[LLVMdev] Loop-Unroll optimization

[Manish Gupta]

Awesome! I am getting the unroll version of the loop.

But I have *no -debug option* with my opt command (I have a Debug build)?

On Tue, May 3, 2011 at 5:10 PM, Arushi Aggarwal <arushi987 at gmail.com> wrote:

> 1. You should run the passes in the same opt command, for passes like loops
> which is an analysis pass provides results to the following passes.
> 2. You can pass a -debug flag to opt to see the some debugging info.
>
> 3. I tried this
>  opt -mem2reg -loops  -loopsimplify -loop-unroll -unroll-count=3 -debug
> loop.o -o tt.bc
>
> and got this message.
>  Loop Size = 14
>   Can't unroll; loop not terminated by a conditional branch.
>
> 4. Looking at LoopUnroll.cpp showed a comment that said -loop-rotate helps,
> so I used the following
>
>  opt -mem2reg -loops  -loopsimplify -loop-rotate -lcssa -loop-unroll
> -unroll-count=3 -debug loop.o -o tt.bc
>
> Getting an unrolled version of the loop.
>
> Arushi
>
>
>
> On Tue, May 3, 2011 at 6:50 PM, Manish Gupta <mgupta.iitr at gmail.com>wrote:
>
>> Even after all the sequence of commands below bit-code is not showing any
>> effect of loop-unrolling
>>
>> *manish at manish:~/Test2$ llvm-gcc-4.2 -O2 -emit-llvm Hello.c -c -o
>> Hello.bc*
>> *manish at manish:~/Test2$ opt-2.8 -loops Hello.bc -o Hello1.bc*
>> *manish at manish:~/Test2$ opt-2.8 -loopsimplify Hello1.bc -o Hello2.bc*
>> *manish at manish:~/Test2$ opt-2.8 -indvars Hello2.bc -o Hello3.bc*
>> *manish at manish:~/Test2$ opt-2.8 -loop-unroll Hello3.bc -o Hello4.bc*
>> *manish at manish:~/Test2$ llvm-dis-2.8 Hello4.bc*
>>
>> My *Hello.c* looks like:
>>   for(i=0; i< 1000; i++)
>>     {
>>       c[i] = a[i] + b[i];
>>      }
>>
>>   printf("%d\n", c[999]);
>> -------------------------------------------------
>>
>> and bit-code in *Hello4.bc*
>> bb3:                                              ; preds = %bb3,
>> %bb3.preheader
>>   %i.17 = phi i32 [ %5, %bb3 ], [ 0, %bb3.preheader ]
>>   %scevgep11 = getelementptr [1000 x i32]* %b, i32 0, i32 %i.17
>>   %scevgep10 = getelementptr [1000 x i32]* %a, i32 0, i32 %i.17
>>   %scevgep = getelementptr [1000 x i32]* %c, i32 0, i32 %i.17
>>   %2 = load i32* %scevgep10, align 4
>>   %3 = load i32* %scevgep11, align 4
>>   %4 = add nsw i32 %3, %2
>>   store i32 %4, i32* %scevgep, align 4
>>   %5 = add nsw i32 %i.17, 1
>>   %exitcond1 = icmp eq i32 %5, 1000
>>   br i1 %exitcond1, label %bb5, label %bb3
>>
>> -----------------------------------------
>>
>> On Tue, May 3, 2011 at 12:32 PM, Arushi Aggarwal <arushi987 at gmail.com>wrote:
>>
>>> Hi,
>>>
>>> You might want to try running -loops -loop-simplify before loop unroll.
>>>
>>> From loop simplify.cpp
>>>
>>> This pass performs several transformations to transform natural loops into a00011 // simpler form, which makes subsequent analyses and transformations simpler and00012 // more effective.
>>>
>>>
>>> Arushi
>>>
>>> On Tue, May 3, 2011 at 2:17 PM, Manish Gupta <mgupta.iitr at gmail.com>wrote:
>>>
>>>> You mean like
>>>>
>>>> *llvm-gcc-4.2 -O2 -emit-llvm Hello.c -c -o Hello.bc*
>>>>
>>>> But still i am not able to observe any effect on bit code by running
>>>>
>>>> *opt-2.8 -loop-unroll Hello.bc -o Hello_unroll.bc*
>>>>
>>>> On Tue, May 3, 2011 at 3:58 AM, Zakk <zakk0610 at gmail.com> wrote:
>>>>
>>>>> Hi, you need to run some optimization passes first. (like -O2)
>>>>>
>>>>> 2011/5/3 Manish Gupta <mgupta.iitr at gmail.com>
>>>>>
>>>>>> I just want to try loop-unroll and see corresponding changes in the
>>>>>> bitcode file. For that any loop will do. Have you been able to test llvm
>>>>>> loop-unroll successfully?
>>>>>>
>>>>>>
>>>>>> On Mon, May 2, 2011 at 10:04 PM, Yuan Pengfei <coolypf at qq.com> wrote:
>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> > The loop that I am trying it on is:
>>>>>>> > for(i=0; i< 1000; i++)
>>>>>>> > {
>>>>>>> > c[i] = a[i] + b[i];
>>>>>>> > }
>>>>>>>
>>>>>>> I can't find any benefit unrolling this loop.
>>>>>>>
>>>>>>> ------------------
>>>>>>> Yuan Pengfei
>>>>>>> Peking Unversity, China
>>>>>>
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> LLVM Developers mailing list
>>>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Best regards,
>>>>> Kuan-Hsu
>>>>>
>>>>>
>>>>>
>>>>
>>>> _______________________________________________
>>>> 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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