identmat(matrix) float *matrix;
{
  *matrix++ = 1.0;
  *matrix++ = 0.0;
  *matrix++ = 0.0;
  *matrix++ = 0.0;
  *matrix++ = 0.0;
  *matrix++ = 1.0;
  *matrix++ = 0.0;
  *matrix++ = 0.0;
  *matrix++ = 0.0;
  *matrix++ = 0.0;
  *matrix++ = 1.0;
  *matrix++ = 0.0;
  *matrix++ = 0.0;
  *matrix++ = 0.0;
  *matrix++ = 0.0;
  *matrix++ = 1.0;
}


x86 assembly (clang, -O0):
<identmat>:
push   %rbp
mov    %rsp,%rbp
mov    %rdi,-0x10(%rbp)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
movss  0xee1(%rip),%xmm0
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
xorps  %xmm0,%xmm0
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
xorps  %xmm0,%xmm0
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
xorps  %xmm0,%xmm0
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
xorps  %xmm0,%xmm0
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
movss  0xe6e(%rip),%xmm0
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
xorps  %xmm0,%xmm0
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
xorps  %xmm0,%xmm0
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
xorps  %xmm0,%xmm0
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
xorps  %xmm0,%xmm0
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
movss  0xdfb(%rip),%xmm0
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
xorps  %xmm0,%xmm0
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
xorps  %xmm0,%xmm0
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
xorps  %xmm0,%xmm0
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
xorps  %xmm0,%xmm0
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x4,%rcx
mov    %rcx,-0x10(%rbp)
movss  0xd88(%rip),%xmm0
movss  %xmm0,(%rax)
mov    -0x4(%rbp),%eax
pop    %rbp
ret

x86 assembly (clang, -O2):
<identmat>:
movl   $0x3f800000,(%rdi)
xorps  %xmm0,%xmm0
movups %xmm0,0x4(%rdi)
movl   $0x3f800000,0x14(%rdi)
movups %xmm0,0x18(%rdi)
movl   $0x3f800000,0x28(%rdi)
movups %xmm0,0x2c(%rdi)
movl   $0x3f800000,0x3c(%rdi)
ret

LLVM IR (-O0):
define i32 @identmat(float* %0) {
%2 = alloca i32
%3 = alloca float*
store float* %0, float** %3
%4 = load float*, float** %3
%5 = getelementptr inbounds float, float* %4, i32 1
store float* %5, float** %3
store float 1.000000e+00, float* %4
%6 = load float*, float** %3
%7 = getelementptr inbounds float, float* %6, i32 1
store float* %7, float** %3
store float 0.000000e+00, float* %6
%8 = load float*, float** %3
%9 = getelementptr inbounds float, float* %8, i32 1
store float* %9, float** %3
store float 0.000000e+00, float* %8
%10 = load float*, float** %3
%11 = getelementptr inbounds float, float* %10, i32 1
store float* %11, float** %3
store float 0.000000e+00, float* %10
%12 = load float*, float** %3
%13 = getelementptr inbounds float, float* %12, i32 1
store float* %13, float** %3
store float 0.000000e+00, float* %12
%14 = load float*, float** %3
%15 = getelementptr inbounds float, float* %14, i32 1
store float* %15, float** %3
store float 1.000000e+00, float* %14
%16 = load float*, float** %3
%17 = getelementptr inbounds float, float* %16, i32 1
store float* %17, float** %3
store float 0.000000e+00, float* %16
%18 = load float*, float** %3
%19 = getelementptr inbounds float, float* %18, i32 1
store float* %19, float** %3
store float 0.000000e+00, float* %18
%20 = load float*, float** %3
%21 = getelementptr inbounds float, float* %20, i32 1
store float* %21, float** %3
store float 0.000000e+00, float* %20
%22 = load float*, float** %3
%23 = getelementptr inbounds float, float* %22, i32 1
store float* %23, float** %3
store float 0.000000e+00, float* %22
%24 = load float*, float** %3
%25 = getelementptr inbounds float, float* %24, i32 1
store float* %25, float** %3
store float 1.000000e+00, float* %24
%26 = load float*, float** %3
%27 = getelementptr inbounds float, float* %26, i32 1
store float* %27, float** %3
store float 0.000000e+00, float* %26
%28 = load float*, float** %3
%29 = getelementptr inbounds float, float* %28, i32 1
store float* %29, float** %3
store float 0.000000e+00, float* %28
%30 = load float*, float** %3
%31 = getelementptr inbounds float, float* %30, i32 1
store float* %31, float** %3
store float 0.000000e+00, float* %30
%32 = load float*, float** %3
%33 = getelementptr inbounds float, float* %32, i32 1
store float* %33, float** %3
store float 0.000000e+00, float* %32
%34 = load float*, float** %3
%35 = getelementptr inbounds float, float* %34, i32 1
store float* %35, float** %3
store float 1.000000e+00, float* %34
%36 = load i32, i32* %2
ret i32 %36
}

LLVM IR (-O2):
define i32 @identmat(float* nocapture writeonly %0) {
%2 = getelementptr inbounds float, float* %0, i64 1
store float 1.000000e+00, float* %0
%3 = getelementptr inbounds float, float* %0, i64 5
%4 = getelementptr inbounds float, float* %0, i64 6
%5 = bitcast float* %2 to i8*
store float 1.000000e+00, float* %3
%6 = getelementptr inbounds float, float* %0, i64 10
%7 = getelementptr inbounds float, float* %0, i64 11
%8 = bitcast float* %4 to i8*
store float 1.000000e+00, float* %6
%9 = getelementptr inbounds float, float* %0, i64 15
%10 = bitcast float* %7 to i8*
store float 1.000000e+00, float* %9
ret i32 undef
}