void RTransform(double *dest, double *src) {
  dest[0 + 4 * 0] = src[0];
  dest[1 + 4 * 0] = src[1];
  dest[2 + 4 * 0] = src[2];
  dest[0 + 4 * 1] = src[3];
  dest[1 + 4 * 1] = src[4];
  dest[2 + 4 * 1] = src[5];
  dest[0 + 4 * 2] = src[6];
  dest[1 + 4 * 2] = src[7];
  dest[2 + 4 * 2] = src[8];
  dest[3 + 4 * 0] = src[9];
  dest[3 + 4 * 1] = src[10];
  dest[3 + 4 * 2] = src[11];
  dest[0 + 4 * 3] = dest[1 + 4 * 3] = dest[2 + 4 * 3] = 0.0;
  dest[3 + 4 * 3] = 1.0;
}


x86 assembly (clang, -O0):
<RTransform>:
push   %rbp
mov    %rsp,%rbp
mov    %rdi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
mov    -0x10(%rbp),%rax
movsd  (%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
movsd  0x8(%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  %xmm0,0x8(%rax)
mov    -0x10(%rbp),%rax
movsd  0x10(%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  %xmm0,0x10(%rax)
mov    -0x10(%rbp),%rax
movsd  0x18(%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  %xmm0,0x20(%rax)
mov    -0x10(%rbp),%rax
movsd  0x20(%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  %xmm0,0x28(%rax)
mov    -0x10(%rbp),%rax
movsd  0x28(%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  %xmm0,0x30(%rax)
mov    -0x10(%rbp),%rax
movsd  0x30(%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  %xmm0,0x40(%rax)
mov    -0x10(%rbp),%rax
movsd  0x38(%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  %xmm0,0x48(%rax)
mov    -0x10(%rbp),%rax
movsd  0x40(%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  %xmm0,0x50(%rax)
mov    -0x10(%rbp),%rax
movsd  0x48(%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  %xmm0,0x18(%rax)
mov    -0x10(%rbp),%rax
movsd  0x50(%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  %xmm0,0x38(%rax)
mov    -0x10(%rbp),%rax
movsd  0x58(%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  %xmm0,0x58(%rax)
mov    -0x8(%rbp),%rax
xorps  %xmm0,%xmm0
movsd  %xmm0,0x70(%rax)
mov    -0x8(%rbp),%rax
xorps  %xmm0,%xmm0
movsd  %xmm0,0x68(%rax)
mov    -0x8(%rbp),%rax
xorps  %xmm0,%xmm0
movsd  %xmm0,0x60(%rax)
mov    -0x8(%rbp),%rax
movsd  0xdee(%rip),%xmm0
movsd  %xmm0,0x78(%rax)
pop    %rbp
ret

x86 assembly (clang, -O2):
<RTransform>:
movsd  (%rsi),%xmm0
movsd  %xmm0,(%rdi)
movsd  0x8(%rsi),%xmm0
movsd  %xmm0,0x8(%rdi)
movsd  0x10(%rsi),%xmm0
movsd  %xmm0,0x10(%rdi)
movsd  0x18(%rsi),%xmm0
movsd  %xmm0,0x20(%rdi)
movsd  0x20(%rsi),%xmm0
movsd  %xmm0,0x28(%rdi)
movsd  0x28(%rsi),%xmm0
movsd  %xmm0,0x30(%rdi)
movsd  0x30(%rsi),%xmm0
movsd  %xmm0,0x40(%rdi)
movsd  0x38(%rsi),%xmm0
movsd  %xmm0,0x48(%rdi)
movsd  0x40(%rsi),%xmm0
movsd  %xmm0,0x50(%rdi)
movsd  0x48(%rsi),%xmm0
movsd  %xmm0,0x18(%rdi)
movsd  0x50(%rsi),%xmm0
movsd  %xmm0,0x38(%rdi)
movsd  0x58(%rsi),%xmm0
movsd  %xmm0,0x58(%rdi)
xorps  %xmm0,%xmm0
movups %xmm0,0x60(%rdi)
movq   $0x0,0x70(%rdi)
movabs $0x3ff0000000000000,%rax
mov    %rax,0x78(%rdi)
ret

