https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94543
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Version|tree-ssa |10.0
Last reconfirmed| |2020-04-14
Status|UNCONFIRMED |NEW
Target| |x86_64-*-* i?86-*-*
Keywords| |missed-optimization
Component|middle-end |rtl-optimization
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
The issue is that we fail to have a proper representation of the target on the
GIMPLE level. We expand to RTL from the optimal
<bb 2> [local count: 1073741824]:
# RANGE [0, 255] NONZERO 255
_1 = MIN_EXPR <x_2(D), 255>;
# RANGE [0, 255] NONZERO 255
_3 = (unsigned int) _1;
return _3;
but that produces
(insn 10 6 9 (set (reg:HI 88)
(const_int 255 [0xff])) "x.c":1:56 -1
(nil))
(insn 9 10 11 (set (reg:CC 17 flags)
(compare:CC (reg/v:HI 84 [ x ])
(const_int 255 [0xff]))) "x.c":1:56 -1
(nil))
(insn 11 9 12 (set (reg:HI 87)
(if_then_else:HI (leu (reg:CC 17 flags)
(const_int 0 [0]))
(reg/v:HI 84 [ x ])
(reg:HI 88))) "x.c":1:56 -1
(nil))
(insn 12 11 13 (set (reg:SI 86)
(zero_extend:SI (reg:HI 87))) "x.c":1:61 -1
(nil))
given fort the (unsigned int) _1 zero-extension we don't have any other
representation on GIMPLE to elide the zero-extension. I'm also not
sure if (subreg:SI (reg:HI 87)) would be correct in all cases.
Marking rtl-optimization but eventually it's also a target issue.
We also don't have anything like a reg-note to tell ranges of a
set? Anyway, even on RTL the range of reg:HI 87 is clearly visible.
