[SLP] Fix for PR31880: shuffle and vectorize repeated scalar ops on extracted elements

Summary:
Currently most of the time vectors of extractelement instructions are
treated as scalars that must be gathered into vectors. But in some
cases, like when we have extractelement instructions from single vector
with different constant indeces or from 2 vectors of the same size, we
can treat this operations as shuffle of a single vector or blending of 2
vectors.
```
define <2 x i8> @g(<2 x i8> %x, <2 x i8> %y) {
  %x0 = extractelement <2 x i8> %x, i32 0
  %y1 = extractelement <2 x i8> %y, i32 1
  %x0x0 = mul i8 %x0, %x0
  %y1y1 = mul i8 %y1, %y1
  %ins1 = insertelement <2 x i8> undef, i8 %x0x0, i32 0
  %ins2 = insertelement <2 x i8> %ins1, i8 %y1y1, i32 1
  ret <2 x i8> %ins2
}
```
can be converted to something like
```
define <2 x i8> @g(<2 x i8> %x, <2 x i8> %y) {
  %1 = shufflevector <2 x i8> %x, <2 x i8> %y, <2 x i32> <i32 0, i32 3>
  %2 = mul <2 x i8> %1, %1
  ret <2 x i8> %2
}
```
Currently this type of conversion is considered as high cost
transformation.

Reviewers: mzolotukhin, delena, mkuper, hfinkel, RKSimon

Subscribers: ashahid, RKSimon, spatel, llvm-commits

Differential Revision: https://reviews.llvm.org/D30200

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@309812 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Vectorize/SLPVectorizer.cpp b/lib/Transforms/Vectorize/SLPVectorizer.cpp
index 93a6d1c00a80c98b562ea44133295e0809c4562a..11bc030e31290cf76991a5ae30b92cc0026ed9fd 100644 (file)
--- a/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -158,6 +158,119 @@ static bool isSplat(ArrayRef<Value *> VL) {
   return true;
 }
 
