[PATCH] lto: Ensure we force a change for file/line/column after clear_line_info

[Richard Biener]

On Fri, 4 Sep 2020, Jakub Jelinek wrote:

> Hi!
> 
> As discussed yesterday:
> On the streamer out side, we call clear_line_info
> in multiple spots which resets the current_* values to something, but on the
> reader side, we don't have corresponding resets in the same location, just have
> the stream_* static variables that keep the current values through the
> entire stream in (so across all the clear_line_info spots in a single LTO
> object but also across jumping from one LTO object to another one).
> Now, in an earlier version of my patch it actually broke LTO bootstrap
> (and a lot of LTO testcases), so for the BLOCK case I've solved it by
> clear_line_info setting current_block to something that should never appear,
> which means that in the LTO stream after the clear_line_info spots including
> the start of the LTO stream we force the block change bit to be set and thus
> BLOCK to be streamed and therefore stream_block from earlier to be
> ignored.  But for the rest I think that is not the case, so I wonder if we
> don't sometimes end up with wrong line/column info because of that, or
> please tell me what prevents that.
> clear_line_info does:
>   ob->current_file = NULL;
>   ob->current_line = 0;
>   ob->current_col = 0;
>   ob->current_sysp = false;
> while I think NULL current_file is something that should likely be different
> from expanded_location (...).file (UNKNOWN_LOCATION/BUILTINS_LOCATION are
> handled separately and not go through the caching), I think line number 0
> can sometimes occur and especially column 0 occurs frequently if we ran out
> of location_t with columns info.  But then we do:
>       bp_pack_value (bp, ob->current_file != xloc.file, 1);
>       bp_pack_value (bp, ob->current_line != xloc.line, 1);
>       bp_pack_value (bp, ob->current_col != xloc.column, 1);
> and stream the details only if the != is true.  If that happens immediately
> after clear_line_info and e.g. xloc.column is 0, we would stream 0 bit and
> not stream the actual value, so on read-in it would reuse whatever
> stream_col etc. were before.  Shouldn't we set some ob->current_* new bit
> that would signal we are immediately past clear_line_info which would force
> all these != checks to non-zero?  Either by oring something into those
> tests, or perhaps:
>   if (ob->current_reset)
>     {
>       if (xloc.file == NULL)
>         ob->current_file = "";
>       if (xloc.line == 0)
>         ob->current_line = 1;
>       if (xloc.column == 0)
>         ob->current_column = 1;
>       ob->current_reset = false;
>     }
> before doing those bp_pack_value calls with a comment, effectively forcing
> all 6 != comparisons to be true?
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux and lto bootstrapped
> on x86_64-linux, ok for trunk?

OK.

Thanks,
Richard.

> 2020-09-03  Jakub Jelinek  <jakub@redhat.com>
> 
> 	* lto-streamer.h (struct output_block): Add reset_locus member.
> 	* lto-streamer-out.c (clear_line_info): Set reset_locus to true.
> 	(lto_output_location_1): If reset_locus, clear it and ensure
> 	current_{file,line,col} is different from xloc members.
> 
> --- gcc/lto-streamer.h.jj	2020-09-03 12:50:54.990753979 +0200
> +++ gcc/lto-streamer.h	2020-09-03 17:11:51.406571519 +0200
> @@ -717,6 +717,7 @@ struct output_block
>    int current_line;
>    int current_col;
>    bool current_sysp;
> +  bool reset_locus;
>    tree current_block;
>  
>    /* Cache of nodes written in this section.  */
> --- gcc/lto-streamer-out.c.jj	2020-09-03 12:50:54.992753950 +0200
> +++ gcc/lto-streamer-out.c	2020-09-03 17:16:44.601311584 +0200
> @@ -60,6 +60,7 @@ clear_line_info (struct output_block *ob
>    ob->current_line = 0;
>    ob->current_col = 0;
>    ob->current_sysp = false;
> +  ob->reset_locus = true;
>    /* Initialize to something that will never appear as block,
>       so that the first location with block in a function etc.
>       always streams a change_block bit and the first block.  */
> @@ -195,6 +196,17 @@ lto_output_location_1 (struct output_blo
>      {
>        expanded_location xloc = expand_location (loc);
>  
> +      if (ob->reset_locus)
> +	{
> +	  if (xloc.file == NULL)
> +	    ob->current_file = "";
> +	  if (xloc.line == 0)
> +	    ob->current_line = 1;
> +	  if (xloc.column == 0)
> +	    ob->current_col = 1;
> +	  ob->reset_locus = false;
> +	}
> +
>        bp_pack_value (bp, ob->current_file != xloc.file, 1);
>        bp_pack_value (bp, ob->current_line != xloc.line, 1);
>        bp_pack_value (bp, ob->current_col != xloc.column, 1);
> 
> 	Jakub
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)