Re: [PATCH 1/2] ivopts: Revert computation of address cost complexity.

[Dimitrije Milosevic <Dimitrije.Milosevic@Syrmia.com>]

Hi Jeff,

> THe part I don't understand is, if you only have BASE+OFF, why does 
> preventing the calculation of more complex addressing modes matter?  ie, 
> what's the point of computing the cost of something like base + off + 
> scaled index when the target can't utilize it?

Well, the complexities of all addressing modes other than BASE + OFFSET are
equal to 0. For targets like Mips, which only has BASE + OFFSET, it would still
be more complex to use a candidate with BASE + INDEX << SCALE + OFFSET
than a candidate with BASE + INDEX, for example, as it has to compensate
the lack of other addressing modes somehow. If complexities for both of
those are equal to 0, in cases where complexities decide which candidate is
to be chosen, a more complex candidate may be picked.

Regards,
Dimitrije


From: Jeff Law <jeffreyalaw@gmail.com>
Sent: Friday, October 28, 2022 1:02 AM
To: Dimitrije Milosevic <Dimitrije.Milosevic@Syrmia.com>; gcc-patches@gcc.gnu.org <gcc-patches@gcc.gnu.org>
Cc: Djordje Todorovic <Djordje.Todorovic@syrmia.com>
Subject: Re: [PATCH 1/2] ivopts: Revert computation of address cost complexity. 
 

On 10/21/22 07:52, Dimitrije Milosevic wrote:
> From: Dimitrije Milošević <dimitrije.milosevic@syrmia.com>
>
> This patch reverts the computation of address cost complexity
> to the legacy one. After f9f69dd, complexity is calculated
> using the valid_mem_ref_p target hook. Architectures like
> Mips only allow BASE + OFFSET addressing modes, which in turn
> prevents the calculation of complexity for other addressing
> modes, resulting in non-optimal candidate selection.
>
> gcc/ChangeLog:
>
>        * tree-ssa-address.cc (multiplier_allowed_in_address_p): Change
>        to non-static.
>        * tree-ssa-address.h (multiplier_allowed_in_address_p): Declare.
>        * tree-ssa-loop-ivopts.cc (compute_symbol_and_var_present): Reintroduce.
>        (compute_min_and_max_offset): Likewise.
>        (get_address_cost): Revert
>        complexity calculation.

THe part I don't understand is, if you only have BASE+OFF, why does 
preventing the calculation of more complex addressing modes matter?  ie, 
what's the point of computing the cost of something like base + off + 
scaled index when the target can't utilize it?


jeff