+/// Checks if the vector of instructions can be represented as a shuffle, like:
+/// %x0 = extractelement <4 x i8> %x, i32 0
+/// %x3 = extractelement <4 x i8> %x, i32 3
+/// %y1 = extractelement <4 x i8> %y, i32 1
+/// %y2 = extractelement <4 x i8> %y, i32 2
+/// %x0x0 = mul i8 %x0, %x0
+/// %x3x3 = mul i8 %x3, %x3
+/// %y1y1 = mul i8 %y1, %y1
+/// %y2y2 = mul i8 %y2, %y2
+/// %ins1 = insertelement <4 x i8> undef, i8 %x0x0, i32 0
+/// %ins2 = insertelement <4 x i8> %ins1, i8 %x3x3, i32 1
+/// %ins3 = insertelement <4 x i8> %ins2, i8 %y1y1, i32 2
+/// %ins4 = insertelement <4 x i8> %ins3, i8 %y2y2, i32 3
+/// ret <4 x i8> %ins4
+/// can be transformed into:
+/// %1 = shufflevector <4 x i8> %x, <4 x i8> %y, <4 x i32> <i32 0, i32 3, i32 5,
+///                                                         i32 6>
+/// %2 = mul <4 x i8> %1, %1
+/// ret <4 x i8> %2
+/// We convert this initially to something like:
+/// %x0 = extractelement <4 x i8> %x, i32 0
+/// %x3 = extractelement <4 x i8> %x, i32 3
+/// %y1 = extractelement <4 x i8> %y, i32 1
+/// %y2 = extractelement <4 x i8> %y, i32 2
+/// %1 = insertelement <4 x i8> undef, i8 %x0, i32 0
+/// %2 = insertelement <4 x i8> %1, i8 %x3, i32 1
+/// %3 = insertelement <4 x i8> %2, i8 %y1, i32 2
+/// %4 = insertelement <4 x i8> %3, i8 %y2, i32 3
+/// %5 = mul <4 x i8> %4, %4
+/// %6 = extractelement <4 x i8> %5, i32 0
+/// %ins1 = insertelement <4 x i8> undef, i8 %6, i32 0
+/// %7 = extractelement <4 x i8> %5, i32 1
+/// %ins2 = insertelement <4 x i8> %ins1, i8 %7, i32 1
+/// %8 = extractelement <4 x i8> %5, i32 2
+/// %ins3 = insertelement <4 x i8> %ins2, i8 %8, i32 2
+/// %9 = extractelement <4 x i8> %5, i32 3
+/// %ins4 = insertelement <4 x i8> %ins3, i8 %9, i32 3
+/// ret <4 x i8> %ins4
+/// InstCombiner transforms this into a shuffle and vector mul
+static Optional<TargetTransformInfo::ShuffleKind>
+isShuffle(ArrayRef<Value *> VL) {
+  auto *EI0 = cast<ExtractElementInst>(VL[0]);
+  unsigned Size = EI0->getVectorOperandType()->getVectorNumElements();
+  Value *Vec1 = nullptr;
+  Value *Vec2 = nullptr;
+  enum ShuffleMode {Unknown, FirstAlternate, SecondAlternate, Permute};
+  ShuffleMode CommonShuffleMode = Unknown;
+  for (unsigned I = 0, E = VL.size(); I < E; ++I) {
+    auto *EI = cast<ExtractElementInst>(VL[I]);
+    auto *Vec = EI->getVectorOperand();
+    // All vector operands must have the same number of vector elements.
+    if (Vec->getType()->getVectorNumElements() != Size)
+      return None;
+    auto *Idx = dyn_cast<ConstantInt>(EI->getIndexOperand());
+    if (!Idx)
+      return None;
+    // Undefined behavior if Idx is negative or >= Size.
+    if (Idx->getValue().uge(Size))
+      continue;
+    unsigned IntIdx = Idx->getValue().getZExtValue();
+    // We can extractelement from undef vector.
+    if (isa<UndefValue>(Vec))
+      continue;
+    // For correct shuffling we have to have at most 2 different vector operands
+    // in all extractelement instructions.
+    if (Vec1 && Vec2 && Vec != Vec1 && Vec != Vec2)
+      return None;
+    if (CommonShuffleMode == Permute)
+      continue;
+    // If the extract index is not the same as the operation number, it is a
+    // permutation.
+    if (IntIdx != I) {
+      CommonShuffleMode = Permute;
+      continue;
+    }
+    // Check the shuffle mode for the current operation.
+    if (!Vec1)
+      Vec1 = Vec;
+    else if (Vec != Vec1)
+      Vec2 = Vec;
+    // Example: shufflevector A, B, <0,5,2,7>
+    // I is odd and IntIdx for A == I - FirstAlternate shuffle.
+    // I is even and IntIdx for B == I - FirstAlternate shuffle.
+    // Example: shufflevector A, B, <4,1,6,3>
+    // I is even and IntIdx for A == I - SecondAlternate shuffle.
+    // I is odd and IntIdx for B == I - SecondAlternate shuffle.
+    const bool IIsEven = I & 1;
+    const bool CurrVecIsA = Vec == Vec1;
+    const bool IIsOdd = !IIsEven;
+    const bool CurrVecIsB = !CurrVecIsA;
+    ShuffleMode CurrentShuffleMode =
+        ((IIsOdd && CurrVecIsA) || (IIsEven && CurrVecIsB)) ? FirstAlternate
+                                                            : SecondAlternate;
+    // Common mode is not set or the same as the shuffle mode of the current
+    // operation - alternate.
+    if (CommonShuffleMode == Unknown)
+      CommonShuffleMode = CurrentShuffleMode;
+    // Common shuffle mode is not the same as the shuffle mode of the current
+    // operation - permutation.
+    if (CommonShuffleMode != CurrentShuffleMode)
+      CommonShuffleMode = Permute;
+  }
+  // If we're not crossing lanes in different vectors, consider it as blending.
+  if ((CommonShuffleMode == FirstAlternate ||
+       CommonShuffleMode == SecondAlternate) &&
+      Vec2)
+    return TargetTransformInfo::SK_Alternate;
+  // If Vec2 was never used, we have a permutation of a single vector, otherwise
+  // we have permutation of 2 vectors.
+  return Vec2 ? TargetTransformInfo::SK_PermuteTwoSrc
+              : TargetTransformInfo::SK_PermuteSingleSrc;
+}
+
 ///\returns Opcode that can be clubbed with \p Op to create an alternate
 /// sequence which can later be merged as a ShuffleVector instruction.
 static unsigned getAltOpcode(unsigned Op) {
@@ -1736,6 +1849,26 @@ int BoUpSLP::getEntryCost(TreeEntry *E) {
     if (isSplat(VL)) {
       return TTI->getShuffleCost(TargetTransformInfo::SK_Broadcast, VecTy, 0);
     }
+    if (getSameOpcode(VL) == Instruction::ExtractElement) {
+      Optional<TargetTransformInfo::ShuffleKind> ShuffleKind = isShuffle(VL);
+      if (ShuffleKind.hasValue()) {
+        int Cost = TTI->getShuffleCost(ShuffleKind.getValue(), VecTy);
+        for (auto *V : VL) {
+          // If all users of instruction are going to be vectorized and this
+          // instruction itself is not going to be vectorized, consider this
+          // instruction as dead and remove its cost from the final cost of the
+          // vectorized tree.
+          if (areAllUsersVectorized(cast<Instruction>(V)) &&
+              !ScalarToTreeEntry.count(V)) {
+            auto *IO = cast<ConstantInt>(
+                cast<ExtractElementInst>(V)->getIndexOperand());
+            Cost -= TTI->getVectorInstrCost(Instruction::ExtractElement, VecTy,
+                                            IO->getZExtValue());
+          }
+        }
+        return Cost;
+      }
+    }
     return getGatherCost(E->Scalars);
   }
   unsigned Opcode = getSameOpcode(VL);

