[LLVMdev] [llvm-commits] [PATCH] MachineRegisterInfo: Don't emit the same livein copy more than once

[Tom Stellard]

On Tue, Feb 14, 2012 at 06:33:34PM -0800, Lang Hames wrote:
> Hi Tom,
> 
> As far as I can tell EmitLiveInCopies is just there to handle physreg
> arguments and return values. Is there any reason for these to change late
> in your backend?
>

No, on our target (AMD HD2XXX - HD6XXX GPUs) before the program begins,
some values are preloaded into registers.  We have special intrinsics
for reading these values (e.g.  llvm.R600.read_reg(i32 reg_idx) ), and
we just have a pass that converts these intrinsics to livein registers
and then calls EmitLiveInCopies().

-Tom

> - Lang.
> 
> 
> On Tue, Feb 14, 2012 at 7:22 AM, Tom Stellard <thomas.stellard at amd.com>wrote:
> 
> > On Mon, Feb 13, 2012 at 10:17:11PM -0800, Lang Hames wrote:
> > > Hi Tom,
> > >
> > > I'm pretty sure this function should only ever be called once, by
> > > SelectionDAG. Do you know where the second call is coming from in your
> > code?
> > >
> > > Cheers,
> > > Lang.
> >
> > Hi Lang,
> >
> > I was calling EmitLiveInCopies() from one of my backend specific passes.
> > If the function can only be called once, then I'll just try to merge
> > that pass with into the SelectionDAG.
> >
> > Thanks,
> > Tom
> >
> > >
> > > On Mon, Feb 13, 2012 at 7:03 PM, Stellard, Thomas <Tom.Stellard at amd.com
> > >wrote:
> > >
> > > > This patch seems to have been lost on the llvm-commits mailing list.
> > > >  Would someone be able to review it?
> > > >
> > > > Thanks,
> > > > Tom
> > > > ________________________________________
> > > > From: llvm-commits-bounces at cs.uiuc.edu [
> > llvm-commits-bounces at cs.uiuc.edu]
> > > > on behalf of Tom Stellard [thomas.stellard at amd.com]
> > > > Sent: Friday, February 03, 2012 1:55 PM
> > > > To: llvm-commits at cs.uiuc.edu
> > > > Subject: Re: [llvm-commits] [PATCH] MachineRegisterInfo: Don't emit the
> > > > same livein copy more than once
> > > >
> > > > On Fri, Jan 27, 2012 at 02:56:03PM -0500, Tom Stellard wrote:
> > > > > ---
> > > > >
> > > > > Is MachineRegisterInfo::EmitLiveInCopies() only meant to be called
> > once
> > > > > per compile?  If I call it more than once, it emits duplicate copies
> > > > > which causes the live interval analysis to fail.
> > > > >
> > > > >  lib/CodeGen/MachineRegisterInfo.cpp |    4 +++-
> > > > >  1 files changed, 3 insertions(+), 1 deletions(-)
> > > > >
> > > > > diff --git a/lib/CodeGen/MachineRegisterInfo.cpp
> > > > b/lib/CodeGen/MachineRegisterInfo.cpp
> > > > > index 266ebf6..fc787f2 100644
> > > > > --- a/lib/CodeGen/MachineRegisterInfo.cpp
> > > > > +++ b/lib/CodeGen/MachineRegisterInfo.cpp
> > > > > @@ -227,7 +227,9 @@
> > > > MachineRegisterInfo::EmitLiveInCopies(MachineBasicBlock *EntryMBB,
> > > > >          // complicated by the debug info code for arguments.
> > > > >          LiveIns.erase(LiveIns.begin() + i);
> > > > >          --i; --e;
> > > > > -      } else {
> > > > > +        //Make sure we don't emit the same livein copies twice, in
> > case
> > > > this
> > > > > +        //function is called more than once.
> > > > > +      } else if (def_empty(LiveIns[i].second)) {
> > > > >          // Emit a copy.
> > > > >          BuildMI(*EntryMBB, EntryMBB->begin(), DebugLoc(),
> > > > >                  TII.get(TargetOpcode::COPY), LiveIns[i].second)
> > > > > --
> > > > > 1.7.6.4
> > > > >
> > > > >
> > > >
> > > > Reposting this as a diff that can be applied via patch -P0 for SVN
> > > > users.
> > > >
> > > > -Tom
> > > >
> > > >
> > > > _______________________________________________
> > > > LLVM Developers mailing list
> > > > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> > > > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> > > >
> >
> >