gcov: make profile merging smarter

Support merging of profiles that are built from a different .o files
but belong to the same source file. Moreover, a checksum is verified
during profile merging and so we can safely combine such profile.

	PR gcov-profile/90364

gcc/ChangeLog:

	* coverage.c (build_info): Emit checksum to the global variable.
	(build_info_type): Add new field for checksum.
	(coverage_obj_finish): Pass object_checksum.
	(coverage_init): Use 0 as checksum for .gcno files.
	* gcov-dump.c (dump_gcov_file): Dump also new checksum field.
	* gcov.c (read_graph_file): Read also checksum.
	* doc/invoke.texi: Document the behaviour change.

libgcc/ChangeLog:

	* libgcov-driver.c (merge_one_data): Skip timestamp and verify
	checksums.
	(write_one_data): Write also checksum.
	* libgcov-util.c (read_gcda_file): Read also checksum field.
	* libgcov.h (struct gcov_info): Add new field.

1 files changed, 5 insertions, 0 deletions

diff --git a/gcc/gcov.c b/gcc/gcov.c
index cf0a49d..829e955 100644
--- a/gcc/gcov.c
+++ b/gcc/gcov.c
@@ -1814,6 +1814,8 @@ read_graph_file (void)
 	       bbg_file_name, v, e);
     }
   bbg_stamp = gcov_read_unsigned ();
+  /* Read checksum.  */
+  gcov_read_unsigned ();
   bbg_cwd = xstrdup (gcov_read_string ());
   bbg_supports_has_unexecuted_blocks = gcov_read_unsigned ();
 
@@ -2031,6 +2033,9 @@ read_count_file (void)
       goto cleanup;
     }
 
+  /* Read checksum.  */
+  gcov_read_unsigned ();
+
   while ((tag = gcov_read_unsigned ()))
     {
       unsigned length = gcov_read_unsigned ();