double det3x3(double *a) {
  double *a00 __attribute__((unused)) = a++;
  double *a10 __attribute__((unused)) = a++;
  double *a20 __attribute__((unused)) = a++;
  double *a01 __attribute__((unused)) = a++;
  double *a11 __attribute__((unused)) = a++;
  double *a21 __attribute__((unused)) = a++;
  double *a02 __attribute__((unused)) = a++;
  double *a12 __attribute__((unused)) = a++;
  double *a22 __attribute__((unused)) = a++;
  ;
  return *a00 * *a11 * *a22 + *a01 * *a12 * *a20 + *a02 * *a10 * *a21 -
         *a00 * *a12 * *a21 - *a01 * *a10 * *a22 - *a02 * *a11 * *a20;
}


x86 assembly (clang, -O0):
<det3x3>:
push   %rbp
mov    %rsp,%rbp
mov    %rdi,-0x8(%rbp)
mov    -0x8(%rbp),%rax
mov    %rax,%rcx
add    $0x8,%rcx
mov    %rcx,-0x8(%rbp)
mov    %rax,-0x10(%rbp)
mov    -0x8(%rbp),%rax
mov    %rax,%rcx
add    $0x8,%rcx
mov    %rcx,-0x8(%rbp)
mov    %rax,-0x18(%rbp)
mov    -0x8(%rbp),%rax
mov    %rax,%rcx
add    $0x8,%rcx
mov    %rcx,-0x8(%rbp)
mov    %rax,-0x20(%rbp)
mov    -0x8(%rbp),%rax
mov    %rax,%rcx
add    $0x8,%rcx
mov    %rcx,-0x8(%rbp)
mov    %rax,-0x28(%rbp)
mov    -0x8(%rbp),%rax
mov    %rax,%rcx
add    $0x8,%rcx
mov    %rcx,-0x8(%rbp)
mov    %rax,-0x30(%rbp)
mov    -0x8(%rbp),%rax
mov    %rax,%rcx
add    $0x8,%rcx
mov    %rcx,-0x8(%rbp)
mov    %rax,-0x38(%rbp)
mov    -0x8(%rbp),%rax
mov    %rax,%rcx
add    $0x8,%rcx
mov    %rcx,-0x8(%rbp)
mov    %rax,-0x40(%rbp)
mov    -0x8(%rbp),%rax
mov    %rax,%rcx
add    $0x8,%rcx
mov    %rcx,-0x8(%rbp)
mov    %rax,-0x48(%rbp)
mov    -0x8(%rbp),%rax
mov    %rax,%rcx
add    $0x8,%rcx
mov    %rcx,-0x8(%rbp)
mov    %rax,-0x50(%rbp)
mov    -0x10(%rbp),%rax
movsd  (%rax),%xmm0
mov    -0x30(%rbp),%rax
mulsd  (%rax),%xmm0
mov    -0x50(%rbp),%rax
movsd  (%rax),%xmm2
mov    -0x28(%rbp),%rax
movsd  (%rax),%xmm1
mov    -0x48(%rbp),%rax
mulsd  (%rax),%xmm1
mov    -0x20(%rbp),%rax
mulsd  (%rax),%xmm1
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
mov    -0x40(%rbp),%rax
movsd  (%rax),%xmm1
mov    -0x18(%rbp),%rax
mulsd  (%rax),%xmm1
mov    -0x38(%rbp),%rax
movsd  (%rax),%xmm2
mulsd  %xmm2,%xmm1
addsd  %xmm0,%xmm1
mov    -0x10(%rbp),%rax
movsd  (%rax),%xmm0
mov    -0x48(%rbp),%rax
mulsd  (%rax),%xmm0
mov    -0x38(%rbp),%rax
movsd  (%rax),%xmm2
movq   %xmm0,%rax
movabs $0x8000000000000000,%rcx
xor    %rcx,%rax
movq   %rax,%xmm0
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
mov    -0x28(%rbp),%rax
movsd  (%rax),%xmm1
mov    -0x18(%rbp),%rax
mulsd  (%rax),%xmm1
mov    -0x50(%rbp),%rax
movsd  (%rax),%xmm2
movq   %xmm1,%rax
movabs $0x8000000000000000,%rcx
xor    %rcx,%rax
movq   %rax,%xmm1
mulsd  %xmm2,%xmm1
addsd  %xmm0,%xmm1
mov    -0x40(%rbp),%rax
movsd  (%rax),%xmm0
mov    -0x30(%rbp),%rax
mulsd  (%rax),%xmm0
mov    -0x20(%rbp),%rax
movsd  (%rax),%xmm2
movq   %xmm0,%rax
movabs $0x8000000000000000,%rcx
xor    %rcx,%rax
movq   %rax,%xmm0
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
pop    %rbp
ret

x86 assembly (clang, -O2):
<det3x3>:
movsd  0x20(%rdi),%xmm1
movsd  (%rdi),%xmm3
movsd  0x8(%rdi),%xmm2
movsd  0x18(%rdi),%xmm4
movsd  0x38(%rdi),%xmm5
movsd  0x30(%rdi),%xmm8
movapd %xmm8,%xmm0
mulsd  %xmm2,%xmm0
mulsd  %xmm4,%xmm2
mulsd  %xmm5,%xmm4
mulsd  %xmm3,%xmm5
mulsd  %xmm1,%xmm3
movsd  0x40(%rdi),%xmm7
movsd  0x10(%rdi),%xmm6
mulsd  %xmm6,%xmm4
mulsd  %xmm7,%xmm3
addsd  %xmm4,%xmm3
movsd  0x28(%rdi),%xmm4
mulsd  %xmm4,%xmm0
addsd  %xmm3,%xmm0
mulsd  %xmm4,%xmm5
subsd  %xmm5,%xmm0
mulsd  %xmm7,%xmm2
subsd  %xmm2,%xmm0
mulsd  %xmm8,%xmm1
mulsd  %xmm6,%xmm1
subsd  %xmm1,%xmm0
ret

