diff --git a/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp b/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
--- a/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
@@ -99,7 +99,7 @@
       if (Width == 0)
         continue;
       assert((Width - 1) < SubRegFromChannelTable.size());
-      assert(Offset < SubRegFromChannelTable[Width].size());
+      assert(Offset < SubRegFromChannelTable[Width - 1].size());
       SubRegFromChannelTable[Width - 1][Offset] = Idx;
     }
   };