block merge

.vscode/launch.json

@@ -10,7 +10,7 @@
             "name": "Debug",
             "program": "${workspaceFolder}/build/sysy",
             // "args": ["../sysytests/functional_2021/069_greatest_common_divisor.sy", "-S", "-o", "build/my.s", "-O1", "-emit-llvm"],
-            "args" : ["-S", "../sysytests/functional_2022/38_op_priority4.sy", "-o", "build/dbg.s", "-emit-llvm", "-O1",],
+            "args" : ["-S", "../sysytests/functional_2022/21_if_test2.sy", "-o", "build/dbg.s", "-emit-llvm", "-O1",],
             "cwd": "${workspaceFolder}"
         },
     ]

include/common.h

@@ -20,6 +20,7 @@
 
 #define uptr(type) std::unique_ptr<type>
 #define sptr(type) std::shared_ptr<type>
+#define wptr(type) std::weak_ptr<type>
 
 template <typename DST, typename SRC>
 inline sptr(DST) shared_cast(SRC src) {

src/main.cpp

@@ -113,14 +113,13 @@ int main(int argc, const char **argv) {
     }
   }
 
-  std::vector<sptr(Pass)> optpasses = {
+  std::vector<uptr(Pass)> optpasses;
-    std::make_shared<PassConstFold>(),
+  optpasses.push_back(std::move(std::make_unique<PassConstFold>()));
-    std::make_shared<PassSCCP>(),
+  optpasses.push_back(std::move(std::make_unique<PassSCCP>()));
-    std::make_shared<PassDCE>(),
+  optpasses.push_back(std::move(std::make_unique<PassDCE>()));
-  };
 
   if (flg_O1) {
-    for (auto pass : optpasses) {
+    for (auto &pass : optpasses) {
       pass->run(visitor.module);
     }
   }

src/pass_dce.cpp

@@ -67,6 +67,7 @@ bool Elim_Unreach_Code(Function *func) {
 
 // Operations defined as critical: I/O statements, linkage code (entry & exit blocks), return values, calls to other
 // procedures From Efficiently Computing SSA Form and the Control Dependence Graph, Zadeck 1991
+// comp 512 Lecture10 gives a clear description
 bool Elim_Dead_Code(Function *func) {
   CFG RCFG;
   RCFG.build_from_func(func, true);
@@ -153,14 +154,7 @@ bool Elim_Dead_Code(Function *func) {
         // rewrite branch to jmp
         inst_br->u_remove_from_usees();
         inst_br->operand_list.clear();
-        sptr(BasicBlock) tmp = nullptr;
+        inst_br->add_operand(*useful_pdom->bb->itr);
-        for (auto _bb : func->bb_list) {
-          if (_bb.get() == useful_pdom->bb) {
-            tmp = _bb;
-            break;
-          }
-        }
-        inst_br->add_operand(tmp);
       }
       else {
         changed = true;
@@ -174,22 +168,144 @@ bool Elim_Dead_Code(Function *func) {
   return changed;
 }
 
