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C99 inline semantics for GCC
- From: gkeating at apple dot com (Geoffrey Keating)
- To: gcc-patches at gcc dot gnu dot org
- Date: Tue, 9 May 2006 01:18:47 -0700 (PDT)
- Subject: C99 inline semantics for GCC
This patch makes GCC's inline implementation, in C99 mode, closer to
what C99 specifies. It implements section 6.7.4 paragraph 6.
On hold for 4.3.
--
- Geoffrey Keating <geoffk@apple.com>
===File ~/patches/gcc-c99inline.patch=======================
Index: ChangeLog
2006-05-09 Geoffrey Keating <geoffk@apple.com>
PR 16622
* doc/extend.texi (Inline): Update.
* c-tree.h (struct language_function): Remove field 'extern_inline'.
* c-decl.c (current_extern_inline): Delete.
(pop_scope): Adjust test for an undefined nested function.
Add warning about undeclared inline function.
(diagnose_mismatched_decls): Update comments. Disallow overriding
of inline functions in a translation unit in C99. Allow inline
declarations in C99 at any time.
(merge_decls): Boolize variables. Handle C99 'extern inline'
semantics.
(grokdeclarator): Set DECL_EXTERNAL here for functions. Handle
C99 inline semantics.
(start_function): Don't clear current_extern_inline. Don't set
DECL_EXTERNAL.
(c_push_function_context): Don't push current_extern_inline.
(c_pop_function_context): Don't restore current_extern_inline.
Index: testsuite/ChangeLog
2006-05-09 Geoffrey Keating <geoffk@apple.com>
PR 16622
* gcc.dg/inline-10.c (main): Don't declare 'main' inline without
defining it.
* gcc.dg/inline-13.c: New.
* gcc.dg/inline-14.c: New.
* gcc.dg/inline-15.c: New.
Index: testsuite/gcc.dg/inline-15.c
===================================================================
--- testsuite/gcc.dg/inline-15.c (revision 0)
+++ testsuite/gcc.dg/inline-15.c (revision 0)
@@ -0,0 +1,7 @@
+/* Check that an error message is produced when a C99 inline function
+ is never defined. */
+/* { dg-do compile } */
+/* { dg-options "-std=c99" } */
+
+extern inline int func1 (void); /* { dg-error "never defined" } */
+inline int func2 (void); /* { dg-error "never defined" } */
Index: testsuite/gcc.dg/inline-10.c
===================================================================
--- testsuite/gcc.dg/inline-10.c (revision 113941)
+++ testsuite/gcc.dg/inline-10.c (working copy)
@@ -3,4 +3,4 @@
/* { dg-do compile } */
/* { dg-options "-std=gnu99 -ffreestanding -pedantic-errors" } */
-inline int main (void);
+inline int main (void) { return 1; }
Index: testsuite/gcc.dg/inline-14.c
===================================================================
--- testsuite/gcc.dg/inline-14.c (revision 0)
+++ testsuite/gcc.dg/inline-14.c (revision 0)
@@ -0,0 +1,23 @@
+/* Check that you can't redefine a C99 inline function. */
+/* { dg-do compile } */
+/* { dg-options "-std=c99" } */
+
+extern inline int func1 (void)
+{ /* { dg-error "previous definition" } */
+ return 1;
+}
+
+inline int func1 (void)
+{ /* { dg-error "redefinition" } */
+ return 1;
+}
+
+inline int func2 (void)
+{ /* { dg-error "previous definition" } */
+ return 2;
+}
+
+inline int func2 (void)
+{ /* { dg-error "redefinition" } */
+ return 2;
+}
Index: testsuite/gcc.dg/inline-13.c
===================================================================
--- testsuite/gcc.dg/inline-13.c (revision 0)
+++ testsuite/gcc.dg/inline-13.c (revision 0)
@@ -0,0 +1,56 @@
+/* Verify basic C99 inline functionality. */
+/* { dg-do compile } */
+/* { dg-options "-std=c99" } */
+/* { dg-final { scan-assembler-not "dontgenerate" } } */
+/* { dg-final { scan-assembler "func1" } } */
+/* { dg-final { scan-assembler "func2" } } */
+/* { dg-final { scan-assembler "func3" } } */
+/* { dg-final { scan-assembler "func4" } } */
+/* { dg-final { scan-assembler "func5" } } */
+/* { dg-final { scan-assembler "func6" } } */
+/* { dg-final { scan-assembler "func7" } } */
+/* { dg-final { scan-assembler "func8" } } */
