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

[Benjamin Kramer]

On 27.10.2012, at 18:15, Sean Silva <silvas at purdue.edu> wrote:

> How does this affect freestanding implementations?

This transform is disabled with -fno-builtin or -ffreestanding.

- Ben

> 
> -- 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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