(BIG CHANGE) Switch instruction identification/execution to use a plain match tree, should improve performance by quite a bit

src/core.rs

@@ -7,7 +7,7 @@
 use crate::{
     consts::{Addr, RegId, RegValue},
     decode::Instruction,
-    instructions::find_runner,
+    instructions::find_and_exec,
     mem::MemConfig,
 };
 
@@ -57,11 +57,9 @@ impl Core {
 
             let instr = Instruction(instr);
 
-            let runner = find_runner(instr);
-
-            if let Some(runner) = runner {
-                let res = runner(self, instr);
+            let res = find_and_exec(instr, self);
 
+            if let Some(res) = res {
                 match res {
                     InstructionResult::Normal => {}
                     InstructionResult::Exception(_e) => {

src/instructions.rs

@@ -4,82 +4,31 @@
 // This file is part of TRVE (https://gitea.taitep.se/taitep/trve)
 // See LICENSE file in the project root for full license text.
 
-use once_cell::sync::Lazy;
-
-mod gen_tools;
-mod opcodes;
 mod rvi;
 
-static INSTRUCTIONS: Lazy<[OpcodeHandler; 32]> = Lazy::new(|| {
-    let mut instructions = std::array::from_fn(|_i| OpcodeHandler {
-        handler: None,
-        splitter: None,
-    });
-
-    rvi::add_instrs(&mut instructions);
-
-    instructions
-});
-
 use crate::{
-    consts::Word,
     core::{Core, InstructionResult},
     decode::Instruction,
 };
 
-type Runner = fn(&mut Core, Instruction) -> InstructionResult;
-
-#[derive(Clone, Copy)]
-struct InstructionHandler {
-    runner: Runner,
-}
-
-struct OpcodeHandler {
-    handler: Option<InstructionHandler>,
-    splitter: Option<Splitter>,
-}
-
-pub fn find_runner(instruction: Instruction) -> Option<Runner> {
-    let opcode_handler = &INSTRUCTIONS[instruction.opcode_noncompressed() as usize];
-    opcode_handler.find_runner(instruction)
-}
-
-impl OpcodeHandler {
-    fn find_runner(&self, instruction: Instruction) -> Option<Runner> {
-        if let Some(splitter) = &self.splitter {
-            splitter.find_runner(instruction)
-        } else {
-            self.handler.map(|h| h.runner)
-        }
+pub(crate) fn find_and_exec(instr: Instruction, core: &mut Core) -> Option<InstructionResult> {
+    match instr.opcode_noncompressed() {
+        0b00100 => match instr.funct3() {
+            // OP_IMM
+            0b000 => Some(rvi::addi(core, instr)),
+            _ => None,
+        },
+        0b00110 => match instr.funct3() {
+            // OP_IMM_32
+            0b000 => Some(rvi::addiw(core, instr)),
+            _ => None,
+        },
+        0b01000 => match instr.funct3() {
+            // STORE
+            0b011 => Some(rvi::sd(core, instr)),
+            _ => None,
+        },
+        0b01101 => Some(rvi::lui(core, instr)),
+        _ => None,
     }
 }
-
-enum Splitter {
-    Funct3Splitter(Box<[OpcodeHandler; 8]>),
-    GeneralSplitter(Box<[GeneralSplitterEntry]>),
-}
-
-impl Splitter {
-    fn find_runner(&self, instruction: Instruction) -> Option<Runner> {
-        match self {
-            Splitter::Funct3Splitter(f3s) => {
-                f3s[instruction.funct3() as usize].find_runner(instruction)
-            }
-            Splitter::GeneralSplitter(entries) => {
-                for entry in entries {
-                    if instruction.0 & entry.mask == entry.value {
-                        return Some(entry.handler.runner);
-                    }
-                }
-
-                None
-            }
-        }
-    }
-}
-
-struct GeneralSplitterEntry {
-    mask: Word,
-    value: Word,
-    handler: InstructionHandler,
-}

