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

[Richard Biener <richard dot guenther at gmail dot com>]

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.

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

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