[X86] Replace some default cases in X86SelectShift with llvm_unreachable.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@316839 91177308-0d34-0410-b5e6-96231b3b80d8

Author: topperc

lib/Target/X86/X86FastISel.cpp

@@ -1791,28 +1791,28 @@ bool X86FastISel::X86SelectShift(const Instruction *I) {
     CReg = X86::CX;
     RC = &X86::GR16RegClass;
     switch (I->getOpcode()) {
+    default: llvm_unreachable("Unexpected shift opcode");
     case Instruction::LShr: OpReg = X86::SHR16rCL; break;
     case Instruction::AShr: OpReg = X86::SAR16rCL; break;
     case Instruction::Shl:  OpReg = X86::SHL16rCL; break;
-    default: return false;
     }
   } else if (I->getType()->isIntegerTy(32)) {
     CReg = X86::ECX;
     RC = &X86::GR32RegClass;
     switch (I->getOpcode()) {
+    default: llvm_unreachable("Unexpected shift opcode");
     case Instruction::LShr: OpReg = X86::SHR32rCL; break;
     case Instruction::AShr: OpReg = X86::SAR32rCL; break;
     case Instruction::Shl:  OpReg = X86::SHL32rCL; break;
-    default: return false;
     }
   } else if (I->getType()->isIntegerTy(64)) {
     CReg = X86::RCX;
     RC = &X86::GR64RegClass;
     switch (I->getOpcode()) {
+    default: llvm_unreachable("Unexpected shift opcode");
     case Instruction::LShr: OpReg = X86::SHR64rCL; break;
     case Instruction::AShr: OpReg = X86::SAR64rCL; break;
     case Instruction::Shl:  OpReg = X86::SHL64rCL; break;
-    default: return false;
     }
   } else {
     return false;