https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85640
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P2
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Looking at trunk we have
# RANGE [1, 5552] NONZERO 8191
# iftmp.2_14 = PHI <5552(6), len_29(5)>
# prephitmp_53 = PHI <_52(6), 0(5)>
_36 = (sizetype) iftmp.2_14;
_37 = buf_11 + _36;
<bb 8> [local count: 1073741824]:
# buf_12 = PHI <buf_11(7), buf_21(11)>
...
<bb 9> [local count: 118111601]:
# _17 = PHI <_6(8)>
# _59 = PHI <_8(8)>
_46 = iftmp.2_14 + 4294967295;
_45 = (sizetype) _46;
_44 = _45 + 1;
buf_47 = buf_11 + _44;
where the final-value replacement failed to elide the +-1 dance because
sizetype _45;
unsigned int _46;
IVOPTs is using tree-affine which performs some extra tricks such as
using range-info to prove it can elide the casts. I think if we
teach the same to SCEV we'd get it optimized again. I'm talking about
/* If inner type has wrapping overflow behavior, fold conversion
for below case:
(T1)(X - CST) -> (T1)X - (T1)CST
if X - CST doesn't overflow by range information. Also handle
(T1)(X + CST) as (T1)(X - (-CST)). */
if (TYPE_UNSIGNED (itype)
...
Note that the plan is to remove the unconditional final-value replacement
and integrate it into passes that would benefit - first of all DCE which
can trigger it if the IV (or the whole loop) can be eliminated.
