On 9/3/21 5:05 PM, Andrew MacLeod wrote:
On 9/3/21 10:41 AM, Aldy Hernandez wrote:
[Andrew, do you see any problem with using the minus relational code
here? It seems like everything matches up.]
I've seen cases in the upcoming jump threader enhancements where we see
a difference of two pointers that are known to be equivalent, and yet we
fail to return 0 for the range. This is because we have no working
range-op entry for POINTER_DIFF_EXPR. The entry we currently have is
a mere placeholder to avoid ignoring POINTER_DIFF_EXPR's so
adjust_pointer_diff_expr() could get a whack at it here:
// def = __builtin_memchr (arg, 0, sz)
// n = def - arg
//
// The range for N can be narrowed to [0, PTRDIFF_MAX - 1].
In theory... but do the non-equality relations make sense? ie ptr1 <
ptr2 ? Perhaps there is no harm in those.. Probably undefined
behaviour if they are not related so we can do whatever...
I originally just copy-pasted the stuff dealing with == and !=, but
figured why not piggyback onto the existing minus code.
I'm ok with doing whatever for undefined behavior. At least it's all
encapsulated in a single place.
Will commit when tests finish.
Thanks.
Aldy
