setup some bpf_module data structures correctly when rw_engine is disabled

Commit db7b8eb0 ("add a BPFModule API to disable rw_engine
sscanf/snprintf functions") permits to disable rw_engine so that
memory can be saved for structures with large arrays. As a result,
the function BPFModule::annotate(), which is used to generate
"sscanf" module, is not called when rw_engine is disabled.

Besides generating "sscanf" module, however, BPFModule::annotate()
also sets up several other data structures which are used for
map/table manipulation. This patch implements BPFModule::annotate_light(),
which will be called when rw_engine is disabled, to
setup these data structures.
Signed-off-by: Yonghong Song <yhs@fb.com>

src/cc/bpf_module.cc

@@ -486,6 +486,20 @@ int BPFModule::load_includes(const string &text) {
   return 0;
 }
 
+void BPFModule::annotate_light() {
+  for (auto fn = mod_->getFunctionList().begin(); fn != mod_->getFunctionList().end(); ++fn)
+    if (!fn->hasFnAttribute(Attribute::NoInline))
+      fn->addFnAttr(Attribute::AlwaysInline);
+
+  size_t id = 0;
+  Path path({id_});
+  for (auto it = ts_->lower_bound(path), up = ts_->upper_bound(path); it != up; ++it) {
+    TableDesc &table = it->second;
+    tables_.push_back(&it->second);
+    table_names_[table.name] = id++;
+  }
+}
+
 int BPFModule::annotate() {
   for (auto fn = mod_->getFunctionList().begin(); fn != mod_->getFunctionList().end(); ++fn)
     if (!fn->hasFnAttribute(Attribute::NoInline))
@@ -945,6 +959,8 @@ int BPFModule::load_b(const string &filename, const string &proto_filename) {
   if (rw_engine_enabled_) {
     if (int rc = annotate())
       return rc;
+  } else {
+    annotate_light();
   }
   if (int rc = finalize())
     return rc;
@@ -966,6 +982,8 @@ int BPFModule::load_c(const string &filename, const char *cflags[], int ncflags)
   if (rw_engine_enabled_) {
     if (int rc = annotate())
       return rc;
+  } else {
+    annotate_light();
   }
   if (int rc = finalize())
     return rc;
@@ -983,6 +1001,8 @@ int BPFModule::load_string(const string &text, const char *cflags[], int ncflags
   if (rw_engine_enabled_) {
     if (int rc = annotate())
       return rc;
+  } else {
+    annotate_light();
   }
 
   if (int rc = finalize())

src/cc/bpf_module.h

@@ -61,6 +61,7 @@ class BPFModule {
   int parse(llvm::Module *mod);
   int finalize();
   int annotate();
+  void annotate_light();
   std::unique_ptr<llvm::ExecutionEngine> finalize_rw(std::unique_ptr<llvm::Module> mod);
   std::string make_reader(llvm::Module *mod, llvm::Type *type);
   std::string make_writer(llvm::Module *mod, llvm::Type *type);