diff --git a/test/Transforms/SLPVectorizer/X86/blending-shuffle.ll b/test/Transforms/SLPVectorizer/X86/blending-shuffle.ll
index ba0059ed4e51ba0527c7d5b11eb9ea871ed4ae9d..55e479a4262705b3b861de3adb4908c6f39b9341 100644 (file)
--- a/test/Transforms/SLPVectorizer/X86/blending-shuffle.ll
+++ b/test/Transforms/SLPVectorizer/X86/blending-shuffle.ll
@@ -3,13 +3,9 @@
 
 define <2 x i8> @g(<2 x i8> %x, <2 x i8> %y) {
 ; CHECK-LABEL: @g(
-; CHECK-NEXT:    [[X0:%.*]] = extractelement <2 x i8> [[X:%.*]], i32 0
-; CHECK-NEXT:    [[Y1:%.*]] = extractelement <2 x i8> [[Y:%.*]], i32 1
-; CHECK-NEXT:    [[X0X0:%.*]] = mul i8 [[X0]], [[X0]]
-; CHECK-NEXT:    [[Y1Y1:%.*]] = mul i8 [[Y1]], [[Y1]]
-; CHECK-NEXT:    [[INS1:%.*]] = insertelement <2 x i8> undef, i8 [[X0X0]], i32 0
-; CHECK-NEXT:    [[INS2:%.*]] = insertelement <2 x i8> [[INS1]], i8 [[Y1Y1]], i32 1
-; CHECK-NEXT:    ret <2 x i8> [[INS2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <2 x i8> [[X:%.*]], <2 x i8> [[Y:%.*]], <2 x i32> <i32 0, i32 3>
+; CHECK-NEXT:    [[TMP2:%.*]] = mul <2 x i8> [[TMP1]], [[TMP1]]
+; CHECK-NEXT:    ret <2 x i8> [[TMP2]]
 ;
   %x0 = extractelement <2 x i8> %x, i32 0
   %y1 = extractelement <2 x i8> %y, i32 1
@@ -22,19 +18,9 @@ define <2 x i8> @g(<2 x i8> %x, <2 x i8> %y) {
 
