Jim Meyering <[EMAIL PROTECTED]> writes:
> Besides, who knows... compilers may eventually be able to optimize
> away that xalloc_die call, in spite of the intermediate size_t.
If GCC ever gets that smart, then it will issue the same
warning as it does now without the unsigned_int hack.
Shouldn't we simply fix GCC instead? Something like the following.
(-Wextra is the new name for -W.) (Also I'd have to document this.)
2005-06-22 Paul Eggert <[EMAIL PROTECTED]>
* c-common.c (shorten_compare): Unless -Wextra is used,
do not warn against comparisons always being false due to
limited range of data type.
--- c-common.c 2005-06-22 12:42:13 -0700
+++ /tmp/c-common.c 2005-06-22 13:14:26 -0700
@@ -2112,7 +2112,8 @@ shorten_compare (tree *op0_ptr, tree *op
type = c_common_unsigned_type (type);
}
- if (TREE_CODE (primop0) != INTEGER_CST)
+ if (extra_warnings && !in_system_header
+ && TREE_CODE (primop0) != INTEGER_CST)
{
if (val == truthvalue_false_node)
warning (0, "comparison is always false due to limited range of
data type");
It will take a while for this fix to propagate, though. In the
meantime, why not modify the definition of xalloc_oversized(n,s) to
always return 0 if if s is a constant and if the size of n is such
that the comparison cannot possibly fail. Something like this?
(completely untested):
2005-06-22 Paul Eggert <[EMAIL PROTECTED]>
* xalloc.h: Work around a bogus GCC 4.0.0 warning "comparison is always
false due to limited range of data type". Problem reported by
Oskar Liljeblad.
(xalloc_lt, xalloc_lt_always_false): New macros.
(xalloc_oversized): Use them.
--- xalloc.h 2005-05-14 01:02:58 -0700
+++ /tmp/xalloc.h 2005-06-22 13:53:19 -0700
@@ -56,6 +56,22 @@ void *x2nrealloc (void *p, size_t *pn, s
void *xmemdup (void const *p, size_t s);
char *xstrdup (char const *str);
+/* Work around a bogus GCC 4.0.0 warning "comparison is always false
+ due to limited range of data type". */
+
+# define xalloc_lt(m, n) (! xalloc_lt_always_false (m, n) && (m) < (n))
+# if __GNUC__ < 4
+# define xalloc_lt_always_false(a, b) 0
+# else
+# ifndef CHAR_BIT
+# include <limits.h>
+# endif
+# define xalloc_lt_always_false(m, n) \
+ (__builtin_constant_p (m) \
+ && sizeof (n) < sizeof (size_t) \
+ && (size_t) 1 << (sizeof (n) * CHAR_BIT) <= (m)) \
+# endif
+
/* Return 1 if an array of N objects, each of size S, cannot exist due
to size arithmetic overflow. S must be positive and N must be
nonnegative. This is a macro, not an inline function, so that it
@@ -69,7 +85,8 @@ char *xstrdup (char const *str);
exactly-SIZE_MAX allocations on such hosts; this avoids a test and
branch when S is known to be 1. */
# define xalloc_oversized(n, s) \
- ((size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) < (n))
+ xalloc_lt ((size_t) (sizeof(ptrdiff_t) <= sizeof(size_t) ? -1 : -2) / (s),
\
+ n)
# ifdef __cplusplus
}
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