Asking the third time, why remove Reset_live_stmt() and add Set_bb(null)?
Sun
On Fri, Dec 23, 2011 at 2:29 PM, Jian-Xin Lai <laij...@gmail.com> wrote:
> The line is this one:
> stmt->Reset_live_stmt(); // WHIRL SSA: mark stmt dead
> This line is introduced by WHIRL SSA. The rename pass is in WHIRL SSA,
> not in HSSA. It's different problem.
>
> 2011/12/23 Sun Chan <sun.c...@gmail.com>:
>> I am still confused. You said you "added this line when we hit a
>> bug...", which line? I also recall Fred has issue with you folks
>> adding an extra rename pass.
>> My question, that you have not address, is why add this Set_bb(NULL)
>> and remove the line
>> Reset_live_stmt()?
>> Sun
>>
>> On Fri, Dec 23, 2011 at 2:17 PM, Jian-Xin Lai <laij...@gmail.com> wrote:
>>> Set_bb(NULL) is used to distinguish the real dead code(already removed
>>> from the BB) and unvisited code (marked to dead at the beginning of
>>> DCE). An alternative approach is to introduce a new flag for real dead
>>> code but it requires more changes. Since the statement has been
>>> removed from the BB, I think it's OK to set the BB to NULL.
>>>
>>> I recalled the reason why I added this line when we hit a bug in WHIRL
>>> SSA. It's also caused by the similar case that an opnd of phi comes
>>> from a chi associated to a dead statement and the version of that phi
>>> opnd is wrong. We added an extra rename pass to WHIRL SSA to correct
>>> the version. With the extra rename pass, this change becomes
>>> unnecessary. (This rename pass is necessary because the WHIRL CFG is
>>> not identical to HSSA CFG and the rename pass is needed to correct the
>>> order of phi opnds.)
>>>
>>> 2011/12/22 Sun Chan <sun.c...@gmail.com>:
>>>> can you go over why the second change, set_BB(null)? And remove the
>>>> mark Reset_live_stmt()?
>>>> Sun
>>>>
>>>> On Thu, Dec 22, 2011 at 3:54 PM, Jian-Xin Lai <laij...@gmail.com> wrote:
>>>>> Hi,
>>>>>
>>>>> Here is a smaller case for bug #897 and a new patch based on Gang's
>>>>> current work. Could a gatekeeper review it? Thank you very much.
>>>>>
>>>>> A smaller case:
>>>>> 1 int g_1;
>>>>> 2 int* g_2;
>>>>> 3 int* func(int* p_1, short p_2) {
>>>>> 4 int **l_1;
>>>>> 5 const unsigned long l_2 = 0x2A1DFCF9L;
>>>>> 6 for ( ; ; p_2 = foo() ) {
>>>>> 7 int ***l_3 = &l_1;
>>>>> 8 (*l_3) = &g_2;
>>>>> 9 if (!l_2) {
>>>>> 10 // The following code is unreachable
>>>>> 11 if ((bar())) {
>>>>> 12 (*g_2) |= g_1;
>>>>> 13 (**l_1) |= (*p_1);
>>>>> 14 g_2 = &g_1;
>>>>> 15 }
>>>>> 16 }
>>>>> 17 }
>>>>> 18 }
>>>>>
>>>>> in DCE phase, the unreachable code elimination runs at first and all
>>>>> the statements in the if block is removed and set to NOT_LIVE. In the
>>>>> later Dead store elimination phase, as Gang's explaination, we follow
>>>>> the U-D chain of g_2, which is a global variable and has CHI on line
>>>>> 6(foo), 11(bar), 12 (*g_2) and a real dec in line 14. When we mark the
>>>>> call of foo (line 6) to be LIVE, the CHI of g_2 is also LIVE and
>>>>> following the U-D chain, the CHI's on bar() and (*g_2) is also marked
>>>>> to LIVE. When marking (*g_2) to live, we also mark that BB to live.
>>>>> But the BB is empty (all statements have been removed in earlier
>>>>> phase) and the assertion occures.
>>>>>
>>>>> Here is a new patch:
>>>>> Index: osprey/be/opt/opt_dce.cxx
>>>>> ===================================================================
>>>>> --- osprey/be/opt/opt_dce.cxx (revision 3855)
>>>>> +++ osprey/be/opt/opt_dce.cxx (working copy)
>>>>> @@ -2619,7 +2619,10 @@
>>>>> // NOTE: May at some time always have a defining statement, so
>>>>> // we could remove the check for a null defstmt
>>>>> // (i.e., if live-in values get some dummy def stmt)
>>>>> - if ( cr->Defstmt() != NULL && !cr->Defstmt()->Live_stmt() ) {
>>>>> + // if defining statement doesn't belong to any BB, it's been
>>>>> + // removed in early unreachable code elimination phase.
>>>>> + if ( cr->Defstmt() != NULL && !cr->Defstmt()->Live_stmt() &&
>>>>> + cr->Defstmt()->Bb() != NULL ) {
>>>>> // if we're making this statement live just because it's
>>>>> // associated with a chi, see if we can get rid of "i = i"
>>>>> // assignments. This only happens when zero-version is
>>>>> Index: osprey/be/opt/opt_bb.cxx
>>>>> ===================================================================
>>>>> --- osprey/be/opt/opt_bb.cxx (revision 3855)
>>>>> +++ osprey/be/opt/opt_bb.cxx (working copy)
>>>>> @@ -734,6 +734,7 @@
>>>>>
>>>>> _stmtlist.Remove(stmt);
>>>>> - stmt->Reset_live_stmt(); // WHIRL SSA: mark stmt dead
>>>>> + stmt->Set_bb(NULL);
>>>>> }
>>>>>
>>>>> void
>>>>>
>>>>> If the statement has been removed from the BB, we reset its BB to
>>>>> NULL. In the later phase, if a statement's BB is NULL, which means the
>>>>> statement has been removed and we don't need to mark it to live.
>>>>> Reseting the bb of dead statement to NULL also helps preventing more
>>>>> bugs when trying to traverse the BB.
>>>>>
>>>>> --
>>>>> Regards,
>>>>> Lai Jian-Xin
>>>>>
>>>>> ------------------------------------------------------------------------------
>>>>> Write once. Port to many.
>>>>> Get the SDK and tools to simplify cross-platform app development. Create
>>>>> new or port existing apps to sell to consumers worldwide. Explore the
>>>>> Intel AppUpSM program developer opportunity. appdeveloper.intel.com/join
>>>>> http://p.sf.net/sfu/intel-appdev
>>>>> _______________________________________________
>>>>> Open64-devel mailing list
>>>>> Open64-devel@lists.sourceforge.net
>>>>> https://lists.sourceforge.net/lists/listinfo/open64-devel
>>>
>>>
>>>
>>> --
>>> Regards,
>>> Lai Jian-Xin
>
>
>
> --
> Regards,
> Lai Jian-Xin
------------------------------------------------------------------------------
Write once. Port to many.
Get the SDK and tools to simplify cross-platform app development. Create
new or port existing apps to sell to consumers worldwide. Explore the
Intel AppUpSM program developer opportunity. appdeveloper.intel.com/join
http://p.sf.net/sfu/intel-appdev
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