https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86965
--- Comment #3 from Michael_S <already5chosen at yahoo dot com> ---
(In reply to sandra from comment #1)
> I'm not sure what command-line options you were using, but with -O2 the bad2
> case now generates the expected code.
>
With 8.2.0 the problem exists both with -O2 and with -Os.
So, may be, a newer version got lucky and some other change eliminated my
problem.
> Looking at the bad1 case, this is what's coming out of the tree optimizers,
> and what the back end has to deal with for RTL expansion:
>
> bad1 (const signed char * str, int * res)
> {
> int c;
> signed char _1;
> int _2;
> int _11;
> signed char _12;
> _Bool _13;
>
> <bb 2> [local count: 1073741824]:
> _1 = *str_6(D);
> c_8 = (int) _1;
> _2 = c_8 + -48;
> *res_9(D) = _2;
> _12 = _1 & -33;
> _13 = _12 == 69;
> _11 = (int) _13;
> return _11;
>
> }
>
> The code coming out of RTL expand is a mess too; there's no QImode "and"
> instruction, it can't use the SImode "andi" instruction because that it only
> accepts small unsigned constants (not -33), and then it has to sign-extend
> the QImode result it computed because the comparison instructions need
> SImode too.
>
> FWIW I think the real bug here is in the tree reassoc1 pass: it shouldn't
> attempt this optimization if there is no optab support for bitwise AND in
> the appropriate mode. So I'm reclassifying this as a tree-optimization bug
> rather than a target bug; if the maintainers dispute that, feel free to
> switch it back and I will take another look see if I can do something in the
> backend to recombine the insns.
I am not a compiler expert. Never understood functionality of each and every
gcc pass. Sorry.
The only thing I know, at least on simple targets, like Nios2, is which code I
would like for compiler to generate.
