add general backend performance optimizations

src/ir/passes/CSE.cpp

@@ -1,5 +1,6 @@
 #include "ir/PassManager.h"
 #include <iostream>
+#include <unordered_map>
 #include <vector>
 #include <tuple>
 
@@ -56,10 +57,30 @@ bool RunCSE(Function* func) {
 
   for (const auto& bbPtr : func->GetBlocks()) {
     std::vector<Instruction*> seen_instructions;
+    std::unordered_map<Value*, Instruction*> available_loads;
     std::vector<Instruction*> to_erase;
 
     for (const auto& instPtr : bbPtr->GetInstructions()) {
       auto* inst = instPtr.get();
+
+      if (inst->GetOpcode() == Opcode::Load) {
+        auto* load = static_cast<LoadInst*>(inst);
+        auto it = available_loads.find(load->GetPtr());
+        if (it != available_loads.end()) {
+          inst->ReplaceAllUsesWith(it->second);
+          to_erase.push_back(inst);
+          changed = true;
+          continue;
+        }
+        available_loads[load->GetPtr()] = inst;
+        continue;
+      }
+
+      if (inst->GetOpcode() == Opcode::Store ||
+          inst->GetOpcode() == Opcode::Call) {
+        available_loads.clear();
+      }
+
       Instruction* match = nullptr;
       for (auto* seen : seen_instructions) {
         if (IsEquivalent(inst, seen)) {

src/mir/AsmPrinter.cpp

@@ -25,7 +25,7 @@ bool IsFloatReg(PhysReg reg) {
 }
 
 void PrintStackAccess(std::ostream& os, const char* mnemonic, PhysReg reg,
-                      int offset) {
+                      int offset, int frame_size) {
   bool is_float = IsFloatReg(reg);
   const char* ldr_cmd = is_float ? "ldr" : "ldr";
   const char* str_cmd = is_float ? "str" : "str";
@@ -37,10 +37,24 @@ void PrintStackAccess(std::ostream& os, const char* mnemonic, PhysReg reg,
     } else {
       os << "  " << mnemonic << " " << PhysRegName(reg) << ", [x29, #" << offset << "]\n";
     }
+  } else {
+    int sp_offset = frame_size + offset;
+    int access_size = 4;
+    if ((reg >= PhysReg::X0 && reg <= PhysReg::X28) ||
+        reg == PhysReg::X29 || reg == PhysReg::X30 ||
+        reg == PhysReg::SP) {
+      access_size = 8;
+    }
+    int max_offset = access_size == 8 ? 32760 : 16380;
+    if (sp_offset >= 0 && sp_offset <= max_offset &&
+        sp_offset % access_size == 0) {
+      os << "  " << base_mnemonic << " " << PhysRegName(reg)
+         << ", [sp, #" << sp_offset << "]\n";
     } else {
       os << "  ldr x10, =" << offset << "\n";
       os << "  " << base_mnemonic << " " << PhysRegName(reg) << ", [x29, x10]\n";
     }
+  }
 }
 
 std::string GetBlockLabel(const std::string& func_name, const std::string& block_name) {
@@ -125,12 +139,14 @@ void PrintAsm(const MachineFunction& function, std::ostream& os) {
         }
         case Opcode::LoadStack: {
           const auto& slot = GetFrameSlot(function, ops.at(1));
-          PrintStackAccess(os, "ldur", ops.at(0).GetReg(), slot.offset);
+          PrintStackAccess(os, "ldur", ops.at(0).GetReg(), slot.offset,
+                           function.GetFrameSize());
           break;
         }
         case Opcode::StoreStack: {
           const auto& slot = GetFrameSlot(function, ops.at(1));
-          PrintStackAccess(os, "stur", ops.at(0).GetReg(), slot.offset);
+          PrintStackAccess(os, "stur", ops.at(0).GetReg(), slot.offset,
+                           function.GetFrameSize());
           break;
         }
         case Opcode::AddRR:

src/mir/passes/Peephole.cpp

@@ -7,6 +7,10 @@ namespace mir {
 
 namespace {
 
+int AlignTo(int value, int align) {
+  return ((value + align - 1) / align) * align;
+}
+
 PhysReg NormalizeReg(PhysReg reg) {
   int r = static_cast<int>(reg);
   // Map 64-bit X0-X28 registers to 32-bit W0-W28 registers to handle aliasing
@@ -96,6 +100,29 @@ std::vector<MachineInstr> SimplifyCompareToBranch(
   return simplified;
 }
 
+void CompactFrameSlots(MachineFunction& function) {
+  std::unordered_set<int> used_slots;
+  for (const auto& block : function.GetBlocks()) {
+    for (const auto& inst : block.GetInstructions()) {
+      for (const auto& opnd : inst.GetOperands()) {
+        if (opnd.GetKind() == Operand::Kind::FrameIndex) {
+          used_slots.insert(opnd.GetFrameIndex());
+        }
+      }
+    }
+  }
+
+  int cursor = 0;
+  for (const auto& slot : function.GetFrameSlots()) {
+    if (used_slots.find(slot.index) == used_slots.end()) {
+      continue;
+    }
+    cursor += slot.size;
+    function.GetFrameSlot(slot.index).offset = -cursor;
+  }
+  function.SetFrameSize(AlignTo(cursor, 16));
+}
+
 } // namespace
 
 void RunPeephole(MachineFunction& function) {
@@ -285,6 +312,8 @@ void RunPeephole(MachineFunction& function) {
     }
     insts = std::move(optimized);
   }
+
+  CompactFrameSlots(function);
 }
 
 } // namespace mir