diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -14972,24 +14972,36 @@
     // Example (even elements from first vector):
     // vector_shuffle<0,16,1,17,2,18,3,19,4,20,5,21,6,22,7,23> t1, <zero>
     if (Mask[0] < NumElts)
-      for (int i = 1, e = Mask.size(); i < e; i += 2)
+      for (int i = 1, e = Mask.size(); i < e; i += 2) {
+        if (ShuffV[i] < 0)
+          continue;
         ShuffV[i] = (ShuffV[i - 1] + NumElts);
+      }
     // Example (odd elements from first vector):
     // vector_shuffle<16,0,17,1,18,2,19,3,20,4,21,5,22,6,23,7> t1, <zero>
     else
-      for (int i = 0, e = Mask.size(); i < e; i += 2)
+      for (int i = 0, e = Mask.size(); i < e; i += 2) {
+        if (ShuffV[i] < 0)
+          continue;
         ShuffV[i] = (ShuffV[i + 1] + NumElts);
+      }
   } else {
     // Example (even elements from first vector):
     // vector_shuffle<0,16,1,17,2,18,3,19,4,20,5,21,6,22,7,23> <zero>, t1
     if (Mask[0] < NumElts)
-      for (int i = 0, e = Mask.size(); i < e; i += 2)
+      for (int i = 0, e = Mask.size(); i < e; i += 2) {
+        if (ShuffV[i] < 0)
+          continue;
         ShuffV[i] = ShuffV[i + 1] - NumElts;
+      }
     // Example (odd elements from first vector):
     // vector_shuffle<16,0,17,1,18,2,19,3,20,4,21,5,22,6,23,7> <zero>, t1
     else
-      for (int i = 1, e = Mask.size(); i < e; i += 2)
+      for (int i = 1, e = Mask.size(); i < e; i += 2) {
+        if (ShuffV[i] < 0)
+          continue;
         ShuffV[i] = ShuffV[i - 1] - NumElts;
+      }
   }
 
   // If the RHS has undefs, we need to remove them since we may have created