 define <4 x i8> @h(<4 x i8> %x, <4 x i8> %y) {
 ; CHECK-LABEL: @h(
-; CHECK-NEXT:    [[X0:%.*]] = extractelement <4 x i8> [[X:%.*]], i32 0
-; CHECK-NEXT:    [[X3:%.*]] = extractelement <4 x i8> [[X]], i32 3
-; CHECK-NEXT:    [[Y1:%.*]] = extractelement <4 x i8> [[Y:%.*]], i32 1
-; CHECK-NEXT:    [[Y2:%.*]] = extractelement <4 x i8> [[Y]], i32 2
-; CHECK-NEXT:    [[X0X0:%.*]] = mul i8 [[X0]], [[X0]]
-; CHECK-NEXT:    [[X3X3:%.*]] = mul i8 [[X3]], [[X3]]
-; CHECK-NEXT:    [[Y1Y1:%.*]] = mul i8 [[Y1]], [[Y1]]
-; CHECK-NEXT:    [[Y2Y2:%.*]] = mul i8 [[Y2]], [[Y2]]
-; CHECK-NEXT:    [[INS1:%.*]] = insertelement <4 x i8> undef, i8 [[X0X0]], i32 0
-; CHECK-NEXT:    [[INS2:%.*]] = insertelement <4 x i8> [[INS1]], i8 [[X3X3]], i32 1
-; CHECK-NEXT:    [[INS3:%.*]] = insertelement <4 x i8> [[INS2]], i8 [[Y1Y1]], i32 2
-; CHECK-NEXT:    [[INS4:%.*]] = insertelement <4 x i8> [[INS3]], i8 [[Y2Y2]], i32 3
-; CHECK-NEXT:    ret <4 x i8> [[INS4]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x i8> [[X:%.*]], <4 x i8> [[Y:%.*]], <4 x i32> <i32 0, i32 3, i32 5, i32 6>
+; CHECK-NEXT:    [[TMP2:%.*]] = mul <4 x i8> [[TMP1]], [[TMP1]]
+; CHECK-NEXT:    ret <4 x i8> [[TMP2]]
 ;
   %x0 = extractelement <4 x i8> %x, i32 0
   %x3 = extractelement <4 x i8> %x, i32 3
@@ -53,16 +39,9 @@ define <4 x i8> @h(<4 x i8> %x, <4 x i8> %y) {
 
 define <4 x i8> @h_undef(<4 x i8> %x, <4 x i8> %y) {
 ; CHECK-LABEL: @h_undef(
-; CHECK-NEXT:    [[X3:%.*]] = extractelement <4 x i8> [[X:%.*]], i32 3
-; CHECK-NEXT:    [[Y1:%.*]] = extractelement <4 x i8> [[Y:%.*]], i32 1
-; CHECK-NEXT:    [[Y2:%.*]] = extractelement <4 x i8> [[Y]], i32 2
-; CHECK-NEXT:    [[X3X3:%.*]] = mul i8 [[X3]], [[X3]]
-; CHECK-NEXT:    [[Y1Y1:%.*]] = mul i8 [[Y1]], [[Y1]]
-; CHECK-NEXT:    [[Y2Y2:%.*]] = mul i8 [[Y2]], [[Y2]]
-; CHECK-NEXT:    [[INS2:%.*]] = insertelement <4 x i8> undef, i8 [[X3X3]], i32 1
-; CHECK-NEXT:    [[INS3:%.*]] = insertelement <4 x i8> [[INS2]], i8 [[Y1Y1]], i32 2
-; CHECK-NEXT:    [[INS4:%.*]] = insertelement <4 x i8> [[INS3]], i8 [[Y2Y2]], i32 3
-; CHECK-NEXT:    ret <4 x i8> [[INS4]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x i8> [[X:%.*]], <4 x i8> [[Y:%.*]], <4 x i32> <i32 undef, i32 3, i32 5, i32 6>
+; CHECK-NEXT:    [[TMP2:%.*]] = mul <4 x i8> [[TMP1]], [[TMP1]]
+; CHECK-NEXT:    ret <4 x i8> [[TMP2]]
 ;
   %x0 = extractelement <4 x i8> undef, i32 0
   %x3 = extractelement <4 x i8> %x, i32 3
@@ -81,17 +60,13 @@ define <4 x i8> @h_undef(<4 x i8> %x, <4 x i8> %y) {
 
