void u3d_matrixTransposeInRawData(float dst_raw_data[16],
                                  float src_raw_data[16]) {
  dst_raw_data[0] = src_raw_data[0];
  dst_raw_data[5] = src_raw_data[5];
  dst_raw_data[10] = src_raw_data[10];
  dst_raw_data[15] = src_raw_data[15];
  dst_raw_data[1] = src_raw_data[4];
  dst_raw_data[4] = src_raw_data[1];
  dst_raw_data[2] = src_raw_data[8];
  dst_raw_data[8] = src_raw_data[2];
  dst_raw_data[3] = src_raw_data[12];
  dst_raw_data[12] = src_raw_data[3];
  dst_raw_data[6] = src_raw_data[9];
  dst_raw_data[9] = src_raw_data[6];
  dst_raw_data[7] = src_raw_data[13];
  dst_raw_data[13] = src_raw_data[7];
  dst_raw_data[11] = src_raw_data[14];
  dst_raw_data[14] = src_raw_data[11];
}


x86 assembly (clang, -O0):
<u3d_matrixTransposeInRawData>:
push   %rbp
mov    %rsp,%rbp
mov    %rdi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
mov    -0x10(%rbp),%rax
movss  (%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
movss  0x14(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x14(%rax)
mov    -0x10(%rbp),%rax
movss  0x28(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x28(%rax)
mov    -0x10(%rbp),%rax
movss  0x3c(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x3c(%rax)
mov    -0x10(%rbp),%rax
movss  0x10(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x4(%rax)
mov    -0x10(%rbp),%rax
movss  0x4(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x10(%rax)
mov    -0x10(%rbp),%rax
movss  0x20(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x8(%rax)
mov    -0x10(%rbp),%rax
movss  0x8(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x20(%rax)
mov    -0x10(%rbp),%rax
movss  0x30(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0xc(%rax)
mov    -0x10(%rbp),%rax
movss  0xc(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x30(%rax)
mov    -0x10(%rbp),%rax
movss  0x24(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x18(%rax)
mov    -0x10(%rbp),%rax
movss  0x18(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x24(%rax)
mov    -0x10(%rbp),%rax
movss  0x34(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x1c(%rax)
mov    -0x10(%rbp),%rax
movss  0x1c(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x34(%rax)
mov    -0x10(%rbp),%rax
movss  0x38(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x2c(%rax)
mov    -0x10(%rbp),%rax
movss  0x2c(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x38(%rax)
pop    %rbp
ret

x86 assembly (clang, -O2):
<u3d_matrixTransposeInRawData>:
movss  (%rsi),%xmm0
movss  %xmm0,(%rdi)
movss  0x14(%rsi),%xmm0
movss  %xmm0,0x14(%rdi)
movss  0x28(%rsi),%xmm0
movss  %xmm0,0x28(%rdi)
movss  0x3c(%rsi),%xmm0
movss  %xmm0,0x3c(%rdi)
movss  0x10(%rsi),%xmm0
movss  %xmm0,0x4(%rdi)
movss  0x4(%rsi),%xmm0
movss  %xmm0,0x10(%rdi)
movss  0x20(%rsi),%xmm0
movss  %xmm0,0x8(%rdi)
movss  0x8(%rsi),%xmm0
movss  %xmm0,0x20(%rdi)
movss  0x30(%rsi),%xmm0
movss  %xmm0,0xc(%rdi)
movss  0xc(%rsi),%xmm0
movss  %xmm0,0x30(%rdi)
movss  0x24(%rsi),%xmm0
movss  %xmm0,0x18(%rdi)
movss  0x18(%rsi),%xmm0
movss  %xmm0,0x24(%rdi)
movss  0x34(%rsi),%xmm0
movss  %xmm0,0x1c(%rdi)
movss  0x1c(%rsi),%xmm0
movss  %xmm0,0x34(%rdi)
movss  0x38(%rsi),%xmm0
movss  %xmm0,0x2c(%rdi)
movss  0x2c(%rsi),%xmm0
movss  %xmm0,0x38(%rdi)
ret

