From b485553ed855ae4fc5b96f4753e8e66f89d21abd Mon Sep 17 00:00:00 2001
From: Yang Liu <liuyang22@iscas.ac.cn>
Date: Sat, 17 Feb 2024 14:38:31 +0800
Subject: backend/rv64: Implement Identity

---
 src/dynarmic/backend/riscv64/emit_riscv64.cpp |  8 +++++++-
 src/dynarmic/backend/riscv64/reg_alloc.cpp    | 13 +++++++++++++
 src/dynarmic/backend/riscv64/reg_alloc.h      |  2 ++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/dynarmic/backend/riscv64/emit_riscv64.cpp b/src/dynarmic/backend/riscv64/emit_riscv64.cpp
index 1ac24b3e..54eb73c1 100644
--- a/src/dynarmic/backend/riscv64/emit_riscv64.cpp
+++ b/src/dynarmic/backend/riscv64/emit_riscv64.cpp
@@ -23,12 +23,18 @@ namespace Dynarmic::Backend::RV64 {
 
 template<IR::Opcode op>
 void EmitIR(biscuit::Assembler&, EmitContext&, IR::Inst*) {
-    ASSERT_FALSE("Unimplemented opcode {}", op);
+    ASSERT_FALSE("Unimplemented opcode {} ", op);
 }
 
 template<>
 void EmitIR<IR::Opcode::Void>(biscuit::Assembler&, EmitContext&, IR::Inst*) {}
 
+template<>
+void EmitIR<IR::Opcode::Identity>(biscuit::Assembler&, EmitContext& ctx, IR::Inst* inst) {
+    auto args = ctx.reg_alloc.GetArgumentInfo(inst);
+    ctx.reg_alloc.DefineAsExisting(inst, args[0]);
+}
+
 template<>
 void EmitIR<IR::Opcode::A32GetRegister>(biscuit::Assembler& as, EmitContext& ctx, IR::Inst* inst);
 template<>
diff --git a/src/dynarmic/backend/riscv64/reg_alloc.cpp b/src/dynarmic/backend/riscv64/reg_alloc.cpp
index 245c961f..1451b430 100644
--- a/src/dynarmic/backend/riscv64/reg_alloc.cpp
+++ b/src/dynarmic/backend/riscv64/reg_alloc.cpp
@@ -125,6 +125,19 @@ void RegAlloc::UpdateAllUses() {
     }
 }
 
+void RegAlloc::DefineAsExisting(IR::Inst* inst, Argument& arg) {
+    ASSERT(!ValueLocation(inst));
+
+    if (arg.value.IsImmediate()) {
+        inst->ReplaceUsesWith(arg.value);
+        return;
+    }
+
+    auto& info = ValueInfo(arg.value.GetInst());
+    info.values.emplace_back(inst);
+    info.expected_uses += inst->UseCount();
+}
+
 void RegAlloc::AssertNoMoreUses() const {
     const auto is_empty = [](const auto& i) { return i.IsCompletelyEmpty(); };
     ASSERT(std::all_of(gprs.begin(), gprs.end(), is_empty));
diff --git a/src/dynarmic/backend/riscv64/reg_alloc.h b/src/dynarmic/backend/riscv64/reg_alloc.h
index e457bc84..d80f588b 100644
--- a/src/dynarmic/backend/riscv64/reg_alloc.h
+++ b/src/dynarmic/backend/riscv64/reg_alloc.h
@@ -118,6 +118,8 @@ public:
     auto WriteX(IR::Inst* inst) { return RAReg<biscuit::GPR>{*this, true, IR::Value{inst}}; }
     auto WriteD(IR::Inst* inst) { return RAReg<biscuit::FPR>{*this, true, IR::Value{inst}}; }
 
+    void DefineAsExisting(IR::Inst* inst, Argument& arg);
+
     void SpillAll();
 
     template<typename... Ts>
-- 
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