Would the updated comments in the attached patch more accurately
describe the purpose of the IMPLICIT_P flag and
the builtin_decl_explicit() and builtin_decl_implicit() functions?
I ended up here while trying to understand the differences between
the functions on different targets and decide which one should be
used to diagnose bugs like the one below:
long double fabsl (); // missing prototype
long double f (int x)
{
return fabsl (x); // want a warning here
}
I think we want the warning regardless of IMPLICIT_P so the warning
code should call builtin_decl_explicit() to obtain fabsl's expected
type, even if the target's runtime doesn't support the function on
the basis of the comment:
When a program uses floorf we may assume that the floorf function
has the expected meaning
Thanks
Martin
gcc/ChangeLog:
* builtins.def (DEF_BUILTIN): Update comment..
* tree.h (builtin_decl_explicit): Same.
(builtin_decl_implicit): Same.
Index: gcc/tree.h
===================================================================
--- gcc/tree.h (revision 266320)
+++ gcc/tree.h (working copy)
@@ -5220,7 +5220,9 @@ is_lang_specific (const_tree t)
#define BUILTIN_VALID_P(FNCODE) \
(IN_RANGE ((int)FNCODE, ((int)BUILT_IN_NONE) + 1, ((int) END_BUILTINS) - 1))
-/* Return the tree node for an explicit standard builtin function or NULL. */
+/* Return the tree node for the built-in function declaration corresponding
+ to FNCODE or NULL. */
+
static inline tree
builtin_decl_explicit (enum built_in_function fncode)
{
@@ -5229,7 +5231,12 @@ builtin_decl_explicit (enum built_in_function fnco
return builtin_info[(size_t)fncode].decl;
}
-/* Return the tree node for an implicit builtin function or NULL. */
+/* Return the tree node for the built-in function declaration corresponding
+ to FNCODE if its IMPLICIT_P flag has been set or NULL otherwise.
+ IMPLICIT_P is clear for library built-ins that GCC implements but that
+ may not be implemented in the runtime library on the target. See also
+ the DEF_BUILTIN macro in builtins.def. */
+
static inline tree
builtin_decl_implicit (enum built_in_function fncode)
{
Index: gcc/builtins.def
===================================================================
--- gcc/builtins.def (revision 266320)
+++ gcc/builtins.def (working copy)
@@ -54,12 +54,13 @@ along with GCC; see the file COPYING3. If not see
ATTRs is an attribute list as defined in builtin-attrs.def that
describes the attributes of this builtin function.
- IMPLICIT specifies condition when the builtin can be produced by
- compiler. For instance C90 reserves floorf function, but does not
- define it's meaning. When user uses floorf we may assume that the
- floorf has the meaning we expect, but we can't produce floorf by
- simplifying floor((double)float) since the runtime need not implement
- it.
+ IMPLICIT specifies the condition when calls to the builtin can be
+ introduced by GCC. For instance C90 reserves the floorf function,
+ but does not define its meaning. When a program uses floorf we
+ may assume that the floorf function has the expected meaning and
+ signature, but we may not transform the call floor((double)flt)
+ into a call to floorf(flt) since the runtime need not implement
+ the latter.
The builtins is registered only if COND is true. */
