backend/rv64: Implement Identity

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<>

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));

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>