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RE: ICE in gcc.dg/pr77834.c test for MIPS


> From: Segher Boessenkool
> 
> Ah.  Is there a PR for it yet?  Please open one, if not.
> 

Yes, PR79150. I got carried away with the mailing and forgot about the PR, sorry.
I have updated the PR thread with all of the things we've discussed in this thread (and some more).
Let's continue this discussion over there.

> 
> So this is generated during expand?  I don't see how it ends up on an
> edge.
> 

Yes, everything is happening during expand. I tried to explain some of this in
my update to the PR thread.

> > In some cases there will be no loop,
> > some cases there will be a loop ending with the conditional jump and
> > some cases will have a loop and other instructions after the conditional
> > jump. The 1st and 3rd form will get through the logic in
> > commit_one_edge_insertion (albeit that the 3rd form will have incorrect
> > cfg actually) but the 2nd form is rejected because of ending with a jump.
> 
> You can easily turn the 2nd form into the 3rd by emitting some no-op
> instruction last.  If you can live with 3rd for GCC 7, that may be a
> good solution for now.
> 

This is a good point, but I don't know if it's the right solution.

> > Other than coping with the potential for sub blocks here or letting them
> > through and leaving later code to split the blocks then I see no other
> > way forward.  I agree it should be possible to process just the blocks
> > with jump instructions in the middle and that is actually going to be
> > exactly one block in this case.  I don't know if updating the CFG while
> > edges are being iterated on in commit_edge_insertions is safe though
> > and am somewhat out of my comfort zone in general!
> 
> Yeah I'm really not seeing where/when your movmem is emitted.
> 

It is emitted through emit_partition_copy in insert_partition_copy_on_edge
(gcc/tree-outof-ssa.c:261).

Regards,
Toma


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