https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121382
Tamar Christina <tnfchris at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |tnfchris at gcc dot
gnu.org
--- Comment #6 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
Looks like because it thinks that
f = f - e;
if (c - 9 * f) {
__builtin_abort();
is always true, but misses the obvious case that when c == 0 and e ==
2147483647 c will be 0 and stay 0.
This happens because after propagating the initial value of f into the
expression
f = 2147483647 - e;
if (c - 9 * f) {
__builtin_abort();
The following IV candidate is generated
Candidate 7:
Depend on inv.exprs: 2
Var befor: ivtmp.12
Var after: ivtmp.12
Incr POS: before exit test
IV struct:
Type: unsigned int
Base: (unsigned int) e_8(D) * 9 + (unsigned int) c.0_5
Step: (unsigned int) (e_8(D) * 9)
Biv: N
Overflowness wrto loop niter: Overflow
instead of
Candidate 6:
Depend on inv.exprs: 2
Var befor: ivtmp.11
Var after: ivtmp.11
Incr POS: before exit test
IV struct:
Type: unsigned int
Base: (unsigned int) ((2147483647 - e_8(D)) * -9 + c.0_5)
Step: (unsigned int) (e_8(D) * 9)
Biv: N
Overflowness wrto loop niter: Overflow
which now makes it that the base expression can't be 0 because it's known that
e_8 is 5 or 2147483647.
So mine.
