Re: Extended doubt regarding the bug 93432

[Martin Sebor <msebor@gmail.com>]

On 2/11/22 11:10, Krishna Narayanan wrote:
> Hello,
> I tried to run the gcc in the debugger but I am getting a repetitive 
> error for header files,I tried using -I followed by the path of the 
> header file (-I/home/krishna/objdir/gcc) in the command but still the 
> error is persistent.
> Error:
> In file included from *tree-ssa-uninit.c:22*:
> *system.h:209:10*: fatal error: safe-ctype.h: No such file or directory
>    209 | #include "safe-ctype.h"
>        |          ^~~~~~~~~~~~~~
> compilation terminated.
> How do I resolve this?Can you please help me out with this and where did 
> I go wrong?

I usually create a translation unit (a .i file for a C source and
a .ii file for a C++ source) by compiling the .c or .C file with
the -E option and then start GCC the debugger on that file.  For
example, with an unoptimized GCC stage1 build with -g3 enabled in
/build/gcc-master, I invoke it in GDB like so:

   $ /build/gcc-master/gcc/xgcc -B /build/gcc-master/gcc tu.i -wrapper 
gdb,--arg

(In Emacs, I use gdb,-i=mi,--arg as the trailing pieces.) This lets
me avoid many of the -I command line options that the GCC driver
otherwise passes to to th compiler implicitly.

Martin

> Thanks and regards,
> Krishna Narayanan.
> 
> 
> On Wed, Feb 9, 2022 at 3:20 AM Martin Sebor <msebor@gmail.com 
> <mailto:msebor@gmail.com>> wrote:
> 
>     On 2/8/22 10:37, Jonathan Wakely via Gcc-help wrote:
>      > On Tue, 8 Feb 2022 at 17:18, Krishna Narayanan <
>      > krishnanarayanan132002@gmail.com
>     <mailto:krishnanarayanan132002@gmail.com>> wrote:
>      >
>      >> Thanks for your response,Could you please clarify if this is a bug?
>      >>
>      >
>      > It warns with -O1, which is the documented behaviour:
>      >
>      >        The effectiveness of some warnings depends on
>     optimizations also
>      > being enabled. For example -Wsuggest-final-types is more
>      >        effective with link-time optimization and
>     -Wmaybe-uninitialized does
>      > not warn at all unless optimization is enabled.
> 
>     Yes, although the latter sentence is no longer completely accurate.
>     Since GCC 11 -Wmaybe-uninitialized doesn't need optimization to trigger
>     for code that passes an uninitialized object to a function that takes
>     a const reference.  Let me update the manual with that.
> 
>      > So no, I don't think it' a bug. GCC is behaving as designed.
>     Ideally it
>      > would be better at warning without optimization, but changing
>     that would be
>      > hard.
> 
>     It might be tricky to handle this case without causing false positives
>     in others.
> 
>     Krishna, to understand why some of these cases are diagnosed and others
>     aren't, you need to look at either the dump from the uninit pass
>     (-fdump-tree-uninit) with -O1 and above, or at some early dump (e.g.,
>     -fdump-tree-ssa) at -O0.  Here's a link to the former on Godbolt for
>     your example:
> 
>     https://gcc.godbolt.org/z/89c4s7o6E
>     <https://gcc.godbolt.org/z/89c4s7o6E>
> 
>     The best way is of course to step through GCC in a debugger (for
>     the uninitialized warnings the code is in gcc/tree-ssa-uninit.cc).
> 
>     Martin
> 
>      >
>      >
>      >
>      >
>      >
>      >> Regards,
>      >> Krishna Narayanan.
>      >>
>      >> On Tue, Feb 8, 2022 at 10:28 PM Jonathan Wakely
>     <jwakely.gcc@gmail.com <mailto:jwakely.gcc@gmail.com>>
>      >> wrote:
>      >>
>      >>>
>      >>>
>      >>> On Tue, 8 Feb 2022 at 16:25, Krishna Narayanan via Gcc-help <
>      >>> gcc-help@gcc.gnu.org <mailto:gcc-help@gcc.gnu.org>> wrote:
>      >>>
>      >>>> Hello,
>      >>>> As an extension to the bug 93432
>      >>>> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93432
>     <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93432>), I would like to
>      >>>> add a few more points,here in the given code
>      >>>> (https://godbolt.org/z/sYjqjqh3d
>     <https://godbolt.org/z/sYjqjqh3d>) there is a warning averted but there
>      >>>> is no warning shown for this code
>      >>>> (https://gcc.godbolt.org/z/oo5sf4oec
>     <https://gcc.godbolt.org/z/oo5sf4oec>) .
>      >>>> I tried it with "-fno-strict-aliasing -fwrapv
>      >>>> -fno-aggressive-loop-optimizations" and
>     "fsanitize=undefined".There
>      >>>> are no errors for gcc but clang has runtime errors,the error for
>      >>>> clang: https://gcc.godbolt.org/z/1hq8x1o8E
>     <https://gcc.godbolt.org/z/1hq8x1o8E> .
>      >>>>
>      >>>> Can we have a warning in the second case as well? It will be
>     much more
>      >>>> convenient as there is a lapse of initialization.
>      >>>>
>      >>>
>      >>> Yes, ideally it would warn.
>      >>>
>      >>>
>      >>>
>      >>
>