Fix handling errors in switch instruction by PNaCl bitcode reader.

lib/Bitcode/NaCl/Reader/NaClBitcodeReader.cpp

Index: lib/Bitcode/NaCl/Reader/NaClBitcodeReader.cpp
diff --git a/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.cpp b/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.cpp
index 4bfe85ce6d13a672da0b022d61087166c6ab2d72..f555f9d8d49f4aff911af3cde3ea4fe302f49b85 100644
--- a/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.cpp
+++ b/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.cpp
@@ -1510,13 +1510,19 @@ std::error_code NaClBitcodeReader::ParseFunctionBody(Function *F) {
                        "Incomplete case entry in SWITCH record");
         uint64_t NumItems = Record[CurIdx++];
         bool isSingleNumber = Record[CurIdx++];
-        if (NumItems != 1 || !isSingleNumber)
+        if (NumItems != 1 || !isSingleNumber) {
+          delete SI;

[JF, 2015/08/18 17:07:46]

Can this file as well as upstream lib/Bitcode/Reader/BitcodeReader.cpp use a
unique_ptr instead? All temporaries would have a well-bounded lifetime, and
would transfer ownership to I (also changed to unique_ptr) cleanly.

Or are switches special compared to other ops?

[Karl, 2015/08/19 19:39:00]

Switches are not special. The code was written this way because the upstream was
written this way. What makes this case different that most is that you can't
create a complete switch instruction with a single constructor. Rather, you
create a switch instruction with just the default branch, and then add each of
the cases by calling method addCase().

Hence, the switch is created up front, before the cases are processed. This
results in having to delete the switch if there is an error in the case.

I agree that a unique_ptr would be better in this case, and that the upstream
code should be fixed to use it as well. Fixing this CL to use unique_ptr in this
case.

           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) {
+          delete SI;
+          return Error(InvalidValue, "Invalid branch in SWITCH case");
+        }
         SI->addCase(ConstantInt::get(Context, CaseValue), DestBB);
       }
       I = SI;