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Re: [PATCH] Fix PR42509, wrong-code from the RTL alias oracle


Richard Guenther wrote:

> 	PR middle-end/42509
> 	* alias.c (nonoverlapping_memrefs_p): For spill-slot accesses
> 	require a non-NULL MEM_OFFSET.

What are your thoughts on backporting this to the 4.4 branch?

It seems that this problem never existed in 4.3 and earlier because
it was introduced by IRA and the spill_slot_decl logic; and the bug
is fixed in 4.5 and later.  However, it exists as latent bug in 4.4.

Now, I was unable to construct a problem to deliberately trigger
the issue (you need just the right interaction between reload,
alias, and cross-jumping ...).  However, it seems to have occured
in an out-of-tree port:
http://gcc.gnu.org/ml/gcc/2010-04/msg00243.html

Since the fix looks to me as if it couldn't really have any adverse
effects, and it fixes a potentially hard to track down latent wrong
code generation bug, it might be good to backport ...

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com


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