[PATCH] Support "nothrow" function attribute
Roger Sayle
roger@eyesopen.com
Fri May 17 07:16:00 GMT 2002
This is a repost of my patch from December 3rd of last year
http://gcc.gnu.org/ml/gcc-patches/2001-12/msg00296.html to
add support for a "nothrow" attribute that has been updated to
match current CVS.
The use of __attribute__((nothrow)) should simplify header files
that may be read by both gcc and g++ that specify that a function
cannot throw a C++ exception. This allows better code generation
in C++, without breaking the C parser. It should also be useful
for "exceptions in C" at some point in the future.
The real motivation however is to allow built-ins to easily be
marked as nothrow. This is a pre-requisite for a dramatic
simplification of parts of the g++ front end that should also
improve C++ compile-time performance.
Retested on i686-pc-linux-gnu with a complete "make bootstrap" and
"make -k check" (all languages except Ada) with no new testsuite
regressions.
Although the patch itself hasn't been reviewed, it has won
"critical acclaim" from both Joseph Myers and Gabriel Dos Reis:
http://gcc.gnu.org/ml/gcc-patches/2002-02/msg00091.html
Ok for mainline?
2002-05-17 Roger Sayle <roger@eyesopen.com>
* c-common.c: Add support for __attribute__((nothrow)) to specify
that a function cannot throw an exception (using TREE_NOTHROW).
(handle_nothrow_attribute): New function to process this attribute.
* doc/extend.texi: Document the new nothrow function attribute.
* gcc.c-torture/compile/attribs-1.c: New test case.
Index: c-common.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/c-common.c,v
retrieving revision 1.324
diff -c -3 -p -r1.324 c-common.c
*** c-common.c 16 May 2002 19:09:36 -0000 1.324
--- c-common.c 17 May 2002 02:56:52 -0000
*************** static tree handle_deprecated_attribute
*** 344,349 ****
--- 344,351 ----
bool *));
static tree handle_vector_size_attribute PARAMS ((tree *, tree, tree, int,
bool *));
+ static tree handle_nothrow_attribute PARAMS ((tree *, tree, tree, int,
+ bool *));
static tree vector_size_helper PARAMS ((tree, tree));
/* Table of machine-independent attributes common to all C-like languages. */
*************** const struct attribute_spec c_common_att
*** 406,411 ****
--- 408,415 ----
handle_vector_size_attribute },
{ "visibility", 1, 1, true, false, false,
handle_visibility_attribute },
+ { "nothrow", 0, 0, true, false, false,
+ handle_nothrow_attribute },
{ NULL, 0, 0, false, false, false, NULL }
};
*************** handle_deprecated_attribute (node, name,
*** 5407,5412 ****
--- 5411,5439 ----
else
warning ("`%s' attribute ignored",
IDENTIFIER_POINTER (name));
+ }
+
+ return NULL_TREE;
+ }
+
+ /* Handle a "nothrow" attribute; arguments as in
+ struct attribute_spec.handler. */
+
+ static tree
+ handle_nothrow_attribute (node, name, args, flags, no_add_attrs)
+ tree *node;
+ tree name;
+ tree args ATTRIBUTE_UNUSED;
+ int flags ATTRIBUTE_UNUSED;
+ bool *no_add_attrs;
+ {
+ if (TREE_CODE (*node) == FUNCTION_DECL)
+ TREE_NOTHROW (*node) = 1;
+ /* ??? TODO: Support types. */
+ else
+ {
+ warning ("`%s' attribute ignored", IDENTIFIER_POINTER (name));
+ *no_add_attrs = true;
}
return NULL_TREE;
Index: doc/extend.texi
===================================================================
RCS file: /cvs/gcc/gcc/gcc/doc/extend.texi,v
retrieving revision 1.70
diff -c -3 -p -r1.70 extend.texi
*** doc/extend.texi 11 May 2002 16:25:04 -0000 1.70
--- doc/extend.texi 17 May 2002 02:56:54 -0000
*************** attributes when making a declaration. T
*** 1881,1887 ****
attribute specification inside double parentheses. The following
attributes are currently defined for functions on all targets:
@code{noreturn}, @code{noinline}, @code{always_inline},
! @code{pure}, @code{const},
@code{format}, @code{format_arg}, @code{no_instrument_function},
@code{section}, @code{constructor}, @code{destructor}, @code{used},
@code{unused}, @code{deprecated}, @code{weak}, @code{malloc}, and
--- 1881,1887 ----
attribute specification inside double parentheses. The following
attributes are currently defined for functions on all targets:
@code{noreturn}, @code{noinline}, @code{always_inline},
! @code{pure}, @code{const}, @code{nothrow},
@code{format}, @code{format_arg}, @code{no_instrument_function},
@code{section}, @code{constructor}, @code{destructor}, @code{used},
@code{unused}, @code{deprecated}, @code{weak}, @code{malloc}, and
*************** extern const intfn square;
*** 2005,2010 ****
--- 2005,2018 ----
This approach does not work in GNU C++ from 2.6.0 on, since the language
specifies that the @samp{const} must be attached to the return value.
