r254750 - in /trunk: config/ChangeLog config/bo...

[aoliva@gcc.gnu.org]

Author: aoliva
Date: Wed Nov 15 03:11:37 2017
New Revision: 254750

URL: https://gcc.gnu.org/viewcvs?rev=254750&root=gcc&view=rev
Log:
Use compare-debug for bootstrap-debug-lean to ignore != DW_AT_producer

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.

Modified:
    trunk/config/ChangeLog
    trunk/config/bootstrap-debug-lean.mk
    trunk/gcc/ChangeLog
    trunk/gcc/dwarf2out.c