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I checked by hand, and this looks like a false positive to me. It doesn't come up without
NOTE: I have hand-modified my build/bootstrap-lto.mk to use -Ofast. It's possible that using the bootstrap-O3 build-config will reproduce it as well.
$ ~/src/gcc-trunk/configure --enable-bootstrap --prefix=/home/matt
--enable-clocale=gnu --with-system-zlib --with-demangler-in-ld --enable-lto
--with-build-config=bootstrap-lto --enable-build-with-cxx --disable-libmudflap
--with-cpu=core2 --with-tune=core2 --disable-libssp
$ make -j7 profiledbootstrap
/home/matt/src/gcc-trunk/gcc/cp/parser.c: In function ‘bool cp_parser_ctor_initializer_opt_and_function_body(cp_parser*)’:
/home/matt/src/gcc-trunk/gcc/cp/parser.c:17533:43: error: ‘list’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
Most likely what is happening is cp_parser_compound_statement is being inlined and it is not cost worthly to do the jump thread for check_body_p.
Narrowed this down to -O2 -fipa-cp-clone that triggers the warning.
I think I may be seeing something similar.
I've been trying to bootstrap using "-g -O3" in BOOT_CFLAGS.
That doesn't work, but "-g -O2" of course does.
After trying out all the flags individually that
make the difference from -O2 to -O3, it is the -fipa-cp-clone
flag that is the only one that breaks bootstrap. The rest of
the flags are fine.
On trunk snapshot of 20130130, I get
../../src/trunk/gcc/c/c-parser.c: In function ‘c_expr c_parser_postfix_expression_after_primary(c_parser*, location_t, c_expr)’:
../../src/trunk/gcc/c/c-parser.c:6908:16: error: ‘origtypes’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
This looks a false positive to me.
http://gcc.gnu.org/ml/gcc-patches/2013-02/msg00324.html ought to fix the origtypes issue.
(In reply to comment #3)
> I've been trying to bootstrap using "-g -O3" in BOOT_CFLAGS.
> That doesn't work, but "-g -O2" of course does.
I am pleased to be able to say that BOOT_CFLAGS= -g -O3
works for revision 196574 (Sat 09 March 2013).
I'll use this as my new default build setting,
so when it stops working I'll be able to put in a bug report.
This is a long way from -g -O3 being the default
for all architectures, but it is a good step forward.
I think this bug is fixed.