void addScaledVector(double *v, double *d, double s) {
  v[0] += d[0] * s;
  v[1] += d[1] * s;
  v[2] += d[2] * s;
}


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

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

LLVM IR (-O0):
define void @addScaledVector(double* %0, double* %1, double %2) {
%4 = alloca double*
%5 = alloca double*
%6 = alloca double
store double* %0, double** %4
store double* %1, double** %5
store double %2, double* %6
%7 = load double*, double** %5
%8 = getelementptr inbounds double, double* %7, i64 0
%9 = load double, double* %8
%10 = load double, double* %6
%11 = load double*, double** %4
%12 = getelementptr inbounds double, double* %11, i64 0
%13 = load double, double* %12
%14 = call double @llvm.fmuladd.f64(double %9, double %10, double %13)
store double %14, double* %12
%15 = load double*, double** %5
%16 = getelementptr inbounds double, double* %15, i64 1
%17 = load double, double* %16
%18 = load double, double* %6
%19 = load double*, double** %4
%20 = getelementptr inbounds double, double* %19, i64 1
%21 = load double, double* %20
%22 = call double @llvm.fmuladd.f64(double %17, double %18, double %21)
store double %22, double* %20
%23 = load double*, double** %5
%24 = getelementptr inbounds double, double* %23, i64 2
%25 = load double, double* %24
%26 = load double, double* %6
%27 = load double*, double** %4
%28 = getelementptr inbounds double, double* %27, i64 2
%29 = load double, double* %28
%30 = call double @llvm.fmuladd.f64(double %25, double %26, double %29)
store double %30, double* %28
ret void
}

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