A couple GIMPLE questions

[Gary Oblock <gary@amperecomputing.com>]

First off one of the questions just me being curious but
second is quite serious. Note, this is GIMPLE coming
into my optimization and not something I've modified.

Here's the C code:

type_t *
do_comp( type_t *data, size_t len)
{
  type_t *res;
  type_t *x = min_of_x( data, len);
  type_t *y = max_of_y( data, len);

  res = y;
  if ( x < y ) res = 0;
  return res;
}

And here's the resulting GIMPLE:

;; Function do_comp.constprop (do_comp.constprop.0, funcdef_no=5, decl_uid=4392, cgraph_uid=3, symbol_order=68) (executed once)

do_comp.constprop (struct type_t * data)
{
  struct type_t * res;
  struct type_t * x;
  struct type_t * y;
  size_t len;

  <bb 5> [local count: 1073741824]:

  <bb 2> [local count: 1073741824]:
  x_2 = min_of_x (data_1(D), 10000);
  y_3 = max_of_y (data_1(D), 10000);
  if (x_2 < y_3)
    goto <bb 3>; [29.00%]
  else
    goto <bb 4>; [71.00%]

  <bb 3> [local count: 311385128]:

  <bb 4> [local count: 1073741824]:
  # res_4 = PHI <y_3(2), 0B(3)>
  return res_4;

}

The silly question first. In the "if" stmt how does GCC
get those probabilities? Which it shows as 29.00% and
71.00%. I believe they should both be 50.00%.

The serious question is what is going on with this phi?
    res_4 = PHI <y_3(2), 0B(3)>

This makes zero sense practicality wise to me and how is
it supposed to be recognized and used? Note, I really do
need to transform the "0B" into something else for my
structure reorganization optimization.

Thanks,

Gary Oblock




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