[llvm-commits] [llvm] r166875 - in /llvm/trunk: lib/Transforms/Scalar/LoopIdiomRecognize.cpp test/Transforms/LoopIdiom/basic.ll

[Sean Silva]

How does this affect freestanding implementations?

-- Sean Silva

On Sat, Oct 27, 2012 at 10:25 AM, Benjamin Kramer
<benny.kra at googlemail.com> wrote:
> Author: d0k
> Date: Sat Oct 27 09:25:51 2012
> New Revision: 166875
>
> URL: http://llvm.org/viewvc/llvm-project?rev=166875&view=rev
> Log:
> LoopIdiom: Recognize memmove loops.
>
> This turns loops like
>   for (unsigned i = 0; i != n; ++i)
>     p[i] = p[i+1];
> into memmove, which has a highly optimized implementation in most libcs.
>
> This was really easy with the new DependenceAnalysis :)
>
> Modified:
>     llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
>     llvm/trunk/test/Transforms/LoopIdiom/basic.ll
>
> Modified: llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp?rev=166875&r1=166874&r2=166875&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp Sat Oct 27 09:25:51 2012
> @@ -16,7 +16,7 @@
>  // TODO List:
>  //
>  // Future loop memory idioms to recognize:
> -//   memcmp, memmove, strlen, etc.
> +//   memcmp, strlen, etc.
>  // Future floating point idioms to recognize in -ffast-math mode:
>  //   fpowi
>  // Future integer operation idioms to recognize:
> @@ -60,8 +60,9 @@
>  #include "llvm/Transforms/Utils/Local.h"
>  using namespace llvm;
>
> -STATISTIC(NumMemSet, "Number of memset's formed from loop stores");
> -STATISTIC(NumMemCpy, "Number of memcpy's formed from loop load+stores");
> +STATISTIC(NumMemSet, "Number of memsets formed from loop stores");
> +STATISTIC(NumMemCpy, "Number of memcpys formed from loop load+stores");
> +STATISTIC(NumMemMove, "Number of memmoves formed from loop load+stores");
>
>  namespace {
>    class LoopIdiomRecognize : public LoopPass {
> @@ -532,6 +533,7 @@
>    // stores) in the loop. We ignore the direct dependency between SI and LI here
>    // and check it later.
>    DependenceAnalysis &DA = getAnalysis<DependenceAnalysis>();
> +  bool isMemcpySafe = true;
>    for (Loop::block_iterator BI = CurLoop->block_begin(),
>         BE = CurLoop->block_end(); BI != BE; ++BI)
>      for (BasicBlock::iterator I = (*BI)->begin(), E = (*BI)->end(); I != E; ++I)
> @@ -552,8 +554,14 @@
>    // Now check the dependency between SI and LI. If there is no dependency we
>    // can safely emit a memcpy.
>    OwningPtr<Dependence> Dep(DA.depends(SI, LI, true));
> -  if (Dep)
> -    return false;
> +  if (Dep) {
> +    // If there is a dependence but the direction is positive we can still
> +    // safely turn this into memmove.
> +    if (Dep->getLevels() != 1 ||
> +        Dep->getDirection(1) != Dependence::DVEntry::GT)
> +      return false;
> +    isMemcpySafe = false;
> +  }
>
>    // The trip count of the loop and the base pointer of the addrec SCEV is
>    // guaranteed to be loop invariant, which means that it should dominate the
> @@ -590,12 +598,19 @@
>    Value *NumBytes =
>      Expander.expandCodeFor(NumBytesS, IntPtr, Preheader->getTerminator());
>
> -  CallInst *NewCall =
> -    Builder.CreateMemCpy(StoreBasePtr, LoadBasePtr, NumBytes,
> -                         std::min(SI->getAlignment(), LI->getAlignment()));
> +  CallInst *NewCall;
> +  unsigned Align = std::min(SI->getAlignment(), LI->getAlignment());
> +  if (isMemcpySafe) {
> +    NewCall = Builder.CreateMemCpy(StoreBasePtr, LoadBasePtr, NumBytes, Align);
> +    ++NumMemCpy;
> +  } else {
> +    NewCall = Builder.CreateMemMove(StoreBasePtr, LoadBasePtr, NumBytes, Align);
> +    ++NumMemMove;
> +  }
>    NewCall->setDebugLoc(SI->getDebugLoc());
>
> -  DEBUG(dbgs() << "  Formed memcpy: " << *NewCall << "\n"
> +  DEBUG(dbgs() << "  Formed " << (isMemcpySafe ? "memcpy: " : "memmove: ")
> +               << *NewCall << "\n"
>                 << "    from load ptr=" << *LoadEv << " at: " << *LI << "\n"
>                 << "    from store ptr=" << *StoreEv << " at: " << *SI << "\n");
>
> @@ -603,6 +618,5 @@
>    // Okay, the memset has been formed.  Zap the original store and anything that
>    // feeds into it.
>    deleteDeadInstruction(SI, *SE, TLI);
> -  ++NumMemCpy;
>    return true;
>  }
>
> Modified: llvm/trunk/test/Transforms/LoopIdiom/basic.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopIdiom/basic.ll?rev=166875&r1=166874&r2=166875&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/LoopIdiom/basic.ll (original)
> +++ llvm/trunk/test/Transforms/LoopIdiom/basic.ll Sat Oct 27 09:25:51 2012
> @@ -383,4 +383,26 @@
>
>  }
>
> + at p = common global [1024 x i8] zeroinitializer, align 16
>
> +define void @test15(i32 %n) nounwind {
> +entry:
> +  %cmp6 = icmp eq i32 %n, 0
> +  br i1 %cmp6, label %for.end, label %for.body
> +
> +for.body:                                         ; preds = %entry, %for.body
> +  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %entry ]
> +  %indvars.iv.next = add i64 %indvars.iv, 1
> +  %arrayidx = getelementptr inbounds [1024 x i8]* @p, i64 0, i64 %indvars.iv.next
> +  %0 = load i8* %arrayidx, align 1
> +  %arrayidx2 = getelementptr inbounds [1024 x i8]* @p, i64 0, i64 %indvars.iv
> +  store i8 %0, i8* %arrayidx2, align 1
> +  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
> +  %exitcond = icmp eq i32 %lftr.wideiv, %n
> +  br i1 %exitcond, label %for.end, label %for.body
> +
> +for.end:                                          ; preds = %for.body, %entry
> +  ret void
> +; CHECK: @test15
> +; CHECK: call void @llvm.memmove.p0i8.p0i8.i64(i8* getelementptr inbounds ([1024 x i8]* @p, i32 0, i32 0), i8* getelementptr inbounds ([1024 x i8]* @p, i64 0, i64 1),
> +}
>
>
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