Re: [rtl] combine a vec_concat of 2 vec_selects from the same vector

[Marc Glisse <marc dot glisse at inria dot fr>]

On Sun, 9 Sep 2012, Marc Glisse wrote:

> Hello,
>
> this patch lets the compiler try to rewrite:
>
> (vec_concat (vec_select x [a]) (vec_select x [b]))
>
> as:
>
> vec_select x [a b]
>
> or even just "x" if appropriate.
>
> In a first iteration I was restricting it to b-a==1, but it seemed better not 
> to: it helps for {v[1],v[0]} and doesn't change anything for unknown 
> patterns.
>
> Note that I am planning to do a similar optimization at tree level, but it 
> shouldn't make this one useless because such patterns can be created during 
> rtl passes. The testcase may need an additional -fno-tree-xxx to still be 
> useful at that point though.

Since the tree-ssa patch was reviewed faster, assume there is a 
-fno-tree-forwprop in dg-options for the testcase.

> bootstrap+testsuite on x86_64-linux-gnu.
>
> 2012-09-09  Marc Glisse  <marc.glisse@inria.fr>
>
> gcc/
> 	* simplify-rtx.c (simplify_binary_operation_1): Handle vec_concat
> 	of vec_selects from the same vector.
>
> gcc/testsuite/
> 	* gcc.target/i386/vect-rebuild.c: New testcase.

http://gcc.gnu.org/ml/gcc-patches/2012-09/msg00540.html

--
Marc Glisse