Fix handling errors in switch instruction by PNaCl bitcode reader.

lib/Bitcode/NaCl/Reader/NaClBitcodeReader.cpp

 //===- NaClBitcodeReader.cpp ----------------------------------------------===//
 //     Internal NaClBitcodeReader implementation
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
@@ skipping 1832 matching lines @@
 
       Value *Cond = getValue(Record, 1, NextValueNo);
       BasicBlock *Default = getBasicBlock(Record[2]);
       if (OpTy == 0 || Cond == 0 || Default == 0)
         return Error(InvalidRecord, "Invalid SWITCH record");
 
       Cond = ConvertOpToScalar(Cond, CurBBNo);
       // TODO(kschimpf): Deal with values that are too large for NumCases.
       size_t NumCases = Record[3];
 
-      SwitchInst *SI = SwitchInst::Create(Cond, Default, NumCases);
+      std::unique_ptr<SwitchInst> SI(
+          SwitchInst::Create(Cond, Default, NumCases));
 
       size_t CurIdx = 4;
       for (size_t i = 0; i != NumCases; ++i) {
         // The PNaCl bitcode format has vestigial support for case
         // ranges, but we no longer support reading them because
         // no-one produced them.
         // See https://code.google.com/p/nativeclient/issues/detail?id=3758
         if (CurIdx + 3 >= Record.size())
           return Error(InvalidRecord,
                        "Incomplete case entry in SWITCH record");
         uint64_t NumItems = Record[CurIdx++];
         bool isSingleNumber = Record[CurIdx++];
         if (NumItems != 1 || !isSingleNumber)
           return Error(InvalidRecord,
                        "Case ranges are not supported in PNaCl bitcode");
 
         APInt CaseValue(ValueBitWidth,
                         NaClDecodeSignRotatedValue(Record[CurIdx++]));
         BasicBlock *DestBB = getBasicBlock(Record[CurIdx++]);
+        if (DestBB == nullptr)
+          return Error(InvalidValue, "Invalid branch in SWITCH case");
         SI->addCase(ConstantInt::get(Context, CaseValue), DestBB);
       }
-      I = SI;
+      I = SI.release();

[JF, 2015/08/20 16:24:00]

At this point it's probably better to do the change upstream and then copy it
over here: I'd like `I` to be a `unique_ptr`, and all the other intermediate
instructions (not just switch).

[Karl, 2015/08/20 18:30:51]

Acknowledged.

       break;
     }
     case naclbitc::FUNC_CODE_INST_UNREACHABLE: // UNREACHABLE
       I = new UnreachableInst(Context);
       break;
     case naclbitc::FUNC_CODE_INST_PHI: { // PHI: [ty, val0,bb0, ...]
       if (Record.size() < 1 || ((Record.size()-1)&1))
         return Error(InvalidRecord, "Invalid PHI record");
       Type *Ty = getTypeByID(Record[0]);
       if (!Ty) return Error(InvalidType, "Invalid PHI record");
@@ skipping 467 matching lines @@
   if (std::error_code EC = M->materializeAllPermanently()) {
     delete M;
     return EC;
   }
 
   // TODO: Restore the use-lists to the in-memory state when the bitcode was
   // written.  We must defer until the Module has been fully materialized.
 
   return M;
 }