Re: Compiler Weirdness and possible bug ( was Re: Controlling optimization level per function )
Re: Compiler Weirdness and possible bug ( was Re: Controlling optimization level per function )
- Subject: Re: Compiler Weirdness and possible bug ( was Re: Controlling optimization level per function )
- From: Jocelyn Houle <email@hidden>
- Date: Sat, 10 Jul 2010 08:11:48 -0400
According to:
http://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
GCC has a -Winit-self which, when using with -Wuninitialized, should have warned you.
I looked back in the previous GCC versions doc, and found it even in GCC 4.2:
http://gcc.gnu.org/onlinedocs/gcc-4.2.0/gcc/Warning-Options.html
(and even earlier). But using it doesn't seem to work.
So even though the C/C++ spec might not require a warning, the GCC folks clearly wanted to allow it, but it seems broken.
On 2010-07-09, at 18:21, Eric Gorr wrote:
> Ok. So, it seems clang should probably emit a warning about this.
>
> Sent from my iPad
>
> On Jul 9, 2010, at 6:05 PM, Mark Wagner <email@hidden> wrote:
>
>> On Fri, Jul 9, 2010 at 14:35, Eric Gorr <email@hidden> wrote:
>>
>>> If it is undefined behavior, then it still seems like a bug in the compiler
>>> in that a warning or error should be emitted for this odd line of code.
>>> In any case, writing this line of code was clearly an error in the real
>>> application and simply getting rid of it fixed the problem I was having.
>>> Still....would like to have a better understanding of what the actual
>>> problem is.... (undefined behavior or just a bug in the compilers)
>>> Any thoughts?
>>
>> It is undefined behavior (you're accessing the value of the variable
>> "kMinimumWidth" before setting it), and since it's undefined, the C
>> standard permits the compiler to do whatever it wants to (up to and
>> including making demons fly out of your nose).
>>
>> --
>> Mark
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