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Re: [PATCH, PR81192] Fix sigsegv in find_same_succ_bb


On Sun, 2 Jul 2017, Tom de Vries wrote:

> Hi,
> 
> consider this test-case:
> ...
> unsigned a;
> int b, c;
> 
> static int
> fn1 (int p1, int p2)
> {
>   return p1 > 2147483647 - p2 ? p1 : p1 + p2;
> }
> 
> void
> fn2 (void)
> {
>   int j;
>   a = 30;
>   for (; a;)
>     for (; c; b = fn1 (j, 1))
>       ;
> }
> ...
> 
> When compiling the test-case with -Os, just before tail-merge it looks as in
> before.pdf.
> 
> During tail-merge, it runs into a sigsegv.
> 
> What happens is the following:
> - tail-merge decides to merge blocks 4 and 6, and removes block 6.
> - bb8, a predecessor of block 6, is marked as member of
>   deleted_bb_preds.
> - during update_worklist, same_succ_flush_bb is called for bb8
> - same_succ_flush_bb runs into a sigsegv because
>   BB_SAME_SUCC (bb8) == NULL
> - the reason that BB_SAME_SUCC (bb8) == NULL, is because it hit the
>   bb->loop_father->latch == bb clause in find_same_succ_bb at the start
>   of the tail-merge pass.
> 
> This patch fixes the sigsegv by doing an early-out in same_succ_flush_bb if
> BB_SAME_SUCC () == NULL.
> 
> Bootstrapped and reg-tested on x86_64.
> 
> OK for trunk and gcc-[567]-branch?

Ok for trunk and branches.  Mind the gcc-6 branch is frozen right now.

Thanks,
Richard.

> Thanks,
> - Tom
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)


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