Re: [PATCH GCC8][07/33]Offset validity check in address expression

[Richard Biener <richard dot guenther at gmail dot com>]

On Tue, May 2, 2017 at 7:06 PM, Bin.Cheng <amker.cheng@gmail.com> wrote:
> On Mon, Apr 24, 2017 at 11:34 AM, Richard Biener
> <richard.guenther@gmail.com> wrote:
>> On Tue, Apr 18, 2017 at 12:41 PM, Bin Cheng <Bin.Cheng@arm.com> wrote:
>>> Hi,
>>> For now, we check validity of offset by computing the maximum offset then checking if
>>> offset is smaller than the max offset.  This is inaccurate, for example, some targets
>>> may require offset to be aligned by power of 2.  This patch introduces new interface
>>> checking validity of offset.  It also buffers rtx among different calls.
>>>
>>> Is it OK?
>>
>> -  static vec<HOST_WIDE_INT> max_offset_list;
>> -
>> +  auto_vec<rtx> addr_list;
>>    as = TYPE_ADDR_SPACE (TREE_TYPE (use->iv->base));
>>    mem_mode = TYPE_MODE (TREE_TYPE (*use->op_p));
>>
>> -  num = max_offset_list.length ();
>> +  num = addr_list.length ();
>>    list_index = (unsigned) as * MAX_MACHINE_MODE + (unsigned) mem_mode;
>>    if (list_index >= num)
>>
>> num here is always zero and thus the compare is always true.
>>
>> +      addr_list.safe_grow_cleared (list_index + MAX_MACHINE_MODE);
>> +      for (; num < addr_list.length (); num++)
>> +       addr_list[num] = NULL;
>>
>> the loop is now redundant (safe_grow_cleared)
>>
>> +  addr = addr_list[list_index];
>> +  if (!addr)
>>      {
>>
>> always true again...
>>
>> I wonder if you really indented to drop 'static' from addr_list?
>> There's no caching
>> across function calls.
> Right, the redundancy is because I tried to cache across function
> calls with declarations like:
>   static unsigned num = 0;
>   static GTY ((skip)) rtx *addr_list = NULL;
> But this doesn't work, the addr_list[list_index] still gets corrupted somehow.

Well, you need GTY (()), not GTY((skip)) on them.  Not sure if it works
for function-scope decls, you have to check.  Look at whether a GC
root is created for the variable in gt-tree-ssa-loop-ivopts.h (need to tweak
GTFILES in the makefile plus include that generated file).  tree-ssa-address.c
uses a global root for mem_addr_template_list for example.

Richard.



> Thanks,
> bin
>>
>> +         /* Split group if aksed to, or the offset against the first
>> +            use can't fit in offset part of addressing mode.  IV uses
>> +            having the same offset are still kept in one group.  */
>> +         if (offset != 0 &&
>> +             (split_p || !addr_offset_valid_p (use, offset)))
>>
>> && goes to the next line.
>>
>> Richard.
>>
>>
>>
>>> Thanks,
>>> bin
>>> 2017-04-11  Bin Cheng  <bin.cheng@arm.com>
>>>
>>>         * tree-ssa-loop-ivopts.c (compute_max_addr_offset): Delete.
>>>         (addr_offset_valid_p): New function.
>>>         (split_address_groups): Check offset validity with above function.