[PATCH GCC][1/2]Feed bound computation to folder in loop split

[Richard Biener]

On Wed, Jul 26, 2017 at 9:48 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Tue, Jul 25, 2017 at 7:45 PM, Marc Glisse <marc.glisse@inria.fr> wrote:
>> On Tue, 25 Jul 2017, Richard Biener wrote:
>>
>>>> I think we need Richard to say what the intent is for the valueization
>>>> function. It is used both to stop looking at defining stmt if the return
>>>> is
>>>> NULL, and to replace/optimize one SSA_NAME with another, but currently it
>>>> seems hard to prevent looking at the defining statement without
>>>> preventing
>>>> from looking at the SSA_NAME at all.
>>>
>>>
>>> Yeah, this semantic overloading is an issue.  For gimple_build we have
>>> nothing
>>> to "valueize" but we only use it to tell genmatch that it may not look at
>>> the
>>> SSA_NAME_DEF_STMT.
>>>
>>>> I guess we'll need a fix in genmatch...
>>>
>>>
>>> I'll have a look tomorrow.
>>
>>
>> My impression yesterday was that we could replace the current do_valueize
>> wrapper by 2 wrappers (without touching the valueize callbacks):
>> - may_check_def_stmt, which returns a bool corresponding to the current
>> do_valueize != NULL_TREE
>> - maybe_valueize, which tries to valueize, but if it gets a NULL_TREE, it
>> returns its argument unchanged.
>>
>> Not very confident about it though.
>
> Note I've been there in the past (twice I think) but always ran into existing
> latent issues.  So hopefully we've resolved those, I'm testing the following
> simplified variant of what I had back in time.
>
> It'll produce
>
>   switch (TREE_CODE (op0))
>     {
>     case SSA_NAME:
>       if (gimple *def_stmt = get_def (valueize, op0))
>         {
>           if (gassign *def = dyn_cast <gassign *> (def_stmt))
>             switch (gimple_assign_rhs_code (def))
>               {
>               case MINUS_EXPR:
>                 {
>                   tree o20 = gimple_assign_rhs1 (def);
>                   o20 = do_valueize (valueize, o20);
>                   tree o21 = gimple_assign_rhs2 (def);
>                   o21 = do_valueize (valueize, o21);
>                   if (op1 == o21 || (operand_equal_p (op1, o21, 0) &&
> types_match (op1, o21)))
>                     {
>
> which also indents less which is nice.
>
> Bootstrap/regtest running on x86_64-unknown-linux-gnu.

Now applied with

        * gcc/testsuite/gcc.dg/pr70920-2.c: Adjust for transform already
        happening in ccp1.
        * gcc/testsuite/gcc.dg/pr70920-4.c: Likewise.

that shows it's working (CCP is one of the passes eventually running
into this issue).

Richard.

> Richard.
>
> 2017-07-26  Richard Biener  <rguenther@suse.de>
>
>         * gimple-match-head.c (do_valueize): Return OP if valueize
>         returns NULL_TREE.
>         (get_def): New helper to get at the def stmt of a SSA name
>         if valueize allows.
>         * genmatch.c (dt_node::gen_kids_1): Use get_def instead of
>         do_valueize to get at the def stmt.
>         (dt_operand::gen_gimple_expr): Simplify do_valueize calls.
>
>
>> --
>> Marc Glisse