void normalize(dir_vect) double *dir_vect;
{
  double sum;
  sum = sqrt(dir_vect[0] * dir_vect[0] + dir_vect[1] * dir_vect[1] +
             dir_vect[2] * dir_vect[2]);
  dir_vect[0] /= sum;
  dir_vect[1] /= sum;
  dir_vect[2] /= sum;
}


x86 assembly (clang, -O0):
<normalize>:
push   %rbp
mov    %rsp,%rbp
sub    $0x10,%rsp
mov    %rdi,-0x8(%rbp)
mov    -0x8(%rbp),%rax
movsd  (%rax),%xmm1
mov    -0x8(%rbp),%rax
movsd  (%rax),%xmm2
mov    -0x8(%rbp),%rax
movsd  0x8(%rax),%xmm0
mov    -0x8(%rbp),%rax
mulsd  0x8(%rax),%xmm0
mulsd  %xmm2,%xmm1
addsd  %xmm0,%xmm1
mov    -0x8(%rbp),%rax
movsd  0x10(%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  0x10(%rax),%xmm2
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
call   1030 <sqrt@plt>
movsd  %xmm0,-0x10(%rbp)
movsd  -0x10(%rbp),%xmm1
mov    -0x8(%rbp),%rax
movsd  (%rax),%xmm0
divsd  %xmm1,%xmm0
movsd  %xmm0,(%rax)
movsd  -0x10(%rbp),%xmm1
mov    -0x8(%rbp),%rax
movsd  0x8(%rax),%xmm0
divsd  %xmm1,%xmm0
movsd  %xmm0,0x8(%rax)
movsd  -0x10(%rbp),%xmm1
mov    -0x8(%rbp),%rax
movsd  0x10(%rax),%xmm0
divsd  %xmm1,%xmm0
movsd  %xmm0,0x10(%rax)
add    $0x10,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<normalize>:
push   %rbx
mov    %rdi,%rbx
movsd  (%rdi),%xmm1
movsd  0x8(%rdi),%xmm0
mulsd  %xmm0,%xmm0
mulsd  %xmm1,%xmm1
addsd  %xmm0,%xmm1
movsd  0x10(%rdi),%xmm0
mulsd  %xmm0,%xmm0
addsd  %xmm1,%xmm0
xorpd  %xmm1,%xmm1
ucomisd %xmm1,%xmm0
jb     1146 <normalize+0x36>
sqrtsd %xmm0,%xmm0
jmp    114b <normalize+0x3b>
call   1030 <sqrt@plt>
movupd (%rbx),%xmm1
movapd %xmm0,%xmm2
unpcklpd %xmm0,%xmm2
divpd  %xmm2,%xmm1
movupd %xmm1,(%rbx)
movsd  0x10(%rbx),%xmm1
divsd  %xmm0,%xmm1
movsd  %xmm1,0x10(%rbx)
pop    %rbx
ret

LLVM IR (-O0):
define void @normalize(double* %0) {
%2 = alloca double*
%3 = alloca double
store double* %0, double** %2
%4 = load double*, double** %2
%5 = getelementptr inbounds double, double* %4, i64 0
%6 = load double, double* %5
%7 = load double*, double** %2
%8 = getelementptr inbounds double, double* %7, i64 0
%9 = load double, double* %8
%10 = load double*, double** %2
%11 = getelementptr inbounds double, double* %10, i64 1
%12 = load double, double* %11
%13 = load double*, double** %2
%14 = getelementptr inbounds double, double* %13, i64 1
%15 = load double, double* %14
%16 = fmul double %12, %15
%17 = call double @llvm.fmuladd.f64(double %6, double %9, double %16)
%18 = load double*, double** %2
%19 = getelementptr inbounds double, double* %18, i64 2
%20 = load double, double* %19
%21 = load double*, double** %2
%22 = getelementptr inbounds double, double* %21, i64 2
%23 = load double, double* %22
%24 = call double @llvm.fmuladd.f64(double %20, double %23, double %17)
%25 = call double @sqrt(double %24)
store double %25, double* %3
%26 = load double, double* %3
%27 = load double*, double** %2
%28 = getelementptr inbounds double, double* %27, i64 0
%29 = load double, double* %28
%30 = fdiv double %29, %26
store double %30, double* %28
%31 = load double, double* %3
%32 = load double*, double** %2
%33 = getelementptr inbounds double, double* %32, i64 1
%34 = load double, double* %33
%35 = fdiv double %34, %31
store double %35, double* %33
%36 = load double, double* %3
%37 = load double*, double** %2
%38 = getelementptr inbounds double, double* %37, i64 2
%39 = load double, double* %38
%40 = fdiv double %39, %36
store double %40, double* %38
ret void
}

LLVM IR (-O2):
define void @normalize(double* nocapture %0) {
%2 = load double, double* %0
%3 = getelementptr inbounds double, double* %0, i64 1
%4 = load double, double* %3
%5 = fmul double %4, %4
%6 = tail call double @llvm.fmuladd.f64(double %2, double %2, double %5)
%7 = getelementptr inbounds double, double* %0, i64 2
%8 = load double, double* %7
%9 = tail call double @llvm.fmuladd.f64(double %8, double %8, double %6)
%10 = tail call double @sqrt(double %9)
%11 = bitcast double* %0 to <2 x double>*
%12 = load <2 x double>, <2 x double>* %11
%13 = insertelement <2 x double> poison, double %10, i64 0
%14 = shufflevector <2 x double> %13, <2 x double> poison, <2 x i32> zeroinitializer
%15 = fdiv <2 x double> %12, %14
%16 = bitcast double* %0 to <2 x double>*
store <2 x double> %15, <2 x double>* %16
%17 = load double, double* %7
%18 = fdiv double %17, %10
store double %18, double* %7
ret void
}