diff --git a/source/runtime/backend/reg_alloc.cpp b/source/runtime/backend/reg_alloc.cpp
index a4fe38f..9dddd96 100644
--- a/source/runtime/backend/reg_alloc.cpp
+++ b/source/runtime/backend/reg_alloc.cpp
@@ -6,12 +6,29 @@
 
 namespace swift::runtime::backend {
 
-ir::HostFPR RegAlloc::ValueFPR(const ir::Value& value) {
-    return {};
-}
+RegAlloc::RegAlloc(u32 instr_size, const GPRSMask& gprs, const FPRSMask& fprs)
+        : alloc_result{instr_size}, gprs(gprs), fprs(fprs) {}
 
-ir::HostGPR RegAlloc::ValueGPR(const ir::Value& value) {
-    return {};
+void RegAlloc::MapRegister(u32 id, ir::HostFPR fpr) {
+    alloc_result[id].type = FPR;
+    alloc_result[id].slot = fpr.id;
 }
 
+void RegAlloc::MapRegister(u32 id, ir::HostGPR gpr) {
+    alloc_result[id].type = GPR;
+    alloc_result[id].slot = gpr.id;
 }
+
+ir::HostFPR RegAlloc::ValueFPR(const ir::Value& value) { return {}; }
+
+ir::HostGPR RegAlloc::ValueGPR(const ir::Value& value) { return {}; }
+
+ir::HostGPR RegAlloc::ValueGPR(u32 id) { return ir::HostGPR{alloc_result[id].slot}; }
+
+ir::HostFPR RegAlloc::ValueFPR(u32 id) { return ir::HostFPR{alloc_result[id].slot}; }
+
+const GPRSMask& RegAlloc::GetGprs() const { return gprs; }
+
+const FPRSMask& RegAlloc::GetFprs() const { return fprs; }
+
+}  // namespace swift::runtime::backend
diff --git a/source/runtime/backend/reg_alloc.h b/source/runtime/backend/reg_alloc.h
index b60a1e2..a6d8b80 100644
--- a/source/runtime/backend/reg_alloc.h
+++ b/source/runtime/backend/reg_alloc.h
@@ -4,6 +4,7 @@
 
 #pragma once
 
+#include <bit>
 #include "base/common_funcs.h"
 #include "runtime/common/types.h"
 #include "runtime/ir/block.h"
@@ -11,10 +12,59 @@
 
 namespace swift::runtime::backend {
 
+template<typename T = u32>
+class RegisterMask {
+public:
+
+    explicit RegisterMask() : mask() {}
+
+    explicit RegisterMask(T mask) : mask(mask) {}
+
+    auto GetFirstMarked() {
+        return std::countr_zero(mask);
+    }
+
+    auto GetFirstClear() {
+        return std::countr_one(mask);
+    }
+
+    auto GetMarkedCount() {
+        return std::popcount(mask);
+    }
+
+    auto GetClearCount() {
+        return GetAllCount() - std::popcount(mask);
+    }
+
+    auto GetAllCount() {
+        return sizeof(T) * 8;
+    }
+
+    bool Get(u32 bit) {
+        return mask & (T(1) << bit);
+    }
+
+    void Mark(u32 bit) {
+        mask |= (T(1) << bit);
+    }
+
+    void Clear(u32 bit) {
+        mask &= ~(T(1) << bit);
+    }
+
+private:
+    T mask;
+};
+
+using GPRSMask = RegisterMask<u32>;
+using FPRSMask = RegisterMask<u32>;
+
 class RegAlloc : DeleteCopyAndMove {
 public:
 
-    enum Type : u8 {
+    explicit RegAlloc(u32 instr_size, const GPRSMask& gprs, const FPRSMask& fprs);
+
+    enum Type : u16 {
         NONE,
         GPR,
         FPR,
@@ -22,21 +72,27 @@ class RegAlloc : DeleteCopyAndMove {
     };
 
     struct Map {
-        union {
-            ir::HostGPR gpr;
-            ir::HostFPR fpr;
-            ir::SpillSlot spill;
-        };
         Type type{NONE};
-        u32 dirty_gprs{};
-        u32 dirty_fprs{};
+        u16 slot{};
+        GPRSMask dirty_gprs{0};
+        FPRSMask dirty_fprs{0};
     };
 
+    const GPRSMask& GetGprs() const;
+    const FPRSMask& GetFprs() const;
+
+    void MapRegister(u32 id, ir::HostGPR gpr);
+    void MapRegister(u32 id, ir::HostFPR fpr);
+
     ir::HostGPR ValueGPR(const ir::Value &value);
     ir::HostFPR ValueFPR(const ir::Value &value);
+    ir::HostGPR ValueGPR(u32 id);
+    ir::HostFPR ValueFPR(u32 id);
 
 private:
     Vector<Map> alloc_result;
+    const GPRSMask gprs;
+    const FPRSMask fprs;
 };
 