+ @cindex @code{nothrow} function attribute
+ @item nothrow
+ The @code{nothrow} attribute is used to inform the compiler that a
+ function cannot throw a C++ exception. For example, most functions
+ in the standard C library can be guaranteed not to throw an exception
+ with the notable exceptions of @code{qsort} and @code{bsearch} that
+ take function pointer arguments. The @code{nothrow} attribute is not
+ implemented in GCC versions earlier than 3.2.
@item format (@var{archetype}, @var{string-index}, @var{first-to-check})
@cindex @code{format} function attribute
*** /dev/null Thu Aug 30 14:30:55 2001
--- gcc.c-torture/compile/attribs-1.c Thu May 16 20:57:22 2002
***************
*** 0 ****
--- 1,37 ----
+ /* Copyright (C) 2001, 2002 Free Software Foundation.
+
+ Test that all GCC function attributes are correctly parsed.
+
+ Written by Roger Sayle, 1st December 2001. */
+
+ struct tm;
+ typedef __SIZE_TYPE__ size_t;
+
+ extern void abort (void) __attribute__ ((noreturn));
+ extern int abs (int) __attribute__ ((const));
+ extern size_t strlen (const char *) __attribute__ ((pure));
+ extern void *malloc (size_t) __attribute__ ((malloc));
+ extern double sqrt (double) __attribute__ ((nothrow));
+
+ extern int printf (const char *, ...) __attribute__ ((format (printf, 1, 2)));
+ extern int scanf (const char *, ...) __attribute__ ((format (scanf, 1, 2)));
+ extern size_t strftime (char *, size_t, const char *, const struct tm*)
+ __attribute__ ((format (strftime, 3, 0)));
+ extern size_t strfmon (char *, size_t, const char *, ...)
+ __attribute__ ((format (strfmon, 3, 4)));
+
+ extern char *dgettext (const char *, const char *)
+ __attribute__ ((format_arg (2)));
+
+ extern void foo (void) __attribute__ ((section ("cross")));
+ extern void flarg (void) __attribute__ ((no_instrument_function));
+ extern void grok (void) __attribute__ ((no_check_memory_usage));
+
+ extern void genesis (void) __attribute__ ((constructor));
+ extern void revelation (void) __attribute__ ((destructor));
+
+ /* Not all platforms support "weak" function attributes. */
+ /* extern void strong (void) __attribute__ ((weak)); */
+
+ extern void superman (void) __attribute__ ((alias ("clark_kent")));
+
Roger
--
Roger Sayle, E-mail: roger@eyesopen.com
OpenEye Scientific Software, WWW: http://www.eyesopen.com/
Suite 1107, 3600 Cerrillos Road, Tel: (+1) 505-473-7385
Santa Fe, New Mexico, 87507. Fax: (+1) 505-473-0833
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