[llvm] r339500 - [UnJ] Create a hasInvariantIterationCount function. NFC

[Philip Reames via llvm-commits]

This API needs some revisions.  The current description/naming leaves 
open the following questions:

 1. What is returned for a single loop which has no statically known
    exit count?
 2. In the case of a 3-deep nest, which parent loop is considered?

Possible naming suggestions:

hasIterationCountInvariantInParent
hasIterationCountInvariantInNest


On 08/10/2018 11:57 PM, David Green via llvm-commits wrote:
> Author: dmgreen
> Date: Fri Aug 10 23:57:28 2018
> New Revision: 339500
>
> URL: http://llvm.org/viewvc/llvm-project?rev=339500&view=rev
> Log:
> [UnJ] Create a hasInvariantIterationCount function. NFC
>
> Pulled out a separate function for some code that calculates
> if an inner loop iteration count is invariant to it's outer
> loop.
>
> Differential Revision: https://reviews.llvm.org/D50063
>
> Modified:
>      llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h
>      llvm/trunk/lib/Transforms/Utils/LoopUnrollAndJam.cpp
>      llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp
>
> Modified: llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h?rev=339500&r1=339499&r2=339500&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h (original)
> +++ llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h Fri Aug 10 23:57:28 2018
> @@ -490,6 +490,10 @@ void addStringMetadataToLoop(Loop *TheLo
>   /// estimate can not be made.
>   Optional<unsigned> getLoopEstimatedTripCount(Loop *L);
>   
> +/// Check inner loop (L) backedge count is known to be invariant on all iterations
> +/// of its outer loop. If the loop has no parent, this is trivially true.
> +bool hasInvariantIterationCount(Loop *L, ScalarEvolution &SE);
> +
>   /// Helper to consistently add the set of standard passes to a loop pass's \c
>   /// AnalysisUsage.
>   ///
>
> Modified: llvm/trunk/lib/Transforms/Utils/LoopUnrollAndJam.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LoopUnrollAndJam.cpp?rev=339500&r1=339499&r2=339500&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Utils/LoopUnrollAndJam.cpp (original)
> +++ llvm/trunk/lib/Transforms/Utils/LoopUnrollAndJam.cpp Fri Aug 10 23:57:28 2018
> @@ -754,20 +754,7 @@ bool llvm::isSafeToUnrollAndJam(Loop *L,
>   
>     // Check inner loop backedge count is consistent on all iterations of the
>     // outer loop
> -  auto CheckInnerLoopIterationCountInvariant = [](Loop *SubLoop, Loop *OuterL,
> -                                                  ScalarEvolution &SE) {
> -    BasicBlock *SubLoopLatch = SubLoop->getLoopLatch();
> -    const SCEV *SubLoopBECountSC = SE.getExitCount(SubLoop, SubLoopLatch);
> -    if (isa<SCEVCouldNotCompute>(SubLoopBECountSC) ||
> -        !SubLoopBECountSC->getType()->isIntegerTy())
> -      return false;
> -    ScalarEvolution::LoopDisposition LD =
> -        SE.getLoopDisposition(SubLoopBECountSC, OuterL);
> -    if (LD != ScalarEvolution::LoopInvariant)
> -      return false;
> -    return true;
> -  };
> -  if (!CheckInnerLoopIterationCountInvariant(SubLoop, L, SE)) {
> +  if (!hasInvariantIterationCount(SubLoop, SE)) {
>       LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; Inner loop iteration count is "
>                            "not consistent on each iteration\n");
>       return false;
>
> Modified: llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp?rev=339500&r1=339499&r2=339500&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp (original)
> +++ llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp Fri Aug 10 23:57:28 2018
> @@ -1521,6 +1521,28 @@ Optional<unsigned> llvm::getLoopEstimate
>       return (FalseVal + (TrueVal / 2)) / TrueVal;
>   }
>   
> +bool llvm::hasInvariantIterationCount(Loop *InnerLoop,
> +                                      ScalarEvolution &SE) {
> +  Loop *OuterL = InnerLoop->getParentLoop();
> +  if (!OuterL)
> +    return true;
> +
> +  // Get the backedge taken count for the inner loop
> +  BasicBlock *InnerLoopLatch = InnerLoop->getLoopLatch();
> +  const SCEV *InnerLoopBECountSC = SE.getExitCount(InnerLoop, InnerLoopLatch);
> +  if (isa<SCEVCouldNotCompute>(InnerLoopBECountSC) ||
> +      !InnerLoopBECountSC->getType()->isIntegerTy())
> +    return false;
> +
> +  // Get whether count is invariant to the outer loop
> +  ScalarEvolution::LoopDisposition LD =
> +      SE.getLoopDisposition(InnerLoopBECountSC, OuterL);
> +  if (LD != ScalarEvolution::LoopInvariant)
> +    return false;
> +
> +  return true;
> +}
> +
>   /// Adds a 'fast' flag to floating point operations.
>   static Value *addFastMathFlag(Value *V) {
>     if (isa<FPMathOperator>(V)) {
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20180813/5f16fcf6/attachment.html>