On Thu, Apr 7, 2016 at 10:30 AM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On April 6, 2016 8:21:35 PM GMT+02:00, "Bin.Cheng" <amker.ch...@gmail.com>
> wrote:
>>On Wed, Apr 6, 2016 at 5:07 PM, Bin.Cheng <amker.ch...@gmail.com>
>>wrote:
>>> Hi,
>>> Function if_convertible_phi_p has below check on virtual PHI nodes:
>>>
>>>
>>> if (any_mask_load_store)
>>> return true;
>>>
>>> /* When there were no if-convertible stores, check
>>> that there are no memory writes in the branches of the loop to
>>be
>>> if-converted. */
>>> if (virtual_operand_p (gimple_phi_result (phi)))
>>> {
>>> imm_use_iterator imm_iter;
>>> use_operand_p use_p;
>>>
>>> if (bb != loop->header)
>>> {
>>> if (dump_file && (dump_flags & TDF_DETAILS))
>>> fprintf (dump_file, "Virtual phi not on loop->header.\n");
>>> return false;
>>> }
>>>
>>> FOR_EACH_IMM_USE_FAST (use_p, imm_iter, gimple_phi_result
>>(phi))
>>> {
>>> if (gimple_code (USE_STMT (use_p)) == GIMPLE_PHI
>>> && USE_STMT (use_p) != phi)
>>> {
>>> if (dump_file && (dump_flags & TDF_DETAILS))
>>> fprintf (dump_file, "Difficult to handle this virtual
>>phi.\n");
>>> return false;
>>> }
>>> }
>>> }
>>>
>>> Since the check is short-cut by any_mask_load_store, when the check
>>is
>>> triggered, it means there is virtual phi node but no conditional
>>> memory stores? Is this possible? Plus, any_mask_load_store is set
>>by
>>> below code in if_convertible_gimple_assign_stmt_p:
>>> if (ifcvt_can_use_mask_load_store (stmt))
>>> {
>>> gimple_set_plf (stmt, GF_PLF_2, true);
>>> *any_mask_load_store = true;
>>> return true;
>>> }
>>>
>>> So in theory it's possible to skip aforementioned check when only
>>mask
>>> load is encountered.
>>>
>>> Any ideas?
>>It's possible to have a loop like:
>>
>><bb header>
>> .MEM_2232 = PHI <.MEM_574(179), .MEM_1247(183)>
>> ...
>> if (cond)
>> goto <bb 1>
>> else
>> goto <bb2>
>>
>><bb 1>: //empty
>><bb2>:
>> .MEM_1247 = PHI <.MEM_2232(180), .MEM_2232(181)>
>> if (cond2)
>> goto <bb exit>
>> else
>> goto <bb latch>
>>
>><bb latch>:
>> goto <bb header>
>>
>>So can we handle the PHI which can be degenerated in if-cvt?
>
> I believe the check is bogus and we should drop it.
We do need to handle aforementioned case though. I suppose an
additional pass of dce before if-conv will fix the problem, or some
light weight functions can?
Thanks,
bin