+/* { dg-final { scan-assembler "func9" } } */
+
+inline int dontgenerate1 (void)
+{
+ return 1;
+}
+
+inline int dontgenerate2 (void);
+inline int dontgenerate2 (void)
+{
+ return 2;
+}
+
+inline int dontgenerate3 (void)
+{
+ return 3;
+}
+inline int dontgenerate3 (void);
+
+extern inline int func1 (void) { return 1; }
+
+extern inline int func2 (void);
+inline int func2 (void) { return 2; }
+
+inline int func3 (void) { return 3; }
+extern inline int func3 (void);
+
+inline int func4 (void);
+extern inline int func4 (void) { return 4; }
+
+extern inline int func5 (void) { return 5; }
+inline int func5 (void);
+
+extern int func6 (void);
+inline int func6 (void) { return 6; }
+
+inline int func7 (void) { return 7; }
+extern int func7 (void);
+
+inline int func8 (void);
+extern int func8 (void) { return 8; }
+
+extern int func9 (void) { return 9; }
+inline int func9 (void);
Index: c-tree.h
===================================================================
--- c-tree.h (revision 113941)
+++ c-tree.h (working copy)
@@ -377,7 +377,6 @@
int returns_null;
int returns_abnormally;
int warn_about_return_type;
- int extern_inline;
};
/* Save lists of labels used or defined in particular contexts.
Index: c-decl.c
===================================================================
--- c-decl.c (revision 113941)
+++ c-decl.c (working copy)
@@ -154,10 +154,6 @@
static int warn_about_return_type;
-/* Nonzero when starting a function declared `extern inline'. */
-
-static int current_extern_inline;
-
/* Nonzero when the current toplevel function contains a declaration
of a nested function which is never defined. */
@@ -793,11 +789,22 @@
&& DECL_ABSTRACT_ORIGIN (p) != p)
TREE_ADDRESSABLE (DECL_ABSTRACT_ORIGIN (p)) = 1;
if (!DECL_EXTERNAL (p)
- && DECL_INITIAL (p) == 0)
+ && !DECL_INITIAL (p)
+ && scope != file_scope
+ && scope != external_scope)
{
error ("nested function %q+D declared but never defined", p);
undef_nested_function = true;
}
+ /* C99 6.7.4p6: "a function with external linkage... declared
+ with an inline function specifier ... shall also be defined in the
+ same translation unit." */
+ else if (DECL_DECLARED_INLINE_P (p)
+ && TREE_PUBLIC (p)
+ && !DECL_INITIAL (p)
+ && flag_isoc99)
+ pedwarn ("inline function %q+D declared but never defined", p);
+
goto common_symbol;
case VAR_DECL:
@@ -1282,10 +1289,11 @@
/* Function declarations can either be 'static' or 'extern' (no
qualifier is equivalent to 'extern' - C99 6.2.2p5) and therefore
- can never conflict with each other on account of linkage (6.2.2p4).
- Multiple definitions are not allowed (6.9p3,5) but GCC permits
- two definitions if one is 'extern inline' and one is not. The non-
- extern-inline definition supersedes the extern-inline definition. */
+ can never conflict with each other on account of linkage
+ (6.2.2p4). Multiple definitions are not allowed (6.9p3,5) but
+ gnu89 mode permits two definitions if one is 'extern inline' and
+ one is not. The non- extern-inline definition supersedes the
+ extern-inline definition. */
else if (TREE_CODE (newdecl) == FUNCTION_DECL)
{
@@ -1311,16 +1319,11 @@
{
/* If both decls are in the same TU and the new declaration
isn't overriding an extern inline reject the new decl.
- When we handle c99 style inline rules we'll want to reject
- the following:
-
- DECL_EXTERN_INLINE (olddecl)
- && !DECL_EXTERN_INLINE (newdecl)
-
- if they're in the same translation unit. Until we implement
- the full semantics we accept the construct. */
- if (!(DECL_EXTERN_INLINE (olddecl)
- && !DECL_EXTERN_INLINE (newdecl))
+ In c99, no overriding is allowed in the same translation
+ unit. */
+ if ((!DECL_EXTERN_INLINE (olddecl)
+ || DECL_EXTERN_INLINE (newdecl)
+ || flag_isoc99)
&& same_translation_unit_p (newdecl, olddecl))
{
error ("redefinition of %q+D", newdecl);
@@ -1511,9 +1514,13 @@
??? Should we still warn about this now we have unit-at-a-time
mode and can get it right?
