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  6. <title>V Language Compiler Discussion</title>
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  79. </style>
  80. </head>
  81. <body>
  82. <h1>V Language Compiler: Output, Performance, and Comparison with GCC</h1>
  83.  
  84. <h2>What is the output of the Vlang compiler? ASM or C?</h2>
  85. <p>The <strong>V programming language</strong> (Vlang) compiler can produce <strong>multiple types of output</strong>, depending on the compilation mode and target backend:</p>
  86.  
  87. <h3>1. C code (default in early versions)</h3>
  88. <ul>
  89. <li>Historically, V <strong>transpiled to C</strong> as an intermediate step.</li>
  90. <li>The generated C code was then compiled using a C compiler (like <code>gcc</code> or <code>clang</code>) to produce a native binary.</li>
  91. <li>This is still supported and can be explicitly requested with:
  92. <pre><code>v -o program.c program.v</code></pre>
  93. </li>
  94. </ul>
  95.  
  96. <h3>2. Native machine code (via direct compilation or x64 backend)</h3>
  97. <ul>
  98. <li>Starting around <strong>V 0.2+</strong>, the V compiler introduced a <strong>native backend</strong> that can <strong>emit x86_64 assembly directly</strong> (without going through C).</li>
  99. <li>This backend can generate <strong>assembly (.s)</strong> or <strong>directly produce an executable</strong>.</li>
  100. <li>On supported platforms (mainly x86_64 Linux/macOS/Windows), V now <strong>prefers its native backend by default</strong>, bypassing C entirely for faster compilation.</li>
  101. <li>You can force native compilation with:
  102. <pre><code>v -native program.v</code></pre>
  103. </li>
  104. </ul>
  105.  
  106. <h3>3. LLVM IR (experimental)</h3>
  107. <ul>
  108. <li>There is also <strong>experimental support for an LLVM backend</strong>, which would emit LLVM IR, but this is not the default and is still under development.</li>
  109. </ul>
  110.  
  111. <h3>Summary</h3>
  112. <table>
  113. <thead>
  114. <tr>
  115. <th>Backend</th>
  116. <th>Output</th>
  117. <th>Default?</th>
  118. <th>Status</th>
  119. </tr>
  120. </thead>
  121. <tbody>
  122. <tr>
  123. <td>C backend</td>
  124. <td>C source code</td>
  125. <td>No (legacy)</td>
  126. <td>Fully supported</td>
  127. </tr>
  128. <tr>
  129. <td>Native backend</td>
  130. <td>x86_64 assembly → executable</td>
  131. <td><strong>Yes</strong> (on x64)</td>
  132. <td>Primary path</td>
  133. </tr>
  134. <tr>
  135. <td>LLVM backend</td>
  136. <td>LLVM IR</td>
  137. <td>No</td>
  138. <td>Experimental</td>
  139. </tr>
  140. </tbody>
  141. </table>
  142.  
  143. <blockquote>
  144. <p>✅ <strong>As of V 0.4+ (2023–2025)</strong>, the <strong>default output is a native executable</strong>, generated via V’s <strong>own x64 code generator</strong> (which internally produces and assembles x86_64 assembly). The C backend remains available for portability (e.g., compiling to architectures not yet supported by the native backend, like ARM).</p>
  145. </blockquote>
  146.  
  147. <p>You can check what your V compiler is doing by using:
  148. <pre><code>v -show-coutput program.v # shows generated C (if using C backend)
  149. v -show-asm program.v # shows generated assembly (if using native backend)</code></pre>
  150. </p>
  151.  
  152. <h2>Is the speed of V 0.4 the same as V 0.2?</h2>
  153. <p>Great question! The <strong>speed of V 0.4 vs. V 0.2</strong> can differ in <strong>two distinct dimensions</strong>, and it’s important to clarify which one you mean:</p>
  154.  
  155. <h3>1. Compilation Speed (how fast <code>v</code> compiles your code)</h3>
  156. <ul>
  157. <li><strong>V 0.4 is significantly faster</strong> at compiling than V 0.2.</li>
  158. <li>The V compiler was already designed for speed, but between 0.2 and 0.4:
  159. <ul>
  160. <li>The <strong>native x64 backend</strong> matured and became the default (no more C intermediate step on x86_64), eliminating the overhead of calling <code>gcc</code>/<code>clang</code> and parsing/translating to C.</li>
  161. <li>Improvements in parsing, hashing, and module caching reduced redundant work.</li>
  162. <li>The compiler became <strong>self-hosted</strong> (written in V and bootstrapped), allowing tighter optimization.</li>
  163. </ul>
  164. </li>
  165. <li><strong>Result</strong>: In V 0.4, hello-world compiles in <strong>~1–15 ms</strong> on modern hardware, and large projects compile <strong>~2–5× faster</strong> than in V 0.2 (especially when the C backend was used).</li>
  166. </ul>
  167.  
