cfgrtl: Fix up locus comparison in unique_locus_on_edge_between_p [PR104237]

  Hi!

The testcase in the PR (not included for the testsuite because we don't
have an (easy) way to -fcompare-debug LTO, we'd need 2 compilations/linking,
one with -g and one with -g0 and -fdump-rtl-final= at the end of lto1
and compare that) has different code generation for -g vs. -g0.

The difference appears during expansion, where we have a goto_locus
that is at -O0 compared to the INSN_LOCATION of the previous and next insn
across an edge.  With -g0 the locations are equal and so no nop is added.
With -g the locations aren't equal and so a nop is added holding that
location.

The reason for the different location is in the way how we stream in
locations by lto1.
We have lto_location_cache::apply_location_cache that is called with some
set of expanded locations, qsorts them, creates location_t's for those
and remembers the last expanded location.
lto_location_cache::input_location_and_block when read in expanded_location
is equal to the last expanded location just reuses the last location_t
(or adds/changes/removes LOCATION_BLOCK in it), when it is not queues
it for next apply_location_cache.  Now, when streaming in -g input, we can
see extra locations that don't appear with -g0, and if we are unlucky
enough, those can be sorted last during apply_location_cache and affect
what locations are used from the single entry cache next.
In particular, second apply_location_cache with non-empty loc_cache in
the testcase has 14 locations with -g0 and 16 with -g and those 2 extra
ones sort both last (they are the same).  The last one from -g0 then
appears to be input_location_and_block sourced again, for -g0 triggers
the single entry cache, while for -g it doesn't and so apply_location_cache
will create for it another location_t with the same content.

The following patch fixes it by comparing everything we care about the
location instead (well, better in addition) to a simple location_t ==
location_t check.  I think we don't care about the sysp flag for debug
info...

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2022-01-28  Jakub Jelinek  <jakub@redhat.com>

	PR lto/104237
	* cfgrtl.cc (loc_equal): New function.
	(unique_locus_on_edge_between_p): Use it.


	Jakub
  

On Fri, 28 Jan 2022, Jakub Jelinek wrote:

> Hi!
> 
> The testcase in the PR (not included for the testsuite because we don't
> have an (easy) way to -fcompare-debug LTO, we'd need 2 compilations/linking,
> one with -g and one with -g0 and -fdump-rtl-final= at the end of lto1
> and compare that) has different code generation for -g vs. -g0.
> 
> The difference appears during expansion, where we have a goto_locus
> that is at -O0 compared to the INSN_LOCATION of the previous and next insn
> across an edge.  With -g0 the locations are equal and so no nop is added.
> With -g the locations aren't equal and so a nop is added holding that
> location.
> 
> The reason for the different location is in the way how we stream in
> locations by lto1.
> We have lto_location_cache::apply_location_cache that is called with some
> set of expanded locations, qsorts them, creates location_t's for those
> and remembers the last expanded location.
> lto_location_cache::input_location_and_block when read in expanded_location
> is equal to the last expanded location just reuses the last location_t
> (or adds/changes/removes LOCATION_BLOCK in it), when it is not queues
> it for next apply_location_cache.  Now, when streaming in -g input, we can
> see extra locations that don't appear with -g0, and if we are unlucky
> enough, those can be sorted last during apply_location_cache and affect
> what locations are used from the single entry cache next.
> In particular, second apply_location_cache with non-empty loc_cache in
> the testcase has 14 locations with -g0 and 16 with -g and those 2 extra
> ones sort both last (they are the same).  The last one from -g0 then
> appears to be input_location_and_block sourced again, for -g0 triggers
> the single entry cache, while for -g it doesn't and so apply_location_cache
> will create for it another location_t with the same content.
> 
> The following patch fixes it by comparing everything we care about the
> location instead (well, better in addition) to a simple location_t ==
> location_t check.  I think we don't care about the sysp flag for debug
> info...
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK.

Thanks,
Richard.

> 2022-01-28  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR lto/104237
> 	* cfgrtl.cc (loc_equal): New function.
> 	(unique_locus_on_edge_between_p): Use it.
> 
> --- gcc/cfgrtl.cc.jj	2022-01-18 11:58:58.947991128 +0100
> +++ gcc/cfgrtl.cc	2022-01-27 19:32:13.949937750 +0100
> @@ -778,6 +778,29 @@ rtl_split_block (basic_block bb, void *i
>    return new_bb;
>  }
>  
> +/* Return true if LOC1 and LOC2 are equivalent for
> +   unique_locus_on_edge_between_p purposes.  */
> +
> +static bool
> +loc_equal (location_t loc1, location_t loc2)
> +{
> +  if (loc1 == loc2)
> +    return true;
> +
> +  expanded_location loce1 = expand_location (loc1);
> +  expanded_location loce2 = expand_location (loc2);
> +
> +  if (loce1.line != loce2.line
> +      || loce1.column != loce2.column
> +      || loce1.data != loce2.data)
> +    return false;
> +  if (loce1.file == loce2.file)
> +    return true;
> +  return (loce1.file != NULL
> +	  && loce2.file != NULL
> +	  && filename_cmp (loce1.file, loce2.file) == 0);
> +}
> +
>  /* Return true if the single edge between blocks A and B is the only place
>     in RTL which holds some unique locus.  */
>  
> @@ -796,7 +819,7 @@ unique_locus_on_edge_between_p (basic_bl
>    while (insn != end && (!NONDEBUG_INSN_P (insn) || !INSN_HAS_LOCATION (insn)))
>      insn = PREV_INSN (insn);
>  
> -  if (insn != end && INSN_LOCATION (insn) == goto_locus)
> +  if (insn != end && loc_equal (INSN_LOCATION (insn), goto_locus))
>      return false;
>  
>    /* Then scan block B forward.  */
> @@ -808,7 +831,7 @@ unique_locus_on_edge_between_p (basic_bl
>  	insn = NEXT_INSN (insn);
>  
>        if (insn != end && INSN_HAS_LOCATION (insn)
> -	  && INSN_LOCATION (insn) == goto_locus)
> +	  && loc_equal (INSN_LOCATION (insn), goto_locus))
>  	return false;
>      }
>  
> 
> 	Jakub
> 
>