Hi Tobias,
A test case (gcc/testsuite/gcc.dg/graphite/pr18792.c) came up when we removed
`graphite-scop-detection.c:limit_scops'.
The test case is a scop where entry==exit,
BB5 (*#) -> BB6 (#);
BB6 -> BB5;
In this case BB2 is out of the scop. This is basically an empty (infinite) loop
with no entry.
--
(gdb) p debug_loops(3)
loop_0 (header = 0, latch = 1, niter = )
{
bb_2 (preds = {bb_0 }, succs = {bb_8 bb_3 })
{
<bb 2>:
# VUSE <.MEM_7(D)>
_5 = *x_10(D)[3];
if (_5 < 0.0)
goto <bb 8>;
else
goto <bb 3>;
}
bb_3 (preds = {bb_2 }, succs = {bb_4 bb_7 })
{
<bb 3>:
if (_5>= 0.0)
goto <bb 4>;
else
goto <bb 7>;
}
bb_4 (preds = {bb_3 bb_8 }, succs = {bb_9 })
{
<bb 4>:
# .MEM_19 = PHI <.MEM_7(D)(3), .MEM_14(8)>
}
bb_9 (preds = {bb_4 }, succs = {bb_5 })
{
<bb 9>:
}
bb_7 (preds = {bb_3 }, succs = {bb_1 })
{
<bb 7>:
# VUSE <.MEM_7(D)>
return;
}
bb_8 (preds = {bb_2 }, succs = {bb_4 })
{
<bb 8>:
# .MEM_14 = VDEF <.MEM_7(D)>
*x_10(D)[3] = 0.0;
goto <bb 4>;
}
loop_2 (header = 5, latch = 6, niter = scev_not_known)
{
bb_5 (preds = {bb_9 bb_6 }, succs = {bb_6 })
{
<bb 5>:
# .MEM_25 = PHI <.MEM_19(9), .MEM_25(6)>
}
bb_6 (preds = {bb_5 }, succs = {bb_5 })
{
<bb 6>:
goto <bb 5>;
}
}
}
digraph all {
0 [label=<
<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
<TR><TD WIDTH="50" BGCOLOR="#ffffff"> 0 </TD></TR>
</TABLE>>, shape=box, style="setlinewidth(0)"]
2 [label=<
<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
<TR><TD WIDTH="50" BGCOLOR="#ffffff"> 2 </TD></TR>
</TABLE>>, shape=box, style="setlinewidth(0)"]
3 [label=<
<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
<TR><TD WIDTH="50" BGCOLOR="#ffffff"> 3 </TD></TR>
</TABLE>>, shape=box, style="setlinewidth(0)"]
4 [label=<
<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
<TR><TD WIDTH="50" BGCOLOR="#ffffff"> 4 </TD></TR>
</TABLE>>, shape=box, style="setlinewidth(0)"]
9 [label=<
<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
<TR><TD WIDTH="50" BGCOLOR="#ffffff"> 9 </TD></TR>
</TABLE>>, shape=box, style="setlinewidth(0)"]
5 [label=<
<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
<TR><TD WIDTH="50" BGCOLOR="#e41a1c"> 5*# </TD></TR>
</TABLE>>, shape=box, style="setlinewidth(0)"]
6 [label=<
<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
<TR><TD WIDTH="50" BGCOLOR="#e41a1c"> 6 </TD></TR>
</TABLE>>, shape=box, style="setlinewidth(0)"]
7 [label=<
<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
<TR><TD WIDTH="50" BGCOLOR="#ffffff"> 7 </TD></TR>
</TABLE>>, shape=box, style="setlinewidth(0)"]
8 [label=<
<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
<TR><TD WIDTH="50" BGCOLOR="#ffffff"> 8 </TD></TR>
</TABLE>>, shape=box, style="setlinewidth(0)"]
1 [label=<
<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
<TR><TD WIDTH="50" BGCOLOR="#ffffff"> 1 </TD></TR>
</TABLE>>, shape=box, style="setlinewidth(0)"]
0 -> 2;
2 -> 8;
2 -> 3;
3 -> 4;
3 -> 7;
4 -> 9;
9 -> 5;
5 -> 6;
6 -> 5;
7 -> 1;
8 -> 4;
}
-Aditya
----------------------------------------
> Date: Tue, 30 Jun 2015 08:11:01 +0200
> From: [email protected]
> To: [email protected]; [email protected]
> CC: [email protected]
> Subject: Re: [PATCH] Discard Scops for which entry==exit
>
> On 06/30/2015 02:09 AM, Sebastian Pop wrote:
>> On Mon, Jun 29, 2015 at 3:04 PM, Aditya Kumar <[email protected]> wrote:
>>> In this patch we discard the scops where entry and exit are the same BB.
>>> This is an effort to remove graphite-scop-detection.c:limit_scops.
>>> Removing the limit_scops function introduces correctness regressions.
>>> We are making relevant changes in incremental steps to fix those bugs,
>>> and finally we intend to remove limit_scops.
>>>
>>> 2015-06-29 Aditya Kumar <[email protected]>
>>> Sebastian Pop <[email protected]>
>>>
>>> * graphite-scop-detection.c (build_scops_1): Discard scops for which
>>> entry==exit
>>
>> Looks good to me.
>> Let's wait on comments from Tobi before pushing this patch.
>
> Hi Sebastian,
>
> the commit message should probably give a short reasoning why scops with
> entry == exit need to be discarded. I currently don't see why they would
> be incorrect/problematic (despite being possibly very small/empty).
>
> Tobias
