GlobalDCE.cc

#include "../IRContextPass.h"
#include "tir/Constant.h"
#include "utils/PassManager.h"
 
using std::string_view;
using utils::Pass;
using utils::PassManager;
 
class GlobalDCE final : public Pass {
public:
   GlobalDCE(PassManager& PM) noexcept : Pass(PM) {}
   void Run() override {
      tir::CompilationUnit& CU = GetPass<IRContextPass>().CU();
      bool changed;
      do {
         changed = removeAllGlobals(CU);
      } while(changed);
   }
   string_view Name() const override { return "globaldce"; }
   string_view Desc() const override { return "Global Dead Code Elimination"; }
 
private:
   bool removeAllGlobals(tir::CompilationUnit& CU) {
      std::vector<std::string> toRemove;
      for(auto p : CU.global_objects_kv()) {
         auto [name, go] = p;
         if(go->isExternalLinkage()) continue;
         if(!go->users().empty()) continue;
         // Destroy the global object
         if(auto fn = dyn_cast<tir::Function>(go)) {
            for(auto bb : fn->body()) {
               auto* inst = *bb->begin();
               while(inst) {
                  auto next = inst->next();
                  inst->eraseFromParent();
                  inst = next;
               }
            }
         }
         toRemove.push_back(std::string{name});
      }
      for(auto name : toRemove) {
         CU.removeGlobalObject(name);
      }
      return toRemove.size() > 0;
   }
 
private:
   void computeDependencies() override {
      ComputeDependency(GetPass<IRContextPass>());
   }
};
 
REGISTER_PASS(GlobalDCE);