[X86][NFC] Remove useless code in X86MCCodeEmitter.cpp

Neither the switch in A nor the switch in B is fully covered, so we
don't need write an impossible format there.

diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
index 5e9aaef..d48777b 100644 (file)
--- a/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
@@ -949,7 +949,6 @@ PrefixKind X86MCCodeEmitter::emitVEXOpcodePrefix(int MemOperand,
   }
   case X86II::MRM_C0:
   case X86II::RawFrm:
-  case X86II::PrefixByte:
     break;
   case X86II::MRMDestMemFSIB:
   case X86II::MRMDestMem: {
@@ -1246,10 +1245,6 @@ PrefixKind X86MCCodeEmitter::emitREXPrefix(int MemOperand, const MCInst &MI,
   case X86II::MRM7r:
     Prefix.setB(MI, CurOp++);
     break;
-  case X86II::MRMr0:
-    llvm_unreachable("MRMr0 format never need REX prefix!");
-  case X86II::MRMDestMemFSIB:
-    llvm_unreachable("FSIB format never need REX prefix!");
   }
   PrefixKind Kind = Prefix.determineOptimalKind();
   if (Kind && UsesHighByteReg)