match"); 464 case Cl::CM_NotBlockQualified: return MLV_NotBlockQualified; 465 case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty; 466 case Cl::CM_ConstQualified: return MLV_ConstQualified; 467 case Cl::CM_ArrayType: return MLV_ArrayType; 468 case Cl::CM_IncompleteType: return MLV_IncompleteType; 469 } 470 llvm_unreachable("Unhandled modifiable type"); 471} 472