[LLVMdev] Cloning block for newbie

[Michael Ilseman]

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;
>> > }
>> >
>> >
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>> >
>
>