从移植到性能优化：2026 年 Chromium V8 在RISC-V 平台上的技术进展

SAS陆亚涵yahan@SECTIONSECTION认识V8RVA23后端优化性能验证AV8是什么5asV8是Google开源的高性能JavaScript/WebAssembly引擎：内嵌于Chrome浏览器，负责网页JavaScr析与执行，支撑动态交互与异步逻辑——页面渲染由BlinkNode.js的运行时内核，广泛服务于服务器端开发与V8执行管线作为动态语言虚拟机，V8采用多层次执行架构：解释器（Ignition）负责快速启动，多层JIT编译器（Sparkplug、Maglev、TurboFan）逐级优化热点代码，并配合精确式垃圾回收实现内存自动管理；启动快照（Snapshot）机制通过预序列化上下文加速冷启动。功能移植结束，性能优化与日常维护双线并行SECTIONSECTION认识V8RVA23后端优化性能验证Linuxv7.0-rc1RVA23强制覆盖率68%→100%览基础浮点基础浮点标量增强ZICOND标量增强ZICOND控制流完整性ZICFISS控制流完整性ZICFISSRVA23U64SECTIONSECTION 认识V8RVA23后端优化性能验证ProfileImpactonBuiltinSizeBuiltin总体积(byte)指针压缩关指针压缩开rv64gcv2,620,3962,762,304rva23u642,567,5562,690,052差值−52,840(−2.02%)−72,252(−2.62%)rv64gcv关指针压缩rva23关指针压缩Δrv64gcv开指针压缩rva23开指针压缩ΔASM24,90424,608_29626,45226,064_388BCH455,736440,100_15,636475,644452,436_23,208CPP11,28011,28011,28011,280TFC658,432643,644_14,788694,844675,716_19,128TFH426,688420,900_5,788452,412443,296_9,116TFJ884,496869,556_14,940934,172916,812_17,360TFS158,860157,468_1,392167,500164,448_3,052优化二：Sub32优化word32相等判断RISC-V无条件码寄存器·Word32Eq/Ne只看低32位·Before·旧路径sllit0,a,32sllit1,b,32beqt0,t1,<target>相等判断是纯开销After·新路径subwt0,a,bbeqt0,zero,<target>优化思路：优化思路：subw自带符号扩展subw会对32位结果做符号扩展；所以subwt,a,b结果为0⇔a、b低32位相等。用算术的符号扩展，替代显式符号扩展。优化后效果:builtinsize减少：_66,760B（__2.42%）32位ALU/窄加载天然自带符号扩展·3f7ae316feb等6提交背景背景After3f7ae3add32(sext(a),sext(b))add32(a,b)3f7ae3sext(add32(x,y))add32(x,y)0a62f7sext(trunc(x))x0a62f7cmp0_32(trunc(x))cmp0_64(x)25f050cmp0_32(and32(a,b))cmp0_64(and3ccde78store32(p,trunc(x))store32(p,x)ccde78sar32(trunc(x),n)sar32(x,n)ccde78cmp0_32(load32(p))cmp0_64(load32(p))035307mulovf32(sext(a),sext(b))mulovf32(a,02bf58mulovf32(a,sext(K))mulovf32(a,K')**K′：li时已完成32位符号扩展效果builtinsize减少：_16.4826个builtin受影响指针压缩+静态root→V8的类型判断大量退化为32位比较②32位值符号扩展到64位寄存器①指针压缩PointerCompressionptr=base+index64位指针拆分成基地址base和32位index：内存base只保留一份,对象存储时只存index代价:寻址范围限制在4gb优化四立即数溢出检查：不算溢出，比较大小sext.w不可省：先把x规整成32位符号扩展形，有符号比较才成立旧路径走通用溢出检查：真的把溢出位算进kScratchReg，再判符号关键关键x±imm溢出⟺result与x的大小关系反转→不用算溢出位，直接比较即可溢出→bltresult<x溢出→bgt溢出→bltresult<x溢出→bgt...code...auipct0,entry...code...auipct0,entry..code...FinishCode():auipcx0,#wordsj0←池守卫...code...auipct0,entry...code...auipcx0,#words常量池池一旦emit就关闭写入：后续常量再也进不去常量池位置可能在代码中间代码末尾跳过池的j每池1条（4B）0条汇编器检查每128条指令一次不再检查去重范围单个池内整个codeobjectSECTION第4/4SECTION第4/4章性能验证认识V8RVA23后端优化性能验证SpacemiTK3套件RV64GCRVA23提升Octane分↑11,495.0→11,804.9+2.70%SunSpiderms↓426.0→417.2+2.11%Krakenms↓→2,572.8+18.10%同二进制、同板；正值=RVA23更快K3·2025.01构建→2026.10RVA23套件2025-01RVA23提升Octane分↑10,480.2→11,804.9+12.6%SunSpiderms↓473.4→417.2+13.5%Krakenms↓4,114.8→2,572.8+59.9%k3·原始耗时ms，2025-01→当前RVA23分组4个crypto2025-011,862.9→RVA23496.8其余10项2,251.9→2,076.0①移植已完成：①移植已完成：五级执行管线全链路打通2020riscv-collab/v8riscv64-dev→2021-02上游化→2024Maglev启用Ignition→Sparkplug→Maglev→Turboshaft→Liftoff②扩展已接入13项浮点/位操作/标量增强/控制流完整性/向量——与RVA23profile逐项对齐FPUFP64FPURVVZBAZBBZBSZFA