[CostModel] Add SK_ExtractSubvector handling to getInstructionThroughput (PR39368)

Add ShuffleVectorInst::isExtractSubvectorMask helper to match shuffle masks.

llvm-svn: 346510

2 files changed, 37 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/TargetTransformInfo.cpp b/llvm/lib/Analysis/TargetTransformInfo.cpp
index 6e4eb8ff0cd..a6a1a872b65 100644
--- a/llvm/lib/Analysis/TargetTransformInfo.cpp
+++ b/llvm/lib/Analysis/TargetTransformInfo.cpp
@@ -1108,14 +1108,20 @@ int TargetTransformInfo::getInstructionThroughput(const Instruction *I) const {
   }
   case Instruction::ShuffleVector: {
     const ShuffleVectorInst *Shuffle = cast<ShuffleVectorInst>(I);
-    // TODO: Identify and add costs for insert/extract subvector, etc.
+    Type *Ty = Shuffle->getType();
+    Type *SrcTy = Shuffle->getOperand(0)->getType();
+
+    // TODO: Identify and add costs for insert subvector, etc.
+    int SubIndex;
+    if (Shuffle->isExtractSubvectorMask(SubIndex))
+      return TTIImpl->getShuffleCost(SK_ExtractSubvector, Ty, SubIndex, SrcTy);
+
     if (Shuffle->changesLength())
       return -1;
 
     if (Shuffle->isIdentity())
       return 0;
 
-    Type *Ty = Shuffle->getType();
     if (Shuffle->isReverse())
       return TTIImpl->getShuffleCost(SK_Reverse, Ty, 0, nullptr);
 
diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
index 7d4b6df18d9..66fdb462e82 100644
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -1798,6 +1798,35 @@ bool ShuffleVectorInst::isTransposeMask(ArrayRef<int> Mask) {
   return true;
 }
 
+bool ShuffleVectorInst::isExtractSubvectorMask(ArrayRef<int> Mask,
+                                               int NumSrcElts, int &Index) {
+  // Must extract from a single source.
+  if (!isSingleSourceMaskImpl(Mask, NumSrcElts))
+    return false;
+
+  // Must be smaller (else this is an Identity shuffle).
+  if (NumSrcElts <= Mask.size())
+    return false;
+
+  // Find start of extraction, accounting that we may start with an UNDEF.
+  int SubIndex = -1;
+  for (int i = 0, e = Mask.size(); i != e; ++i) {
+    int M = Mask[i];
+    if (M < 0)
+      continue;
+    int Offset = (M % NumSrcElts) - i;
+    if (0 <= SubIndex && SubIndex != Offset)
+      return false;
+    SubIndex = Offset;
+  }
+
+  if (0 <= SubIndex) {
+    Index = SubIndex;
+    return true;
+  }
+  return false;
+}
+
 bool ShuffleVectorInst::isIdentityWithPadding() const {
   int NumOpElts = Op<0>()->getType()->getVectorNumElements();
   int NumMaskElts = getType()->getVectorNumElements();