@memcpy vs std.mem.cpy

_comparison.zig

const std = @import("std");

const size = 64;

var targetBase: [size]u8 = undefined;
var srcBase: [size]u8 = []u8{42} ** size;

export var target = targetBase[0..size];
export var src = srcBase[0..size];

export fn at_memcpy() [*]u8 {
    @memcpy(target.ptr, src.ptr, size);
    return target.ptr;
}

export fn std_mem_copy() [*]u8 {
    std.mem.copy(u8, target, src);
    return target.ptr;
}

comparison.wat

(module
  (type (;0;) (func))
  (type (;1;) (func (result i32)))
  (func $__wasm_call_ctors (type 0))
  (func $at_memcpy (type 1) (result i32)
    (local i32 i32)
    i32.const 0
    i32.load offset=1088
    local.tee 0
    i32.const 0
    i32.load offset=1160
    local.tee 1
    i64.load align=1
    i64.store align=1
    local.get 0
    i32.const 8
    i32.add
    local.get 1
    i32.const 8
    i32.add
    i64.load align=1
    i64.store align=1
    local.get 0
    i32.const 16
    i32.add
    local.get 1
    i32.const 16
    i32.add
    i64.load align=1
    i64.store align=1
    local.get 0
    i32.const 24
    i32.add
    local.get 1
    i32.const 24
    i32.add
    i64.load align=1
    i64.store align=1
    local.get 0
    i32.const 32
    i32.add
    local.get 1
    i32.const 32
    i32.add
    i64.load align=1
    i64.store align=1
    local.get 0
    i32.const 40
    i32.add
    local.get 1
    i32.const 40
    i32.add
    i64.load align=1
    i64.store align=1
    local.get 0
    i32.const 48
    i32.add
    local.get 1
    i32.const 48
    i32.add
    i64.load align=1
    i64.store align=1
    local.get 0
    i32.const 56
    i32.add
    local.get 1
    i32.const 56
    i32.add
    i64.load align=1
    i64.store align=1
    local.get 0)
  (func $std_mem_copy (type 1) (result i32)
    (local i32 i32)
    block  ;; label = @1
      i32.const 0
      i32.load offset=1164
      local.tee 0
      i32.eqz
      br_if 0 (;@1;)
      i32.const 0
      local.set 1
      loop  ;; label = @2
        i32.const 0
        i32.load offset=1088
        local.get 1
        i32.add
        i32.const 0
        i32.load offset=1160
        local.get 1
        i32.add
        i32.load8_u
        i32.store8
        local.get 0
        local.get 1
        i32.const 1
        i32.add
        local.tee 1
        i32.ne
        br_if 0 (;@2;)
      end
    end
    i32.const 0
    i32.load offset=1088)
  (table (;0;) 1 1 funcref)
  (memory (;0;) 2)
  (global (;0;) (mut i32) (i32.const 66704))
  (global (;1;) i32 (i32.const 66704))
  (global (;2;) i32 (i32.const 1168))
  (global (;3;) i32 (i32.const 1088))
  (global (;4;) i32 (i32.const 1160))
  (export "memory" (memory 0))
  (export "__heap_base" (global 1))
  (export "__data_end" (global 2))
  (export "at_memcpy" (func $at_memcpy))
  (export "target" (global 3))
  (export "src" (global 4))
  (export "std_mem_copy" (func $std_mem_copy))
  (data (;0;) (i32.const 1024) "\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00")
  (data (;1;) (i32.const 1088) "\00\04\00\00@\00\00\00****************************************************************H\04\00\00@\00\00\00"))

twiggy-analysis

 Shallow Bytes │ Shallow % │ Item
───────────────┼───────────┼──────────────────────────────
           148 ┊    24.63% ┊ at_memcpy
            86 ┊    14.31% ┊ data[1]
            80 ┊    13.31% ┊ std_mem_copy
            70 ┊    11.65% ┊ data[0]
            47 ┊     7.82% ┊ "function names" subsection