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Re: Aliasing: look through pointer's def stmt

On Fri, Oct 25, 2013 at 10:59 AM, Richard Biener
<> wrote:
> On Fri, Oct 25, 2013 at 8:11 AM, Marc Glisse <> wrote:
>> On Thu, 24 Oct 2013, Jeff Law wrote:
>>> On 10/24/13 23:23, Marc Glisse wrote:
>>>> Hello,
>>>> I noticed that in some cases we were failing to find aliasing
>>>> information because we were only looking at an SSA_NAME variable,
>>>> missing the fact that it was really an ADDR_EXPR. The attached patch
>>>> passes bootstrap+testsuite, does it make sense? (I am a bit afraid of
>>>> losing some type information for instance)
>>>> I didn't investigate the 2 tests where I had to remove dg-bogus, because
>>>> removing dg-bogus sounds like a bonus...
>>>> 2013-10-25  Marc Glisse  <>
>>>> gcc/
>>>>      * tree-ssa-alias.c (ao_ref_init_from_ptr_and_size): Look for an
>>>>      ADDR_EXPR in the defining statement.
>>> Shouldn't the ADDR_EXPR have been propagated into the use?
>> Maybe when the address is a constant, but here it comes from malloc.
> points-to should have "propagated" the alias info, so no, looking at
> def-stmts in random places like this isn't ok.  Where does alias info
> get lost?

It doesn't get lost, but this is the missed optimization that malloc
results still alias with global pointers (here a function argument).
Taking into account the offset shouldn't change anything.

I suppose you are looking for the memcpy to be folded into an
assignment?  Which ao_ref_from_ptr_and_size is critical for
the transform - it doesn't seem to be the one in memory op folding.


> Thanks,
> Richard.
>> --
>> Marc Glisse

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