[llvm-commits] Trivial warning

[Bill Schmidt]

On Fri, 2012-11-16 at 12:32 -0600, Hal Finkel wrote:
> ----- Original Message -----
> > From: "Roman Divacky" <rdivacky at freebsd.org>
> > To: "Hal Finkel" <hfinkel at anl.gov>
> > Cc: llvm-commits at cs.uiuc.edu, "Joe Abbey" <jabbey at arxan.com>
> > Sent: Friday, November 16, 2012 12:13:53 PM
> > Subject: Re: [llvm-commits] Trivial warning
> > 
> > On Fri, Nov 16, 2012 at 11:38:07AM -0600, Hal Finkel wrote:
> > > ----- Original Message -----
> > > > From: "Benjamin Kramer" <benny.kra at gmail.com>
> > > > To: "Joe Abbey" <jabbey at arxan.com>
> > > > Cc: "Hal Finkel" <hfinkel at anl.gov>, llvm-commits at cs.uiuc.edu
> > > > Sent: Friday, November 16, 2012 10:00:47 AM
> > > > Subject: Re: [llvm-commits] Trivial warning
> > > > 
> > > > 
> > > > On 16.11.2012, at 13:11, Joe Abbey <jabbey at arxan.com> wrote:
> > > > 
> > > > > On Nov 16, 2012, at 12:38 AM, Joe Abbey <jabbey at arxan.com>
> > > > > wrote:
> > > > > 
> > > > >> Hal (et al),
> > > > >> 
> > > > >> One of my build bots reported a warning:
> > > > >> PPCRegisterInfo.cpp:501:51: warning: cast from type ???const
> > > > >> llvm::MachineFunction*??? to type ???llvm::MachineFunction*???
> > > > >> casts
> > > > >> away qualifiers [-Wcast-qual]
> > > > >> Index: lib/Target/PowerPC/PPCRegisterInfo.cpp
> > > > >> ===================================================================
> > > > >> --- lib/Target/PowerPC/PPCRegisterInfo.cpp	(revision 168110)
> > > > >> +++ lib/Target/PowerPC/PPCRegisterInfo.cpp	(working copy)
> > > > >> @@ -498,7 +498,8 @@
> > > > >>      } else if (CRSpillFrameIdx) {
> > > > >>        FrameIdx = CRSpillFrameIdx;
> > > > >>      } else {
> > > > >> -      MachineFrameInfo *MFI = ((MachineFunction
> > > > >> &)MF).getFrameInfo();
> > > > >> +      MachineFrameInfo *MFI =
> > > > >> +        (const_cast<MachineFunction &>MF).getFrameInfo();
> > > > >>        FrameIdx = MFI->CreateFixedObject((uint64_t)4,
> > > > >>        (int64_t)-4,
> > > > >>        true);
> > > > >>        CRSpillFrameIdx = FrameIdx;
> > > > >>      }
> > > > >> 
> > > > >> Ok to commit?
> > > > > 
> > > > > Past Joe,
> > > > > 
> > > > > Make sure your current build is setup to do PowerPC builds.
> > > > > 
> > > > > Also, swapping a warning for an error is a horrible trade???
> > > > > let's
> > > > > try that patch again:
> > > > > 
> > > > > Index: lib/Target/PowerPC/PPCRegisterInfo.cpp
> > > > > ===================================================================
> > > > > --- lib/Target/PowerPC/PPCRegisterInfo.cpp	(revision 168110)
> > > > > +++ lib/Target/PowerPC/PPCRegisterInfo.cpp	(working copy)
> > > > > @@ -498,7 +498,8 @@
> > > > >      } else if (CRSpillFrameIdx) {
> > > > >        FrameIdx = CRSpillFrameIdx;
> > > > >      } else {
> > > > > -      MachineFrameInfo *MFI = ((MachineFunction
> > > > > &)MF).getFrameInfo();
> > > > > +      MachineFrameInfo *MFI =
> > > > > +        (const_cast<MachineFunction &>(MF)).getFrameInfo();
> > > > >        FrameIdx = MFI->CreateFixedObject((uint64_t)4,
> > > > >        (int64_t)-4,
> > > > >        true);
> > > > >        CRSpillFrameIdx = FrameIdx;
> > > > >      }
> > > > 
> > > > While this would be the right way to silence the warning, the
> > > > whole
> > > > thing looks like a horrible hack to me. Shouldn't the FrameIdx
> > > > generated in a place where MF isn't const?
> > > 
> > > Roman, you had looked at these const issues, right? Do you have an
> > > opinion on this?
> > 
> > I actively avoided any const_cast<>s in my const rage :)
> > 
> > This code was contributed by wschmidt@ and iirc it needs to be
> > like this because PPC is special (addressing against fp).
> 
> Bill, opinion?
> 

It looks to me like this has been changed a couple of times now:

Original code:
      MachineFrameInfo *MFI = ((MachineFunction &)MF).getFrameInfo();

Fixed in 165941 by Micah Villnow:

165941   mvillmow       MachineFrameInfo *MFI =
(const_cast<MachineFunction &>(MF)).getFrameInfo();

Reverted by Chandler in 167222:

167222  chandlerc       MachineFrameInfo *MFI = ((MachineFunction
&)MF).getFrameInfo();

And now it's under discussion again...

I don't know of a better way to do this, so if anyone feels it's too
much of a bloody hack, I welcome suggestions.  Seems to me like the
const_cast is the best alternative, but it's probably worth asking
Chandler why he reverted Micah's change.

My two cents,
Bill



> > 
> > I think Bill didnt see an easy way to fix this. I think const_cast<>
> > in here is better than C style cast.
> 
> Agreed.
> 
>  -Hal
> 
> > 
> > Roman
> > 
>