Re: [RFC] [Patch]: Try and vectorize with shift for mult expr with power 2 integer constant.

[Jeff Law <law@redhat.com>]

On 08/02/2015 05:03 AM, Kumar, Venkataramanan wrote:
> Hi Jakub,
>
> Thank you for reviewing the patch.
>
> I have incorporated your comments in the attached patch.
Note Jakub is on PTO for the next 3 weeks.


>
>
>
> vectorize_mults_via_shift.diff.txt
>
>
> diff --git a/gcc/testsuite/gcc.dg/vect/vect-mult-patterns.c b/gcc/testsuite/gcc.dg/vect/vect-mult-patterns.c
Jakub would probably like more testcases :-)

The most obvious thing to test would be other shift factors.

A negative test to verify we don't try to turn a multiply by 
non-constant or multiply by a constant that is not a power of 2 into shifts.

[ Would it make sense, for example, to turn a multiply by 3 into a 
shift-add sequence?  As Jakub said, choose_mult_variant can be your 
friend. ]



> @@ -2147,6 +2152,140 @@ vect_recog_vector_vector_shift_pattern (vec<gimple> *stmts,
>     return pattern_stmt;
>   }
>
> +/* Detect multiplication by constant which are postive or negatives of power 2,
s/postive/positive/


Jeff