Definitely don't complain if the decls are in different translation
- units. */
+ units.
+ C99 permits this, so don't warn in that case. (The function
+ may not be inlined everywhere in function-at-a-time mode, but
+ we still shouldn't warn.) */
if (DECL_DECLARED_INLINE_P (newdecl) && !DECL_DECLARED_INLINE_P (olddecl)
- && same_translation_unit_p (olddecl, newdecl))
+ && same_translation_unit_p (olddecl, newdecl)
+ && ! flag_isoc99)
{
if (TREE_USED (olddecl))
{
@@ -1590,12 +1597,13 @@
static void
merge_decls (tree newdecl, tree olddecl, tree newtype, tree oldtype)
{
- int new_is_definition = (TREE_CODE (newdecl) == FUNCTION_DECL
- && DECL_INITIAL (newdecl) != 0);
- int new_is_prototype = (TREE_CODE (newdecl) == FUNCTION_DECL
- && TYPE_ARG_TYPES (TREE_TYPE (newdecl)) != 0);
- int old_is_prototype = (TREE_CODE (olddecl) == FUNCTION_DECL
- && TYPE_ARG_TYPES (TREE_TYPE (olddecl)) != 0);
+ bool new_is_definition = (TREE_CODE (newdecl) == FUNCTION_DECL
+ && DECL_INITIAL (newdecl) != 0);
+ bool new_is_prototype = (TREE_CODE (newdecl) == FUNCTION_DECL
+ && TYPE_ARG_TYPES (TREE_TYPE (newdecl)) != 0);
+ bool old_is_prototype = (TREE_CODE (olddecl) == FUNCTION_DECL
+ && TYPE_ARG_TYPES (TREE_TYPE (olddecl)) != 0);
+ bool extern_changed = false;
/* For real parm decl following a forward decl, rechain the old decl
in its new location and clear TREE_ASM_WRITTEN (it's not a
@@ -1742,6 +1750,18 @@
}
}
+ /* In c99, 'extern' declaration before (or after) 'inline' means this
+ function is not DECL_EXTERNAL. */
+ if (TREE_CODE (newdecl) == FUNCTION_DECL
+ && (DECL_DECLARED_INLINE_P (newdecl)
+ || DECL_DECLARED_INLINE_P (olddecl))
+ && (!DECL_DECLARED_INLINE_P (newdecl)
+ || !DECL_DECLARED_INLINE_P (olddecl)
+ || !DECL_EXTERNAL (olddecl))
+ && DECL_EXTERNAL (newdecl)
+ && flag_isoc99)
+ DECL_EXTERNAL (newdecl) = 0;
+
if (DECL_EXTERNAL (newdecl))
{
TREE_STATIC (newdecl) = TREE_STATIC (olddecl);
@@ -1761,7 +1781,7 @@
TREE_PUBLIC (olddecl) = TREE_PUBLIC (newdecl);
}
- if (TREE_CODE (newdecl) == FUNCTION_DECL)
+ if (TREE_CODE (newdecl) == FUNCTION_DECL)
{
/* If we're redefining a function previously defined as extern
inline, make sure we emit debug info for the inline before we
@@ -1834,6 +1854,8 @@
}
}
+ extern_changed = DECL_EXTERNAL (olddecl) && !DECL_EXTERNAL (newdecl);
+
/* Copy most of the decl-specific fields of NEWDECL into OLDDECL.
