Re: [PATCH] Extend store ccp

["Richard Guenther" <richard dot guenther at gmail dot com>]

On 3/23/07, Revital1 Eres <ERES@il.ibm.com> wrote:
> Hello,
>
> This patch enhance store ccp to propagate constants from stores to
> loads when the previous implementation failed due to alias uncertainty.
> The testcase attached demonstrates this optimization:
>
> S[5].x = 0;
> S[5].y = 0;
>
> x = S[5].x;
> y = S[5].y;
>
> Previously x = S[5].x; failed to be replaced with x = 0.  This patch
> fixes this problem by allowing the propagation of constants if all the
> stores in the alias group are initialized with the same constant.
>
> I used the get_stmt_rhs_def_stmt () function Richard Guenther
> introduced in his patch to walk the virtual def-use chains
> with adjustments to make it suitable for this optimization.
> (http://gcc.gnu.org/ml/gcc-patches/2006-02/msg00669.html)
>
> Bootstrap and tested on PPC. OK for mainline?

You confused me a lot in that you use a name for get_def_of_stmt_rhs ()
that doesn't look like it checks for a single constant value ;)   Maybe
just make it return true or false and call it stmt_rhs_constant_val_p
(stmt, val).

Or even fold it into it's only use, all_vdef_have_same_lattice_const_value.

Did you check compile-time and runtime effects of this patch like on SPEC?  I
suppose we can eliminate array zero initialization if there follows
different initialzation
with this patch.

Thanks,
Richard.

> :ADDPATCH tree-ssa optimization:
>
> Thanks,
> Revital
>
> 2007-03-22  Revital Eres  <eres@il.ibm.com>
>
>         * tree-ssa-propagate.c (all_vdef_have_same_lattice_const_value):
>           New function to get the defining stmt.
>           (get_def_of_stmt_rhs): New helper function
>           which walks on the virtual use-def chain to get the defining
> stmt.
>           (replace_vuses_in): Call all_vdef_have_same_lattice_const_value
>           to perform the final replacement and add new parameter which
>           indicates whether store cpp analysis should be extended to
>           analyze memory references based on the virtual use-def chain.
>           (do_store_ccp): New function.
>           (substitute_and_fold): Add new parameter.
>         * tree-ssa-propagate.h (all_vdef_have_same_lattice_const_value):
>            Declare.
>            (substitute_and_fold): Change declaration.
>         * tree-vrp.c (vrp_finalize): Call substitute_and_fold with new
> argument .
>         * tree-ssa-ccp.c (ccp_finalize): Likewise.
>           (visit_assignment): Call all_vdef_have_same_lattice_const_value
> while
>            performing the propogation.
>        * tree-ssa-copy.c (fini_copy_prop): Call substitute_and_fold with
> new
>           argument.
>         * testsuite/gcc.dg/store_ccp_test.c: New test.
>
> (See attached file: patch_ccp_22_3.txt)(See attached file:
> store_ccp_test.txt)