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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