This patch changes the coverage unlinking to be less aggressive. As David
pointed out, when experimenting with random optimization options along side
-fuse-coverage and -frandom-seed, it is inconvenient for gcc to remove the
coverage data file. The reason it was doing so, is because -frandom-seed
prevents a unique stamp being placed in the coverage data to distinguish
execution of the newly optimized program from execution of the older incarnation
of it. libgcov would get confused and give errors about mismatched function
checksums.
This patch tweaks things. With -fuse-coverage we read in the coverage data file
and its stamp. We can feed that stamp into the stamp to be used for the output
coverage data, and hence effectively distinguish generations of coverage data
even when -frandom-seed prevents randomness. We also don't need to delete the
data file if we're not producing coverage data for the new compilation.
Manual testing shows this patch is preventing deletion of the data file in the
circumstances I understand David's using. David, care to try this patch out to
see if it resolves your use case?
The changes to tree.c merely extend the crc32 code to allow it to generate a crc
from a 32-bit unsigned, in addition to the byte variant already present.
testing on i686-pc-linux-gnu shows no regressions.
nathan
2012-06-23 Nathan Sidwell <nat...@acm.org>
* coverage.c (bbg_file_stamp): New.
(read_counts_file): Merge incoming stamp with bbg_file_stamp.
(build_info): Write bbg_file_stamp.
(coverage_init): Initialize bbg_file_stamp. Read counts file
before writing graph header.
(coverage_finish): Don't unlink the data file if we can generate a
unique file stamp.
* tree.h (crc32_unsigned): Declare.
* tree.c (crc32_unsigned_bits): New, broken out of ...
(crc32_byte): ... here. Use it.
(crc32_unsigned): New.
Index: coverage.c
===================================================================
--- coverage.c (revision 188900)
+++ coverage.c (working copy)
@@ -101,6 +101,9 @@ static GTY(()) tree gcov_fn_info_ptr_typ
we're not writing to the notes file. */
static char *bbg_file_name;
+/* File stamp for graph file. */
+static unsigned bbg_file_stamp;
+
/* Name of the count data file. */
static char *da_file_name;
@@ -205,8 +208,9 @@ read_counts_file (void)
return;
}
- /* Read and discard the stamp. */
- gcov_read_unsigned ();
+ /* Read the stamp, used for creating a generation count. */
+ tag = gcov_read_unsigned ();
+ bbg_file_stamp = crc32_unsigned (bbg_file_stamp, tag);
counts_hash = htab_create (10,
htab_counts_entry_hash, htab_counts_entry_eq,
@@ -905,7 +909,7 @@ build_info (tree info_type, tree fn_ary)
/* stamp */
CONSTRUCTOR_APPEND_ELT (v1, info_fields,
build_int_cstu (TREE_TYPE (info_fields),
- local_tick));
+ bbg_file_stamp));
info_fields = DECL_CHAIN (info_fields);
/* Filename */
@@ -1101,6 +1105,11 @@ coverage_init (const char *filename)
memcpy (da_file_name + prefix_len, filename, len);
strcpy (da_file_name + prefix_len + len, GCOV_DATA_SUFFIX);
+ bbg_file_stamp = local_tick;
+
+ if (flag_branch_probabilities)
+ read_counts_file ();
+
/* Name of bbg file. */
if (flag_test_coverage && !flag_compare_debug)
{
@@ -1117,12 +1126,9 @@ coverage_init (const char *filename)
{
gcov_write_unsigned (GCOV_NOTE_MAGIC);
gcov_write_unsigned (GCOV_VERSION);
- gcov_write_unsigned (local_tick);
+ gcov_write_unsigned (bbg_file_stamp);
}
}
-
- if (flag_branch_probabilities)
- read_counts_file ();
}
/* Performs file-level cleanup. Close graph file, generate coverage
@@ -1133,10 +1139,11 @@ coverage_finish (void)
{
if (bbg_file_name && gcov_close ())
unlink (bbg_file_name);
-
- if (!local_tick || local_tick == (unsigned)-1)
- /* Only remove the da file, if we cannot stamp it. If we can
- stamp it, libgcov will DTRT. */
+
+ if (!flag_branch_probabilities && flag_test_coverage
+ && (!local_tick || local_tick == (unsigned)-1))
+ /* Only remove the da file, if we're emitting coverage code and
+ cannot uniquely stamp it. If we can stamp it, libgcov will DTRT. */
unlink (da_file_name);
if (coverage_obj_init ())
Index: tree.c
===================================================================
--- tree.c (revision 188900)
+++ tree.c (working copy)
@@ -8734,23 +8734,37 @@ dump_tree_statistics (void)
/* Generate a crc32 of a byte. */
-unsigned
-crc32_byte (unsigned chksum, char byte)
+static unsigned
+crc32_unsigned_bits (unsigned chksum, unsigned value, unsigned bits)
{
- unsigned value = (unsigned) byte << 24;
- unsigned ix;
+ unsigned ix;
- for (ix = 8; ix--; value <<= 1)
- {
- unsigned feedback;
-
- feedback = (value ^ chksum) & 0x80000000 ? 0x04c11db7 : 0;
- chksum <<= 1;
- chksum ^= feedback;
- }
+ for (ix = bits; ix--; value <<= 1)
+ {
+ unsigned feedback;
+
+ feedback = (value ^ chksum) & 0x80000000 ? 0x04c11db7 : 0;
+ chksum <<= 1;
+ chksum ^= feedback;
+ }
return chksum;
}
+/* Generate a crc32 of a 32-bit unsigned. */
+
+unsigned
+crc32_unsigned (unsigned chksum, unsigned value)
+{
+ return crc32_unsigned_bits (chksum, value, 32);
+}
+
+/* Generate a crc32 of a byte. */
+
+unsigned
+crc32_byte (unsigned chksum, char byte)
+{
+ return crc32_unsigned_bits (chksum, (unsigned) byte << 24, 8);
+}
/* Generate a crc32 of a string. */
Index: tree.h
===================================================================
--- tree.h (revision 188900)
+++ tree.h (working copy)
@@ -5168,6 +5168,7 @@ inlined_function_outer_scope_p (const_tr
/* In tree.c */
extern unsigned crc32_string (unsigned, const char *);
extern unsigned crc32_byte (unsigned, char);
+extern unsigned crc32_unsigned (unsigned, unsigned);
extern void clean_symbol_name (char *);
extern tree get_file_function_name (const char *);
extern tree get_callee_fndecl (const_tree);
