https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85234
--- Comment #6 from Jeffrey A. Law <law at gcc dot gnu.org> ---
ISTM this should likely be tackled in both the gimple and RTL levels. In
gimple it would be a suitable match.pd pattern. For RTL it would be
simplify-rtx.
Gimple looks pretty straighforward. If we take the first example we have:
_1 = ~x_4(D);
_2 = _1 >> 3;
_3 = _2 != 0;
_5 = (int) _3;
Working backwards from that we can build a suitable matcher (and obviously it
needs to be generalized). For the simplified form we'd target something like:
x.0_1 = (unsigned int) x_3(D);
_2 = x.0_1 <= 4294967287;
_4 = (int) _2;
On the RTL side we're going to see something like this in simplify-rtx:
(set (reg:SI 143 [ _3 ])
(ne:SI (lshiftrt:SI (reg:SI 144 [ x ])
(const_int 3 [0x3]))
(const_int 536870911 [0x1fffffff])))
And I think we target something like this for the simplified RTL:
(set (reg:SI 143)
(leu:SI (reg 144) (const_int -9))
