https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110202
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2023-06-10
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #3)
> Well, there is nothing magic on exactly 0x55 immediate, there are 256
> possible immediates, most of them use all of A, B, C, some of them use just
> A, B, others just B, C, others just A, C, others just A, others just B,
> others just C, others none of them.
> And I must say I don't immediately see easy rules how to find out from the
> immediate value which set is which, so unless we find some easy rule for
> that, we'd need to hardcode the mapping between the 256 values to a bitmask
> which inputs are actually used.
> And then the question is how to represent that in RTL to make it clear that
> some operands are mentioned but their value isn't really used.
In the case of 0x55, an idea might be to split (or expand) it into how ~ is
represented.
That is:
(insn:TI 6 3 12 2 (set (reg:V8DI 20 xmm0 [85])
(xor:V8DI (mem:V8DI (reg/v/f:DI 5 di [orig:84 a ] [84]) [0 *a_3(D)+0
S64 A512])
(const_vector:V8DI [
(const_int -1 [0xffffffffffffffff]) repeated x8
]))) "/app/example.cpp":21:14 6764 {*one_cmplv8di2}
(expr_list:REG_DEAD (reg/v/f:DI 5 di [orig:84 a ] [84])
(nil)))
