Re: [tree-ssa] live analysis on local static functions

[Andrew MacLeod <amacleod at redhat dot com>]

On Tue, 2003-10-14 at 12:10, Jan Hubicka wrote:

> 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 get out of ssa producing:

q ()
{
  char * <U1244>;
  char * retval.2;
  char * T.1;


  # BLOCK 0.  PRED: -1.  SUCC: 1.
  {
    {
      static char * a = (char *)"";


      #   VUSE <a_1>;
      <U1244> = a;
      goto <U11d0>;;
    };

    # BLOCK 1.  PRED: 0.  SUCC: 2.
    <U11d0>:;;
    (void)0;
  };

  # BLOCK 2.  PRED: 1.  SUCC: -2.
  (void)0;
  return <U1244>;;
}

and then the call to remove useless crud produces the final, incorrect,
code of:

;; Function q (q)

q ()
{
  char * <U1244>;

  {
    <U1244> = a;
    <U11d0>:;;
  };
  return <U1244>;;
}


> 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.

I assume the useless stmt remover ought to check to see if there is a
static initializer in a BIND_EXPR before removing a DECL with an
initializer which is not marked used.    

Either that, or has_hidden_use() ought to be set on A.

Neither is true right now.

There are other choices too :-)

Andrew

FOr instance, It does get fixed with:

Index: tree-cfg.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/Attic/tree-cfg.c,v
retrieving revision 1.1.4.173
diff -c -p -r1.1.4.173 tree-cfg.c
*** tree-cfg.c	6 Oct 2003 14:34:25 -0000	1.1.4.173
--- tree-cfg.c	14 Oct 2003 16:41:37 -0000
*************** remove_useless_stmts_and_vars_bind (tree
*** 1398,1403 ****
--- 1398,1404 ----
  	      && ! ann->used
  	      && ! ann->has_hidden_use
  	      && ! TREE_ADDRESSABLE (vars)
+ 	      && ! (TREE_STATIC (vars) && DECL_INITIAL (vars) != 0)
  	      && (DECL_ARTIFICIAL (vars) || optimize >= 2))
  	    {
  	      /* Remove the variable from the BLOCK structures.  */