void mat3_fromMat2d(float *dst, float *a) {
  dst[0] = a[0];
  dst[1] = a[1];
  dst[2] = 0;
  dst[3] = a[2];
  dst[4] = a[3];
  dst[5] = 0;
  dst[6] = a[4];
  dst[7] = a[5];
  dst[8] = 1;
}


x86 assembly (clang, -O0):
<mat3_fromMat2d>:
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  0x4(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x4(%rax)
mov    -0x8(%rbp),%rax
xorps  %xmm0,%xmm0
movss  %xmm0,0x8(%rax)
mov    -0x10(%rbp),%rax
movss  0x8(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0xc(%rax)
mov    -0x10(%rbp),%rax
movss  0xc(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x10(%rax)
mov    -0x8(%rbp),%rax
xorps  %xmm0,%xmm0
movss  %xmm0,0x14(%rax)
mov    -0x10(%rbp),%rax
movss  0x10(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x18(%rax)
mov    -0x10(%rbp),%rax
movss  0x14(%rax),%xmm0
mov    -0x8(%rbp),%rax
movss  %xmm0,0x1c(%rax)
mov    -0x8(%rbp),%rax
movss  0xe66(%rip),%xmm0
movss  %xmm0,0x20(%rax)
pop    %rbp
ret

x86 assembly (clang, -O2):
<mat3_fromMat2d>:
movss  (%rsi),%xmm0
movss  %xmm0,(%rdi)
movss  0x4(%rsi),%xmm0
movss  %xmm0,0x4(%rdi)
movl   $0x0,0x8(%rdi)
movss  0x8(%rsi),%xmm0
movss  %xmm0,0xc(%rdi)
movss  0xc(%rsi),%xmm0
movss  %xmm0,0x10(%rdi)
movl   $0x0,0x14(%rdi)
movss  0x10(%rsi),%xmm0
movss  %xmm0,0x18(%rdi)
movss  0x14(%rsi),%xmm0
movss  %xmm0,0x1c(%rdi)
movl   $0x3f800000,0x20(%rdi)
ret

LLVM IR (-O0):
define void @mat3_fromMat2d(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 1
%12 = load float, float* %11
%13 = load float*, float** %3
%14 = getelementptr inbounds float, float* %13, i64 1
store float %12, float* %14
%15 = load float*, float** %3
%16 = getelementptr inbounds float, float* %15, i64 2
store float 0.000000e+00, float* %16
%17 = load float*, float** %4
%18 = getelementptr inbounds float, float* %17, i64 2
%19 = load float, float* %18
%20 = load float*, float** %3
%21 = getelementptr inbounds float, float* %20, i64 3
store float %19, float* %21
%22 = load float*, float** %4
%23 = getelementptr inbounds float, float* %22, i64 3
%24 = load float, float* %23
%25 = load float*, float** %3
%26 = getelementptr inbounds float, float* %25, i64 4
store float %24, float* %26
%27 = load float*, float** %3
%28 = getelementptr inbounds float, float* %27, i64 5
store float 0.000000e+00, float* %28
%29 = load float*, float** %4
%30 = getelementptr inbounds float, float* %29, i64 4
%31 = load float, float* %30
%32 = load float*, float** %3
%33 = getelementptr inbounds float, float* %32, i64 6
store float %31, float* %33
%34 = load float*, float** %4
%35 = getelementptr inbounds float, float* %34, i64 5
%36 = load float, float* %35
%37 = load float*, float** %3
%38 = getelementptr inbounds float, float* %37, i64 7
store float %36, float* %38
%39 = load float*, float** %3
%40 = getelementptr inbounds float, float* %39, i64 8
store float 1.000000e+00, float* %40
ret void
}

LLVM IR (-O2):
define void @mat3_fromMat2d(float* nocapture writeonly %0, float* nocapture %1) {
%3 = load float, float* %1
store float %3, float* %0
%4 = getelementptr inbounds float, float* %1, i64 1
%5 = load float, float* %4
%6 = getelementptr inbounds float, float* %0, i64 1
store float %5, float* %6
%7 = getelementptr inbounds float, float* %0, i64 2
store float 0.000000e+00, float* %7
%8 = getelementptr inbounds float, float* %1, i64 2
%9 = load float, float* %8
%10 = getelementptr inbounds float, float* %0, i64 3
store float %9, float* %10
%11 = getelementptr inbounds float, float* %1, i64 3
%12 = load float, float* %11
%13 = getelementptr inbounds float, float* %0, i64 4
store float %12, float* %13
%14 = getelementptr inbounds float, float* %0, i64 5
store float 0.000000e+00, float* %14
%15 = getelementptr inbounds float, float* %1, i64 4
%16 = load float, float* %15
%17 = getelementptr inbounds float, float* %0, i64 6
store float %16, float* %17
%18 = getelementptr inbounds float, float* %1, i64 5
%19 = load float, float* %18
%20 = getelementptr inbounds float, float* %0, i64 7
store float %19, float* %20
%21 = getelementptr inbounds float, float* %0, i64 8
store float 1.000000e+00, float* %21
ret void
}