Cost model: Add check for reverse shuffles to CostModel analysis

Check for reverse shuffles in the CostModel analysis pass and query
TargetTransform info accordingly. This allows us we can write test cases for
reverse shuffles.

radar://13171406

llvm-svn: 174932

1 files changed, 18 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/CostModel.cpp b/llvm/lib/Analysis/CostModel.cpp
index 8435e397077..44684a9685b 100644
--- a/llvm/lib/Analysis/CostModel.cpp
+++ b/llvm/lib/Analysis/CostModel.cpp
@@ -80,6 +80,13 @@ CostModelAnalysis::runOnFunction(Function &F) {
  return false;
 }
 
+static bool isReverseVectorMask(SmallVector<int, 16> &Mask) {
+  for (unsigned i = 0, MaskSize = Mask.size(); i < MaskSize; ++i)
+    if (Mask[i] > 0 && Mask[i] != (int)(MaskSize - 1 - i))
+      return false;
+  return true;
+}
+
 unsigned CostModelAnalysis::getInstructionCost(const Instruction *I) const {
   if (!TTI)
     return -1;
@@ -171,6 +178,17 @@ unsigned CostModelAnalysis::getInstructionCost(const Instruction *I) const {
       return TTI->getVectorInstrCost(I->getOpcode(),
                                      IE->getType(), Idx);
     }
+  case Instruction::ShuffleVector: {
+    const ShuffleVectorInst *Shuffle = cast<ShuffleVectorInst>(I);
+    Type *VecTypOp0 = Shuffle->getOperand(0)->getType();
+    unsigned NumVecElems = VecTypOp0->getVectorNumElements();
+    SmallVector<int, 16> Mask = Shuffle->getShuffleMask();
+
+    if (NumVecElems == Mask.size() && isReverseVectorMask(Mask))
+      return TTI->getShuffleCost(TargetTransformInfo::SK_Reverse, VecTypOp0, 0,
+                                 0);
+    return -1;
+  }
   default:
     // We don't have any information on this instruction.
     return -1;