Semantic analysis for C++ reinterpret_cast and const_cast. Patch by Sebastian Redl.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@58094 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaExprCXX.cpp b/lib/Sema/SemaExprCXX.cpp
index c206e1a..5c62a93 100644
--- a/lib/Sema/SemaExprCXX.cpp
+++ b/lib/Sema/SemaExprCXX.cpp
@@ -17,6 +17,8 @@
#include "clang/Parse/DeclSpec.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Basic/Diagnostic.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/Support/Debug.h"
using namespace clang;
/// ActOnCXXCasts - Parse {dynamic,static,reinterpret,const}_cast's.
@@ -27,22 +29,347 @@
SourceLocation LParenLoc, ExprTy *E,
SourceLocation RParenLoc) {
CXXCastExpr::Opcode Op;
+ Expr *Ex = (Expr*)E;
+ QualType DestType = QualType::getFromOpaquePtr(Ty);
switch (Kind) {
default: assert(0 && "Unknown C++ cast!");
- case tok::kw_const_cast: Op = CXXCastExpr::ConstCast; break;
- case tok::kw_dynamic_cast: Op = CXXCastExpr::DynamicCast; break;
- case tok::kw_reinterpret_cast: Op = CXXCastExpr::ReinterpretCast; break;
- case tok::kw_static_cast: Op = CXXCastExpr::StaticCast; break;
+ case tok::kw_const_cast:
+ Op = CXXCastExpr::ConstCast;
+ CheckConstCast(OpLoc, Ex, DestType);
+ break;
+ case tok::kw_dynamic_cast:
+ Op = CXXCastExpr::DynamicCast;
+ break;
+ case tok::kw_reinterpret_cast:
+ Op = CXXCastExpr::ReinterpretCast;
+ CheckReinterpretCast(OpLoc, Ex, DestType);
+ break;
+ case tok::kw_static_cast:
+ Op = CXXCastExpr::StaticCast;
+ break;
}
- return new CXXCastExpr(Op, QualType::getFromOpaquePtr(Ty), (Expr*)E, OpLoc);
+ return new CXXCastExpr(Op, DestType, Ex, OpLoc);
+}
+
+/// CheckConstCast - Check that a const_cast\<DestType\>(SrcExpr) is valid.
+/// Refer to C++ 5.2.11 for details. const_cast is typically used in code
+/// like this:
+/// const char *str = "literal";
+/// legacy_function(const_cast\<char*\>(str));
+void
+Sema::CheckConstCast(SourceLocation OpLoc, Expr *&SrcExpr, QualType DestType)
+{
+ QualType OrigDestType = DestType, OrigSrcType = SrcExpr->getType();
+
+ DestType = Context.getCanonicalType(DestType);
+ QualType SrcType = SrcExpr->getType();
+ if (const ReferenceType *DestTypeTmp = DestType->getAsReferenceType()) {
+ if (SrcExpr->isLvalue(Context) != Expr::LV_Valid) {
+ // Cannot cast non-lvalue to reference type.
+ Diag(OpLoc, diag::err_bad_cxx_cast_rvalue,
+ "const_cast", OrigDestType.getAsString());
+ return;
+ }
+
+ // C++ 5.2.11p4: An lvalue of type T1 can be [cast] to an lvalue of type T2
+ // [...] if a pointer to T1 can be [cast] to the type pointer to T2.
+ DestType = Context.getPointerType(DestTypeTmp->getPointeeType());
+ if (const ReferenceType *SrcTypeTmp = SrcType->getAsReferenceType()) {
+ // FIXME: This shouldn't actually be possible, but right now it is.
+ SrcType = SrcTypeTmp->getPointeeType();
+ }
+ SrcType = Context.getPointerType(SrcType);
+ } else {
+ // C++ 5.2.11p1: Otherwise, the result is an rvalue and the
+ // lvalue-to-rvalue, array-to-pointer, and function-to-pointer standard
+ // conversions are performed on the expression.
+ DefaultFunctionArrayConversion(SrcExpr);
+ SrcType = SrcExpr->getType();
+ }
+
+ if (!DestType->isPointerType()) {
+ // Cannot cast to non-pointer, non-reference type. Note that, if DestType
+ // was a reference type, we converted it to a pointer above.
+ // C++ 5.2.11p3: For two pointer types [...]
