[BOLT] Check if the symbol is not weak in simplify-rodata-loads

[Amir]

Summary

Weak symbols are typically zero. Don't use them in simplification.
Follow-up to D152944.

bolt/include/bolt/Core/BinaryData.h

public:
   bool nameStartsWith(StringRef Prefix) const;
 
   bool hasSymbol(const MCSymbol *Symbol) const {
     return llvm::is_contained(Symbols, Symbol);
   }
 
   bool isAbsolute() const;
   bool isMoveable() const;
+  bool isWeak() const;
 
   uint64_t getAddress() const { return Address; }
   uint64_t getEndAddress() const { return Address + Size; }
   uint64_t getOffset() const;
   uint64_t getSize() const { return Size; }
   uint16_t getAlignment() const { return Alignment; }
 
   BinarySection &getSection() { return *Section; }

bolt/lib/Core/BinaryData.cpp

 cl::opt<bool>
     PrintSymbolAliases("print-aliases",
                        cl::desc("print aliases when printing objects"),
                        cl::Hidden, cl::cat(BoltCategory));
 }
 
 bool BinaryData::isAbsolute() const { return Flags & SymbolRef::SF_Absolute; }
 
+bool BinaryData::isWeak() const { return Flags & SymbolRef::SF_Weak; }
+
 bool BinaryData::isMoveable() const {
   return (!isAbsolute() && (IsMoveable && (!Parent || isTopLevelJumpTable())));
 }
 
 void BinaryData::merge(const BinaryData *Other) {
   assert(!Size || !Other->Size || Size == Other->Size);
   assert(Address == Other->Address);
   assert(*Section == *Other->Section);

bolt/lib/Passes/BinaryPasses.cpp

for (MCInst &Inst : *BB) {
             MIB->getTargetSymbolInfo(DispOpI->getExpr());
 
         if (!DisplSymbol)
           continue;
 
         // Look up the symbol address in the global symbols map of the binary
         // context object.
         BinaryData *BD = BC.getBinaryDataByName(DisplSymbol->getName());
-        if (!BD)
+        if (!BD || BD->isWeak())
           continue;
         TargetAddress = BD->getAddress() + DisplOffset;
       } else if (!MIB->evaluateMemOperandTarget(Inst, TargetAddress)) {
         continue;
       }
 
       // Get the contents of the section containing the target address of the
       // memory operand. We are only interested in read-only sections.