LLVM IR (-O0):
define void @RTransform(double* %0, double* %1) {
%3 = alloca double*
%4 = alloca double*
store double* %0, double** %3
store double* %1, double** %4
%5 = load double*, double** %4
%6 = getelementptr inbounds double, double* %5, i64 0
%7 = load double, double* %6
%8 = load double*, double** %3
%9 = getelementptr inbounds double, double* %8, i64 0
store double %7, double* %9
%10 = load double*, double** %4
%11 = getelementptr inbounds double, double* %10, i64 1
%12 = load double, double* %11
%13 = load double*, double** %3
%14 = getelementptr inbounds double, double* %13, i64 1
store double %12, double* %14
%15 = load double*, double** %4
%16 = getelementptr inbounds double, double* %15, i64 2
%17 = load double, double* %16
%18 = load double*, double** %3
%19 = getelementptr inbounds double, double* %18, i64 2
store double %17, double* %19
%20 = load double*, double** %4
%21 = getelementptr inbounds double, double* %20, i64 3
%22 = load double, double* %21
%23 = load double*, double** %3
%24 = getelementptr inbounds double, double* %23, i64 4
store double %22, double* %24
%25 = load double*, double** %4
%26 = getelementptr inbounds double, double* %25, i64 4
%27 = load double, double* %26
%28 = load double*, double** %3
%29 = getelementptr inbounds double, double* %28, i64 5
store double %27, double* %29
%30 = load double*, double** %4
%31 = getelementptr inbounds double, double* %30, i64 5
%32 = load double, double* %31
%33 = load double*, double** %3
%34 = getelementptr inbounds double, double* %33, i64 6
store double %32, double* %34
%35 = load double*, double** %4
%36 = getelementptr inbounds double, double* %35, i64 6
%37 = load double, double* %36
%38 = load double*, double** %3
%39 = getelementptr inbounds double, double* %38, i64 8
store double %37, double* %39
%40 = load double*, double** %4
%41 = getelementptr inbounds double, double* %40, i64 7
%42 = load double, double* %41
%43 = load double*, double** %3
%44 = getelementptr inbounds double, double* %43, i64 9
store double %42, double* %44
%45 = load double*, double** %4
%46 = getelementptr inbounds double, double* %45, i64 8
%47 = load double, double* %46
%48 = load double*, double** %3
%49 = getelementptr inbounds double, double* %48, i64 10
store double %47, double* %49
%50 = load double*, double** %4
%51 = getelementptr inbounds double, double* %50, i64 9
%52 = load double, double* %51
%53 = load double*, double** %3
%54 = getelementptr inbounds double, double* %53, i64 3
store double %52, double* %54
%55 = load double*, double** %4
%56 = getelementptr inbounds double, double* %55, i64 10
%57 = load double, double* %56
%58 = load double*, double** %3
%59 = getelementptr inbounds double, double* %58, i64 7
store double %57, double* %59
%60 = load double*, double** %4
%61 = getelementptr inbounds double, double* %60, i64 11
%62 = load double, double* %61
%63 = load double*, double** %3
%64 = getelementptr inbounds double, double* %63, i64 11
store double %62, double* %64
%65 = load double*, double** %3
%66 = getelementptr inbounds double, double* %65, i64 14
store double 0.000000e+00, double* %66
%67 = load double*, double** %3
%68 = getelementptr inbounds double, double* %67, i64 13
store double 0.000000e+00, double* %68
%69 = load double*, double** %3
%70 = getelementptr inbounds double, double* %69, i64 12
store double 0.000000e+00, double* %70
%71 = load double*, double** %3
%72 = getelementptr inbounds double, double* %71, i64 15
store double 1.000000e+00, double* %72
ret void
}

LLVM IR (-O2):
define void @RTransform(double* nocapture writeonly %0, double* nocapture %1) {
%3 = load double, double* %1
store double %3, double* %0
%4 = getelementptr inbounds double, double* %1, i64 1
%5 = load double, double* %4
%6 = getelementptr inbounds double, double* %0, i64 1
store double %5, double* %6
%7 = getelementptr inbounds double, double* %1, i64 2
%8 = load double, double* %7
%9 = getelementptr inbounds double, double* %0, i64 2
store double %8, double* %9
%10 = getelementptr inbounds double, double* %1, i64 3
%11 = load double, double* %10
%12 = getelementptr inbounds double, double* %0, i64 4
store double %11, double* %12
%13 = getelementptr inbounds double, double* %1, i64 4
%14 = load double, double* %13
%15 = getelementptr inbounds double, double* %0, i64 5
store double %14, double* %15
%16 = getelementptr inbounds double, double* %1, i64 5
%17 = load double, double* %16
%18 = getelementptr inbounds double, double* %0, i64 6
store double %17, double* %18
%19 = getelementptr inbounds double, double* %1, i64 6
%20 = load double, double* %19
%21 = getelementptr inbounds double, double* %0, i64 8
store double %20, double* %21
%22 = getelementptr inbounds double, double* %1, i64 7
%23 = load double, double* %22
%24 = getelementptr inbounds double, double* %0, i64 9
store double %23, double* %24
%25 = getelementptr inbounds double, double* %1, i64 8
%26 = load double, double* %25
%27 = getelementptr inbounds double, double* %0, i64 10
store double %26, double* %27
%28 = getelementptr inbounds double, double* %1, i64 9
%29 = load double, double* %28
%30 = getelementptr inbounds double, double* %0, i64 3
store double %29, double* %30
%31 = getelementptr inbounds double, double* %1, i64 10
%32 = load double, double* %31
%33 = getelementptr inbounds double, double* %0, i64 7
store double %32, double* %33
%34 = getelementptr inbounds double, double* %1, i64 11
%35 = load double, double* %34
%36 = getelementptr inbounds double, double* %0, i64 11
store double %35, double* %36
%37 = getelementptr inbounds double, double* %0, i64 12
%38 = getelementptr inbounds double, double* %0, i64 15
%39 = bitcast double* %37 to i8*
store double 1.000000e+00, double* %38
ret void
}