void multbyP(double *lhs, double *rhs) {
  lhs[0] = rhs[0] * (2);
  lhs[1] = rhs[1] * (2);
  lhs[2] = rhs[2] * (2);
  lhs[3] = 0;
  lhs[4] = 0;
  lhs[5] = 0;
  lhs[6] = 0;
  lhs[7] = 0;
  lhs[8] = 0;
  lhs[9] = 0;
  lhs[10] = 0;
}


x86 assembly (clang, -O0):
<multbyP>:
push   %rbp
mov    %rsp,%rbp
mov    %rdi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
mov    -0x10(%rbp),%rax
movsd  0xee8(%rip),%xmm0
mulsd  (%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  %xmm0,(%rax)
mov    -0x10(%rbp),%rax
movsd  0xed0(%rip),%xmm0
mulsd  0x8(%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  %xmm0,0x8(%rax)
mov    -0x10(%rbp),%rax
movsd  0xeb6(%rip),%xmm0
mulsd  0x10(%rax),%xmm0
mov    -0x8(%rbp),%rax
movsd  %xmm0,0x10(%rax)
mov    -0x8(%rbp),%rax
xorps  %xmm0,%xmm0
movsd  %xmm0,0x18(%rax)
mov    -0x8(%rbp),%rax
xorps  %xmm0,%xmm0
movsd  %xmm0,0x20(%rax)
mov    -0x8(%rbp),%rax
xorps  %xmm0,%xmm0
movsd  %xmm0,0x28(%rax)
mov    -0x8(%rbp),%rax
xorps  %xmm0,%xmm0
movsd  %xmm0,0x30(%rax)
mov    -0x8(%rbp),%rax
xorps  %xmm0,%xmm0
movsd  %xmm0,0x38(%rax)
mov    -0x8(%rbp),%rax
xorps  %xmm0,%xmm0
movsd  %xmm0,0x40(%rax)
mov    -0x8(%rbp),%rax
xorps  %xmm0,%xmm0
movsd  %xmm0,0x48(%rax)
mov    -0x8(%rbp),%rax
xorps  %xmm0,%xmm0
movsd  %xmm0,0x50(%rax)
pop    %rbp
ret

x86 assembly (clang, -O2):
<multbyP>:
movsd  (%rsi),%xmm0
addsd  %xmm0,%xmm0
movsd  %xmm0,(%rdi)
movsd  0x8(%rsi),%xmm0
addsd  %xmm0,%xmm0
movsd  %xmm0,0x8(%rdi)
movsd  0x10(%rsi),%xmm0
addsd  %xmm0,%xmm0
movsd  %xmm0,0x10(%rdi)
xorpd  %xmm0,%xmm0
movupd %xmm0,0x18(%rdi)
movupd %xmm0,0x28(%rdi)
movupd %xmm0,0x38(%rdi)
movupd %xmm0,0x48(%rdi)
ret

LLVM IR (-O0):
define void @multbyP(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 = fmul double %7, 2.000000e+00
%9 = load double*, double** %3
%10 = getelementptr inbounds double, double* %9, i64 0
store double %8, double* %10
%11 = load double*, double** %4
%12 = getelementptr inbounds double, double* %11, i64 1
%13 = load double, double* %12
%14 = fmul double %13, 2.000000e+00
%15 = load double*, double** %3
%16 = getelementptr inbounds double, double* %15, i64 1
store double %14, double* %16
%17 = load double*, double** %4
%18 = getelementptr inbounds double, double* %17, i64 2
%19 = load double, double* %18
%20 = fmul double %19, 2.000000e+00
%21 = load double*, double** %3
%22 = getelementptr inbounds double, double* %21, i64 2
store double %20, double* %22
%23 = load double*, double** %3
%24 = getelementptr inbounds double, double* %23, i64 3
store double 0.000000e+00, double* %24
%25 = load double*, double** %3
%26 = getelementptr inbounds double, double* %25, i64 4
store double 0.000000e+00, double* %26
%27 = load double*, double** %3
%28 = getelementptr inbounds double, double* %27, i64 5
store double 0.000000e+00, double* %28
%29 = load double*, double** %3
%30 = getelementptr inbounds double, double* %29, i64 6
store double 0.000000e+00, double* %30
%31 = load double*, double** %3
%32 = getelementptr inbounds double, double* %31, i64 7
store double 0.000000e+00, double* %32
%33 = load double*, double** %3
%34 = getelementptr inbounds double, double* %33, i64 8
store double 0.000000e+00, double* %34
%35 = load double*, double** %3
%36 = getelementptr inbounds double, double* %35, i64 9
store double 0.000000e+00, double* %36
%37 = load double*, double** %3
%38 = getelementptr inbounds double, double* %37, i64 10
store double 0.000000e+00, double* %38
ret void
}

LLVM IR (-O2):
define void @multbyP(double* nocapture writeonly %0, double* nocapture %1) {
%3 = load double, double* %1
%4 = fmul double %3, 2.000000e+00
store double %4, double* %0
%5 = getelementptr inbounds double, double* %1, i64 1
%6 = load double, double* %5
%7 = fmul double %6, 2.000000e+00
%8 = getelementptr inbounds double, double* %0, i64 1
store double %7, double* %8
%9 = getelementptr inbounds double, double* %1, i64 2
%10 = load double, double* %9
%11 = fmul double %10, 2.000000e+00
%12 = getelementptr inbounds double, double* %0, i64 2
store double %11, double* %12
%13 = getelementptr inbounds double, double* %0, i64 3
%14 = bitcast double* %13 to i8*
ret void
}