  168. <h3>2. Runtime Performance (how fast the generated program runs)</h3>
  169. <ul>
  170. <li>This is more nuanced.</li>
  171. <li><strong>V 0.2</strong> relied heavily on the <strong>C backend</strong>, so runtime performance depended on the quality of the generated C and the optimizations of <code>gcc</code>/<code>clang</code>.</li>
  172. <li><strong>V 0.4</strong> uses a <strong>handwritten native x64 code generator</strong>, which:
  173. <ul>
  174. <li>Produces <strong>simple, correct, but not highly optimized</strong> assembly by default.</li>
  175. <li><strong>Does not yet include advanced optimizations</strong> like instruction scheduling, vectorization, or sophisticated register allocation found in LLVM/GCC.</li>
  176. <li>However, it avoids C runtime overhead and uses a lean runtime model (no GC by default, bounds checking can be disabled).</li>
  177. </ul>
  178. </li>
  179. <li><strong>Net effect</strong>:
  180. <ul>
  181. <li>For <strong>simple, low-level code</strong>, V 0.4 <strong>native output is often comparable</strong> to C (within ~5–15%).</li>
  182. <li>For <strong>compute-intensive or complex code</strong>, V 0.2 (via <code>-prod</code> + <code>clang -O2</code>) could sometimes outperform V 0.4’s native backend—because <code>clang</code> applies aggressive optimizations that V’s native backend doesn’t yet implement.</li>
  183. <li>But: V 0.4 <strong>can still use the C backend</strong> (<code>v -c</code>), so you can get <strong>identical (or better) runtime performance</strong> to V 0.2 if needed.</li>
  184. </ul>
  185. </li>
  186. </ul>
  187.  
  188. <blockquote>
  189. <p>🔧 Tip: To maximize runtime speed in V 0.4, use:
  190. <pre><code>v -prod -c program.v # uses C backend + aggressive optimizations</code></pre>
  191. This often matches or exceeds C performance.
  192. </p>
  193. </blockquote>
  194.  
  195. <h3>Summary</h3>
  196. <table>
  197. <thead>
  198. <tr>
  199. <th>Aspect</th>
  200. <th>V 0.2</th>
  201. <th>V 0.4</th>
  202. <th>Verdict</th>
  203. </tr>
  204. </thead>
  205. <tbody>
  206. <tr>
  207. <td><strong>Compilation speed</strong></td>
  208. <td>Fast (via C)</td>
  209. <td><strong>Much faster</strong> (native backend by default)</td>
  210. <td>✅ <strong>V 0.4 wins</strong></td>
  211. </tr>
  212. <tr>
  213. <td><strong>Runtime speed</strong></td>
  214. <td>Good (thanks to GCC/Clang)</td>
  215. <td>Good (native), <strong>or better</strong> (with <code>-c -prod</code>)</td>
  216. <td>↔️ <strong>Comparable or better in V 0.4</strong></td>
  217. </tr>
  218. </tbody>
  219. </table>
  220.  
  221. <h2>V 0.4 compared to <code>gcc -O2</code>?</h2>
  222. <p>Great follow-up! Comparing <strong>V 0.4</strong> (with its default native backend) to <strong><code>gcc -O2</code></strong> (a mature, highly optimized C compiler) reveals important trade-offs in <strong>runtime performance</strong>, <strong>binary size</strong>, and <strong>optimization maturity</strong>.</p>
  223.  
  224. <blockquote>
  225. <p>🔍 <strong>Short Answer</strong>:<br>
  226. <strong>For most real-world programs, <code>gcc -O2</code> still produces faster code than V 0.4’s native backend.</strong><br>
  227. However, <strong>V 0.4 using its C backend (<code>v -c -prod</code>) can match or nearly match <code>gcc -O2</code> performance</strong>, because it <em>uses</em> <code>gcc -O2</code> (or <code>clang -O2</code>) under the hood.
  228. </p>
  229. </blockquote>
  230.  
  231. <h3>1. V 0.4 (native backend) vs. <code>gcc -O2</code></h3>
  232. <ul>
  233. <li><strong>V’s native backend</strong> (default on x86_64) generates x86_64 assembly directly.
  234. <ul>
  235. <li>✅ <em>Pros</em>: Extremely fast compilation; no external deps; minimal runtime.</li>
  236. <li>❌ <em>Cons</em>: <strong>Limited optimizations</strong> — basic register allocation, no loop unrolling, no vectorization (SIMD), no advanced constant propagation, no inter-procedural analysis.</li>
  237. </ul>
  238. </li>
  239. <li><strong><code>gcc -O2</code></strong>:
  240. <ul>
  241. <li>Applies <strong>decades of compiler research</strong>: instruction scheduling, dead code elimination, function inlining, auto-vectorization (sometimes), profile-guided optimization readiness, etc.</li>
  242. </ul>
  243. </li>
  244. <li><strong>Performance gap</strong>:
  245. <ul>
  246. <li>On <strong>numeric kernels</strong> (e.g., matrix multiply, FFT, Mandelbrot): <code>gcc -O2</code> is often <strong>1.5× to 3× faster</strong>.</li>
  247. <li>On <strong>I/O-bound or simple logic</strong> (e.g., parsing, file copying): difference is <strong>negligible (&lt;10%)</strong>.</li>
  248. <li>On <strong>memory-heavy code</strong>: V may suffer due to less optimal layout or lack of alias analysis.</li>
  249. </ul>
  250. </li>
  251. </ul>
  252.  
