[llvm-commits] [llvm] r169223 - /llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp

[Hal Finkel]

----- Original Message -----
> From: "Nadav Rotem" <nrotem at apple.com>
> To: llvm-commits at cs.uiuc.edu
> Sent: Tuesday, December 4, 2012 1:11:52 AM
> Subject: [llvm-commits] [llvm] r169223 -	/llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
> 
> Author: nadav
> Date: Tue Dec  4 01:11:52 2012
> New Revision: 169223
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=169223&view=rev
> Log:
> Give scalar if-converted blocks half the score because they are not
> always executed due to CF.

Should we make use of branch weights here? If nothing else, LowerExpectIntrinsic transforms uses of __builtin_expect into branch weights.

 -Hal

> 
> Modified:
>     llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
> 
> Modified: llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp?rev=169223&r1=169222&r2=169223&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp (original)
> +++ llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp Tue Dec  4
> 01:11:52 2012
> @@ -2159,17 +2159,17 @@
>  
>      // For each instruction in the old loop.
>      for (BasicBlock::iterator it = BB->begin(), e = BB->end(); it !=
>      e; ++it) {
> -
>        unsigned C = getInstructionCost(it, VF);
>        Cost += C;
>        DEBUG(dbgs() << "LV: Found an estimated cost of "<< C <<" for
>        VF " <<
>              VF << " For instruction: "<< *it << "\n");
>      }
>  
> -    // TODO: if-converted blocks can have a high-nest level. We need
> to
> -    // calculate the loop nest level and multiply the cost
> accordingly.
> -    if (Legal->blockNeedsPredication(*bb))
> -      BlockCost *= 2;
> +    // We assume that if-converted blocks have a 50% chance of being
> executed.
> +    // When the code is scalar then some of the blocks are avoided
> due to CF.
> +    // When the code is vectorized we execute all code paths.
> +    if (Legal->blockNeedsPredication(*bb) && VF == 1)
> +      BlockCost /= 2;
>  
>      Cost += BlockCost;
>    }
> 
> 
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-- 
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory