[LLVMdev] Cloning block for newbie

[Nileih Cimeil]

Thank you for your help. It's working now.

I wasn't aware of the usefulness of the User class. The ValueMapper.cpp's
"RemapInstruction()" also helped me a lot to remap phi nodes and metadatas.

Thank you very much.

2012/6/21 Michael Ilseman <michael at lunarg.com>

> Please reply-all so that the thread is kept on llvmdev.
>
> The LLVM Programmer's Manual has examples of how to iterate over many
> common structures, such as instructions in a basic block[1]. Other
> than that, you can check the source code or doxygen[2].
>
> Basically, you loop over the instructions as detailed in the
> programmer's manual[1], and loop over the operands using User's
> op_iterators[2] checking to see if they have entries in ValueMap[3].
> If they do, you set that operand to use ValueMap's entry.
>
> [1] http://llvm.org/docs/ProgrammersManual.html#iterate_basicblock
> [2] http://llvm.org/doxygen/classllvm_1_1User.html
> [3] http://llvm.org/doxygen/classllvm_1_1ValueMap.html
>
> On Thu, Jun 21, 2012 at 1:49 PM, Nileih Cimeil <nileih at gmail.com> wrote:
> > Thank you for your quick answer...
> >
> >
> > "You can loop over the instruction's operands to see if they are
> > contained in VMap"
> >
> > I have no clue of to do that, do you have an example ?
> >
> >
> >
> > 2012/6/21 Michael Ilseman <michael at lunarg.com>
> >>
> >> CloneBasicBlock does a fairly shallow cloning; the instructions
> >> themselves are cloned but their operands are not replaced with any
> >> previously cloned values.
> >>
> >> Example:
> >> orig:
> >>  %a = ...
> >>  %b = fadd %a, ...
> >>
> >> clone:
> >>  %a.clone = ...
> >>  %b.clone = fadd %a, ... ; Note that this references the old %a and
> >> not %a.clone!
> >>
> >> You can loop over the instruction's operands to see if they are
> >> contained in VMap and replace them if need be. You'll find it helpful
> >> to view the IR after doing the clone, e.g. "alteredBB->dump()". You
> >> may also need to update phi nodes in the cloned block and elsewhere,
> >> depending on how you plan on inserting the clone into your CFG.
> >>
> >> On Thu, Jun 21, 2012 at 11:47 AM, Nileih Cimeil <nileih at gmail.com>
> wrote:
> >> > Hello everybody.
> >> >
> >> > I'm quite new to LLVM and I'm encontering problems with cloning basic
> >> > blocks. My two basic blocks are in the same function and it doesn't
> >> > really
> >> > matter how the cloned one behave for the moment. Of course, to do so,
> I
> >> > used
> >> > the cloning.h 's method "CloneBasicBlock" but I have the "Instruction
> >> > does
> >> > not dominate all uses!" error.
> >> > I know what it means, I just don't know how to get rid of it without
> >> > getting
> >> > more complicated errors. (I tried manipulating the VMap, the
> metadatas,
> >> > cloning each instruction one by one,...).
> >> >
> >> > Is there a way to know if an instruction is a definition (so I could
> >> > remove
> >> > or rename the value)?
> >> > Is there a VMap book for newbies?
> >> > Is there some documentations I forgot to look at?
> >> >
> >> >
> >> > Thank you.
> >> >
> >> >
> >> >
> >> > virtual BasicBlock* createAlteredBasicBlock(BasicBlock * basicBlock,
> >> > const
> >> > Twine &  Name = "", Function * F = 0){
> >> >
> >> >             ValueToValueMapTy VMap;
> >> >             BasicBlock * alteredBB = llvm::CloneBasicBlock
> (basicBlock,
> >> > VMap, Name, F);
> >> >
> >> >             return alteredBB;
> >> > }
> >> >
> >> >
> >> > _______________________________________________
> >> > LLVM Developers mailing list
> >> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> >> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >> >
> >
> >
>
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