-// 高级编译器18.2
+static std::vector<BasicBlock*> post_order;
+static std::unordered_set<BasicBlock*> visit;
+
+static void get_post_order(BasicBlock* rt) {
+  visit.insert(rt);
+  for (auto succ : rt->succ_list) {
+    if (!INSET(visit, succ.get())) {
+      get_post_order(succ.get());
+    }
+  }
+  post_order.push_back(rt);
+}
+
+
+
+// 高级编译器18.2, comp512 Lecture10 gives a clearer version
 bool Fuse_Block(Function *func) {
+  auto is_branch = [](Instruction* inst) {
+    return dynamic_cast<InstBranch*>(inst) && inst->operand_list.size() == 3;
+  };
+  visit.clear(); post_order.clear();
+  get_post_order(func->bb_list.front().get());
+  for (auto bb : post_order) {
+    LOG(DEBUG) << "visit " << bb->to_string();
+    if (is_branch(bb->inst_list.back().get())) {
+      auto inst = bb->inst_list.back().get();
+      if (inst->operand_list[1] == inst->operand_list[2]) {
+        auto target = shared_cast<BasicBlock>(inst->operand_list[1]);
+        if (shared_cast<InstPhi>(target->inst_list.front())) continue;
+        auto pred_itr = STD_FIND(target->pred_list, *bb->itr);
+        target->pred_list.erase(pred_itr);
+        inst->u_remove_from_usees();
+        inst->operand_list.clear();
+        inst->add_operand(target);
+        bb->succ_list.clear();
+        bb->succ_list.push_back(target);
+      }
+    }
+    else if (auto inst = dynamic_cast<InstBranch*>(bb->inst_list.back().get())) {
+      auto target = shared_cast<BasicBlock>(inst->operand_list[0]);
+      assert(target);
+      // branch has side-effect on phi nodes, dealing with that is beyond this shabby compiler's capability, thus simply ignore
+      if (shared_cast<InstPhi>(target->inst_list.front())) continue;
+      if (bb->inst_list.size() == 1) {
+        /* bb_i -> bb_j
+         bb_i has only one jump, and bb_j can be any
+         1. replace bb_i with bb_j in all of its preds' succ_list
+         2. replace bb_i with bb_i's preds in bb_j's pred_list
+         3. if bb_j starts with phi, replace entry associated with bb_i with the same value, copy may be needed
+        */
+        if (bb == func->bb_list.front().get()) {
+          LOG(WARNING) << "block merge reach entry, skipped due to possible side effect";
+          // bb->succ_list.clear();
+          // bb->inst_list.back()->u_remove_from_usees();
+          // bb->inst_list.erase(bb->inst_list.back()->inst_itr);
+          // bb->parent_func->bb_list.erase(bb->itr);
+          // func->bb_list.erase(target->itr);
+          // func->bb_list.push_front(target);
+          // target->pred_list.clear();
+          // target->itr = func->bb_list.begin();
+          continue;
+        }
+        auto bb_index_target_succ = GETINDEX(target->pred_list, *bb->itr);
+        for (auto pred : bb->pred_list) {
+          // find the pos of bb in pred's succlist, and replace with target, in-place
+          auto itr = STD_FIND(pred->succ_list, *bb->itr);
+          *itr = target;
+          // remember to rewrite pred's jump/branch
+          auto op_itr = STD_FIND(pred->inst_list.back()->operand_list, *bb->itr);
+          *op_itr = target;
+          // for target, there's no need to keep this in-place, we delete it and push new
+          target->pred_list.push_back(pred);
+        }
+        // remove bb from target
+        target->pred_list.remove(*bb->itr);
+        // clear bb
+        bb->pred_list.clear();
+        bb->succ_list.clear();
+        bb->inst_list.back()->u_remove_from_usees();
+        assert(bb->inst_list.back()->use_list.empty());
+        bb->inst_list.erase(bb->inst_list.back()->inst_itr);
+        func->bb_list.erase(bb->itr);
+      }
+      else if (target->pred_list.size() == 1) {
+        /* bb_i -> bb_j, where i is the only pred of j
+        for simplicity, merge j into i
+        */
+        assert(!shared_cast<InstPhi>(target->inst_list.front()));
+        bb->succ_list.clear();
+        for (auto succ : target->succ_list) {
+          bb->succ_list.push_back(succ);
+          auto itr = STD_FIND(succ->pred_list, target);
+          *itr = *bb->itr;
+        }
+        // remove bb_i's last jump
+        bb->inst_list.back()->u_remove_from_usees();
+        bb->inst_list.pop_back();
+        // clear target and transfer insts
+        target->succ_list.clear();
+        target->pred_list.clear();
+        while (!target->inst_list.empty()) {
+          bb->inst_list.push_back(target->inst_list.front());
+          target->inst_list.pop_front();
+        }
+        func->bb_list.erase(target->itr);
+      }
+    }
+  }
   return false;
 }
 
+/*
+clear some strange pattern
+*/
+static void other_clear(Function* func) {
+  for (auto bb : func->bb_list) {
+    for (auto itr = bb->inst_list.begin(); itr != bb->inst_list.end(); ) {
+      auto inst = *itr ++;
+      if (shared_cast<InstPhi>(inst)) {
+        if (inst->operand_list.size() == 1) {
+          LOG(DEBUG) << "remove trivial phi";
+          inst->u_replace_users(inst->operand_list[0]);
+          inst->u_remove_from_usees();
+          bb->inst_list.erase(inst->inst_itr);
+        }
+      }
+    }
+  }
+}
+
 void PassDCE::run(const Module &module) {
   LOG(INFO) << "Run pass " << pass_name;
   for (auto func : module.function_list) {
-    if (func->is_libfunc()) continue;
+    if (func->is_libfunc()) continue;    
-    auto again = true;
+    Elim_Dead_Code(func.get());
-    while (again) {
+    Elim_Unreach_Code(func.get());
-      again = false;
+    other_clear(func.get());
-      again = Elim_Dead_Code(func.get()) || again;
+    // Fuse_Block(func.get());
-      again = Elim_Unreach_Code(func.get()) && again;
-      again = Fuse_Block(func.get()) || again;
-    }
   }
 }
 

src/visitor_llir_gen.cpp

@@ -168,11 +168,6 @@ static void _gen_blocks(std::ostream &ostr, const std::list<BasicBlockPtr_t> &bl
             assert(bb_dest->ir_seqno >= 0);
             ostr << "label %" << bb_dest->ir_seqno;
           }
-          else if (auto const_cond = shared_cast<ConstantInt>(inst->operand_list[0])) {
-            //! temporary patch after sccp, but it is often incorrect for phi
-            auto target_bb = const_cond->value ? inst->operand_list[1] : inst->operand_list[2];
-            ostr << "label %" << shared_cast<BasicBlock>(target_bb)->ir_seqno;
-          }
           else {
             assert(shared_cast<Instruction>(inst->operand_list[0]));
             assert(Type::isType<IntegerType>(inst->operand_list[0]->type));