 }
diff --git a/source/runtime/ir/args.h b/source/runtime/ir/args.h
index efe1b60..da6cdb5 100644
--- a/source/runtime/ir/args.h
+++ b/source/runtime/ir/args.h
@@ -81,7 +81,7 @@ class Value {
 
     void Use() const;
     void UnUse() const;
-    u16 Id() const;
+    [[nodiscard]] u16 Id() const;
 
 private:
     Inst* inst{};
diff --git a/source/runtime/ir/hir_builder.cpp b/source/runtime/ir/hir_builder.cpp
index f9fd236..d85a603 100644
--- a/source/runtime/ir/hir_builder.cpp
+++ b/source/runtime/ir/hir_builder.cpp
@@ -176,7 +176,6 @@ void HIRFunction::MergeAdjacentBlocks(HIRBlock* left, HIRBlock* right) {}
 bool HIRFunction::SplitBlock(HIRBlock* new_block, HIRBlock* old_block) { return false; }
 
 void HIRFunction::IdByRPO() {
-    std::destroy(values.begin(), values.end());
     u32 cur_inst_id{0};
     // Re id inst
     StackVector<HIRValue*, 32> function_values{};
diff --git a/source/runtime/ir/hir_builder.h b/source/runtime/ir/hir_builder.h
index 9647c8f..848b773 100644
--- a/source/runtime/ir/hir_builder.h
+++ b/source/runtime/ir/hir_builder.h
@@ -116,7 +116,7 @@ struct HIRValue {
     void Use(Inst* inst, u8 idx);
     void UnUse(Inst* inst, u8 idx);
 
-    u16 GetOrderId() const;
+    [[nodiscard]] u16 GetOrderId() const;
 
     // for rbtree compare
     static NOINLINE int Compare(const HIRValue& lhs, const HIRValue& rhs) {
@@ -229,6 +229,7 @@ class HIRFunction : public DataContext {
         ASSERT(current_block);
         auto inst = new Inst(op);
         inst->SetArgs(args...);
+        inst->SetId(inst_order_id++);
         current_block->block->AppendInst(inst);
         AppendValue(current_block, inst);
         return inst;
diff --git a/source/runtime/ir/opts/register_alloc_pass.cpp b/source/runtime/ir/opts/register_alloc_pass.cpp
index 2224497..2720a61 100644
--- a/source/runtime/ir/opts/register_alloc_pass.cpp
+++ b/source/runtime/ir/opts/register_alloc_pass.cpp
@@ -7,6 +7,7 @@
 namespace swift::runtime::ir {
 
 struct LiveInterval {
+    Inst* inst{};
     u32 start{};
     u32 end{};
 
@@ -22,10 +23,26 @@ struct LiveInterval {
 class LinearScanAllocator {
 public:
     explicit LinearScanAllocator(HIRFunction* function, backend::RegAlloc* alloc)
-            : function(function), block(), reg_alloc(alloc), live_interval{function->MaxInstrCount()}, active_lives() {}
+            : function(function)
+            , block()
+            , reg_alloc(alloc)
+            , live_interval()
+            , active_lives() {
+        active_gprs = alloc->GetGprs();
+        active_fprs = alloc->GetFprs();
+        live_interval.reserve(function->MaxInstrCount());
+    }
 
     explicit LinearScanAllocator(Block* block, backend::RegAlloc* alloc)
-            : function(), block(block), reg_alloc(alloc), live_interval{block->GetInstList().size()}, active_lives() {}
+            : function()
+            , block(block)
+            , reg_alloc(alloc)
+            , live_interval()
+            , active_lives() {
+        active_gprs = alloc->GetGprs();
+        active_fprs = alloc->GetFprs();
+        live_interval.reserve(block->GetInstList().size());
+    }
 
     void AllocateRegisters() {
         // Step 1: Collect live intervals
@@ -42,51 +59,93 @@ class LinearScanAllocator {
         for (auto& interval : live_interval) {
             ExpireOldIntervals(interval);
 
-//            if (active_lives.size() == static_cast<size_t>(numAvailableRegisters)) {
-//                SpillAtInterval(interval);
-//            } else {
-//                int reg = AllocateRegister();
-//                interval.registerAssigned = reg;
-//                active_lives.push_back(interval);
-//                AssignRegisterToVariable(interval.variable, reg);
-//            }
+            if (!IsFloatValue(interval.inst)) {
+                if (auto alloc = AllocGPR(); alloc >= 0) {
+                    active_lives.push_back(interval);
+                    reg_alloc->MapRegister(interval.inst->Id(), HostGPR{(u16)alloc});
+                } else {
+                    SpillAtInterval(interval);
+                }
+            } else {
+                if (auto alloc = AllocFPR(); alloc >= 0) {
+                    active_lives.push_back(interval);
+                    reg_alloc->MapRegister(interval.inst->Id(), HostFPR{(u16)alloc});
+                } else {
+                    SpillAtInterval(interval);
+                }
+            }
         }
     }
 
