https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104985
--- Comment #15 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Segher Boessenkool from comment #14)
> Are you sure this only ever handles pseudos? It is completely broken if not.
Yes, I am.
All the 4 uses of SUBST_MODE look like:
if (regno < FIRST_PSEUDO_REGISTER)
newpat_dest = gen_rtx_REG (compare_mode, regno);
else
{
SUBST_MODE (regno_reg_rtx[regno], compare_mode);
newpat_dest = regno_reg_rtx[regno];
}
> Changing the mode of regno_reg_rtx[...] is always wrong, too.
>
> Patches 2 and 3 look better, but need a lot more explanation. What does "m"
> mean, to start with?
m stands for mode.
enum undo_kind { UNDO_RTX, UNDO_INT, UNDO_MODE, UNDO_LINKS };
...
union { rtx r; int i; machine_mode m; struct insn_link *l; } old_contents;
union { rtx *r; int *i; struct insn_link **l; } where;
There are 2 ways to look at those names, one is that they somehow describe
their type (but for where what they point to), the other is that it
sign the undo_kind (first letter after UNDO_ in lowercase).
In the latter case, UNDO_MODE was the only outlier that used where.r instead of
where.m.
Note, I've posted the patch (last version) to gcc-patches, so patch review can
happen there:
https://gcc.gnu.org/pipermail/gcc-patches/2022-March/592450.html