 define i8 @i(<4 x i8> %x, <4 x i8> %y) {
 ; CHECK-LABEL: @i(
-; CHECK-NEXT:    [[X0:%.*]] = extractelement <4 x i8> [[X:%.*]], i32 0
-; CHECK-NEXT:    [[X3:%.*]] = extractelement <4 x i8> [[X]], i32 3
-; CHECK-NEXT:    [[Y1:%.*]] = extractelement <4 x i8> [[Y:%.*]], i32 1
-; CHECK-NEXT:    [[Y2:%.*]] = extractelement <4 x i8> [[Y]], i32 2
-; CHECK-NEXT:    [[X0X0:%.*]] = mul i8 [[X0]], [[X0]]
-; CHECK-NEXT:    [[X3X3:%.*]] = mul i8 [[X3]], [[X3]]
-; CHECK-NEXT:    [[Y1Y1:%.*]] = mul i8 [[Y1]], [[Y1]]
-; CHECK-NEXT:    [[Y2Y2:%.*]] = mul i8 [[Y2]], [[Y2]]
-; CHECK-NEXT:    [[TMP1:%.*]] = add i8 [[X0X0]], [[X3X3]]
-; CHECK-NEXT:    [[TMP2:%.*]] = add i8 [[Y1Y1]], [[Y2Y2]]
-; CHECK-NEXT:    [[TMP3:%.*]] = add i8 [[TMP1]], [[TMP2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x i8> [[X:%.*]], <4 x i8> [[Y:%.*]], <4 x i32> <i32 0, i32 3, i32 5, i32 6>
+; CHECK-NEXT:    [[TMP2:%.*]] = mul <4 x i8> [[TMP1]], [[TMP1]]
+; CHECK-NEXT:    [[RDX_SHUF:%.*]] = shufflevector <4 x i8> [[TMP2]], <4 x i8> undef, <4 x i32> <i32 2, i32 3, i32 undef, i32 undef>
+; CHECK-NEXT:    [[BIN_RDX:%.*]] = add <4 x i8> [[TMP2]], [[RDX_SHUF]]
+; CHECK-NEXT:    [[RDX_SHUF1:%.*]] = shufflevector <4 x i8> [[BIN_RDX]], <4 x i8> undef, <4 x i32> <i32 1, i32 undef, i32 undef, i32 undef>
+; CHECK-NEXT:    [[BIN_RDX2:%.*]] = add <4 x i8> [[BIN_RDX]], [[RDX_SHUF1]]
+; CHECK-NEXT:    [[TMP3:%.*]] = extractelement <4 x i8> [[BIN_RDX2]], i32 0
 ; CHECK-NEXT:    ret i8 [[TMP3]]
 ;
   %x0 = extractelement <4 x i8> %x, i32 0
@@ -110,18 +85,15 @@ define i8 @i(<4 x i8> %x, <4 x i8> %y) {
 
 define i8 @j(<4 x i8> %x, <4 x i8> %y) {
 ; CHECK-LABEL: @j(
-; CHECK-NEXT:    [[X0:%.*]] = extractelement <4 x i8> [[X:%.*]], i32 0
-; CHECK-NEXT:    [[X3:%.*]] = extractelement <4 x i8> [[X]], i32 3
-; CHECK-NEXT:    [[Y1:%.*]] = extractelement <4 x i8> [[Y:%.*]], i32 1
-; CHECK-NEXT:    [[Y2:%.*]] = extractelement <4 x i8> [[Y]], i32 2
-; CHECK-NEXT:    [[X0X0:%.*]] = mul i8 [[X0]], [[X0]]
-; CHECK-NEXT:    [[X3X3:%.*]] = mul i8 [[X3]], [[X3]]
-; CHECK-NEXT:    [[Y1Y1:%.*]] = mul i8 [[Y1]], [[Y1]]
-; CHECK-NEXT:    [[Y2Y2:%.*]] = mul i8 [[Y2]], [[Y2]]
-; CHECK-NEXT:    [[TMP1:%.*]] = add i8 [[X0X0]], [[X3X3]]
-; CHECK-NEXT:    [[TMP2:%.*]] = add i8 [[Y1Y1]], [[Y2Y2]]
-; CHECK-NEXT:    [[TMP3:%.*]] = sdiv i8 [[TMP1]], [[TMP2]]
-; CHECK-NEXT:    ret i8 [[TMP3]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x i8> [[X:%.*]], <4 x i8> [[Y:%.*]], <2 x i32> <i32 0, i32 5>
+; CHECK-NEXT:    [[TMP2:%.*]] = mul <2 x i8> [[TMP1]], [[TMP1]]
+; CHECK-NEXT:    [[TMP3:%.*]] = shufflevector <4 x i8> [[X]], <4 x i8> [[Y]], <2 x i32> <i32 3, i32 6>
+; CHECK-NEXT:    [[TMP4:%.*]] = mul <2 x i8> [[TMP3]], [[TMP3]]
+; CHECK-NEXT:    [[TMP5:%.*]] = add <2 x i8> [[TMP2]], [[TMP4]]
+; CHECK-NEXT:    [[TMP6:%.*]] = extractelement <2 x i8> [[TMP5]], i32 0
+; CHECK-NEXT:    [[TMP7:%.*]] = extractelement <2 x i8> [[TMP5]], i32 1
+; CHECK-NEXT:    [[TMP8:%.*]] = sdiv i8 [[TMP6]], [[TMP7]]
+; CHECK-NEXT:    ret i8 [[TMP8]]
 ;
   %x0 = extractelement <4 x i8> %x, i32 0
   %x3 = extractelement <4 x i8> %x, i32 3
@@ -139,18 +111,15 @@ define i8 @j(<4 x i8> %x, <4 x i8> %y) {
 
