llvm dev - Apr 2014 - [LLVMdev] Why "I = ++I" instead of "++I" in COFFDump.cpp ?

tools/llvm-objdump/COFFDump.cpp has two loops that advance the loop iterator
using "I = ++I" instead of the usual "++I".  For example:

  import_directory_iterator I = Obj->import_directory_begin();
  import_directory_iterator E = Obj->import_directory_end();
  if (I == E)
    return;
  outs() << "The Import Tables:\n";
  for (; I != E; I = ++I) {
      ...
  }

Is there a reason for writing "I = ++I" instead of "++I" ?

- Arch D. Robison

Not that I know of - and if there is... we've got issues. So change it
& find out? :)

On Fri, Apr 4, 2014 at 10:39 AM, Robison, Arch <arch.robison at intel.com>
wrote:
> tools/llvm-objdump/COFFDump.cpp has two loops that advance the loop
iterator using "I = ++I" instead of the usual "++I".  For
example:
>
>   import_directory_iterator I = Obj->import_directory_begin();
>   import_directory_iterator E = Obj->import_directory_end();
>   if (I == E)
>     return;
>   outs() << "The Import Tables:\n";
>   for (; I != E; I = ++I) {
>       ...
>   }
>
> Is there a reason for writing "I = ++I" instead of
"++I" ?
>
> - Arch D. Robison
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

Looks like a bug.  This can probably be simplified with C++11.


On Fri, Apr 4, 2014 at 10:39 AM, Robison, Arch <arch.robison at
intel.com>wrote:
> tools/llvm-objdump/COFFDump.cpp has two loops that advance the loop
> iterator using "I = ++I" instead of the usual "++I". 
For example:
>
>   import_directory_iterator I = Obj->import_directory_begin();
>   import_directory_iterator E = Obj->import_directory_end();
>   if (I == E)
>     return;
>   outs() << "The Import Tables:\n";
>   for (; I != E; I = ++I) {
>       ...
>   }
>
> Is there a reason for writing "I = ++I" instead of
"++I" ?
>
> - Arch D. Robison
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
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Oops, meant to send this to the mailing list instead of to Reid
privately. (Why cc the mailing list instead of just sending to the
mailing list?)

In article <CACs=tyJ6zaHeiS0eNhBkdcZE--JY4k7yH9_P1yFbGqod6uymMw at
mail.gmail.com>,
    Reid Kleckner <rnk at google.com> writes:
> Looks like a bug.  This can probably be simplified with C++11.
> 
> On Fri, Apr 4, 2014 at 10:39 AM, Robison, Arch <arch.robison at
intel.com>wrote:
> 
> >   for (; I != E; I = ++I) {
> >       ...
> >   }
> >
> > Is there a reason for writing "I = ++I" instead of
"++I" ?
I don't see how it's a bug because functionality isn't impacted by
this.  It's simply a redundant assignment.

I also don't see what C++11 has to do with this.

    i = i;

has always been legal since the very first implementation of C and has
always been a pointless expression.

Had the code been:

    i = i++;

then we would have had a real problem since i++ returns the old value
of i before it was incremented and the loop would be infinite.
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