llvm dev - Aug 2012 - [LLVMdev] How to call some transformation passes (LoopRotate and LoopUnroll) from my own pass

Hello,

I wrote my own pass which needs to do some loop unrolling.

I can perform loop unrolling via opt:

opt -mem2reg -loops -loop-simplify -loop-rotate -lcssa -loop-unroll
-unroll-count=50 mytest.bc -o mytest.bc

This command works perfectly. 

However, what I really want is to produce the **same behavior** but
from my own pass (i.e., I don't want to use opt). I wrote a Module
pass which already calls other analysis and transformation passes in
its getAnalysisUsage method:


void MyPass::getAnalysisUsage(AnalysisUsage& AU) const {
  AU.addRequired<LoopInfo>();
  AU.addPreserved<LoopInfo>();
  AU.addRequiredID(LoopSimplifyID);
  AU.addPreservedID(LoopSimplifyID);
  AU.addRequiredID(LCSSAID);
  AU.addPreservedID(LCSSAID);
}    

However, I couldn't figure out how to call the LoopRotate and
LoopUnroll passes since I cannot use addRequiredID or addRequired for
these two transformations.

In Scalar.h, I found:
> Pass *createLoopUnrollPass(int Threshold = -1, int Count = -1, int
AllowPartial = -1);
> Pass *createLoopRotatePass();

Is to call these methods the way to go? How?, can somebody show me an
excerpt?

P.S. I tried hard on Google but I couldn't find anything related.

Thanks!

Jorge

Hi, Jorge.

When you put these "AU.addRequired<OtherPass>();", you are
telling to
the pass manager that your pass will use the other passes.

You can actually call the other passes with get analysis, like this:

LoopInfo &li = getAnalysis<LoopInfo>();

I hope it helps.

Regards,

Raphael Ernani

2012/8/6 Jorge Navas <navas at comp.nus.edu.sg>:
>
> Hello,
>
> I wrote my own pass which needs to do some loop unrolling.
>
> I can perform loop unrolling via opt:
>
> opt -mem2reg -loops -loop-simplify -loop-rotate -lcssa -loop-unroll
> -unroll-count=50 mytest.bc -o mytest.bc
>
> This command works perfectly.
>
> However, what I really want is to produce the **same behavior** but
> from my own pass (i.e., I don't want to use opt). I wrote a Module
> pass which already calls other analysis and transformation passes in
> its getAnalysisUsage method:
>
>
> void MyPass::getAnalysisUsage(AnalysisUsage& AU) const {
>   AU.addRequired<LoopInfo>();
>   AU.addPreserved<LoopInfo>();
>   AU.addRequiredID(LoopSimplifyID);
>   AU.addPreservedID(LoopSimplifyID);
>   AU.addRequiredID(LCSSAID);
>   AU.addPreservedID(LCSSAID);
> }
>
> However, I couldn't figure out how to call the LoopRotate and
> LoopUnroll passes since I cannot use addRequiredID or addRequired for
> these two transformations.
>
> In Scalar.h, I found:
>
>> Pass *createLoopUnrollPass(int Threshold = -1, int Count = -1, int
AllowPartial = -1);
>> Pass *createLoopRotatePass();
>
>
> Is to call these methods the way to go? How?, can somebody show me an
> excerpt?
>
> P.S. I tried hard on Google but I couldn't find anything related.
>
> Thanks!
>
> Jorge
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

