diff --git a/llvm/tools/llvm-exegesis/lib/X86/Target.cpp b/llvm/tools/llvm-exegesis/lib/X86/Target.cpp
--- a/llvm/tools/llvm-exegesis/lib/X86/Target.cpp
+++ b/llvm/tools/llvm-exegesis/lib/X86/Target.cpp
@@ -196,6 +196,21 @@
   if (OpcodeName.startswith("POP") || OpcodeName.startswith("PUSH") ||
       OpcodeName.startswith("ADJCALLSTACK") || OpcodeName.startswith("LEAVE"))
     return "unsupported opcode: Push/Pop/AdjCallStack/Leave";
+  switch (Instr.Description.Opcode) {
+  case X86::LFS16rm:
+  case X86::LFS32rm:
+  case X86::LFS64rm:
+  case X86::LGS16rm:
+  case X86::LGS32rm:
+  case X86::LGS64rm:
+  case X86::LSS16rm:
+  case X86::LSS32rm:
+  case X86::LSS64rm:
+  case X86::SYSENTER:
+    return "unsupported opcode";
+  default:
+    break;
+  }
   if (const auto reason = isInvalidMemoryInstr(Instr))
     return reason;
   // We do not handle instructions with OPERAND_PCREL.