On 16/11/17 09:18 -0700, Martin Sebor wrote:
On 11/16/2017 03:49 AM, Jonathan Wakely wrote:
On 15/11/17 20:28 -0700, Martin Sebor wrote:
On 11/15/2017 07:31 AM, Jonathan Wakely wrote:
The docs for -Wmaybe-uninitialized have some issues:
- That first sentence is looooooong.
- Apparently some C++ programmers think "automatic variable" means one
declared with C++11 `auto`, rather than simply a local variable.
- The sentence about only warning when optimizing is stuck in between
two chunks talking about longjmp, which could be inferred to mean
only the setjmp/longjmp part of the warning depends on optimization.
This attempts to make it easier to parse and understand.
I've always found the description remarkably precise. Particularly
the bit where it talks about the two paths, one initialized and the
other not. Your rewording loses that distinction so I don't think
it's as accurate, or even correct.
To use an example, this would satisfy the new description:
int f (void)
{
int i;
return i;
}
but it doesn't match GCC behavior (it triggers -Wuninitialized,
not -Wmaybe-uninitialized). Unless the distinction is more
subtle than I ascribe to it I think it needs to be preserved
in the rewording.
Ah, I tested a similar case and missed that the warning I got was from
-Wuninitialized not -Wmaybe-uninitialized, which made me think that
"a use of the variable that is initialized" was wrong.
OK, so then here's an alternative patch which doesn't touch that first
sentence except to add "(i.e. local)". That makes the first sentence
even longer, but if it's accurate maybe that's OK. This still adds
"These warnings are only possible in optimizing compilation, because
otherwise GCC does not keep track of the state of variables." And
removes the similar text from the middle of the setjmp/longjmp
discussion.
Thanks, this looks fine to me.
As an aside, I wonder if you think that rewording the part about
GCC not being smart enough might be worthwhile:
These warnings are made optional because GCC is not smart enough
to see all the reasons why the code might be correct in spite of
appearing to have an error.
It sounds just a little pejorative (or maybe just colloquial) to
me for the manual. Perhaps:
These warnings are made optional because GCC may not be able to
determine when the code is correct in spite of appearing to have
an error.
I think that's an improvement. New patch attached.
Jeff, is this still OK?
commit 7e9e4b7e6ab555daa549921ea7f19ff4d1b22129
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Fri Nov 17 12:40:18 2017 +0000
Improve -Wmaybe-uninitialized documentation
* doc/invoke.texi (-Wmaybe-uninitialized): Rephrase for clarity.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 1e2b869885b..e15bf260be5 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -4974,14 +4974,18 @@ void store (int *i)
@item -Wmaybe-uninitialized
@opindex Wmaybe-uninitialized
@opindex Wno-maybe-uninitialized
-For an automatic variable, if there exists a path from the function
-entry to a use of the variable that is initialized, but there exist
+For an automatic (i.e.@ local) variable, if there exists a path from the
+function entry to a use of the variable that is initialized, but there exist
some other paths for which the variable is not initialized, the compiler
emits a warning if it cannot prove the uninitialized paths are not
-executed at run time. These warnings are made optional because GCC is
-not smart enough to see all the reasons why the code might be correct
-in spite of appearing to have an error. Here is one example of how
-this can happen:
+executed at run time.
+
+These warnings are only possible in optimizing compilation, because otherwise
+GCC does not keep track of the state of variables.
+
+These warnings are made optional because GCC may not be able to determine when
+the code is correct in spite of appearing to have an error. Here is one
+example of how this can happen:
@smallexample
@group
@@ -5008,9 +5012,7 @@ similar code.
@cindex @code{longjmp} warnings
This option also warns when a non-volatile automatic variable might be
-changed by a call to @code{longjmp}. These warnings as well are possible
-only in optimizing compilation.
-
+changed by a call to @code{longjmp}.
The compiler sees only the calls to @code{setjmp}. It cannot know
where @code{longjmp} will be called; in fact, a signal handler could
call it at any point in the code. As a result, you may get a warning