  253. <blockquote>
  254. <p>📌 Example: In the <a href="https://github.com/vlang/v/tree/master/benchmarks">V benchmarks</a>, the native backend is typically <strong>10–40% slower</strong> than <code>gcc -O2</code> on CPU-intensive tasks.</p>
  255. </blockquote>
  256.  
  257. <h3>2. V 0.4 (C backend + <code>-prod</code>) vs. <code>gcc -O2</code></h3>
  258. <p>When you compile with:
  259. <pre><code>v -c -prod program.v</code></pre>
  260. V:
  261. <ul>
  262. <li>Generates clean, human-readable C code.</li>
  263. <li>Invokes <code>gcc -O2</code> (or <code>clang -O2</code>) with <strong>aggressive flags</strong> (<code>-ffast-math</code>, <code>-march=native</code>, etc. in <code>-prod</code> mode).</li>
  264. <li>Disables safety checks (bounds, overflow, etc.).</li>
  265. </ul>
  266. </p>
  267.  
  268. <blockquote>
  269. <p>✅ <strong>Result</strong>: The generated binary is <strong>often within 1–5% of hand-written C compiled with <code>gcc -O2</code></strong>—sometimes even <strong>faster</strong>, because V avoids heap allocations where C might not.</p>
  270. </blockquote>
  271.  
  272. <blockquote>
  273. <p>📌 Real-world note: Projects like <strong>V’s <code>vpm</code> (package manager)</strong> or <strong><code>vweb</code></strong> show near-identical performance between hand-tuned C and V (via C backend).</p>
  274. </blockquote>
  275.  
  276. <h3>3. Binary Size & Memory Use</h3>
  277. <ul>
  278. <li><strong>V native</strong>: Very small binaries (often &lt;100 KB for hello-world), no libc dependency in freestanding mode.</li>
  279. <li><strong>V via C + gcc -O2</strong>: Slightly larger due to C runtime, but still lean.</li>
  280. <li><strong>Memory safety</strong>: V enables bounds checks by default (slight overhead); disable with <code>-prod</code> or <code>-skip-unused-checks</code>.</li>
  281. </ul>
  282.  
  283. <h3>Summary Table</h3>
  284. <table>
  285. <thead>
  286. <tr>
  287. <th>Configuration</th>
  288. <th>Runtime Speed vs. <code>gcc -O2</code></th>
  289. <th>Compilation Speed</th>
  290. <th>Notes</th>
  291. </tr>
  292. </thead>
  293. <tbody>
  294. <tr>
  295. <td><strong>V 0.4 (native backend)</strong></td>
  296. <td><strong>~60–90%</strong> of <code>gcc -O2</code></td>
  297. <td>⚡ Extremely fast</td>
  298. <td>Best for dev builds, scripts</td>
  299. </tr>
  300. <tr>
  301. <td><strong>V 0.4 (<code>-c -prod</code>)</strong></td>
  302. <td><strong>~95–102%</strong> of <code>gcc -O2</code></td>
  303. <td>Fast (~1–2× slower than native)</td>
  304. <td>Best for release builds</td>
  305. </tr>
  306. <tr>
  307. <td><strong>Hand-written C + <code>gcc -O2</code></strong></td>
  308. <td>Baseline (100%)</td>
  309. <td>Slower than V</td>
  310. <td>Gold standard for performance</td>
  311. </tr>
  312. </tbody>
  313. </table>
  314.  
  315. <h3>Outlook</h3>
  316. <p>The V team is actively improving the native backend:</p>
  317. <ul>
  318. <li>Adding <strong>SSA-based IR</strong> (planned)</li>
  319. <li>Implementing <strong>scalar replacement, LICM, basic vectorization</strong></li>
  320. <li>But <strong>full parity with GCC/LLVM</strong> is years away — and may never be the goal, since V can <strong>leverage existing C toolchains</strong> when needed.</li>
  321. </ul>
  322.  
  323. <h3>Recommendation</h3>
  324. <ul>
  325. <li>Use <strong><code>v -c -prod</code></strong> for production binaries where performance matters.</li>
  326. <li>Use <strong>native backend</strong> for development (blazing-fast iteration).</li>
  327. <li>Don’t compare V’s <em>default</em> output to <code>gcc -O2</code> — compare <strong><code>v -c -prod</code></strong> instead.</li>
  328. </ul>
  329.  
  330. <div class="timestamp">
  331. Exported on Friday, December 12, 2025
  332. </div>
  333. </body>
  334. </html>
  335.  
  336.  
Tags: vlang
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