On Aug 6, 2012, at 6:04 AM, Jorge Navas <navas at comp.nus.edu.sg> wrote:
> 
> Hello,
> 
> I wrote my own pass which needs to do some loop unrolling.
> 
> I can perform loop unrolling via opt:
> 
> opt -mem2reg -loops -loop-simplify -loop-rotate -lcssa -loop-unroll
> -unroll-count=50 mytest.bc -o mytest.bc
> 
> This command works perfectly. 
> 
> However, what I really want is to produce the **same behavior** but
> from my own pass (i.e., I don't want to use opt). I wrote a Module
> pass which already calls other analysis and transformation passes in
> its getAnalysisUsage method:
> 
> 
> void MyPass::getAnalysisUsage(AnalysisUsage& AU) const {
>  AU.addRequired<LoopInfo>();
>  AU.addPreserved<LoopInfo>();
>  AU.addRequiredID(LoopSimplifyID);
>  AU.addPreservedID(LoopSimplifyID);
>  AU.addRequiredID(LCSSAID);
>  AU.addPreservedID(LCSSAID);
> }    
> 
> However, I couldn't figure out how to call the LoopRotate and
> LoopUnroll passes since I cannot use addRequiredID or addRequired for
> these two transformations.
> 
> In Scalar.h, I found:
> 
>> Pass *createLoopUnrollPass(int Threshold = -1, int Count = -1, int
AllowPartial = -1);
>> Pass *createLoopRotatePass();
> 
> 
> Is to call these methods the way to go? How?, can somebody show me an
> excerpt?
The create*Pass methods give you a Pass instance that you can add to a pass
manager. If you're replacing "opt", you should look at the opt
driver, opt.cpp to see how to do this. You can call addRequired<X> from
your pass to force the PassManager to run X before your pass.

If you want to do these transformations within a single pass, then the
transformations need to be exposed as a utility. llvm::UnrollLoop() currently
is, but LoopRotation is not. LoopRotation could be exposed as a utility (or you
could copy the relevant code), but you should try not to do that. The llvm
strategy is that loop rotation should do the right thing when it runs before
your pass. If loop rotation needs more information to what you want it to do,
then you can create a some new analysis that loop rotation requires.

You may want to try browsing the online docs, such as...
http://llvm.org/docs/WritingAnLLVMPass.html

Hope that helps.

-Andy

Thanks!

I understand now much better.

Jorge
On Monday, August 6, 2012 at 10:25:24 (-0700), Andrew Trick
wrote:
>> 
>> On Aug 6, 2012, at 6:04 AM, Jorge Navas <navas at
comp.nus.edu.sg> wrote:
>> 
>> > 
>> > Hello,
>> > 
>> > I wrote my own pass which needs to do some loop unrolling.
>> > 
>> > I can perform loop unrolling via opt:
>> > 
>> > opt -mem2reg -loops -loop-simplify -loop-rotate -lcssa
-loop-unroll
>> > -unroll-count=50 mytest.bc -o mytest.bc
>> > 
>> > This command works perfectly. 
>> > 
>> > However, what I really want is to produce the **same behavior**
but
>> > from my own pass (i.e., I don't want to use opt). I wrote a
Module
>> > pass which already calls other analysis and transformation passes
in
>> > its getAnalysisUsage method:
>> > 
>> > 
>> > void MyPass::getAnalysisUsage(AnalysisUsage& AU) const {
>> >  AU.addRequired<LoopInfo>();
>> >  AU.addPreserved<LoopInfo>();
>> >  AU.addRequiredID(LoopSimplifyID);
>> >  AU.addPreservedID(LoopSimplifyID);
>> >  AU.addRequiredID(LCSSAID);
>> >  AU.addPreservedID(LCSSAID);
>> > }    
>> > 
>> > However, I couldn't figure out how to call the LoopRotate and
>> > LoopUnroll passes since I cannot use addRequiredID or addRequired
for
>> > these two transformations.
>> > 
>> > In Scalar.h, I found:
>> > 
>> >> Pass *createLoopUnrollPass(int Threshold = -1, int Count = -1,
int AllowPartial = -1);
>> >> Pass *createLoopRotatePass();
>> > 
>> > 
>> > Is to call these methods the way to go? How?, can somebody show me
an
>> > excerpt?
>> 
>> The create*Pass methods give you a Pass instance that you can add to a
pass manager. If you're replacing "opt", you should look at the
opt driver, opt.cpp to see how to do this. You can call addRequired<X>
from your pass to force the PassManager to run X before your pass.
>> 
>> If you want to do these transformations within a single pass, then the
transformations need to be exposed as a utility. llvm::UnrollLoop() currently
is, but LoopRotation is not. LoopRotation could be exposed as a utility (or you
could copy the relevant code), but you should try not to do that. The llvm
strategy is that loop rotation should do the right thing when it runs before
your pass. If loop rotation needs more information to what you want it to do,
then you can create a some new analysis that loop rotation requires.
>> 
>> You may want to try browsing the online docs, such as...
>> http://llvm.org/docs/WritingAnLLVMPass.html
>> 
>> Hope that helps.
>> 
>> -Andy