[Bug c/65445] New: Improve [-W...] display for -Wformat

[Bug c/65445] New: Improve [-W...] display for -Wformat

[burnus at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65445

            Bug ID: 65445
           Summary: Improve [-W...] display for -Wformat
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org

Currently, the -Wformat suboptions (-Wformat-contains-nul, etc.) are shown as
"[-Wformat=]" - it would be useful to have the individual flag (such as
[-Wformat-contains-nul]) instead.

Originally reported as PR 65040 comment 18

[Bug c/65445] Improve [-W...] display for -Wformat

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65445

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-03-17
                 CC|                            |mpolacek at gcc dot gnu.org
     Ever confirmed|0                           |1

[Bug c/65445] Improve [-W...] display for -Wformat

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65445

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu.org

--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
There is a trivial fix, which is to use the appropriate OPT_Wx flag when
calling warning().

However, Joseph and I think that if the warning was enabled via a group option,
then it would be better to print both, such as:

[-Wformat=,-Wformat-contains-null]

This should be feasible now that options relationships are encoded in the *.opt
files. One would need to build in the opt*.awk scripts a static data-structure
that given OPT_Wx gives a list of OPT_Wy options that enable it. Something
like:

static int opts_enable_opt_table [] = {
...
2, OPT_Wall, OPT_Wc++-compat, /* OPT_Wenum_compare */
1, OPT_Wformat,               /* OPT_Wformat_contains_nul */
...
};

static int opts_enable_opt_index [] = {
...
/* OPT_Wenum_compare */ 50,
/* OPT_Wformat_contains_nul */ 53,
/* OPT_Wall */ -1,
....
};

such that opts_enable_opt_table[opts_enable_opt_index[OPT_Wformat_contains_nul]
+ 1] == OPT_Wformat

Then add a function that given an OPT_Wx, returns which OPT_Wy options that
enable it are enabled at this moment. Then, use this function when printing the
warning in diagnostics.c.
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65448

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

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--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Michal Malecki from comment #0)
> Most tools that use these error reports simply skip the first three lines,
> as they do not look like "standard compiler error format". It would be nice
> to have at least an option to change the format into something like this:

Which tools? Shouldn't those tools be fixed instead? 

Perhaps this would have been a better way to do it (although I would prefer the
notes after the error, and it could just not say "note:", to be consistent with
what we do for template instantiations), if we could start over again, but now
GCC has always behaved like this, if we change it, it may break other tools.
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd164

Alexandre Oliva <aoliva at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |aoliva at gcc dot gnu.org

--- Comment #6 from Alexandre Oliva <aoliva at gcc dot gnu.org> ---
The problem starts in the first copyrename pass.  We refrain from coalescing
variables if neither has a usable root.  This causes us to fail to coalesce
partitions that we would coalesce if only we tried them in a different order
(i.e., P1 and P2 fail but either one coalesces with P3, and then the other
would coalesce with that union).  This is exactly what happens in AO_myload
with -DOPT: partitions _3 and _6 won't coalesce, and then result_4 and _6
coalesce, which would enable _3 to coalesce too.  This in turn brings
additional rootless variables into stm_load, which again fail to coalesce
because we try them first (_36 and _4 fails, and l_11 and _36 passes, so that
with _4 would work).  Without -DOPT, we succeed in coalescing result (there are
fewer SSA names), and when that is inlined, it gets there with a root symbol,
so that coalescing of _36 and result_4 succeeds.  In both cases, we coalesce
l_11 with result_36, and it is precisely because _4 remains separate that we
end up introducing copies in new blocks when going out of SSA into RTL.

Coalescing SSA names even when neither has a root removes the optimization
differences for this testcase.