Re: [libgomp, openacc, openmp, PR83046] Prune removed funcs from offload table

[Jakub Jelinek <jakub@redhat.com>]

On Fri, Dec 29, 2017 at 02:07:49PM +0100, Tom de Vries wrote:
> --- a/gcc/lto-streamer-out.c
> +++ b/gcc/lto-streamer-out.c
> @@ -41,6 +41,7 @@ along with GCC; see the file COPYING3.  If not see
>  #include "builtins.h"
>  #include "gomp-constants.h"
>  #include "debug.h"
> +#include "omp-offload.h"
>  
>  
>  static void lto_write_tree (struct output_block*, tree, bool);
> @@ -2355,6 +2356,31 @@ lto_output (void)
>    int i, n_nodes;
>    lto_symtab_encoder_t encoder = lto_get_out_decl_state ()->symtab_node_encoder;
>  
> +  bool truncated_p = false;

I don't think you need this var.

> +  unsigned int write_index = 0;
> +  for (unsigned read_index = 0; read_index < vec_safe_length (offload_funcs);
> +       read_index++)
> +    {
> +      tree fn_decl = (*offload_funcs)[read_index];
> +      bool remove_p = cgraph_node::get (fn_decl) == NULL;
> +      if (remove_p)
> +	{
> +	  truncated_p = true;
> +	  continue;
> +	}
> +
> +      if (write_index != read_index)
> +	(*offload_funcs)[write_index] = (*offload_funcs)[read_index];
> +
> +      write_index++;
> +    }
> +  if (truncated_p)
> +    offload_funcs->truncate (write_index);

Either you truncate unconditionally, truncate is extremely cheap operation,
or if you really wanted to guard it, you could just do
  if (read_index != write_index)

> +
> +  if (!flag_lto)
> +    for (unsigned i = 0; i < vec_safe_length (offload_funcs); i++)
> +      DECL_PRESERVE_P ((*offload_funcs)[i]) = 1;

Can you please do this inside of the above loop, you have fn_decl already
there, just do it after the
      if (remove_p)
	continue;
And, I think you can do it unconditionally at that point, or, can you use
in_lto_p instead of flag_lto?  flag_lto is set even during the -flto
compilation of the sources before LTO is streamed, there is no need to
pessimize that code, we can still remove it, we just can't remove anything
after we've streamed LTO bytecode (for either the host or offloading
targets).

> @@ -7058,7 +7058,11 @@ expand_omp_target (struct omp_region *region)
>  
>        /* Add the new function to the offload table.  */
>        if (ENABLE_OFFLOADING)
> -	vec_safe_push (offload_funcs, child_fn);
> +	{
> +	  if (flag_lto)
> +	    DECL_PRESERVE_P (child_fn) = 1;

And use if (in_lto_p) here too.

Ok for trunk with those changes.

	Jakub