Joern Rennecke <joern.renne...@embecosm.com> writes:
> Quoting Richard Sandiford <rdsandif...@googlemail.com>:
>> I think instead the set-up loop should have:
>>
>> if (GET_CODE (body) == ADDR_VEC || GET_CODE (body) == ADDR_DIFF_VEC)
>> {
>> #ifdef CASE_VECTOR_SHORTEN_MODE
>> if (increasing && GET_CODE (body) == ADDR_DIFF_VEC)
>> PUT_MODE (body, CASE_VECTOR_SHORTEN_MODE (0, 0, body));
>> #endif
>> /* This only takes room if read-only data goes into the text
>> section. */
>> if (JUMP_TABLES_IN_TEXT_SECTION
>> || readonly_data_section == text_section)
>> insn_lengths[uid] = (XVECLEN (body,
>> GET_CODE (body) == ADDR_DIFF_VEC)
>> * GET_MODE_SIZE (GET_MODE (body)));
>> /* Alignment is handled by ADDR_VEC_ALIGN. */
>> }
>>
>> (with just the CASE_VECTOR_SHORTEN_MODE part being new).
>> We then start with the most optimistic length possible,
>> as with everything else.
>
> Well, ports could always tailor the initial mode with CASE_VECTOR_MODE,
> but it is indeed simpler when the branch shortening pass provide a
> sensible initialization.
That, plus I think CASE_VECTOR_MODE should always be the conservatively
correct mode.
> How about putting this at the end of this block:
> #ifdef CASE_VECTOR_SHORTEN_MODE
> if (optimize)
> {
> /* Look for ADDR_DIFF_VECs, and initialize their minimum and maximum
> label fields. */
OK, that does sound better.
> With regards to in what way it would make sense to change increasing to
> something other than optimize, I think we could have a flag to control
> this, which is turned on by default at -O1; it could then be turned off
> if people want only some other (quicker?) optimizations, or if they want
> to work around a machine-specific bug triggered by a single source file.
> I.e. optimize might be set when increasing is not. Vice versa it makes
> little sense - iterating branch shortening is certainly an optimization.
> So is using CASE_VECTOR_SHORTEN_MODE, but it does not require iterating,
> as we've already calculated the required addresses in the preliminary pass
> before the main loop.
> So it makes sense to keep the condition for CASE_VECTOR_SHORTEN_MODE
> as 'optimize' (or use a different flag, e.g. case_vector_shorten_p),
> and have this at the end of this initial CASE_VECTOR_SHORTEN_MODE block:
>
> flags.min_after_base = min > rel;
> flags.max_after_base = max > rel;
> ADDR_DIFF_VEC_FLAGS (pat) = flags;
>
> + if (increasing)
> + PUT_MODE (body, CASE_VECTOR_SHORTEN_MODE (0, 0, body));
> }
> }
> #endif /* CASE_VECTOR_SHORTEN_MODE */
>
> continue;
> }
> #endif /* CASE_VECTOR_SHORTEN_MODE */
>
>
>
>> The main shortening if statement should then be conditional on:
>>
>> #ifdef CASE_VECTOR_SHORTEN_MODE
>> if (increasing
>> && JUMP_P (insn)
>> && GET_CODE (PATTERN (insn)) == ADDR_DIFF_VEC)
>
> As explained above, CASE_VECTOR_SHORTEN_MODE can make in the
> decreasing/non-iterating branch shortening mode.
>
> so I think the code for changing the mode should be
> if (!increasing
> || (GET_MODE_SIZE (vec_mode)
> >= GET_MODE_SIZE (GET_MODE (body))))
> PUT_MODE (body, vec_mode);
OK, sounds good.
Richard