LLVM IR (-O0):
define double @det3x3(double* %0) {
%2 = alloca double*
%3 = alloca double*
%4 = alloca double*
%5 = alloca double*
%6 = alloca double*
%7 = alloca double*
%8 = alloca double*
%9 = alloca double*
%10 = alloca double*
%11 = alloca double*
store double* %0, double** %2
%12 = load double*, double** %2
%13 = getelementptr inbounds double, double* %12, i32 1
store double* %13, double** %2
store double* %12, double** %3
%14 = load double*, double** %2
%15 = getelementptr inbounds double, double* %14, i32 1
store double* %15, double** %2
store double* %14, double** %4
%16 = load double*, double** %2
%17 = getelementptr inbounds double, double* %16, i32 1
store double* %17, double** %2
store double* %16, double** %5
%18 = load double*, double** %2
%19 = getelementptr inbounds double, double* %18, i32 1
store double* %19, double** %2
store double* %18, double** %6
%20 = load double*, double** %2
%21 = getelementptr inbounds double, double* %20, i32 1
store double* %21, double** %2
store double* %20, double** %7
%22 = load double*, double** %2
%23 = getelementptr inbounds double, double* %22, i32 1
store double* %23, double** %2
store double* %22, double** %8
%24 = load double*, double** %2
%25 = getelementptr inbounds double, double* %24, i32 1
store double* %25, double** %2
store double* %24, double** %9
%26 = load double*, double** %2
%27 = getelementptr inbounds double, double* %26, i32 1
store double* %27, double** %2
store double* %26, double** %10
%28 = load double*, double** %2
%29 = getelementptr inbounds double, double* %28, i32 1
store double* %29, double** %2
store double* %28, double** %11
%30 = load double*, double** %3
%31 = load double, double* %30
%32 = load double*, double** %7
%33 = load double, double* %32
%34 = fmul double %31, %33
%35 = load double*, double** %11
%36 = load double, double* %35
%37 = load double*, double** %6
%38 = load double, double* %37
%39 = load double*, double** %10
%40 = load double, double* %39
%41 = fmul double %38, %40
%42 = load double*, double** %5
%43 = load double, double* %42
%44 = fmul double %41, %43
%45 = call double @llvm.fmuladd.f64(double %34, double %36, double %44)
%46 = load double*, double** %9
%47 = load double, double* %46
%48 = load double*, double** %4
%49 = load double, double* %48
%50 = fmul double %47, %49
%51 = load double*, double** %8
%52 = load double, double* %51
%53 = call double @llvm.fmuladd.f64(double %50, double %52, double %45)
%54 = load double*, double** %3
%55 = load double, double* %54
%56 = load double*, double** %10
%57 = load double, double* %56
%58 = fmul double %55, %57
%59 = load double*, double** %8
%60 = load double, double* %59
%61 = fneg double %58
%62 = call double @llvm.fmuladd.f64(double %61, double %60, double %53)
%63 = load double*, double** %6
%64 = load double, double* %63
%65 = load double*, double** %4
%66 = load double, double* %65
%67 = fmul double %64, %66
%68 = load double*, double** %11
%69 = load double, double* %68
%70 = fneg double %67
%71 = call double @llvm.fmuladd.f64(double %70, double %69, double %62)
%72 = load double*, double** %9
%73 = load double, double* %72
%74 = load double*, double** %7
%75 = load double, double* %74
%76 = fmul double %73, %75
%77 = load double*, double** %5
%78 = load double, double* %77
%79 = fneg double %76
%80 = call double @llvm.fmuladd.f64(double %79, double %78, double %71)
ret double %80
}

LLVM IR (-O2):
define double @det3x3(double* nocapture %0) {
%2 = getelementptr inbounds double, double* %0, i64 1
%3 = getelementptr inbounds double, double* %0, i64 2
%4 = getelementptr inbounds double, double* %0, i64 3
%5 = getelementptr inbounds double, double* %0, i64 4
%6 = getelementptr inbounds double, double* %0, i64 5
%7 = getelementptr inbounds double, double* %0, i64 6
%8 = getelementptr inbounds double, double* %0, i64 7
%9 = getelementptr inbounds double, double* %0, i64 8
%10 = load double, double* %0
%11 = load double, double* %5
%12 = fmul double %10, %11
%13 = load double, double* %9
%14 = load double, double* %4
%15 = load double, double* %8
%16 = fmul double %14, %15
%17 = load double, double* %3
%18 = fmul double %16, %17
%19 = tail call double @llvm.fmuladd.f64(double %12, double %13, double %18)
%20 = load double, double* %7
%21 = load double, double* %2
%22 = fmul double %20, %21
%23 = load double, double* %6
%24 = tail call double @llvm.fmuladd.f64(double %22, double %23, double %19)
%25 = fneg double %10
%26 = fmul double %15, %25
%27 = tail call double @llvm.fmuladd.f64(double %26, double %23, double %24)
%28 = fneg double %14
%29 = fmul double %21, %28
%30 = tail call double @llvm.fmuladd.f64(double %29, double %13, double %27)
%31 = fneg double %20
%32 = fmul double %11, %31
%33 = tail call double @llvm.fmuladd.f64(double %32, double %17, double %30)
ret double %33
}