 define i8 @k(<4 x i8> %x) {
 ; CHECK-LABEL: @k(
-; CHECK-NEXT:    [[X0:%.*]] = extractelement <4 x i8> [[X:%.*]], i32 0
-; CHECK-NEXT:    [[X3:%.*]] = extractelement <4 x i8> [[X]], i32 3
-; CHECK-NEXT:    [[X1:%.*]] = extractelement <4 x i8> [[X]], i32 1
-; CHECK-NEXT:    [[X2:%.*]] = extractelement <4 x i8> [[X]], i32 2
-; CHECK-NEXT:    [[X0X0:%.*]] = mul i8 [[X0]], [[X0]]
-; CHECK-NEXT:    [[X3X3:%.*]] = mul i8 [[X3]], [[X3]]
-; CHECK-NEXT:    [[X1X1:%.*]] = mul i8 [[X1]], [[X1]]
-; CHECK-NEXT:    [[X2X2:%.*]] = mul i8 [[X2]], [[X2]]
-; CHECK-NEXT:    [[TMP1:%.*]] = add i8 [[X0X0]], [[X3X3]]
-; CHECK-NEXT:    [[TMP2:%.*]] = add i8 [[X1X1]], [[X2X2]]
-; CHECK-NEXT:    [[TMP3:%.*]] = sdiv i8 [[TMP1]], [[TMP2]]
-; CHECK-NEXT:    ret i8 [[TMP3]]
+; CHECK-NEXT:    [[TMP1:%.*]] = mul <4 x i8> [[X:%.*]], [[X]]
+; CHECK-NEXT:    [[TMP2:%.*]] = shufflevector <4 x i8> [[TMP1]], <4 x i8> undef, <2 x i32> <i32 0, i32 1>
+; CHECK-NEXT:    [[TMP3:%.*]] = mul <4 x i8> [[X]], [[X]]
+; CHECK-NEXT:    [[TMP4:%.*]] = shufflevector <4 x i8> [[TMP3]], <4 x i8> undef, <2 x i32> <i32 3, i32 2>
+; CHECK-NEXT:    [[TMP5:%.*]] = add <2 x i8> [[TMP2]], [[TMP4]]
+; CHECK-NEXT:    [[TMP6:%.*]] = extractelement <2 x i8> [[TMP5]], i32 0
+; CHECK-NEXT:    [[TMP7:%.*]] = extractelement <2 x i8> [[TMP5]], i32 1
+; CHECK-NEXT:    [[TMP8:%.*]] = sdiv i8 [[TMP6]], [[TMP7]]
+; CHECK-NEXT:    ret i8 [[TMP8]]
 ;
   %x0 = extractelement <4 x i8> %x, i32 0
   %x3 = extractelement <4 x i8> %x, i32 3