peephole

.vscode/launch.json

@@ -11,7 +11,7 @@
             "program": "${workspaceFolder}/build/sysy",
             // "args": ["../sysytests/functional_2021/069_greatest_common_divisor.sy", "-S", "-o", "build/my.s", "-O1", "-emit-llvm"],
             // "args" : ["-S", "../sysytests/functional_2022/21_if_test2.sy", "-o", "build/dbg.s", "-emit-llvm", "-O1",],
-            "args" : ["-S", "../sysytests/functional_h_2022/04_break_continue.sy", "-o", "build/dbg.s", "-emit-llvm", "-O1",],
+            "args" : ["-S", "../sysytests/functional_h_2022/29_long_line.sy", "-o", "build/dbg.s", "-emit-llvm", "-O1",],
             "cwd": "${workspaceFolder}"
         },
     ]

include/mc_pass.h

@@ -76,4 +76,10 @@ private:
   std::set<MInstMove *, MvCmp> active_moves;
 };
 
+class PassPeepHole final : public MCPass {
+public:
+  PassPeepHole() : MCPass("peep hole") {}
+  void run(const MCModule &module) override;
+};
+
 } // namespace CompSysY

src/algo_dominance.cpp

@@ -256,7 +256,8 @@ void CFG::calculate() {
           changed = true;
           it      = node->dom.erase(it);
         }
-        else ++it;
+        else
+          ++it;
       }
     }
   }

src/main.cpp

@@ -147,7 +147,10 @@ int main(int argc, const char **argv) {
     mc_module.MC2ASM(ofs_virt_asm_file, true);
     ofs_virt_asm_file.close();
 
-    std::vector<sptr(MCPass)> mc_passes = {std::make_shared<PassRegAlloc>()};
+    std::vector<sptr(MCPass)> mc_passes = {
+      std::make_shared<PassRegAlloc>(),
+      std::make_shared<PassPeepHole>(),
+    };
     for (auto pass : mc_passes) {
       pass->run(mc_module);
     }

src/pass_dce.cpp

@@ -45,6 +45,7 @@ void remove_block(sptr(BasicBlock) victim) {
 
 // 高级编译器18.1
 bool Elim_Unreach_Code(Function *func) {
+  LOG(INFO) << "[DCE] Unreachable code elim";
   bool again   = true;
   bool changed = false;
   std::unordered_set<BasicBlock *> reachable;
@@ -69,6 +70,7 @@ bool Elim_Unreach_Code(Function *func) {
 // 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) {
+  LOG(INFO) << "[DCE] Dead code elim";
   CFG RCFG;
   RCFG.build_from_func(func, true);
   RCFG.calculate();
@@ -181,14 +183,12 @@ static void get_post_order(BasicBlock* rt) {
   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();
+  LOG(INFO) << "[DCE] Branch merge";
+  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) {
     if (is_branch(bb->inst_list.back().get())) {
@@ -208,7 +208,8 @@ bool Fuse_Block(Function *func) {
     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
+      // 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

src/pass_peephole.cpp

@@ -0,0 +1,112 @@
+#include "mc_pass.h"
+
+namespace CompSysY {
+
+static void peephole(MFunction *func) {
+  auto check_mv_ident = [](MInstMove *inst) {
+    if (inst->dst.is_reg() && inst->src.is_reg()) {
+      if (inst->dst.value == inst->src.value) {
+        return true;
+      }
+    }
+    return false;
+  };
+  auto check_mv_dup = [](MInstMove *inst1, MInstMove *inst2) {
+    if (inst1->dst.value == inst2->dst.value) {
+      if (inst1->src.is_reg() && inst2->src.is_reg()) {
+        // for regs, tags may differ
+        return inst1->src.value == inst2->src.value;
+      }
+      // for imm and glob, compare their tag and value
+      return inst1->src == inst2->src;
+    }
+    return false;
+  };
+  auto check_useless_bin = [](MInstBinary *inst) {
+    if (!inst->op2.is_imm()) return false;
+    if (inst->op1 != inst->dst) return false;
+    switch (inst->inst_tag) {
+      case MInstTag::Add: return inst->op2.value == 0;
+      case MInstTag::Sub: return inst->op2.value == 0;
+      case MInstTag::Lsh: return inst->op2.value == 0;
+      case MInstTag::Rsh: return inst->op2.value == 0;
+      default: break;
+    }
+    return false;
+  };
+  auto check_trivial_jmp = [](MInstJump *inst) {
+    // jump to the next block
+    auto next_bb = std::next(inst->parent_bb->itr);
+    if (next_bb != inst->parent_bb->parent_func->bb_list.end()) {
+      if (inst->target == *next_bb) {
+        return true;
+      }
+    }
+    return false;
+  };
+  auto check_useless_ld = [](MInstLoad *inst_ld, MInstStore *inst_st) {
+    // load from the same addr after a store can be converted into a mov
+    if (inst_ld->addr.value == inst_st->addr.value) {
+      if (inst_ld->offset == inst_st->offset) {
+        return true;
+      }
+    }
+    return false;
+  };
+  for (auto bb : func->bb_list) {
+    for (auto itr = bb->inst_list.begin(); itr != bb->inst_list.end();) {
+      auto inst = *itr++;
+      if (auto inst_mv = shared_cast<MInstMove>(inst)) {
+        if (check_mv_ident(inst_mv.get())) {
+          bb->inst_list.erase(inst->itr);
+          continue;
+        }
+        auto next_inst_itr = std::next(inst->itr);
+        if (next_inst_itr != bb->inst_list.end()) {
+          if (auto inst_mv2 = shared_cast<MInstMove>(*next_inst_itr)) {
+            if (check_mv_dup(inst_mv.get(), inst_mv2.get())) {
+              bb->inst_list.erase(inst->itr);
+              VLOG(6) << "[PeepHole] remove duplicate move";
+            }
+          }
+        }
+      }
+      else if (auto inst_bin = shared_cast<MInstBinary>(inst)) {
+        if (check_useless_bin(inst_bin.get())) {
+          bb->inst_list.erase(inst->itr);
+          VLOG(6) << "[PeepHole] remove identical binary";
+        }
+      }
+      else if (auto inst_jmp = shared_cast<MInstJump>(inst)) {
+        if (check_trivial_jmp(inst_jmp.get())) {
+          bb->inst_list.erase(inst->itr);
+          VLOG(6) << "[PeepHole] remove trivial jump";
+        }
+      }
+      else if (auto inst_ld = shared_cast<MInstLoad>(inst)) {
+        if (inst_ld->itr == bb->inst_list.begin()) continue;
+        auto prev_inst = std::prev(inst->itr);
+        if (auto inst_st = shared_cast<MInstStore>(*prev_inst)) {
+          if (check_useless_ld(inst_ld.get(), inst_st.get())) {
+            assert(inst_ld->dst.is_reg() && inst_st->data.is_reg());
+            if (inst_ld->dst.value != inst_st->data.value) {
+              auto inst_mv = MInstMove::New(inst_ld, InsertPos::Before);
+              inst_mv->dst = inst_ld->dst;
+              inst_mv->src = inst_st->data;
+            }
+            bb->inst_list.erase(inst_ld->itr);
+            VLOG(6) << "[PeepHole] remove trivial load after store";
+          }
+        }
+      }
+    }
+  }
+}
+
+void PassPeepHole::run(const MCModule &module) {
+  for (auto func : module.function_list) {
+    peephole(func.get());
+  }
+}
+
+} // namespace CompSysY