------- Comment #1 from rguenth at gcc dot gnu dot org 2009-04-26 16:49 -------
SCEV const-prop produces for m
D.2395_7 = n.11_27 + -2147483648;
m_19 = D.2395_7 * 2;
which has undefined signed overflow which triggers VRP to deduce wrong
value ranges.
Analyzing # of iterations of loop 1
exit condition [1, + , 1](no_overflow) < n.11_27
bounds on difference of bases: 0 ... 2147483646
result:
# of iterations (unsigned int) n.11_27 + 4294967295, bounded by 2147483646
(set_nb_iterations_in_loop = (unsigned int) n.11_27 + 4294967295))
(chrec_apply
(varying_loop = 1
)
(chrec = {2, +, 2}_1)
(x = (int) ((unsigned int) n.11_27 + 4294967295))
(res = (n.11_27 + -2147483648) * 2))
4.4 instead uses correct types:
Analyzing # of iterations of loop 1
exit condition [1, + , 1](no_overflow) < n.11_28
bounds on difference of bases: 0 ... 2147483646
result:
# of iterations (unsigned int) n.11_28 + 0x0ffffffff, bounded by 2147483646
(set_nb_iterations_in_loop = (unsigned int) n.11_28 + 0x0ffffffff))
(chrec_apply
(varying_loop = 1
)
(chrec = {2, +, 2}_1)
(x = (int) ((unsigned int) n.11_28 + 0x0ffffffff))
(res = (int) ((unsigned int) n.11_28 * 2)))
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu dot
| |org
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Keywords| |wrong-code
Known to fail| |4.3.3
Known to work| |4.2.4 4.4.0
Last reconfirmed|0000-00-00 00:00:00 |2009-04-26 16:49:41
date| |
Summary|Loop is completely skipped |[4.3 Regressions] Loop is
| |completely skipped due to
| |wrong types in SCEV const-
| |prop
Target Milestone|--- |4.3.4
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39904
