[llvm] r320206 - Avoid constructing an out-of-range value for an enumeration (which results in UB).

[Richard Smith via llvm-commits]

Author: rsmith
Date: Fri Dec  8 14:32:35 2017
New Revision: 320206

URL: http://llvm.org/viewvc/llvm-project?rev=320206&view=rev
Log:
Avoid constructing an out-of-range value for an enumeration (which results in UB).

Modified:
    llvm/trunk/utils/TableGen/X86RecognizableInstr.cpp

Modified: llvm/trunk/utils/TableGen/X86RecognizableInstr.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/TableGen/X86RecognizableInstr.cpp?rev=320206&r1=320205&r2=320206&view=diff
==============================================================================
--- llvm/trunk/utils/TableGen/X86RecognizableInstr.cpp (original)
+++ llvm/trunk/utils/TableGen/X86RecognizableInstr.cpp Fri Dec  8 14:32:35 2017
@@ -706,7 +706,7 @@ void RecognizableInstr::emitDecodePath(D
 #define MAP(from, to)                     \
   case X86Local::MRM_##from:
 
-  OpcodeType    opcodeType  = (OpcodeType)-1;
+  llvm::Optional<OpcodeType> opcodeType;
 
   ModRMFilter*  filter      = nullptr;
   uint8_t       opcodeToSet = 0;
@@ -786,8 +786,7 @@ void RecognizableInstr::emitDecodePath(D
   case X86Local::AdSize64: AddressSize = 64; break;
   }
 
-  assert(opcodeType != (OpcodeType)-1 &&
-         "Opcode type not set");
+  assert(opcodeType && "Opcode type not set");
   assert(filter && "Filter not set");
 
   if (Form == X86Local::AddRegFrm) {
@@ -799,12 +798,12 @@ void RecognizableInstr::emitDecodePath(D
     for (currentOpcode = opcodeToSet;
          currentOpcode < opcodeToSet + 8;
          ++currentOpcode)
-      tables.setTableFields(opcodeType, insnContext(), currentOpcode, *filter,
+      tables.setTableFields(*opcodeType, insnContext(), currentOpcode, *filter,
                             UID, Is32Bit, OpPrefix == 0,
                             IgnoresVEX_L || EncodeRC,
                             VEX_WPrefix == X86Local::VEX_WIG, AddressSize);
   } else {
-    tables.setTableFields(opcodeType, insnContext(), opcodeToSet, *filter, UID,
+    tables.setTableFields(*opcodeType, insnContext(), opcodeToSet, *filter, UID,
                           Is32Bit, OpPrefix == 0, IgnoresVEX_L || EncodeRC,
                           VEX_WPrefix == X86Local::VEX_WIG, AddressSize);
   }