https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81889
--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
Specifically it is PRE code hoisting hoisting (integer(kind=8)) _2 above
if (_2 > 3) making it impossible to set a SSA range info on it.
At cunroll time we still have somewhat useful info on other SSA names in
the loop:
<bb 12> [local count: 912680545]:
# val.11_94 = PHI <0.0(17), val.11_56(20)>
# RANGE [1, 17] NONZERO 7
# S.12_93 = PHI <1(17), S.12_57(20)>
# RANGE [0, 2] NONZERO 3
_16 = S.12_93 + -1;
_17 = xx[_16];
val.11_56 = _17 + val.11_94;
# RANGE [2, 4] NONZERO 7
S.12_57 = S.12_93 + 1;
if (S.12_57 > _106)
goto <bb 26>; [15.00%]
else
goto <bb 20>; [85.00%]
<bb 26> [local count: 136902080]:
# val.11_122 = PHI <val.11_56(12)>
goto <bb 13>; [100.00%]
specifically the range info on S.12 (even if somewhat strange) could be used
to derive a range "backwards" for the number of iterations from base and step
from the increment stmt for example.
Thus for example the following fixes the testcase and exploits any
range info on undefined overflow stmts. Giving that wider testing.
Index: gcc/tree-ssa-loop-niter.c
===================================================================
--- gcc/tree-ssa-loop-niter.c (revision 255539)
+++ gcc/tree-ssa-loop-niter.c (working copy)
@@ -3510,6 +3510,12 @@ infer_loop_bounds_from_signedness (struc
low = lower_bound_in_type (type, type);
high = upper_bound_in_type (type, type);
+ wide_int minv, maxv;
+ if (get_range_info (def, &minv, &maxv) == VR_RANGE)
+ {
+ low = wide_int_to_tree (type, minv);
+ high = wide_int_to_tree (type, maxv);
+ }
record_nonwrapping_iv (loop, base, step, stmt, low, high, false, true);
}