But preserve OLDDECL's DECL_UID and DECL_CONTEXT. */
{
@@ -1876,6 +1898,13 @@
|| (TREE_CODE (olddecl) == VAR_DECL
&& TREE_STATIC (olddecl))))
make_decl_rtl (olddecl);
+
+ /* If we changed a function from DECL_EXTERNAL to !DECL_EXTERNAL,
+ and the definition is coming from the old version, cgraph needs
+ to be called again. */
+ if (extern_changed && !new_is_definition
+ && TREE_CODE (olddecl) == FUNCTION_DECL && DECL_INITIAL (olddecl))
+ cgraph_finalize_function (olddecl, false);
}
/* Handle when a new declaration NEWDECL has the same name as an old
@@ -4638,8 +4667,15 @@
GCC to signify a forward declaration of a nested function. */
if (storage_class == csc_auto && current_scope != file_scope)
DECL_EXTERNAL (decl) = 0;
+ /* In C99, a function which is declared 'inline' with 'extern'
+ is not an external reference (which is confusing). It
+ means that the later definition of the function must be output
+ in this file, C99 6.7.4p6. In GNU C89, a function declared
+ 'extern inline' is an external reference. */
+ else if (declspecs->inline_p)
+ DECL_EXTERNAL (decl) = (storage_class == csc_extern) == !flag_isoc99;
else
- DECL_EXTERNAL (decl) = 1;
+ DECL_EXTERNAL (decl) = !initialized;
/* Record absence of global scope for `static' or `auto'. */
TREE_PUBLIC (decl)
@@ -4669,11 +4705,7 @@
the abstract origin pointing between the declarations,
which will confuse dwarf2out. */
if (initialized)
- {
- DECL_INLINE (decl) = 1;
- if (storage_class == csc_extern)
- current_extern_inline = 1;
- }
+ DECL_INLINE (decl) = 1;
}
/* If -finline-functions, assume it can be inlined. This does
two things: let the function be deferred until it is actually
@@ -5850,7 +5882,6 @@
current_function_returns_null = 0;
current_function_returns_abnormally = 0;
warn_about_return_type = 0;
- current_extern_inline = 0;
c_switch_stack = NULL;
nstack_se = XOBNEW (&parser_obstack, struct c_label_context_se);
@@ -6000,12 +6031,6 @@
warning (OPT_Wmissing_declarations,
"%q+D was used with no declaration before its definition", decl1);
- /* This is a definition, not a reference.
- So normally clear DECL_EXTERNAL.
- However, `extern inline' acts like a declaration
- except for defining how to inline. So set DECL_EXTERNAL in that case. */
- DECL_EXTERNAL (decl1) = current_extern_inline;
-
/* This function exists in static storage.
(This does not mean `static' in the C sense!) */
TREE_STATIC (decl1) = 1;
@@ -6781,7 +6806,6 @@
p->returns_null = current_function_returns_null;
p->returns_abnormally = current_function_returns_abnormally;
p->warn_about_return_type = warn_about_return_type;
- p->extern_inline = current_extern_inline;
}
/* Restore the variables used during compilation of a C function. */
@@ -6810,7 +6834,6 @@
current_function_returns_null = p->returns_null;
current_function_returns_abnormally = p->returns_abnormally;
warn_about_return_type = p->warn_about_return_type;
- current_extern_inline = p->extern_inline;
f->language = NULL;
}
Index: doc/extend.texi
===================================================================
--- doc/extend.texi (revision 113941)
+++ doc/extend.texi (working copy)
@@ -3582,58 +3582,54 @@
@cindex open coding
@cindex macros, inline alternative
-By declaring a function @code{inline}, you can direct GCC to
+By declaring a function inline, you can direct GCC to make
+calls to that function faster. One way GCC can achieve this is to
integrate that function's code into the code for its callers. This
makes execution faster by eliminating the function-call overhead; in
-addition, if any of the actual argument values are constant, their known
-values may permit simplifications at compile time so that not all of the
-inline function's code needs to be included. The effect on code size is
-less predictable; object code may be larger or smaller with function
-inlining, depending on the particular case. Inlining of functions is an
-optimization and it really ``works'' only in optimizing compilation. If
-you don't use @option{-O}, no function is really inline.
+addition, if any of the actual argument values are constant, their
+known values may permit simplifications at compile time so that not
+all of the inline function's code needs to be included. The effect on
+code size is less predictable; object code may be larger or smaller
+with function inlining, depending on the particular case. You can
+also direct GCC to try to integrate all ``simple enough'' functions
+into their callers with the option @option{-finline-functions}.
-Inline functions are included in the ISO C99 standard, but there are
-currently substantial differences between what GCC implements and what
-the ISO C99 standard requires.
+GCC implements three different semantics of declaring a function
+inline. One is available with @option{-std=gnu89}, another when
+@option{-std=c99} or @option{-std=gnu99}, and the third is used when
+compiling C++.
To declare a function inline, use the @code{inline} keyword in its
declaration, like this:
@smallexample
-inline int
+static inline int
inc (int *a)
@{
(*a)++;
@}
@end smallexample
-(If you are writing a header file to be included in ISO C programs, write
-@code{__inline__} instead of @code{inline}. @xref{Alternate Keywords}.)
