Christophe Lyon via Gcc-patches <[email protected]> writes:
> On Mon, Jan 31, 2022 at 7:01 PM Richard Sandiford via Gcc-patches <
> [email protected]> wrote:
>
>> Sorry for the slow response, was out last week.
>>
>> Christophe Lyon via Gcc-patches <[email protected]> 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.
>> > @@ -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.
Thanks,
Richard
