double distance_sq(double *p1, double *p2) {
  double tmp, d2;
  tmp = p1[0] - p2[0];
  d2 = tmp * tmp;
  tmp = p1[1] - p2[1];
  d2 += tmp * tmp;
  tmp = p1[2] - p2[2];
  d2 += tmp * tmp;
  return d2;
}


x86 assembly (clang, -O0):
<distance_sq>:
push   %rbp
mov    %rsp,%rbp
mov    %rdi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
mov    -0x8(%rbp),%rax
movsd  (%rax),%xmm0
mov    -0x10(%rbp),%rax
subsd  (%rax),%xmm0
movsd  %xmm0,-0x18(%rbp)
movsd  -0x18(%rbp),%xmm0
mulsd  -0x18(%rbp),%xmm0
movsd  %xmm0,-0x20(%rbp)
mov    -0x8(%rbp),%rax
movsd  0x8(%rax),%xmm0
mov    -0x10(%rbp),%rax
subsd  0x8(%rax),%xmm0
movsd  %xmm0,-0x18(%rbp)
movsd  -0x18(%rbp),%xmm0
movsd  -0x18(%rbp),%xmm2
movsd  -0x20(%rbp),%xmm1
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  %xmm0,-0x20(%rbp)
mov    -0x8(%rbp),%rax
movsd  0x10(%rax),%xmm0
mov    -0x10(%rbp),%rax
subsd  0x10(%rax),%xmm0
movsd  %xmm0,-0x18(%rbp)
movsd  -0x18(%rbp),%xmm0
movsd  -0x18(%rbp),%xmm2
movsd  -0x20(%rbp),%xmm1
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  %xmm0,-0x20(%rbp)
movsd  -0x20(%rbp),%xmm0
pop    %rbp
ret

x86 assembly (clang, -O2):
<distance_sq>:
movsd  (%rdi),%xmm0
movsd  0x8(%rdi),%xmm1
subsd  (%rsi),%xmm0
subsd  0x8(%rsi),%xmm1
mulsd  %xmm0,%xmm0
mulsd  %xmm1,%xmm1
addsd  %xmm0,%xmm1
movsd  0x10(%rdi),%xmm0
subsd  0x10(%rsi),%xmm0
mulsd  %xmm0,%xmm0
addsd  %xmm1,%xmm0
ret

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

LLVM IR (-O2):
define double @distance_sq(double* nocapture %0, double* nocapture %1) {
%3 = load double, double* %0
%4 = load double, double* %1
%5 = fsub double %3, %4
%6 = fmul double %5, %5
%7 = getelementptr inbounds double, double* %0, i64 1
%8 = load double, double* %7
%9 = getelementptr inbounds double, double* %1, i64 1
%10 = load double, double* %9
%11 = fsub double %8, %10
%12 = tail call double @llvm.fmuladd.f64(double %11, double %11, double %6)
%13 = getelementptr inbounds double, double* %0, i64 2
%14 = load double, double* %13
%15 = getelementptr inbounds double, double* %1, i64 2
%16 = load double, double* %15
%17 = fsub double %14, %16
%18 = tail call double @llvm.fmuladd.f64(double %17, double %17, double %12)
ret double %18
}