llvm dev - Oct 2014 - [LLVMdev] Need guidance regarding MachineFunctionPass

Respected Dr. Criswell,

My problem is that the output of following code looks nothing like any
opcode:






*for(MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); )
{         MachineInstr *mi = I;         int op = mi->getOpcode();
std::cout << op << '\t';    }*

I need to identify specific instructions in my MachineFunctionPass and I
was hoping that I can do that by using *getOpcode(). *I am kinda stuck at
this point. Kindly guide me ! Thank you !

On Thu, Oct 2, 2014 at 4:37 PM, John Criswell <jtcriswel at gmail.com>
wrote:
>  Dear Sachin,
>
> Your description of the problem contains too few details; no one will be
> able to diagnose the problem you're having.  You need to provide more
> information on what, exactly, is not working as you expected.
>
> Regards,
>
> John Criswell
>
>
> On 10/2/14, 5:11 PM, sachin arora wrote:
>
>  Hello,
>
>  I am writing a MachineFunctionPass that inspects the generated machine
> code, and examines each opcode and its corresponding operands. If the
> 'instruction + operands' match a particular sequence, then the pass
should
> replace them with a fixed instruction + operands sequence. I tried using
> MachineInstr's getOpcode and getOperand functions but the pass
didn't work
> as expected.
>
>  Kindly tell me how to proceed or point to appropriate references. Thank
> you !
>
> --
> Regards,
> Sachin
>
>
> _______________________________________________
> LLVM Developers mailing listLLVMdev at cs.uiuc.edu        
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>
>
>
> --
> John Criswell
> Assistant Professor
> Department of Computer Science, University of
Rochesterhttp://www.cs.rochester.edu/u/criswell
>
>

-- 
Regards,
Sachin
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Hi Sachin,
>          int op = mi->getOpcode();
This is a target-specific opcode, and corresponds to one of the values
defined in (from a CMake build directory)
lib/Target/XYZ/XYZGenInstrInfo.inc.

The easiest way to find out which is actually to use
MachineInstr::dump (and/or "llc -debug" from the command-line to print
it out automatically); if it prints something like (to pick a
completely random example from AArch64):

 %X1<def> = LDRXui <fi#3>, 0; mem:LD8[%result] dbg:blockstret.c:20:

Then you'd want to compare "op" against
"AArch64::LDRXui"

Cheers.

Tim.

Thank you Mr. Tim. Is "AArch64" a namespace? Because when I tried
"X86::MOV", it gave me an error saying that first define X86
namespace.
Sorry if I sound stupid but I am new to LLVM. Thank you again.



On Thu, Oct 2, 2014 at 8:16 PM, Tim Northover <t.p.northover at gmail.com>
wrote:
> Hi Sachin,
>
> >          int op = mi->getOpcode();
>
> This is a target-specific opcode, and corresponds to one of the values
> defined in (from a CMake build directory)
> lib/Target/XYZ/XYZGenInstrInfo.inc.
>
> The easiest way to find out which is actually to use
> MachineInstr::dump (and/or "llc -debug" from the command-line to
print
> it out automatically); if it prints something like (to pick a
> completely random example from AArch64):
>
>  %X1<def> = LDRXui <fi#3>, 0; mem:LD8[%result]
dbg:blockstret.c:20:
>
> Then you'd want to compare "op" against
"AArch64::LDRXui"
>
> Cheers.
>
> Tim.
>


-- 
Regards,
Sachin
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