Re: [GSoC][match-and-simplify] factor gimple expressions and builtin functions

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

On Thu, Jun 26, 2014 at 10:11 AM, Prathamesh Kulkarni
<bilbotheelffriend@gmail.com> wrote:
> This patch factors expression checking for GIMPLE.
>
> Generates code as:
> if (TREE_CODE (opname) == SSA_NAME)
> {
>   gimple def_stmt = SSA_NAME_DEF_STMT (opname);
>   if (is_gimple_assign (def_stmt))
>   {
>     if (gimple_assign_rhs_code (def_stmt) == <expr-code1>)
>       {
>          ....
>       }
>     if (gimple_assign_rhs_code (def_stmt) == <expr-code2>)
>       {
>          ....
>       }
>    }
> }
>
> We cannot use switch-case, for convert/nop since
> we use CONVERT_EXPR_CODE_P, so i used if stmt.

Actually we can by using

   case NOP_EXPR:
   case CONVERT_EXPR:

for it.  Note that currently you still do

  if (is_gimple_assign (def_stmt))
    {
       if (gimple_assign_rhs_code (def_stmt) == PLUS_EXPR)
        {
        }
      if (gimple_assign_rhs_code (def_stmt) == MINUS_EXPR)
        {
        }

thus not use else if ().  Of course in the end we want

  switch (gimple_assign_rhs_code (def_stmt))
   {
    case PLUS_EXPR;
  ...
    case MINUS_EXPR:
  ...

> Unfortunately, back-tracking is still done. I shall look into that.

Note that we need to backtrack to the next parent with a 'true'
kid (and from there to its next parent with a 'true' kid).  Possibly
with using a switch-case or proper if-else-if there isn't anything
special to do as the backtracking would work naturally then.

So I suggest to concentrate on getting the code to use

  if (TREE_CODE (op0) == SSA_NAME)
    {
       gimple def_stmt = SSA_NAME_DEF_STMT (op0);
       if (is_gimple_assign  (def_stmt))
         {
           switch (gimple_assign_rhs_code ())
            {
            case PLUS_EXPR:
...
         }
       else if (gimple_call_builtin_p (def_stmt, BUILT_IN_NORMAL))
         {
           switch (DECL_FUNCTION_CODE (gimple_call_fndecl (def_stmt)))
            {
            case BUILT_IN_ABS:
...
         }
     }
  else if (TREE_CODE (op0) == REALPART_EXPR)
... other GENERIC cases

  <true> match (not in else {})

that would backtrack through the <true> cases by means of them
not short-circuited by an else but everything else short-circuited
by proper use of switch () and if - else-if code.

Thanks,
Richard.

> * genmatch.c (dt_node::get_expr_code): New member function.
>      (dt_node::is_gimple_expr): Likewise.
>      (dt_node::is_gimple_fn): Likewise.
>      (dt_operand::kids_type): New struct.
>      (dt_operand::gen_gimple_expr): Remove.
>      (dt_operand::gen_gimple_expr_expr): Remove 2nd argument and
> change return        type to unsigned. Adjust code-gen for
> expressions.
>      (dt_operand::gen_gimple_expr_fn): Remove 2nd argument and change
> return type to unsigned.
>      (dt_operand::grok_kids): New member function.
>      (dt_operand::gen_gimple_kids): Likewise.
>      (dt_operand::gen_gimple): Adjust code-gen for gimple expressions.
> Call dt_operand::gen_gimple_kids.
>      (decision_tree::gen_gimple): Call dt_operand::gen_gimple_kids.
>
> Thanks and Regards,
> Prathamesh