-You can also make all ``simple enough'' functions inline with the option
-@option{-finline-functions}.
+If you are writing a header file to be included in ISO C89 programs, write
+@code{__inline__} instead of @code{inline}. @xref{Alternate Keywords}.
-@opindex Winline
-Note that certain usages in a function definition can make it unsuitable
-for inline substitution. Among these usages are: use of varargs, use of
-alloca, use of variable sized data types (@pxref{Variable Length}),
-use of computed goto (@pxref{Labels as Values}), use of nonlocal goto,
-and nested functions (@pxref{Nested Functions}). Using @option{-Winline}
-will warn when a function marked @code{inline} could not be substituted,
-and will give the reason for the failure.
+The three types of inlining behave similarly in two important cases:
+when the @code{inline} keyword is used on a @code{static} function,
+like the example above, and when a function is first declared without
+using the @code{inline} keyword and then is defined with
+@code{inline}, like this:
-Note that in C and Objective-C, unlike C++, the @code{inline} keyword
-does not affect the linkage of the function.
+@smallexample
+extern int inc (int *a);
+inline int
+inc (int *a)
+@{
+ (*a)++;
+@}
+@end smallexample
-@cindex automatic @code{inline} for C++ member fns
-@cindex @code{inline} automatic for C++ member fns
-@cindex member fns, automatically @code{inline}
-@cindex C++ member fns, automatically @code{inline}
-@opindex fno-default-inline
-GCC automatically inlines member functions defined within the class
-body of C++ programs even if they are not explicitly declared
-@code{inline}. (You can override this with @option{-fno-default-inline};
-@pxref{C++ Dialect Options,,Options Controlling C++ Dialect}.)
+In both of these common cases, the program behaves the same as if you
+had not used the @code{inline} keyword, except for its speed.
@cindex inline functions, omission of
@opindex fkeep-inline-functions
@@ -3649,6 +3645,36 @@
usual. The function must also be compiled as usual if the program
refers to its address, because that can't be inlined.
+@opindex Winline
+Note that certain usages in a function definition can make it unsuitable
+for inline substitution. Among these usages are: use of varargs, use of
+alloca, use of variable sized data types (@pxref{Variable Length}),
+use of computed goto (@pxref{Labels as Values}), use of nonlocal goto,
+and nested functions (@pxref{Nested Functions}). Using @option{-Winline}
+will warn when a function marked @code{inline} could not be substituted,
+and will give the reason for the failure.
+
+@cindex automatic @code{inline} for C++ member fns
+@cindex @code{inline} automatic for C++ member fns
+@cindex member fns, automatically @code{inline}
+@cindex C++ member fns, automatically @code{inline}
+@opindex fno-default-inline
+As required by ISO C++, GCC considers member functions defined within
+the body of a class to be marked inline even if they are
+not explicitly declared with the @code{inline} keyword. You can
+override this with @option{-fno-default-inline}; @pxref{C++ Dialect
+Options,,Options Controlling C++ Dialect}.
+
+GCC does not inline any functions when not optimizing unless you specify
+the @samp{always_inline} attribute for the function, like this:
+
+@smallexample
+/* @r{Prototype.} */
+inline void foo (const char) __attribute__((always_inline));
+@end smallexample
+
+The remainder of this section is specific to GNU C89 inlining.
+
@cindex non-static inline function
When an inline function is not @code{static}, then the compiler must assume
that there may be calls from other source files; since a global symbol can
@@ -3671,21 +3697,6 @@
to be inlined. If any uses of the function remain, they will refer to
the single copy in the library.
-Since GCC eventually will implement ISO C99 semantics for
-inline functions, it is best to use @code{static inline} only
-to guarantee compatibility. (The
-existing semantics will remain available when @option{-std=gnu89} is
-specified, but eventually the default will be @option{-std=gnu99} and
-that will implement the C99 semantics, though it does not do so yet.)
-
-GCC does not inline any functions when not optimizing unless you specify
-the @samp{always_inline} attribute for the function, like this:
-
-@smallexample
-/* @r{Prototype.} */
-inline void foo (const char) __attribute__((always_inline));
-@end smallexample
-
@node Extended Asm
@section Assembler Instructions with C Expression Operands
@cindex extended @code{asm}
============================================================