On 9/2/16, Segher Boessenkool <seg...@kernel.crashing.org> wrote:
> On Fri, Sep 02, 2016 at 05:08:34PM -0400, Eric Gallager wrote:
>> > The only way to know for sure what GCC is warning about is to look at
>> > the uninit dump.
>>
>> How exactly do I generate an uninit dump? I'm not seeing any relevant
>> options in the GCC manual...
>
> -fdump-tree-uninit
>
I tried that but it doesn't look like it produced any dumpfiles...
although adding -save-temps to the command gave me an extra 'note'
that wasn't there before:
$ /usr/local/bin/g++ -std=gnu++98 -fno-PIE -c -g -mdynamic-no-pic
-DIN_GCC -fno-exceptions -fno-rtti -fasynchronous-unwind-tables
-fdump-tree-uninit -fdump-tree-uninit-details
-fdump-tree-uninit-blocks-details -fdump-tree-cddce2
-fdump-tree-cddce2-blocks -dA -dD -dP -freport-bug -fsched-verbose=5
-fchecking=2 -save-temps -Wall -Wextra -Wc++11-compat -Wnarrowing
-Wwrite-strings -Wcast-qual -Wno-format -Wmissing-format-attribute
-Woverloaded-virtual -pedantic -Wno-long-long -Wno-variadic-macros
-Wno-overlength-strings -Wno-implicit-fallthrough -DHAVE_CONFIG_H -I.
-I. -I../../gcc -I../../gcc/. -I../../gcc/../include
-I../../gcc/../libcpp/include
-I/private/var/root/gcc-git/my_oddly_named_builddir/./gmp
-I/private/var/root/gcc-git/gmp
-I/private/var/root/gcc-git/my_oddly_named_builddir/./mpfr/src
-I/private/var/root/gcc-git/mpfr/src
-I/private/var/root/gcc-git/mpc/src -I../../gcc/../libdecnumber
-I../../gcc/../libdecnumber/dpd -I../libdecnumber
-I../../gcc/../libbacktrace
-I/private/var/root/gcc-git/my_oddly_named_builddir/./isl/include
-I/private/var/root/gcc-git/isl/include -o combine.o -MT combine.o
-MMD -MP -MF ./.deps/combine.TPo
../../gcc/combine.c../../gcc/combine.c: In function ‘int
combine_instructions(rtx_insn*, unsigned int)’:
../../gcc/combine.c:1310:8: warning: ‘prev’ may be used uninitialized
in this function [-Wmaybe-uninitialized]
if ((next = try_combine (insn, prev, NULL, NULL,
^~
../../gcc/combine.c:1125:13: note: ‘prev’ was declared here
rtx_insn *prev;
^~~~
I tried again without '-save-temps' and confirmed that the extra
'note' disappeared again.
>> > Moreover, if the warning is bogus and not a regression, it is very
>> > likely that it is reported already here:
>> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=24639
>> >
>> > The effort dedicated to report and analyze the report would be better
>> > spent fixing any of the issues already known.
>> >
>> > Nevertheless, assignments within 'if' are one of the things that make
>> > reading GCC code harder than it needs to be (and combine.c is scary).
>>
>> So would a patch to move the assignment out of the 'if' be better then?
>
> Not really; this idiom is used all over the place in combine (including
> a few times with this same variable!)
>
> It seems to be a regression, anyway? Older versions built fine?
>
>
> Segher
>
I wasn't really paying as close attention with older versions; I was
only looking at the warnings this time to silence the narrowing ones:
https://gcc.gnu.org/ml/gcc-patches/2016-08/msg02129.html
...and so I noticed this one and figured I'd try to silence it as
well. It still built fine anyways; it was just a warning and not an
error after all.
(IOW I don't know if this is a regression or not)
