Patchwork [RTL] Fix PR 51106

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Submitter Andrey Belevantsev
Date April 2, 2012, 2:56 p.m.
Message ID <4F79BE19.8050905@ispras.ru>
Download mbox | patch
Permalink /patch/150172/
State New
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Comments

Andrey Belevantsev - April 2, 2012, 2:56 p.m.
Hello,

On 19.01.2012 18:40, Jakub Jelinek wrote:
> On Thu, Jan 19, 2012 at 06:13:58PM +0400, Andrey Belevantsev wrote:
>> 2012-01-19  Andrey Belevantsev<abel@ispras.ru>
>>
>> 	PR target/51106
>> 	* function.c (instantiate_virtual_regs_in_insn): Use
>> delete_insn_and_edges when removing a wrong asm insn.
>
> This is ok for trunk.
>

After Richi's RTL generation related cleanups went it, the extra 
cleanup_cfg call was added so we are no longer lucky to have the proper 
fallthru edge in this case.  The PR trail has the patch to purge_dead_edges 
making it consider this situation, but I still prefer the below patch that 
fixes only the invalid asm case.  The reason is that I think it unlikely 
that after initial RTL expansion (of which the instantiate virtual regs 
pass seems to be the part) we will get the problematic situation.  However, 
I'm happy to test the PR trail patch, too.

Tested fine on x86-64, ok for trunk?

Andrey

2012-04-02  Andrey Belevantsev  <abel@ispras.ru>

	PR target/51106
	PR middle-end/52650
	* function.c (instantiate_virtual_regs_in_insn): Make sure to set
	the proper fallthru bits when removing a wrong jump asm.
Jakub Jelinek - April 3, 2012, 9:36 a.m.
On Mon, Apr 02, 2012 at 06:56:25PM +0400, Andrey Belevantsev wrote:
> After Richi's RTL generation related cleanups went it, the extra
> cleanup_cfg call was added so we are no longer lucky to have the
> proper fallthru edge in this case.  The PR trail has the patch to
> purge_dead_edges making it consider this situation, but I still
> prefer the below patch that fixes only the invalid asm case.  The
> reason is that I think it unlikely that after initial RTL expansion
> (of which the instantiate virtual regs pass seems to be the part) we
> will get the problematic situation.  However, I'm happy to test the
> PR trail patch, too.

I don't like blindly changing edge into FALLTHRU, generally the edge
could be abnormal, or EH, etc. and making that fallthru is not a good idea.
I'd prefer if wherever the fallthru edge is removed the other normal edge(s)
are adjusted.

	Jakub
Andrey Belevantsev - April 4, 2012, 7:58 a.m.
On 03.04.2012 13:36, Jakub Jelinek wrote:
> On Mon, Apr 02, 2012 at 06:56:25PM +0400, Andrey Belevantsev wrote:
>> After Richi's RTL generation related cleanups went it, the extra
>> cleanup_cfg call was added so we are no longer lucky to have the
>> proper fallthru edge in this case.  The PR trail has the patch to
>> purge_dead_edges making it consider this situation, but I still
>> prefer the below patch that fixes only the invalid asm case.  The
>> reason is that I think it unlikely that after initial RTL expansion
>> (of which the instantiate virtual regs pass seems to be the part) we
>> will get the problematic situation.  However, I'm happy to test the
>> PR trail patch, too.
>
> I don't like blindly changing edge into FALLTHRU, generally the edge
> could be abnormal, or EH, etc. and making that fallthru is not a good idea.
> I'd prefer if wherever the fallthru edge is removed the other normal edge(s)
> are adjusted.

Well, as I mentioned in 
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51106#c18 the removal happens 
in try_optimize_cfg around line 2617, that's the code that deals with 
removing trivially empty block (in the PR case, the succ of the asm goto 
block is trivially empty).  After that we have an asm goto acting as an 
unconditional jump with a single succ edge and no fallthru bit, which seems 
perfectly fine.  We get into trouble when we actually realize that the asm 
is bogus.  Thus I've tried to fix it up at this time.  The options that we 
briefly discussed on IRC with Richi are as follows:

- Fix up try_optimize_cfg in the case of asm gotos, but it is not clear to 
me how do we do this -- we don't yet distinguish between good and bad asm 
goto at this point;

- Fix up function.c as I did but make it more robust.  Either handle more 
cases with strange edges (EH seems also possible after introducing the 
throw attribute for asms), or just remove the asm and insert the 
unconditional jump pointing to the place where the asm was, retaining all 
the flags;

- Fix up purge_dead_edges. as I did initially in 
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51106#c16.  When we find a 
situation of no jump at the end of block and no fallthru edge, assert this 
happens only with single_succ_p and actually make this edge fallthru. 
(Probably also watch out whether we need to make it fake or whatever.)  Or 
as Richi tried, just accept the situation of having no successors here, as 
in -- no fallthru edge on entry to purge_dead_edges and no jump means no 
successors, period.

I think that just nobody deleted unconditional jumps with 
delete_insn_and_edges previously, otherwise I don't understand why this did 
not trigger.

Thoughts?

Andrey

>
> 	Jakub

Patch

diff --git a/gcc/function.c b/gcc/function.c
index 3e903ef..a2638bb 100644
--- a/gcc/function.c
+++ b/gcc/function.c
@@ -1730,6 +1730,15 @@  instantiate_virtual_regs_in_insn (rtx insn)
        if (!check_asm_operands (PATTERN (insn)))
         {
           error_for_asm (insn, "impossible constraint in %<asm%>");
+         if (JUMP_P (insn))
+           {
+             basic_block bb = BLOCK_FOR_INSN (insn);
+             edge e;
+
+             if (single_succ_p (bb)
+                 && !((e = single_succ_edge (bb))->flags & EDGE_FALLTHRU))
+               e->flags |= EDGE_FALLTHRU;
+           }
           delete_insn_and_edges (insn);
         }
      }