Although many GCC extensions are supported, some are not. In particular,
+ the following extensions are known to not be supported:
+
+ - Local Labels: Labels local to a block.
+
- Labels as Values: Getting pointers to labels, and computed gotos.
+
- Nested Functions: As in Algol and Pascal, lexical scoping of functions.
+
- Constructing Calls: Dispatching a call to another function.
+
- Extended Asm: Assembler instructions with C expressions as operands.
+
- Constraints: Constraints for asm operands
+
- Asm Labels: Specifying the assembler name to use for a C symbol.
+
- Explicit Reg Vars: Defining variables residing in specified registers.
+
- Return Address: Getting the return or frame address of a function.
+
- Vector Extensions: Using vector instructions through built-in functions.
+
- Target Builtins: Built-in functions specific to particular targets.
+
- Thread-Local: Per-thread variables.
+
- Pragmas: Pragmas accepted by GCC.
+
+
+ The following GCC extensions are partially supported. An ignored
+ attribute means that the LLVM compiler ignores the presence of the attribute,
+ but the code should still work. An unsupported attribute is one which is
+ ignored by the LLVM compiler, which will cause a different interpretation of
+ the program.
+
+
+ - Variable Length:
+ Arrays whose length is computed at run time.
+ Supported, but allocated stack space is not freed until the function returns (noted above).
+
+ - Function Attributes:
+ Declaring that functions have no side effects, or that they can never return.
+ Supported: format, format_arg, non_null, constructor, destructor, unused, deprecated,
+ warn_unused_result, weak
+ Ignored: noreturn, noinline, always_inline, pure, const, nothrow, malloc
+ no_instrument_function, cdecl
+ Unsupported: used, section, alias, visibility, regparm, stdcall,
+ fastcall, all other target specific attributes
+
+ - Variable Attributes:
+ Specifying attributes of variables.
+ Supported: cleanup, common, nocommon,
+ deprecated, transparent_union,
+ unused, weak
+ Unsupported: aligned, mode, packed,
+ section, shared, tls_model,
+ vector_size, dllimport,
+ dllexport, all target specific attributes.
+
+ - Type Attributes: Specifying attributes of types.
+ Supported: transparent_union, unused,
+ deprecated, may_alias
+ Unsupported: aligned, packed
+ all target specific attributes.
+ - Other Builtins:
+ Other built-in functions.
+ We support all builtins which have a C language equivalent (e.g.,
+ __builtin_cos), __builtin_alloca,
+ __builtin_types_compatible_p, __builtin_choose_expr,
+ __builtin_constant_p, and __builtin_expect (ignored).
+
+
+
+ The following extensions are known to be supported:
+
+ - Statement Exprs: Putting statements and declarations inside expressions.
+
- Typeof:
typeof: referring to the type of an expression.
+ - Lvalues: Using
?:, , and casts in lvalues.
+ - Conditionals: Omitting the middle operand of a
?: expression.
+ - Long Long: Double-word integers.
+
- Complex: Data types for complex numbers.
+
- Hex Floats:Hexadecimal floating-point constants.
+
- Zero Length: Zero-length arrays.
+
- Empty Structures: Structures with no members.
+
- Variadic Macros: Macros with a variable number of arguments.
+
- Escaped Newlines: Slightly looser rules for escaped newlines.
+
- Subscripting: Any array can be subscripted, even if not an lvalue.
+
- Pointer Arith:Arithmetic on
void-pointers and function pointers.
+ - Initializers: Non-constant initializers.
+
- Compound Literals: Compound literals give structures, unions or arrays as values.
+
- Designated Inits: Labeling elements of initializers.
+
+
- Cast to Union:Casting to union type from any member of the union.
+
- Case Ranges: `case 1 ... 9' and such.
+
- Mixed Declarations: Mixing declarations and code.
+
+
- Function Prototypes: Prototype declarations and old-style definitions.
+
- C++ Comments: C++ comments are recognized.
+
- Dollar Signs: Dollar sign is allowed in identifiers.
+
- Character Escapes:
\e stands for the character <ESC>.
+ - Alignment: Inquiring about the alignment of a type or variable.
+
- Inline: Defining inline functions (as fast as macros).
+
- Alternate Keywords:
__const__, __asm__, etc., for header files.
+ - Incomplete Enums:
enum foo;, with details to follow.
+ - Function Names: Printable strings which are the name of the current function.
+
- Unnamed Fields: Unnamed struct/union fields within structs/unions.
+
- Attribute Syntax: Formal syntax for attributes.
+
+
+ If you run into GCC extensions which have not been included in any of these
+ lists, please let us know (also including whether or not they work).
+
+
+
+