cfgrtl: Fix up locus comparison in unique_locus_on_edge_between_p [PR104237]

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...

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.

1 files changed, 25 insertions, 2 deletions

diff --git a/gcc/cfgrtl.cc b/gcc/cfgrtl.cc
index 9ccc65b..5675751 100644
--- a/gcc/cfgrtl.cc
+++ b/gcc/cfgrtl.cc
@@ -778,6 +778,29 @@ rtl_split_block (basic_block bb, void *insnp)
   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_block a, basic_block b)
   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_block a, basic_block b)
 	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;
     }