add benchmark for measuring parser performance

std/zig/bench.zig

@@ -0,0 +1,38 @@
+const std = @import("std");
+const mem = std.mem;
+const warn = std.debug.warn;
+const Tokenizer = std.zig.Tokenizer;
+const Parser = std.zig.Parser;
+const io = std.io;
+
+const source = @embedFile("../os/index.zig");
+var fixed_buffer_mem: [10 * 1024 * 1024]u8 = undefined;
+
+pub fn main() !void {
+    var i: usize = 0;
+    var timer = try std.os.time.Timer.start();
+    const start = timer.lap();
+    const iterations = 100;
+    var memory_used: usize = 0;
+    while (i < iterations) : (i += 1) {
+        memory_used += testOnce();
+    }
+    const end = timer.read();
+    memory_used /= iterations;
+    const elapsed_s = f64(end - start) / std.os.time.ns_per_s;
+    const bytes_per_sec = f64(source.len * iterations) / elapsed_s;
+    const mb_per_sec = bytes_per_sec / (1024 * 1024);
+
+    var stdout_file = try std.io.getStdOut();
+    const stdout = &std.io.FileOutStream.init(&stdout_file).stream;
+    try stdout.print("{.3} MB/s, {} KB used \n", mb_per_sec, memory_used / 1024);
+}
+
+fn testOnce() usize {
+    var fixed_buf_alloc = std.heap.FixedBufferAllocator.init(fixed_buffer_mem[0..]);
+    var allocator = &fixed_buf_alloc.allocator;
+    var tokenizer = Tokenizer.init(source);
+    var parser = Parser.init(&tokenizer, allocator, "(memory buffer)");
+    _ = parser.parse() catch @panic("parse failure");
+    return fixed_buf_alloc.end_index;
+}