llvm dev - Jul 2014 - [LLVMdev] Using CostModel to estimate machine cycles of each instruction

There is CostModel.cpp since LLVM3, I am wondering if anyone can give me 
an concrete example on how to use this pass to estimate cycles used in a 
given IR file.

Thank you very much.


Don

Hi Don,

In it's current version, tha pass can only be used via "opt -cost-model
-analyze". It will then print out the estimated cost for every instruction.

In order to be able to use it from a different pass, I split it into a
source and header file (attached).

You can then add it to your pass dependencies, and use it as follows:
custom::CostModelAnalysis &CM =
getAnalysis<custom::CostModelAnalysis>();
Instruction *Inst = ...
unsigned Cost = CM.getInstructionCost(CI);
if (Cost != (unsigned)(-1)) {
  // do something
}

Hope this helps!
Jonas


On Thu, Jul 17, 2014 at 4:10 AM, <donney.blue at gmail.com> wrote:
> There is CostModel.cpp since LLVM3, I am wondering if anyone can give me
> an concrete example on how to use this pass to estimate cycles used in a
> given IR file.
>
> Thank you very much.
>
>
> Don
> _______________________________________________
> 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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Ya I am using it the same way. By dividing it into header file and
including it from  "llvm/Analysis/CostModel.h"

I believe it returns -1 for all function calls? How can I get make it
return cost of each function call inside my basic block.

One way is running it recursively on calls and return summaries. Is there a
direct way than this?

Thanks!
Manish


On Fri, Jul 18, 2014 at 1:13 AM, Jonas Wagner <jonas.wagner at epfl.ch>
wrote:
> Hi Don,
>
> In it's current version, tha pass can only be used via "opt
-cost-model
> -analyze". It will then print out the estimated cost for every
instruction.
>
> In order to be able to use it from a different pass, I split it into a
> source and header file (attached).
>
> You can then add it to your pass dependencies, and use it as follows:
> custom::CostModelAnalysis &CM =
getAnalysis<custom::CostModelAnalysis>();
> Instruction *Inst = ...
> unsigned Cost = CM.getInstructionCost(CI);
> if (Cost != (unsigned)(-1)) {
>   // do something
> }
>
> Hope this helps!
> Jonas
>
>
> On Thu, Jul 17, 2014 at 4:10 AM, <donney.blue at gmail.com> wrote:
>
>> There is CostModel.cpp since LLVM3, I am wondering if anyone can give
me
>> an concrete example on how to use this pass to estimate cycles used in
a
>> given IR file.
>>
>> Thank you very much.
>>
>>
>> Don
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>
>
> _______________________________________________
> 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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Ya I am using it the same way. By dividing it into header file and
including it from  "llvm/Analysis/CostModel.h"

I believe it returns -1 for all function calls? How can I get make it
return cost of each function call inside my basic block.

One way is running it recursively on calls and return summaries. Is there a
direct way than this?

Thanks!


On Fri, Jul 18, 2014 at 1:13 AM, Jonas Wagner <jonas.wagner at epfl.ch>
wrote:
> Hi Don,
>
> In it's current version, tha pass can only be used via "opt
-cost-model
> -analyze". It will then print out the estimated cost for every
instruction.
>
> In order to be able to use it from a different pass, I split it into a
> source and header file (attached).
>
> You can then add it to your pass dependencies, and use it as follows:
> custom::CostModelAnalysis &CM =
getAnalysis<custom::CostModelAnalysis>();
> Instruction *Inst = ...
> unsigned Cost = CM.getInstructionCost(CI);
> if (Cost != (unsigned)(-1)) {
>   // do something
> }
>
> Hope this helps!
> Jonas
>
>
> On Thu, Jul 17, 2014 at 4:10 AM, <donney.blue at gmail.com> wrote:
>
>> There is CostModel.cpp since LLVM3, I am wondering if anyone can give
me
>> an concrete example on how to use this pass to estimate cycles used in
a
>> given IR file.
>>
>> Thank you very much.
>>
>>
>> Don
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>
>
> _______________________________________________
> 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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On Wed, Jul 16, 2014 at 7:10 PM, <donney.blue at gmail.com> wrote:
> There is CostModel.cpp since LLVM3, I am wondering if anyone can give me
> an concrete example on how to use this pass to estimate cycles used in a
> given IR file.
>
While others have given specific advice about using the cost model
analysis, note that it isn't actually measuring the expected cycles. At
best it is measuring the size / number of instructions in the LLVM IR.
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