+ Diag(OpLoc, diag::err_bad_const_cast_dest, OrigDestType.getAsString());
+ return;
+ }
+ if (DestType->isFunctionPointerType()) {
+ // Cannot cast direct function pointers.
+ // C++ 5.2.11p2: [...] where T is any object type or the void type [...]
+ // T is the ultimate pointee of source and target type.
+ Diag(OpLoc, diag::err_bad_const_cast_dest, OrigDestType.getAsString());
+ return;
+ }
+ SrcType = Context.getCanonicalType(SrcType);
+
+ // Unwrap the pointers. Ignore qualifiers. Terminate early if the types are
+ // completely equal.
+ // FIXME: const_cast should probably not be able to convert between pointers
+ // to different address spaces.
+ // C++ 5.2.11p3 describes the core semantics of const_cast. All cv specifiers
+ // in multi-level pointers may change, but the level count must be the same,
+ // as must be the final pointee type.
+ while (SrcType != DestType && UnwrapSimilarPointerTypes(SrcType, DestType)) {
+ SrcType = SrcType.getUnqualifiedType();
+ DestType = DestType.getUnqualifiedType();
+ }
+
+ // Doug Gregor said to disallow this until users complain.
+#if 0
+ // If we end up with constant arrays of equal size, unwrap those too. A cast
+ // from const int [N] to int (&)[N] is invalid by my reading of the
+ // standard, but g++ accepts it even with -ansi -pedantic.
+ // No more than one level, though, so don't embed this in the unwrap loop
+ // above.
+ const ConstantArrayType *SrcTypeArr, *DestTypeArr;
+ if ((SrcTypeArr = Context.getAsConstantArrayType(SrcType)) &&
+ (DestTypeArr = Context.getAsConstantArrayType(DestType)))
+ {
+ if (SrcTypeArr->getSize() != DestTypeArr->getSize()) {
+ // Different array sizes.
+ Diag(OpLoc, diag::err_bad_cxx_cast_generic, "const_cast",
+ OrigDestType.getAsString(), OrigSrcType.getAsString());
+ return;
+ }
+ SrcType = SrcTypeArr->getElementType().getUnqualifiedType();
+ DestType = DestTypeArr->getElementType().getUnqualifiedType();
+ }
+#endif
+
+ // Since we're dealing in canonical types, the remainder must be the same.
+ if (SrcType != DestType) {
+ // Cast between unrelated types.
+ Diag(OpLoc, diag::err_bad_cxx_cast_generic, "const_cast",
+ OrigDestType.getAsString(), OrigSrcType.getAsString());
+ return;
+ }
+}
+
+/// CheckReinterpretCast - Check that a reinterpret_cast\<DestType\>(SrcExpr) is
+/// valid.
+/// Refer to C++ 5.2.10 for details. reinterpret_cast is typically used in code
+/// like this:
+/// char *bytes = reinterpret_cast\<char*\>(int_ptr);
+void
+Sema::CheckReinterpretCast(SourceLocation OpLoc, Expr *&SrcExpr,
+ QualType DestType)
+{
+ QualType OrigDestType = DestType, OrigSrcType = SrcExpr->getType();
+
+ DestType = Context.getCanonicalType(DestType);
+ QualType SrcType = SrcExpr->getType();
+ if (const ReferenceType *DestTypeTmp = DestType->getAsReferenceType()) {
+ if (SrcExpr->isLvalue(Context) != Expr::LV_Valid) {
+ // Cannot cast non-lvalue to reference type.
+ Diag(OpLoc, diag::err_bad_cxx_cast_rvalue,
+ "reinterpret_cast", OrigDestType.getAsString());
+ return;
+ }
+
+ // C++ 5.2.10p10: [...] a reference cast reinterpret_cast<T&>(x) has the
+ // same effect as the conversion *reinterpret_cast<T*>(&x) with the
+ // built-in & and * operators.
+ // This code does this transformation for the checked types.
+ DestType = Context.getPointerType(DestTypeTmp->getPointeeType());
+ if (const ReferenceType *SrcTypeTmp = SrcType->getAsReferenceType()) {
+ // FIXME: This shouldn't actually be possible, but right now it is.
+ SrcType = SrcTypeTmp->getPointeeType();
+ }
+ SrcType = Context.getPointerType(SrcType);
+ } else {
+ // C++ 5.2.10p1: [...] the lvalue-to-rvalue, array-to-pointer, and
+ // function-to-pointer standard conversions are performed on the
+ // expression v.
