------- Comment #8 from jakub at gcc dot gnu dot org  2010-08-30 14:05 -------
The other issue comes from MEM_ATTRS caching.
considers MEM_EXPR to be equal if:
279  && (p->expr == q->expr
280      || (p->expr != NULL_TREE && q->expr != NULL_TREE
281  && operand_equal_p (p->expr, q->expr, 0))));

With -g there happens to be a different MEM_ATTRS in the cache than without -g,
and as both are operand_equal_p, gcc doesn't care which one it chooses.

As -fcompare-debug does a textual comparison, I guess we'd for
-fdump-final-insns need to dump something that is stable.  E.g. it could print
just iterative_hash_expr (MEM_EXPR (memref), 0) instead of printing the
expression.  I'm not sure whether that would fix this completely, because
I believe if there are collisions, mem_attrs_htab_eq could return true even if
mem_attrs_htab_hash is different.  Therefore perhaps mem_attrs_htab_eq should
also check (size_t) iterative_hash_expr (p->expr, 0) == (size_t)
iterative_hash_expr (q->expr, 0) if operand_equal_p returned true.



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