https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97437
--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Segher Boessenkool from comment #5)
> Trying 7 -> 9:
> 7: r97:SI=0x2a
> 9: {flags:CCC=cmp(r97:SI+r98:SI,r97:SI);r99:SI=r97:SI+r98:SI;}
> REG_DEAD r98:SI
> REG_DEAD r97:SI
> Failed to match this instruction:
> (parallel [
> (set (reg:CC 17 flags)
> (compare:CC (reg:SI 98 [ *b_12(D) ])
> (const_int -42 [0xffffffffffffffd6])))
> (set (reg:SI 99)
> (plus:SI (reg:SI 98 [ *b_12(D) ])
> (const_int 42 [0x2a])))
> ])
>
> On rs6000 we have four special variants for the immediate add-with-carry
> insn patterns: imm 0, imm -1, imm pos, imm neg. All of these have
> different canonical RTL.
The i386 backend has various patterns for that too, the problem is with that
CCmode vs. CCCmode that was used originally here (otherwise sure, I can add
more).
These patterns ensure only CF is valid and so need to use CCCmode which ensures
that users will only query CF flag and nothing else.
