Document Number: WG14 N824/X3J11 98-023 WG14/N824 C9X Public Comment WG14/N824 ================== Sponsoring National Body: J11 Date: 98/05/15 Author: Tom MacDonald Author Affiliation: Silicon Graphics Inc. Postal Address: 655F Lone Oak Drive, Eagan, MN 55409 USA E-mail Address: tam@cray.com Telephone Number: +1 612 6835818 Fax Number: +1 612 6835307 Number of individual comments: 2 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% %% %% Improved Words for Function Inlining %% %% %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 6.5 Declarations Syntax [#1] declaration: declaration-specifiers init-declarator-list-opt ; declaration-specifiers: storage-class-specifier declaration-specifiers-opt type-specifier declaration-specifiers-opt type-qualifier declaration-specifiers-opt function-specifiers ^^^^^^^^^^^^^^^^^^^ function-specifier declaration-specifiers-opt =================================================================== 6.5.4 Function specifiers Syntax [#1] function-specifier: inline Constraints [#2] Function specifiers shall be used only in the declaration of an identifier for a function. [#3] An inline definition (see below) of a function with external linkage shall not contain a definition of an object with static storage duration that can be modified, and shall not contain a reference to an identifier with internal linkage. [#4] The inline function specifier shall not appear in a declaration of main. Semantics [#5] A function declared with an inline function specifier is an inline function. Making a function an inline function suggests that calls to the function be as fast as possible by using, for example, an alternative to the usual function call mechanism known as ``inline substitution''.101 The extent to which such suggestions are effective is implementation-defined.102 [#6] Any function with internal linkage can be an inline function. For a function with external linkage, the following restrictions apply. If a function is declared with an inline function specifier, then it shall also be defined in the same translation unit. If all of the file scope declarations for a function in a translation unit include the inline function specifier without extern, then the definition in that translation unit is an inline definition. An inline definition does not provide an external definition for the function, and does not forbid an external definition in another translation unit. An inline definition provides an alternative to an external definition, which a translator may use to implement any call to the function in the same translation unit. It is unspecified whether a call to the function uses the inline definition or the external definition. ^ ** add a footnote here 101. Inline substitution is not textual substitution, nor does it create a new function. Therefore, for example, the expansion of a macro used within the body of the ** Since an inline definition of a function is distinct from the corresponding external definition, and any other corresponding inline definition in another translation unit, all corresponding objects with static storage duration are also distinct in each of these definitions. =============================================================== The ** footnote clarifies a point made by Hugh Redelmeier in an Email he sent last March. The intent of the current proposal is that an "inline definition of function with external linkage" is distinct from the "external definition of the function". The implementation is at liberty to choose which one it wants to call, but it's calling a different definition of the function. Thus, an static objects inside the function (that cannot be be modified) are distinct, and do not share the same memory as the corresponding static object in either the external definition or a different inline function in another TU. From: "D. Hugh Redelmeier" Date: Fri, 27 Mar 1998 13:55:51 -0500 To: Thomas MacDonald cc: Standard C Subject: Re: (SC22WG14.5346) static objects in inline functions I now see how this is supposed to work, but I don't think that the words achieve this. | The Draft says the following about string literals: | | These arrays need not be distinct provided their | elements have the appropriate values. I guess that the required words are sort of the opposite: implementations are allowed to collapse distinct instances of strings, but are allowed to create multiple instances of the same static in an inline function. I suggest words something like: Each invocation of an inline function may or may not have distinct instances of its static objects. Without these words or something like them, I don't see that the standard allows an implementation to instantiate these statics multiple times. By "its static objects" I meant function statics and string literals -- does this need to be spelled out?