1 files changed, 29 insertions, 0 deletions
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();