Always keep current instruction pointer in a register

This changes the signature of functions implementing instructions and the main loop. The pointer to current instructions has been removed from the state object, is now passed as an argument (rdi register) and next instruction pointer is returned from the instruction function (rax register).

Author: chfast

lib/evmone/analysis.hpp

@@ -86,7 +86,6 @@ struct instr_info;
 
 struct execution_state
 {
-    const instr_info* next_instr{nullptr};
     evmc_status_code status = EVMC_SUCCESS;
     int64_t gas_left = 0;
 
@@ -113,10 +112,10 @@ struct execution_state
     evmc_revision rev = {};
 
     /// Terminates the execution with the given status code.
-    void exit(evmc_status_code status_code) noexcept
+    const instr_info* exit(evmc_status_code status_code) noexcept
     {
         status = status_code;
-        next_instr = nullptr;
+        return nullptr;
     }
 };
 
@@ -134,7 +133,7 @@ union instr_argument
 
 static_assert(sizeof(instr_argument) == sizeof(void*), "Incorrect size of instr_argument");
 
-using exec_fn = void (*)(execution_state&, instr_argument arg);
+using exec_fn = const instr_info* (*)(const instr_info*, execution_state&, instr_argument arg);
 
 /// The evmone intrinsic opcodes.
 ///

lib/evmone/execution.cpp

@@ -22,22 +22,16 @@ evmc_result execute(evmc_instance*, evmc_context* ctx, evmc_revision rev, const
 
     auto state = std::make_unique<execution_state>();
     state->analysis = &analysis;
-    state->next_instr = &state->analysis->instrs[0];
     state->msg = msg;
     state->code = code;
     state->code_size = code_size;
     state->host = evmc::HostContext{ctx};
     state->gas_left = msg->gas;
     state->rev = rev;
-    while (state->next_instr)
-    {
-        const auto& instr = *state->next_instr;
-
-        // Advance next_instr to allow jump opcodes to overwrite it.
-        ++state->next_instr;
 
-        instr.fn(*state, instr.arg);
-    }
+    const instr_info* instr = &state->analysis->instrs[0];
+    while (instr)
+        instr = instr->fn(instr, *state, instr->arg);
 
     evmc_result result{};