On April 8, 2016 4:55:59 PM GMT+02:00, "Bin.Cheng" <amker.ch...@gmail.com>
wrote:
>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?
I don't see any issue with the above?
Richard.
>Thanks,
>bin
