[llvm] r221756 - Use a function_ref now that it works (r221753).

[David Blaikie]

On Tue, Nov 11, 2014 at 6:23 PM, Rafael Espindola <
rafael.espindola at gmail.com> wrote:

> Author: rafael
> Date: Tue Nov 11 20:23:37 2014
> New Revision: 221756
>
> URL: http://llvm.org/viewvc/llvm-project?rev=221756&view=rev
> Log:
> Use a function_ref now that it works (r221753).


> Modified:
>     llvm/trunk/include/llvm/Linker/Linker.h
>
> Modified: llvm/trunk/include/llvm/Linker/Linker.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Linker/Linker.h?rev=221756&r1=221755&r2=221756&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/Linker/Linker.h (original)
> +++ llvm/trunk/include/llvm/Linker/Linker.h Tue Nov 11 20:23:37 2014
> @@ -11,8 +11,8 @@
>  #define LLVM_LINKER_LINKER_H
>
>  #include "llvm/ADT/SmallPtrSet.h"
> +#include "llvm/ADT/STLExtras.h"
>
> -#include <functional>
>
>  namespace llvm {
>  class DiagnosticInfo;
> @@ -25,7 +25,7 @@ class StructType;
>  /// something with it after the linking.
>  class Linker {
>    public:
> -    typedef std::function<void(const DiagnosticInfo &)>
> +    typedef function_ref<void(const DiagnosticInfo &)>
>          DiagnosticHandlerFunction;
>

I think this usage is wrong, unfortunately.

I haven't managed to look at all the Linker code, but at least looking
at "Linker::Linker(Module
*M)" this seems as if it'll have problems.

That ctor initializes the member function_ref with a lambda. That' means
the function_ref will point to the lambda (unlike std::function which would
copy the lambda into itself) - but once the variable's initializer in the
ctor finishes, the lambda will be destroyed, leaving the function_ref
dangling, I think?

Any other caller that does something like:

Linken L([] { ... });
L.functionThatUsesTheMemberFunctionRef();

Will be equally problematic - as the lambda will be destroyed at the end of
the Linker variable's initialization, and the member function_ref will be
left dangling.


>
>      Linker(Module *M, DiagnosticHandlerFunction DiagnosticHandler);
>
>
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