[llvm-commits] Trivial warning

[Bill Schmidt]

On Fri, 2012-11-16 at 13:25 -0600, Hal Finkel wrote:
> ----- Original Message -----
> > From: "David Blaikie" <dblaikie at gmail.com>
> > To: "Bill Schmidt" <wschmidt at linux.vnet.ibm.com>
> > Cc: "Hal Finkel" <hfinkel at anl.gov>, llvm-commits at cs.uiuc.edu, "Joe Abbey" <jabbey at arxan.com>
> > Sent: Friday, November 16, 2012 1:19:30 PM
> > Subject: Re: [llvm-commits] Trivial warning
> > 
> > On Fri, Nov 16, 2012 at 11:13 AM, Bill Schmidt
> > <wschmidt at linux.vnet.ibm.com> wrote:
> > > 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();
> > 
> > It looks like this particular change was reverted without prejudice.
> > The change was part of a much larger & more problematic change that
> > was reverted on those merits - this was just collateral damage.
> 
> In that case, please (re-)apply the const_cast. Can someone please file a PR so that we don't forget to actually fix this problem.

I think what this comes down to is a great big "group LGTM" to Joe for
his second attempt at the patch. :-D

Bill

> 
> Thanks again,
> Hal
> 
> > 
> > >
> > > 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
> > >> >
> > >>
> > >
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> > 
>