On Tue, Feb 1, 2022 at 4:42 AM Richard Sandiford <richard.sandif...@arm.com>
wrote:
> Christophe Lyon via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> > On Mon, Jan 31, 2022 at 7:01 PM Richard Sandiford via Gcc-patches <
> > gcc-patches@gcc.gnu.org> wrote:
> >
> >> Sorry for the slow response, was out last week.
> >>
> >> Christophe Lyon via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> >> > diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
> >> > index feeee16d320..5f559f8fd93 100644
> >> > --- a/gcc/emit-rtl.c
> >> > +++ b/gcc/emit-rtl.c
> >> > @@ -6239,9 +6239,14 @@ init_emit_once (void)
> >> >
> >> > /* For BImode, 1 and -1 are unsigned and signed interpretations
> >> > of the same value. */
> >> > - const_tiny_rtx[0][(int) BImode] = const0_rtx;
> >> > - const_tiny_rtx[1][(int) BImode] = const_true_rtx;
> >> > - const_tiny_rtx[3][(int) BImode] = const_true_rtx;
> >> > + for (mode = MIN_MODE_BOOL;
> >> > + mode <= MAX_MODE_BOOL;
> >> > + mode = (machine_mode)((int)(mode) + 1))
> >> > + {
> >> > + const_tiny_rtx[0][(int) mode] = const0_rtx;
> >> > + const_tiny_rtx[1][(int) mode] = const_true_rtx;
> >> > + const_tiny_rtx[3][(int) mode] = const_true_rtx;
> >> > + }
> >> >
> >> > for (mode = MIN_MODE_PARTIAL_INT;
> >> > mode <= MAX_MODE_PARTIAL_INT;
> >>
> >> Does this do the right thing for:
> >>
> >> gen_int_mode (-1, B2Imode)
> >>
> >> (which is used e.g. in native_decode_vector_rtx)? It looks like it
> >> would give 0b01 rather than 0b11.
> >>
> >> Maybe for non-BImode we should use const1_rtx and constm1_rtx, like with
> >> MODE_INT.
> >>
> >
> > debug_rtx ( gen_int_mode (-1, B2Imode) says:
> > (const_int -1 [0xffffffffffffffff])
> > so that looks right?
>
> Ah, right, I forgot that the mode is unused for the small constant lookup.
> But it looks like CONSTM1_RTX (B2Imode) would be (const_int 1) instead,
> even though the two should be equal.
>
Indeed!
So I changed the above loop into:
/* For BImode, 1 and -1 are unsigned and signed interpretations
of the same value. */
for (mode = MIN_MODE_BOOL;
mode <= MAX_MODE_BOOL;
mode = (machine_mode)((int)(mode) + 1))
{
const_tiny_rtx[0][(int) mode] = const0_rtx;
const_tiny_rtx[1][(int) mode] = const_true_rtx;
- const_tiny_rtx[3][(int) mode] = const_true_rtx;
+ const_tiny_rtx[3][(int) mode] = constm1_rtx;
}
which works, both constants are now equal and the validation still passes.
> >> > @@ -1679,15 +1708,25 @@ emit_class_narrowest_mode (void)
> >> > print_decl ("unsigned char", "class_narrowest_mode",
> >> "MAX_MODE_CLASS");
> >> >
> >> > for (c = 0; c < MAX_MODE_CLASS; c++)
> >> > - /* Bleah, all this to get the comment right for MIN_MODE_INT. */
> >> > - tagged_printf ("MIN_%s", mode_class_names[c],
> >> > - modes[c]
> >> > - ? ((c != MODE_INT || modes[c]->precision != 1)
> >> > - ? modes[c]->name
> >> > - : (modes[c]->next
> >> > - ? modes[c]->next->name
> >> > - : void_mode->name))
> >> > - : void_mode->name);
> >> > + {
> >> > + /* Bleah, all this to get the comment right for MIN_MODE_INT.
> */
> >> > + const char *comment_name = void_mode->name;
> >> > +
> >> > + if (modes[c])
> >> > + if (c != MODE_INT || !modes[c]->boolean)
> >> > + comment_name = modes[c]->name;
> >> > + else
> >> > + {
> >> > + struct mode_data *m = modes[c];
> >> > + while (m->boolean)
> >> > + m = m->next;
> >> > + if (m)
> >> > + comment_name = m->name;
> >> > + else
> >> > + comment_name = void_mode->name;
> >> > + }
> >>
> >> Have you tried bootstrapping the patch on a host of your choice?
> >> I would expect a warning/Werror about an ambiguous else here.
> >>
> > No I hadn't and indeed the build fails
> >
> >>
> >> I guess this reduces to:
> >>
> >> struct mode_data *m = modes[c];
> >> while (m && m->boolean)
> >> m = m->next;
> >> const char *comment_name = (m ? m : void_mode)->name;
> >>
> >> but I don't know if that's more readable.
> >>
> > but to my understanding the problem is that the ambiguous else
> > is the first one, and the code should read:
> > if (modes[c])
> > + {
> > if (c != MODE_INT || !modes[c]->boolean)
> > comment_name = modes[c]->name;
> > else
> > {
> > struct mode_data *m = modes[c];
> > while (m->boolean)
> > m = m->next;
> > if (m)
> > comment_name = m->name;
> > else
> > comment_name = void_mode->name;
> > }
> > + }
>
> Yeah. I just meant that the alternative loop was probably simpler,
> as a replacement for the outer “if”.
>
> It looks like that the outer “if” is effectively a peeled iteration of
> the while loop in the outer “else”. And the “c != MODE_INT” part ought
> to be redundant: as it stands, the boolean modes don't belong to any class.
>
> Ack, I have now:
for (c = 0; c < MAX_MODE_CLASS; c++)
{
/* Bleah, all this to get the comment right for MIN_MODE_INT. */
struct mode_data *m = modes[c];
while (m && m->boolean)
m = m->next;
const char *comment_name = (m ? m : void_mode)->name;
tagged_printf ("MIN_%s", mode_class_names[c], comment_name);
}
Andre, any chance you tried the suggestion of:
ENTRY (Pred1x16_t, V16BI, predicate, 16, pred1, 21)
ENTRY (Pred2x8_t, V8BI, predicate, 8, pred1, 21)
ENTRY (Pred4x4_t, V4BI, predicate, 4, pred1, 21)
Thanks,
Christophe
> Thanks,
> Richard
>
