[llvm-commits] [llvm] r46394 - in /llvm/trunk/lib: Target/PowerPC/PPCAsmPrinter.cpp Transforms/Scalar/SimplifyCFG.cpp

[Bill Wendling]

On Jan 26, 2008, at 12:21 AM, Chris Lattner wrote:

>
> On Jan 25, 2008, at 10:51 PM, Bill Wendling wrote:
>
>> Author: void
>> Date: Sat Jan 26 00:51:24 2008
>> New Revision: 46394
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=46394&view=rev
>> Log:
>> If there are no machine instructions emitted for a function, then
>> insert
>> a "nop" instruction so that we don't have the function's label
>> associated
>> with something that it's not supposed to be associated with.
>
> Thanks Bill, this is looking better.   Some thoughts:
>
>> +  // If the function is empty, then we need to emit *something*.
>> Otherwise, the
>> +  // function's label might be associated with something that it
>> wasn't meant to
>> +  // be associated with. We emit a noop in this situation.
>> +  MachineFunction::iterator I = MF.begin();
>> +
>> +  if (++I == MF.end()) {
>> +    MachineBasicBlock &MBB = MF.front();
>> +
>> +    if (MBB.begin() == MBB.end())
>
> You can use MBB.empty()
>
Good point!

>>
>> +      BuildMI(MBB, MBB.end(), TM.getInstrInfo()->get(PPC::NOP));
>> +  }
>
> Is there any reason to actually make a machineinstr here?  It seems
> like it would be possible to just emit "nop" to the .s file.  The JIT
> doesn't need this.
>
I initially had that, but I thought that it would be better to do  
things though the "print machine instruction" function just so I got  
the syntax correct. But nop is probably safe to emit like that.

> Also, I think this is required on x86 and arm as well, as they have
> the same problem with -fomit-frame-pointer.
>
There's a nop for X86, but I don't see one for ARM in the .td file.

> Thanks for working on this!
>
No problem. :-)

-bw