+ DefaultFunctionArrayConversion(SrcExpr);
+ SrcType = SrcExpr->getType();
+ }
+
+ // Canonicalize source for comparison.
+ SrcType = Context.getCanonicalType(SrcType);
+
+ bool destIsPtr = DestType->isPointerType();
+ bool srcIsPtr = SrcType->isPointerType();
+ if (!destIsPtr && !srcIsPtr) {
+ // Except for std::nullptr_t->integer, which is not supported yet, and
+ // lvalue->reference, which is handled above, at least one of the two
+ // arguments must be a pointer.
+ Diag(OpLoc, diag::err_bad_cxx_cast_generic, "reinterpret_cast",
+ OrigDestType.getAsString(), OrigSrcType.getAsString());
+ return;
+ }
+
+ if (SrcType == DestType) {
+ // C++ 5.2.10p2 has a note that mentions that, subject to all other
+ // restrictions, a cast to the same type is allowed. The intent is not
+ // entirely clear here, since all other paragraphs explicitly forbid casts
+ // to the same type. However, the behavior of compilers is pretty consistent
+ // on this point: allow same-type conversion if the involved are pointers,
+ // disallow otherwise.
+ return;
+ }
+
+ // Note: Clang treats enumeration types as integral types. If this is ever
+ // changed for C++, the additional check here will be redundant.
+ if (DestType->isIntegralType() && !DestType->isEnumeralType()) {
+ assert(srcIsPtr);
+ // C++ 5.2.10p4: A pointer can be explicitly converted to any integral
+ // type large enough to hold it.
+ if (Context.getTypeSize(SrcType) > Context.getTypeSize(DestType)) {
+ Diag(OpLoc, diag::err_bad_reinterpret_cast_small_int,
+ OrigDestType.getAsString());
+ }
+ return;
+ }
+
+ if (SrcType->isIntegralType() || SrcType->isEnumeralType()) {
+ assert(destIsPtr);
+ // C++ 5.2.10p5: A value of integral or enumeration type can be explicitly
+ // converted to a pointer.
+ return;
+ }
+
+ if (!destIsPtr || !srcIsPtr) {
+ // With the valid non-pointer conversions out of the way, we can be even
+ // more stringent.
+ Diag(OpLoc, diag::err_bad_cxx_cast_generic, "reinterpret_cast",
+ OrigDestType.getAsString(), OrigSrcType.getAsString());
+ return;
+ }
+
+ // C++ 5.2.10p2: The reinterpret_cast operator shall not cast away constness.
+ if (CastsAwayConstness(SrcType, DestType)) {
+ Diag(OpLoc, diag::err_bad_cxx_cast_const_away, "reinterpret_cast",
+ OrigDestType.getAsString(), OrigSrcType.getAsString());
+ return;
+ }
+
+ // Not casting away constness, so the only remaining check is for compatible
+ // pointer categories.
+
+ if (SrcType->isFunctionPointerType()) {
+ if (DestType->isFunctionPointerType()) {
+ // C++ 5.2.10p6: A pointer to a function can be explicitly converted to
+ // a pointer to a function of a different type.
+ return;
+ }
+
+ // FIXME: Handle member pointers.
+
+ // C++0x 5.2.10p8: Converting a pointer to a function into a pointer to
+ // an object type or vice versa is conditionally-supported.
+ // Compilers support it in C++03 too, though, because it's necessary for
+ // casting the return value of dlsym() and GetProcAddress().
+ // FIXME: Conditionally-supported behavior should be configurable in the
+ // TargetInfo or similar.
+ if (!getLangOptions().CPlusPlus0x) {
+ Diag(OpLoc, diag::ext_reinterpret_cast_fn_obj);
+ }
+ return;
+ }
+
+ // FIXME: Handle member pointers.
+
+ if (DestType->isFunctionPointerType()) {
+ // See above.
+ if (!getLangOptions().CPlusPlus0x) {
+ Diag(OpLoc, diag::ext_reinterpret_cast_fn_obj);
+ }
+ return;
+ }
+
+ // C++ 5.2.10p7: A pointer to an object can be explicitly converted to
+ // a pointer to an object of different type.
+ // Void pointers are not specified, but supported by every compiler out there.
+ // So we finish by allowing everything that remains - it's got to be two
+ // object pointers.
+}
+
+/// Check if the pointer conversion from SrcType to DestType casts away
+/// constness as defined in C++ 5.2.11p8ff. This is used by the cast checkers.
