[Bug middle-end/13421] IA32 bigmem pointer subtraction and –ftrapv option causes unjustified program abort

["eggert at twinsun dot com" <gcc-bugzilla@gcc.gnu.org>]

------- Additional Comments From eggert at twinsun dot com  2004-04-06 05:13 -------
A point of clarification: even if pointers are changed to be consistently
unsigned internally (which seems to be the right thing to do, if pointer
comparison is unsigned), GCC must still check for overflow when subtracting
pointers. For example, suppose we have the 2 GiB array "a" successfully
allocated by "char *a = malloc (1u<<31);". Then the expression "(a + (1u<<31)) -
a" is of type ptrdiff_t, which is a signed 32-bit integer that cannot represent
(1u<<31). So this expression must generate a trap with -ftrapv, regardless of
whether pointers are unsigned internally.

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13421