[Bug tree-optimization/32723] [4.2 Regression] memory hog in solve_graph

["dberlin at dberlin dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #16 from dberlin at gcc dot gnu dot org  2007-10-31 14:22 -------
Subject: Re:  [4.2 Regression] memory hog in solve_graph

On 31 Oct 2007 13:07:57 -0000, rguenth at gcc dot gnu dot org
<gcc-bugzilla@gcc.gnu.org> wrote:
>
>
> ------- Comment #15 from rguenth at gcc dot gnu dot org  2007-10-31 13:07 -------
> The memory is temporarily needed now by solve_graph(), because the graph has
> 48902 nodes.

48902 nodes is not a lot for the solver, to be honest.

>  On the mainline we have only 3 constraints while for 4.2 we have
> thousands:
>
> ANYTHING = &ANYTHING
> READONLY = &ANYTHING
> INTEGER = &ANYTHING
> ESCAPED_VARS = *ESCAPED_VARS
> NONLOCAL.6 = ESCAPED_VARS
> ESCAPED_VARS = &NONLOCAL.6
> ESCAPED_VARS = &NONLOCAL.6
> infos = ESCAPED_VARS
> c_20089 = ESCAPED_VARS
> ESCAPED_VARS = &c_20089
> c_20089 = &ANYTHING
> c_20089 = &ANYTHING
> ESCAPED_VARS = &c_20089.val
> c_20089.val = ESCAPED_VARS
> infos = &c_20089
> infos = &c_20089.val
> c_200A2 = ESCAPED_VARS
> ESCAPED_VARS = &c_200A2
> ...
>
> the mainline looks like:
>
> ANYTHING = { ANYTHING }
> READONLY = { ANYTHING }
> INTEGER = { ANYTHING }
> D.28988 = same as infos
> D.28988.c = same as infos
> D.28988.b = same as infos
> infos = { ANYTHING }

This is because we compute call clobbering differently for mainline now.
The thing you'd want to add to 4.2 would be location equivalence
optimization, which i never finished for either 4.2 or 4.3 (4.3 has
code to compute it, but we don't substitute the variables).

Location equivalence would turn the escaped_vars set into 1 variable
during propagation, and then expand it back out at the end.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32723