[scan-build] fix warnings emitted on LLVM MachineCode code base

[apelete]

Summary

Fix logic error warnings of the type "called C++ object pointer is
null" emitted by Clang Static Analyzer on the following file:

• lib/MC/MCParser/AsmParser.cpp.

Signed-off-by: Apelete Seketeli <[e-mail]>

[• rafael]

When is Sec null?

[• rafael]

But is the static analyzer correct?

Cheers,
Rafael

[apelete]

In D19970#422371, @rafael wrote:

But is the static analyzer correct?

Cheers,
Rafael

Let's see:

659. MCSection *Sec = getStreamer().getCurrentSection().first;

Here the analyzer seems to be complaining about the fact that the pointer to MCSection type (which is the first element of MCSectionSubPair type that is returned by getStreamer().getCurrentSection().first) might be nullptr.
Digging into the declaration of MCTargetStreamer class which AsmParser class indirectly derives from, it appears that MCSectionSubPair is not initialized by its constructor.

I understand that there is a code path that takes care of such an initialization, but from static analysis point of view that particular code path might not have been taken at this point.

Should I assert Sec value before if (!Sec->getBeginSymbol()) ?

lib/MC/MCParser/AsmParser.cpp

bool AsmParser::Run(bool NoInitialTextSection, bool NoFinalize) {
 
   HadError = false;
   AsmCond StartingCondState = TheCondState;
 
   // If we are generating dwarf for assembly source files save the initial text
   // section and generate a .file directive.
   if (getContext().getGenDwarfForAssembly()) {
     MCSection *Sec = getStreamer().getCurrentSection().first;
-    if (!Sec->getBeginSymbol()) {
+    if (Sec && !Sec->getBeginSymbol()) {
       MCSymbol *SectionStartSym = getContext().createTempSymbol();
       getStreamer().EmitLabel(SectionStartSym);
       Sec->setBeginSymbol(SectionStartSym);
     }
     bool InsertResult = getContext().addGenDwarfSection(Sec);
     assert(InsertResult && ".text section should not have debug info yet");
     (void)InsertResult;
     getContext().setGenDwarfFileNumber(getStreamer().EmitDwarfFileDirective(