[LLVMdev] LoopInfo of a basic block

[Justin Holewinski]

On Mon, Feb 28, 2011 at 6:04 PM, Naznin Fauzia <laboni14 at gmail.com> wrote:

> Thanks Devang and John. My pass is actually a loop pass, not a function
> pass. So, I couldnt override the getAnalysisUsage.
>

A LoopPass is no different from a FunctionPass here.  You can use
getAnalysisUsage and getAnalysis in a LoopPass.


> I am in a loop pass, I know the outermost loop. Now How can I get the
> loopInfo from here? I couldn't find helpful methods in the LoopInfo class
> documents.
>
>
> On Mon, Feb 28, 2011 at 5:52 PM, John Criswell <criswell at illinois.edu>wrote:
>
>>  On 2/28/11 4:43 PM, Devang Patel wrote:
>>
>>
>>  On Feb 28, 2011, at 2:35 PM, Naznin Fauzia wrote:
>>
>> Hi all,
>>
>> How Can I get the Loops around an Instruction?
>>
>> I know I can get the basic block of an instruction using inst.getParent()
>> which returns a BasicBlock*. Now I want to use the getLoopFor(BasicBlock)
>> method of the class LoopInfo.
>> But I dont know how to get the LoopInfo.
>>
>> BasicBlock* bb = inst.getParent();
>>
>> (... what should I add here?)
>>
>> Loop* innerloop = LI -> getLoopFor(bb):
>>
>>
>>  Two steps:
>> 1) In your pass's getAnalysisUsage(), request LoopInfo.
>>
>>   virtual void getAnalysisUsage(AnalysisUsage &AU) const {
>>    AU.addRequired<LoopInfo>();
>>  }
>>
>>  2) In your runOnLoop() method get the analysis.
>>
>>  LoopPass *LI = &getAnalysis<LoopInfo>();
>>
>>  Now, you can do LI->getLoopFor(...)
>>
>>
>> To add to what Devang has said, you may find the doxygen docs on LoopInfo
>> helpful:
>>
>> http://llvm.org/doxygen/classllvm_1_1LoopInfo.html
>>
>> -- John T.
>>
>>
>>
>>  -
>> Devang
>>
>>
>>
>>
>
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-- 

Thanks,

Justin Holewinski
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