[LLVMdev] Another missed optimization opportunity?

[Krzysztof Parzyszek]

On 4/24/2013 1:35 PM, Cameron McInally wrote:
>
> I believe that the wildcard is the extern keyword.
>
> Since the external symbol isn't resolved until link time, I suspect that
> it would be a legal C program to do something like (maybe the language
> lawyers know better though):
>
> XXX> cat test.c
> extern int x;
>
> int kung( ) {
>    return x;
> }
>
> XXX> cat foo.c
> extern int kung();
>
> volatile int x;
>
> int main() {
>    x = 0;
>    return kung();
> }
>
> Ugly programming, but I see no way of the linker having enough
> information to determine that the extern should be volatile and issue an
> warning/error.

6.7.3 Type qualifiers

5 If an attempt is made to modify an object defined with a 
const-qualified type through use of an lvalue with non-const-qualified 
type, the behavior is undefined. If an attempt is made to refer to an 
object defined with a volatile-qualified type through use of an lvalue
with non-volatile-qualified type, the behavior is undefined.

-Krzysztof


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