src/instructions/gen_tools.rs

@@ -1,28 +0,0 @@
-// Copyright (c) 2025 taitep
-// SPDX-License-Identifier: MIT
-//
-// This file is part of TRVE (https://gitea.taitep.se/taitep/trve)
-// See LICENSE file in the project root for full license text.
-
-use std::hint::unreachable_unchecked;
-
-use crate::instructions::{OpcodeHandler, Splitter};
-
-pub fn insert_funct3_splitter(splitter: &mut Option<Splitter>) -> &mut [OpcodeHandler; 8] {
-    match splitter {
-        Some(Splitter::Funct3Splitter(s)) => s.as_mut(),
-        Some(_) => panic!("Unexpected splitter variant"),
-        None => {
-            *splitter = Some(Splitter::Funct3Splitter(Box::new(std::array::from_fn(
-                |_i| OpcodeHandler {
-                    handler: None,
-                    splitter: None,
-                },
-            ))));
-            match splitter {
-                Some(Splitter::Funct3Splitter(s)) => s.as_mut(),
-                _ => unsafe { unreachable_unchecked() },
-            }
-        }
-    }
-}

src/instructions/opcodes.rs

@@ -1,6 +0,0 @@
-//! Opcodes (unless compressed) have the last 2 bits stripped off as they are always 1s for non-compressed instructions.
-
-pub(super) const OP_IMM: u8 = 0b00100;
-pub(super) const OP_IMM_32: u8 = 0b00110;
-
-pub(super) const STORE: u8 = 0b01000;

src/instructions/rvi.rs

@@ -8,28 +8,10 @@ use crate::{
     consts::{Addr, DWord},
     core::{Core, InstructionResult},
     decode::Instruction,
-    instructions::{
-        OpcodeHandler,
-        gen_tools::insert_funct3_splitter,
-        opcodes::{OP_IMM, OP_IMM_32, STORE},
-    },
     mem::PageNum,
 };
 
-pub(super) fn add_instrs(list: &mut [OpcodeHandler; 32]) {
-    let funct3_splitter = insert_funct3_splitter(&mut list[OP_IMM as usize].splitter); // OP-IMM
-    funct3_splitter[0b000].handler = Some(super::InstructionHandler { runner: addi }); // ADDI
-
-    let funct3_splitter = insert_funct3_splitter(&mut list[OP_IMM_32 as usize].splitter); // OP-IMM-32
-    funct3_splitter[0b000].handler = Some(super::InstructionHandler { runner: addiw }); //ADDIW
-
-    let funct3_splitter = insert_funct3_splitter(&mut list[STORE as usize].splitter); // STORE
-    funct3_splitter[0b011].handler = Some(super::InstructionHandler { runner: sd }); // SD
-
-    list[0b01101].handler = Some(super::InstructionHandler { runner: lui }); //LUI
-}
-
-fn addi(core: &mut Core, instr: Instruction) -> InstructionResult {
+pub(super) fn addi(core: &mut Core, instr: Instruction) -> InstructionResult {
     core.reg_write(
         instr.rd(),
         core.reg_read(instr.rs1()).wrapping_add(instr.imm_i()),
@@ -40,7 +22,7 @@ fn addi(core: &mut Core, instr: Instruction) -> InstructionResult {
     InstructionResult::Normal
 }
 
-fn addiw(core: &mut Core, instr: Instruction) -> InstructionResult {
+pub(super) fn addiw(core: &mut Core, instr: Instruction) -> InstructionResult {
     let res = core.reg_read(instr.rs1()).wrapping_add(instr.imm_i()) as i32;
 
     core.reg_write(instr.rd(), res as i64 as u64);
@@ -51,7 +33,7 @@ fn addiw(core: &mut Core, instr: Instruction) -> InstructionResult {
 }
 
 // TODO: Support misaligned memory access
-fn sd(core: &mut Core, instr: Instruction) -> InstructionResult {
+pub(super) fn sd(core: &mut Core, instr: Instruction) -> InstructionResult {
     let addr = core.reg_read(instr.rs1()).wrapping_add(instr.imm_s());
 
     if !addr.is_multiple_of(std::mem::size_of::<DWord>() as Addr) {
@@ -71,7 +53,7 @@ fn sd(core: &mut Core, instr: Instruction) -> InstructionResult {
     }
 }
 
-fn lui(core: &mut Core, instr: Instruction) -> InstructionResult {
+pub(super) fn lui(core: &mut Core, instr: Instruction) -> InstructionResult {
     core.reg_write(instr.rd(), instr.imm_u());
     core.pc = core.pc.wrapping_add(4);
     InstructionResult::Normal