[BOLT][NFC] Refactor EFMM initialization

[maksfb]

Summary

Move EFMM initialization code to emitAndLink(), where EFMM is used.

bolt/lib/Rewrite/RewriteInstance.cpp

static bool shouldDisassemble(const BinaryFunction &BF) {
 
   return !BF.isIgnored();
 }
 
 Error RewriteInstance::discoverStorage() {
   NamedRegionTimer T("discoverStorage", "discover storage", TimerGroupName,
                      TimerGroupDesc, opts::TimeRewrite);
 
-  // Stubs are harmful because RuntimeDyld may try to increase the size of
-  // sections accounting for stubs when we need those sections to match the
-  // same size seen in the input binary, in case this section is a copy
-  // of the original one seen in the binary.
-  BC->EFMM.reset(new ExecutableFileMemoryManager(*BC, /*AllowStubs*/ false));
-  BC->EFMM->setNewSecPrefix(getNewSecPrefix());
-  BC->EFMM->setOrgSecPrefix(getOrgSecPrefix());
-
   auto ELF64LEFile = dyn_cast<ELF64LEObjectFile>(InputFile);
   const ELFFile<ELF64LE> &Obj = ELF64LEFile->getELFFile();
 
   BC->StartFunctionAddress = Obj.getHeader().e_entry;
 
   NextAvailableAddress = 0;
   uint64_t NextAvailableOffset = 0;
   Expected<ELF64LE::PhdrRange> PHsOrErr = Obj.program_headers();
std::unique_ptr<object::ObjectFile> Obj = cantFail(
       object::ObjectFile::createObjectFile(ObjectMemBuffer->getMemBufferRef()),
       "error creating in-memory object");
 
   BOLTSymbolResolver Resolver = BOLTSymbolResolver(*BC);
 
   MCAsmLayout FinalLayout(
       static_cast<MCObjectStreamer *>(Streamer.get())->getAssembler());
 
+  // Disable stubs because RuntimeDyld may try to increase the size of
+  // sections accounting for stubs. We need those sections to match the
+  // same size seen in the input binary, in case this section is a copy
+  // of the original one seen in the binary.
+  BC->EFMM.reset(new ExecutableFileMemoryManager(*BC, /*AllowStubs=*/false));
+  BC->EFMM->setNewSecPrefix(getNewSecPrefix());
+  BC->EFMM->setOrgSecPrefix(getOrgSecPrefix());
+
   RTDyld.reset(new decltype(RTDyld)::element_type(*BC->EFMM, Resolver));
   RTDyld->setProcessAllSections(false);
   RTDyld->loadObject(*Obj);
 
   // Assign addresses to all sections. If key corresponds to the object
   // created by ourselves, call our regular mapping function. If we are
   // loading additional objects as part of runtime libraries for
   // instrumentation, treat them as extra sections.