LLVM IR (-O0):
define void @u3d_matrixTransposeInRawData(float* %0, float* %1) {
%3 = alloca float*
%4 = alloca float*
store float* %0, float** %3
store float* %1, float** %4
%5 = load float*, float** %4
%6 = getelementptr inbounds float, float* %5, i64 0
%7 = load float, float* %6
%8 = load float*, float** %3
%9 = getelementptr inbounds float, float* %8, i64 0
store float %7, float* %9
%10 = load float*, float** %4
%11 = getelementptr inbounds float, float* %10, i64 5
%12 = load float, float* %11
%13 = load float*, float** %3
%14 = getelementptr inbounds float, float* %13, i64 5
store float %12, float* %14
%15 = load float*, float** %4
%16 = getelementptr inbounds float, float* %15, i64 10
%17 = load float, float* %16
%18 = load float*, float** %3
%19 = getelementptr inbounds float, float* %18, i64 10
store float %17, float* %19
%20 = load float*, float** %4
%21 = getelementptr inbounds float, float* %20, i64 15
%22 = load float, float* %21
%23 = load float*, float** %3
%24 = getelementptr inbounds float, float* %23, i64 15
store float %22, float* %24
%25 = load float*, float** %4
%26 = getelementptr inbounds float, float* %25, i64 4
%27 = load float, float* %26
%28 = load float*, float** %3
%29 = getelementptr inbounds float, float* %28, i64 1
store float %27, float* %29
%30 = load float*, float** %4
%31 = getelementptr inbounds float, float* %30, i64 1
%32 = load float, float* %31
%33 = load float*, float** %3
%34 = getelementptr inbounds float, float* %33, i64 4
store float %32, float* %34
%35 = load float*, float** %4
%36 = getelementptr inbounds float, float* %35, i64 8
%37 = load float, float* %36
%38 = load float*, float** %3
%39 = getelementptr inbounds float, float* %38, i64 2
store float %37, float* %39
%40 = load float*, float** %4
%41 = getelementptr inbounds float, float* %40, i64 2
%42 = load float, float* %41
%43 = load float*, float** %3
%44 = getelementptr inbounds float, float* %43, i64 8
store float %42, float* %44
%45 = load float*, float** %4
%46 = getelementptr inbounds float, float* %45, i64 12
%47 = load float, float* %46
%48 = load float*, float** %3
%49 = getelementptr inbounds float, float* %48, i64 3
store float %47, float* %49
%50 = load float*, float** %4
%51 = getelementptr inbounds float, float* %50, i64 3
%52 = load float, float* %51
%53 = load float*, float** %3
%54 = getelementptr inbounds float, float* %53, i64 12
store float %52, float* %54
%55 = load float*, float** %4
%56 = getelementptr inbounds float, float* %55, i64 9
%57 = load float, float* %56
%58 = load float*, float** %3
%59 = getelementptr inbounds float, float* %58, i64 6
store float %57, float* %59
%60 = load float*, float** %4
%61 = getelementptr inbounds float, float* %60, i64 6
%62 = load float, float* %61
%63 = load float*, float** %3
%64 = getelementptr inbounds float, float* %63, i64 9
store float %62, float* %64
%65 = load float*, float** %4
%66 = getelementptr inbounds float, float* %65, i64 13
%67 = load float, float* %66
%68 = load float*, float** %3
%69 = getelementptr inbounds float, float* %68, i64 7
store float %67, float* %69
%70 = load float*, float** %4
%71 = getelementptr inbounds float, float* %70, i64 7
%72 = load float, float* %71
%73 = load float*, float** %3
%74 = getelementptr inbounds float, float* %73, i64 13
store float %72, float* %74
%75 = load float*, float** %4
%76 = getelementptr inbounds float, float* %75, i64 14
%77 = load float, float* %76
%78 = load float*, float** %3
%79 = getelementptr inbounds float, float* %78, i64 11
store float %77, float* %79
%80 = load float*, float** %4
%81 = getelementptr inbounds float, float* %80, i64 11
%82 = load float, float* %81
%83 = load float*, float** %3
%84 = getelementptr inbounds float, float* %83, i64 14
store float %82, float* %84
ret void
}

LLVM IR (-O2):
define void @u3d_matrixTransposeInRawData(float* nocapture writeonly %0, float* nocapture %1) {
%3 = load float, float* %1
store float %3, float* %0
%4 = getelementptr inbounds float, float* %1, i64 5
%5 = load float, float* %4
%6 = getelementptr inbounds float, float* %0, i64 5
store float %5, float* %6
%7 = getelementptr inbounds float, float* %1, i64 10
%8 = load float, float* %7
%9 = getelementptr inbounds float, float* %0, i64 10
store float %8, float* %9
%10 = getelementptr inbounds float, float* %1, i64 15
%11 = load float, float* %10
%12 = getelementptr inbounds float, float* %0, i64 15
store float %11, float* %12
%13 = getelementptr inbounds float, float* %1, i64 4
%14 = load float, float* %13
%15 = getelementptr inbounds float, float* %0, i64 1
store float %14, float* %15
%16 = getelementptr inbounds float, float* %1, i64 1
%17 = load float, float* %16
%18 = getelementptr inbounds float, float* %0, i64 4
store float %17, float* %18
%19 = getelementptr inbounds float, float* %1, i64 8
%20 = load float, float* %19
%21 = getelementptr inbounds float, float* %0, i64 2
store float %20, float* %21
%22 = getelementptr inbounds float, float* %1, i64 2
%23 = load float, float* %22
%24 = getelementptr inbounds float, float* %0, i64 8
store float %23, float* %24
%25 = getelementptr inbounds float, float* %1, i64 12
%26 = load float, float* %25
%27 = getelementptr inbounds float, float* %0, i64 3
store float %26, float* %27
%28 = getelementptr inbounds float, float* %1, i64 3
%29 = load float, float* %28
%30 = getelementptr inbounds float, float* %0, i64 12
store float %29, float* %30
%31 = getelementptr inbounds float, float* %1, i64 9
%32 = load float, float* %31
%33 = getelementptr inbounds float, float* %0, i64 6
store float %32, float* %33
%34 = getelementptr inbounds float, float* %1, i64 6
%35 = load float, float* %34
%36 = getelementptr inbounds float, float* %0, i64 9
store float %35, float* %36
%37 = getelementptr inbounds float, float* %1, i64 13
%38 = load float, float* %37
%39 = getelementptr inbounds float, float* %0, i64 7
store float %38, float* %39
%40 = getelementptr inbounds float, float* %1, i64 7
%41 = load float, float* %40
%42 = getelementptr inbounds float, float* %0, i64 13
store float %41, float* %42
%43 = getelementptr inbounds float, float* %1, i64 14
%44 = load float, float* %43
%45 = getelementptr inbounds float, float* %0, i64 11
store float %44, float* %45
%46 = getelementptr inbounds float, float* %1, i64 11
%47 = load float, float* %46
%48 = getelementptr inbounds float, float* %0, i64 14
store float %47, float* %48
ret void
}