 private:
-
     void CollectLiveIntervals(HIRFunction* hir_function) {
         for (auto& hir_value : hir_function->GetHIRValues()) {
             u32 end{hir_value.GetOrderId()};
             std::for_each(hir_value.uses.begin(), hir_value.uses.end(), [&end](auto& use) {
-                end = std::max(end, (u32) use.inst->Id());
+                end = std::max(end, (u32)use.inst->Id());
             });
-            live_interval[hir_value.GetOrderId()] = {hir_value.GetOrderId(), end};
+            live_interval.push_back({
+                    hir_value.value.Def(), hir_value.GetOrderId(), end});
         }
     }
 
-    void CollectLiveIntervals(Block *lir_block) {
+    void CollectLiveIntervals(Block* lir_block) {}
 
-    }
-
-    void ExpireOldIntervals(LiveInterval &current) {
+    void ExpireOldIntervals(LiveInterval& current) {
         for (auto it = active_lives.begin(); it != active_lives.end();) {
             if (it->end < current.start) {
-//                FreeRegister(it->registerAssigned);
-                it = active_lives.erase(it); // Remove expired intervals
+                if (!IsFloatValue(it->inst)) {
+                    FreeGPR(reg_alloc->ValueGPR(it->inst->Id()).id);
+                } else {
+                    FreeFPR(reg_alloc->ValueFPR(it->inst->Id()).id);
+                }
+                it = active_lives.erase(it);  // Remove expired intervals
             } else {
                 ++it;
             }
         }
     }
 
+    void SpillAtInterval(LiveInterval& interval) {}
+
+    bool IsFloatValue(Inst* inst) {
+        auto value_type = inst->ReturnType();
+        return value_type >= ValueType::V8 && value_type <= ValueType::V256;
+    }
+
+    int AllocGPR() {
+        if (auto alloc = active_gprs.GetFirstClear(); alloc >= 0) {
+            active_gprs.Mark(alloc);
+            return alloc;
+        }
+        return -1;
+    }
+
+    int AllocFPR() {
+        if (auto alloc = active_fprs.GetFirstClear(); alloc >= 0) {
+            active_fprs.Mark(alloc);
+            return alloc;
+        }
+        return -1;
+    }
+
+    void FreeGPR(u32 id) {
+        ASSERT(active_gprs.Get(id));
+        active_gprs.Clear(id);
+    }
+
+    void FreeFPR(u32 id) {
+        ASSERT(active_fprs.Get(id));
+        active_fprs.Clear(id);
+    }
+
     HIRFunction* function;
-    Block *block;
+    Block* block;
     backend::RegAlloc* reg_alloc;
     Vector<LiveInterval> live_interval;
     List<LiveInterval> active_lives;
-    u16 active_general_value{};
-    u16 active_float_value{};
+    backend::GPRSMask active_gprs;
+    backend::FPRSMask active_fprs;
 };
 
 void RegisterAllocPass::Run(HIRBuilder* hir_builder, backend::RegAlloc* reg_alloc) {
diff --git a/source/tests/main_case.cpp b/source/tests/main_case.cpp
index 4b5d699..2b5c09b 100644
--- a/source/tests/main_case.cpp
+++ b/source/tests/main_case.cpp
@@ -2,6 +2,8 @@
 #include "runtime/ir/hir_builder.h"
 #include "runtime/ir/opts/cfg_analysis_pass.h"
 #include "runtime/ir/opts/local_elimination_pass.h"
+#include "runtime/ir/opts/reid_instr_pass.h"
+#include "runtime/ir/opts/register_alloc_pass.h"
 #include "runtime/backend/mem_map.h"
 #include "compiler/slang/slang.h"
 
@@ -57,14 +59,14 @@ TEST_CASE("Test runtime-ir") {
     hir_builder.Return();
     CFGAnalysisPass::Run(&hir_builder);
     LocalEliminationPass::Run(&hir_builder);
-
-    assert(local2.Defined());
+    ReIdInstrPass::Run(&hir_builder);
+    RegAlloc reg_alloc{function->MaxInstrCount(), GPRSMask{0}, FPRSMask{0}};
+    RegisterAllocPass::Run(&hir_builder, &reg_alloc);
 
     MemMap mem_arena{0x100000, true};
 
     auto res = mem_arena.Map(0x100000, 0, MemMap::ReadExe, false);
     ASSERT(res);
-
 }
 
 TEST_CASE("Test runtime-ir-cfg") {
@@ -110,6 +112,7 @@ TEST_CASE("Test runtime-ir-cfg") {
     hir_builder.Return();
     CFGAnalysisPass::Run(&hir_builder);
     LocalEliminationPass::Run(&hir_builder);
+    ReIdInstrPass::Run(&hir_builder);
 
     assert(local2.Defined());