On 16/11/17 10:59 -0700, Jeff Law 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.
patch.txt
commit 3ebe2a74817bbbbb63e27f961e91e6c044d00245
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Thu Nov 16 10:43:51 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 85c980bdfc9..bb68c308166 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -4970,11 +4970,16 @@ 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
s/exist/exists/
?
I think it's correct as written, because it says "there exist some
other paths" i.e. paths plural.
I did consider changing it to "there exists some other path" but I
didn't think that was any better or worse, so didn't change it.
I think with that nit it's ok.
jeff
