[tree-ssa] live analysis on local static functions

[Jan Hubicka]

Hi,
I am looking into the problems with unit-at-a-time on tree-ssa branch.
The testcase I am running into can be reproduced even with
unit-at-a-time disabled and looks like:

static inline char * test()
{
  static char *a="";
  return a;
}
char * q()
{
return test();
}

The dump before last DCE pass is:


;; Function q (q)

q ()
{
  char * <Ub244>;
  char * retval.2;
  char * T.1;

  {
    {
      static char * a = (char *)"";

      <Ub244>_2 = a;
      goto <Ub1d0>;;
    };
    <Ub1d0>:;;
    (void)0;
  };
  (void)0;
  return <Ub244>_2;;
}

and after dce is

;; Function q (q)

q ()
{
  char * <Ub244>;

  {
    <Ub244> = a;
    <Ub1d0>:;;
  };
  return <Ub244>;;
}

so we miss the initializer.  I've tracked down the problem to fact that
variable a does not have flag used set in it's annotation.  It has, when
I disable the inlining.  It is marked in create_ssa_var_map by seeing
VUSE attached to the return statement.  With inline enabled the set also
has VUSE but it's operand is not VAR_DECL itself, but SSA_NAME

I am quite lost here.  I am not sure how the liveness should work.
SHould the SSA_NAME match the expression in bind expr (as one would
expect for valid SSA form?)
Do we really want something like that?  (the place of BIND_EXPR in the
CFG is quite missleading as everything is executed before the function
is done just once).  What would be proper fix for that?
So far I can work around by disabling of removal of BIND_EXPRs for
static variables.  This gets me further in the bootstrap.

Honza