+/// Both arguments must denote pointer types.
+bool
+Sema::CastsAwayConstness(QualType SrcType, QualType DestType)
+{
+ // Casting away constness is defined in C++ 5.2.11p8 with reference to
+ // C++ 4.4.
+ // We piggyback on Sema::IsQualificationConversion for this, since the rules
+ // are non-trivial. So first we construct Tcv *...cv* as described in
+ // C++ 5.2.11p8.
+ SrcType = Context.getCanonicalType(SrcType);
+ DestType = Context.getCanonicalType(DestType);
+
+ QualType UnwrappedSrcType = SrcType, UnwrappedDestType = DestType;
+ llvm::SmallVector<unsigned, 8> cv1, cv2;
+
+ // Find the qualifications.
+ while (UnwrapSimilarPointerTypes(UnwrappedSrcType, UnwrappedDestType)) {
+ cv1.push_back(UnwrappedSrcType.getCVRQualifiers());
+ cv2.push_back(UnwrappedDestType.getCVRQualifiers());
+ }
+ assert(cv1.size() > 0 && "Must have at least one pointer level.");
+
+ // Construct void pointers with those qualifiers (in reverse order of
+ // unwrapping, of course).
+ QualType SrcConstruct = Context.VoidTy;
+ QualType DestConstruct = Context.VoidTy;
+ for (llvm::SmallVector<unsigned, 8>::reverse_iterator i1 = cv1.rbegin(),
+ i2 = cv2.rbegin();
+ i1 != cv1.rend(); ++i1, ++i2)
+ {
+ SrcConstruct = Context.getPointerType(SrcConstruct.getQualifiedType(*i1));
+ DestConstruct = Context.getPointerType(DestConstruct.getQualifiedType(*i2));
+ }
+
+ // Test if they're compatible.
+ return SrcConstruct != DestConstruct &&
+ !IsQualificationConversion(SrcConstruct, DestConstruct);
+}
+
+/// CheckStaticCast - Check that a static_cast\<DestType\>(SrcExpr) is valid.
+void
+Sema::CheckStaticCast(SourceLocation OpLoc, Expr *&SrcExpr, QualType DestType)
+{
+#if 0
+ // 5.2.9/1 sets the ground rule of disallowing casting away constness.
+ // 5.2.9/2 permits everything allowed for direct-init, deferring to 8.5.
+ // Note: for class destination, that's overload resolution over dest's
+ // constructors. Src's conversions are only considered in overload choice.
+ // For any other destination, that's just the clause 4 standards convs.
+ // 5.2.9/4 permits static_cast<cv void>(anything), which is a no-op.
+ // 5.2.9/5 permits explicit non-dynamic downcasts for lvalue-to-reference.
+ // 5.2.9/6 permits reversing all implicit conversions except lvalue-to-rvalue,
+ // function-to-pointer, array decay and to-bool, with some further
+ // restrictions. Defers to 4.
+ // 5.2.9/7 permits integer-to-enum conversion. Interesting note: if the
+ // integer does not correspond to an enum value, the result is unspecified -
+ // but it still has to be some value of the enum. I don't think any compiler
+ // complies with that.
+ // 5.2.9/8 is 5.2.9/5 for pointers.
+ // 5.2.9/9 messes with member pointers. TODO. No need to think about that yet.
+ // 5.2.9/10 permits void* to T*.
+
+ QualType OrigDestType = DestType, OrigSrcType = SrcExpr->getType();
+ DestType = Context.getCanonicalType(DestType);
+ // Tests are ordered by simplicity and a wild guess at commonness.
+
+ if (const BuiltinType *BuiltinDest = DestType->getAsBuiltinType()) {
+ // 5.2.9/4
+ if (BuiltinDest->getKind() == BuiltinType::Void) {
+ return;
+ }
+
+ // Primitive conversions for 5.2.9/2 and 6.
+ }
+#endif
}
/// ActOnCXXBoolLiteral - Parse {true,false} literals.
Action::ExprResult
Sema::ActOnCXXBoolLiteral(SourceLocation OpLoc, tok::TokenKind Kind) {
- assert((Kind != tok::kw_true || Kind != tok::kw_false) &&
+ assert((Kind == tok::kw_true || Kind == tok::kw_false) &&
"Unknown C++ Boolean value!");
return new CXXBoolLiteralExpr(Kind == tok::kw_true, Context.BoolTy, OpLoc);
}