Re: [tree-ssa] Removal of unused vars

[Diego Novillo <dnovillo at redhat dot com>]

On Wed, 2003-06-25 at 21:03, law@redhat.com wrote:

> 	* tree-cfg.c (remove_useless_stmts_and_vars): On the first
> 	iteration, remove unused variables from BIND_EXPRs.
> 	* tree-flow.h (var_ann_d): Add new field USED.
> 	(set_is_used): Prototype.
> 	(remove_useless_stmts_and_vars): Update prototype.
> 	* tree-ssa-live.c (create_ssa_var_map): Note which variables
> 	are used so that we can delete those which are not used.
> 	* tree-ssa.c (create_temp): Mark the new temporary as being used.
> 	(rewrite_out_of_ssa): Note if the call to remove_useless_stmts_and_vars
> 	is the first iteration or not.
> 	(set_is_used): New function.
> 
Jeff,

This produces a regression in alpha:

New regressions in 20030626/gcc.sum.gz:
         FAIL: gcc.c-torture/compile/20010605-1.c
         FAIL: gcc.c-torture/compile/20010605-1.c
         FAIL: gcc.c-torture/compile/20010605-1.c
         FAIL: gcc.c-torture/compile/20010605-1.c
         FAIL: gcc.c-torture/compile/20010605-1.c


main (int argc, char **argv)
{
  int size = 10;

  typedef struct {
    char val[size];
  } block;
  block retframe_block()
    {
      return *(block*)0;
    }

  return 0;
}


We don't seem to flag 'size' as having hidden uses in alpha.  In x86, we
do:

main (argc, argv)
{
  int size;
  static  retframe_block;

  size = 10;
  int = 0;
  return 0;
}


But in alpha, we emit:

main (argc, argv)
{
  static  retframe_block;

  int = 0;
  return 0;
}


If you don't have access to alpha, let me know and I'll add it to my
queue of things to fix.


Thanks.  Diego.