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Re: [4.5] Autoinc support in tree-ssa-loop-ivopts.c

Zdenek Dvorak wrote:

Another thing: is this really the right condition to detect? I would
expect autoinc modes to be useful even in cases where more than one
memory reference and possibly also the exit test are based on the
autoincremented induction variable.
Here's a new patch which has been extensively changed.

One possible condition to test for would be whether the uses closest to the position of the biv increment (either before or after) allow autoincrement. That seems to me rather expensive since we'd have to walk the basic blocks a few times to determine an order for the uses, so I've chosen something slightly weaker: either all uses before the increment, or all uses after the increment must allow autoincrement. This condition gives us a strict superset of opportunites compared to the one used by the previous patch.

The cost of the code in iv_ca_recount_cost is reduced by this since most of the tracking is now done in iv_ca_set{_no,}_cp.

I've added code to test for the availability of each of the four autoinc addressing modes for every machine mode.

Not too much testing yet other than comparing generated code for a lot of examples. If this looks OK to you, I'll start bootstrap etc.

yes, this looks fine.

+ autoinc = false;
+ msize = GET_MODE_SIZE (mem_mode);
+ autoinc_offset = offset;
+ if (stmt_after_inc)
+ autoinc_offset += cstep * ratio; + if (s_offset || symbol_present || var_present || ratio != 1)
+ autoinc = false;
+ else if (0
+ || (has_postinc[mem_mode] && autoinc_offset == 0
+ && msize == cstep)
+ || (has_postdec[mem_mode] && autoinc_offset == 0
+ && msize == -cstep)
+ || (has_preinc[mem_mode] && autoinc_offset == msize
+ && msize == cstep)
+ || (has_predec[mem_mode] && autoinc_offset == -msize
+ && msize == -cstep))
+ autoinc = true;

This is rather hard to read; as far as I can tell, your code is equivalent to

autoinc = false;
if (s_offset == 0 && !symbol_present && !var_present && ratio == 1)
    msize = GET_MODE_SIZE (mem_mode);
    if ((has_postinc[mem_mode] && !stmt_after_inc && msize == cstep)
        || (has_postdec[mem_mode] && !stmt_after_inc && msize == -cstep)
        || (has_preinc[mem_mode] && stmt_after_inc && msize == cstep)
        || (has_predec[mem_mode] && stmt_after_inc && msize == -cstep))
       autoinc = true;

If it is, then that's unintentional. I think the first test for s_offset shouldn't be in there, it was part of one of those late changes before submission...
An example - for postinc, an address before the increment should have offset 0, while an address after the increment should have offset -4.

Also, the if (0) part has to go, that's from when I was still using #ifdef HAVE_...CREMENT blocks.

This loop can be avoided, by doing the computation in iv_ca_set_no_cp
and iv_ca_set_cp;  [...]

However, I find the code as it is now more easily understandable and modifiable than you suggestion. Do you believe it'll make a measurable change?

Bernd -- This footer brought to you by insane German lawmakers. Analog Devices GmbH Wilhelm-Wagenfeld-Str. 6 80807 Muenchen Sitz der Gesellschaft Muenchen, Registergericht Muenchen HRB 40368 Geschaeftsfuehrer Thomas Wessel, William A. Martin, Margaret Seif

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