use memset_patternN in Buffer.fill

bench/snippets/buffer-fill.mjs

@@ -0,0 +1,15 @@
+import { bench, run } from "./runner.mjs";
+
+for (let size of [32, 2048, 1024 * 16, 1024 * 1024 * 2, 1024 * 1024 * 16]) {
+  for (let fillSize of [4, 8, 16, 11]) {
+    const buffer = Buffer.allocUnsafe(size);
+
+    const pattern = "x".repeat(fillSize);
+
+    bench(`Buffer.fill ${size} bytes with ${fillSize} byte value`, () => {
+      buffer.fill(pattern);
+    });
+  }
+}
+
+await run();

src/bun.js/node/buffer.zig

@@ -1,6 +1,7 @@
 const bun = @import("root").bun;
 const JSC = bun.JSC;
 const Encoder = JSC.WebCore.Encoder;
+const Environment = bun.Environment;
 
 pub const BufferVectorized = struct {
     pub fn fill(
@@ -49,23 +50,45 @@ pub const BufferVectorized = struct {
         } catch return false;
 
         switch (written) {
-            0 => {},
-            1 => @memset(buf, buf[0]),
-            else => {
-                var contents = buf[0..written];
-                buf = buf[written..];
+            0 => return true,
+            1 => {
+                @memset(buf, buf[0]);
+                return true;
+            },
+            4 => if (comptime Environment.isMac) {
+                const pattern = buf[0..4];
+                buf = buf[pattern.len..];
+                bun.C.memset_pattern4(buf.ptr, pattern.ptr, buf.len);
+                return true;
+            },
+            8 => if (comptime Environment.isMac) {
+                const pattern = buf[0..8];
+                buf = buf[pattern.len..];
+                bun.C.memset_pattern8(buf.ptr, pattern.ptr, buf.len);
+                return true;
+            },
+            16 => if (comptime Environment.isMac) {
+                const pattern = buf[0..16];
+                buf = buf[pattern.len..];
+                bun.C.memset_pattern16(buf.ptr, pattern.ptr, buf.len);
+                return true;
+            },
+            else => {},
+        }
 
-                while (buf.len >= contents.len) {
-                    bun.copy(u8, buf, contents);
-                    buf = buf[contents.len..];
-                    contents.len *= 2;
-                }
+        var contents = buf[0..written];
+        buf = buf[written..];
 
-                if (buf.len > 0) {
-                    bun.copy(u8, buf, contents[0..buf.len]);
-                }
-            },
+        while (buf.len >= contents.len) {
+            @memcpy(buf[0..contents.len], contents);
+            buf = buf[contents.len..];
+            contents.len *= 2;
+        }
+
+        if (buf.len > 0) {
+            @memcpy(buf, contents[0..buf.len]);
         }
+
         return true;
     }
 };

src/darwin_c.zig

@@ -888,3 +888,7 @@ pub const CLOCK_THREAD_CPUTIME_ID = 1;
 pub const netdb = @cImport({
     @cInclude("netdb.h");
 });
+
+pub extern fn memset_pattern4(buf: [*]u8, pattern: [*]const u8, len: usize) void;
+pub extern fn memset_pattern8(buf: [*]u8, pattern: [*]const u8, len: usize) void;
+pub extern fn memset_pattern16(buf: [*]u8, pattern: [*]const u8, len: usize) void;