Unlike bootstrap-debug, bootstrap-debug-lean used to pass compare using
the traditional compare command, because it compiled both stage2 and
stage3 with options that used to generate identical output
(-fcompare-debug= in stage2 vs -fcompare-debug in stage3).
Since we started adding relevant command-line flags to DW_AT_producer,
this is no longer the case, and stages 2 and 3 object files that differ
in nothing but the DW_AT_producer strings.
-fcompare-debug is short for -fcompare-debug=-gtoggle, so stage3
compiles twice, once with the normal options, once with toggled -g, to
then compare the temporary final dumps. When enabled, both compilations
get from the driver an additional -frandom-seed flag (if none is given
explicitly).
-fcompare-debug= is short for -fno-compare-debug, disabling the second
compilation.
The difference between the DW_AT_producer lines are the different
-fcompare-debug flags, and the presence of the -frandom-seed flag in the
stage3 compilation.
It is easy and sensible enough to filter the -fcompare-debug flags out
of the DW_AT_producer string. This option should never affect the
compilation output, it just determines whether or not to perform an
additional compilation that should produce the same executable output.
However, dropping -frandom-seed is not quite correct, in that it might
have other consequences on the compilation. So, it makes little sense
to make the effort to drop it when it's implicit; for those comparing
compiler output differences, it might even hint at what causes, and
could fix, difficult to explain differences, namely, explicitly
supplying -frandom-seed options.
They don't seem to matter for compiler bootstraps, though, at least
for now, so we can safely refrain from issuing -frandom-seed (or maybe
we already issue it where needed :-), and then, for
bootstrap-debug-lean, use the compare-debug script, that strips out
debug information before comparing the object files.
for config/ChangeLog
* bootstrap-debug-lean.mk (do-compare): Use the
contrib/compare-debug script.
for gcc/ChangeLog
* dwarf2out.c (gen_producer_string): Discard
OPT_fcompare_debug.
From-SVN: r254750
3267bd36aa