diff --git a/lib/Target/X86/X86InstrInfo.cpp b/lib/Target/X86/X86InstrInfo.cpp
index e2762f52381..c1229968e81 100644
--- a/lib/Target/X86/X86InstrInfo.cpp
+++ b/lib/Target/X86/X86InstrInfo.cpp
@@ -6424,7 +6424,7 @@ void X86InstrInfo::genAlternativeCodeSequence(
            Pattern == MachineCombinerPattern::MC_REASSOC_XA_YB)
     Prev = MRI.getUniqueVRegDef(Root.getOperand(2).getReg());
   else
-    assert("Unknown pattern for machine combiner");
+    llvm_unreachable("Unknown pattern for machine combiner");
   
   reassociateOps(Root, *Prev, Pattern, InsInstrs, DelInstrs, InstIdxForVirtReg);
   return;