double xatan(double arg) {
  double argsq;
  double value;
  argsq = arg * arg;
  value = ((((0.161536412982230e2 * argsq + 0.268425481955040e3) * argsq +
             0.115302935154049e4) *
                argsq +
            0.178040631643320e4) *
               argsq +
           0.896785974036639e3);
  value =
      value /
      (((((argsq + 0.589569705084446e2) * argsq + 0.536265374031215e3) * argsq +
         0.166678381488163e4) *
            argsq +
        0.207933497444541e4) *
           argsq +
       0.896785974036639e3);
  return (value * arg);
}


x86 assembly (clang, -O0):
<xatan>:
push   %rbp
mov    %rsp,%rbp
movsd  %xmm0,-0x8(%rbp)
movsd  -0x8(%rbp),%xmm0
mulsd  -0x8(%rbp),%xmm0
movsd  %xmm0,-0x10(%rbp)
movsd  -0x10(%rbp),%xmm0
movsd  0xf13(%rip),%xmm1
mulsd  %xmm1,%xmm0
movsd  0xf0f(%rip),%xmm1
addsd  %xmm1,%xmm0
movsd  -0x10(%rbp),%xmm1
mulsd  %xmm1,%xmm0
movsd  0xeea(%rip),%xmm1
addsd  %xmm1,%xmm0
movsd  -0x10(%rbp),%xmm1
mulsd  %xmm1,%xmm0
movsd  0xecd(%rip),%xmm1
addsd  %xmm1,%xmm0
movsd  -0x10(%rbp),%xmm1
mulsd  %xmm1,%xmm0
movsd  0xe90(%rip),%xmm1
addsd  %xmm1,%xmm0
movsd  %xmm0,-0x18(%rbp)
movsd  -0x18(%rbp),%xmm0
movsd  0xe9a(%rip),%xmm1
addsd  -0x10(%rbp),%xmm1
movsd  -0x10(%rbp),%xmm2
mulsd  %xmm2,%xmm1
movsd  0xe7c(%rip),%xmm2
addsd  %xmm2,%xmm1
movsd  -0x10(%rbp),%xmm2
mulsd  %xmm2,%xmm1
movsd  0xe5f(%rip),%xmm2
addsd  %xmm2,%xmm1
movsd  -0x10(%rbp),%xmm2
mulsd  %xmm2,%xmm1
movsd  0xe42(%rip),%xmm2
addsd  %xmm2,%xmm1
movsd  -0x10(%rbp),%xmm2
mulsd  %xmm2,%xmm1
movsd  0xe25(%rip),%xmm2
addsd  %xmm2,%xmm1
divsd  %xmm1,%xmm0
movsd  %xmm0,-0x18(%rbp)
movsd  -0x18(%rbp),%xmm0
mulsd  -0x8(%rbp),%xmm0
pop    %rbp
ret

x86 assembly (clang, -O2):
<xatan>:
movapd %xmm0,%xmm1
mulsd  %xmm0,%xmm1
movsd  0xef0(%rip),%xmm2
addsd  %xmm1,%xmm2
movapd %xmm1,%xmm3
unpcklpd %xmm2,%xmm3
movapd 0xeec(%rip),%xmm2
unpcklpd %xmm1,%xmm2
mulpd  %xmm3,%xmm2
addpd  0xeec(%rip),%xmm2
unpcklpd %xmm1,%xmm1
mulpd  %xmm1,%xmm2
addpd  0xeec(%rip),%xmm2
mulpd  %xmm1,%xmm2
addpd  0xef0(%rip),%xmm2
mulpd  %xmm1,%xmm2
addpd  0xef4(%rip),%xmm2
movapd %xmm2,%xmm1
unpckhpd %xmm2,%xmm1
divsd  %xmm1,%xmm2
mulsd  %xmm2,%xmm0
ret

LLVM IR (-O0):
define double @xatan(double %0) {
%2 = alloca double
%3 = alloca double
%4 = alloca double
store double %0, double* %2
%5 = load double, double* %2
%6 = load double, double* %2
%7 = fmul double %5, %6
store double %7, double* %3
%8 = load double, double* %3
%9 = call double @llvm.fmuladd.f64(double 0x40302755093F2ECA, double %8, double 0x4070C6CEC62A9EF6)
%10 = load double, double* %3
%11 = call double @llvm.fmuladd.f64(double %9, double %10, double 0x4092041E0E5489F8)
%12 = load double, double* %3
%13 = call double @llvm.fmuladd.f64(double %11, double %12, double 0x409BD1A0116A41AF)
%14 = load double, double* %3
%15 = call double @llvm.fmuladd.f64(double %13, double %14, double 0x408C0649ACC176F5)
store double %15, double* %4
%16 = load double, double* %4
%17 = load double, double* %3
%18 = fadd double %17, 0x404D7A7E027680C6
%19 = load double, double* %3
%20 = call double @llvm.fmuladd.f64(double %18, double %19, double 0x4080C21F7C6B8A35)
%21 = load double, double* %3
%22 = call double @llvm.fmuladd.f64(double %20, double %21, double 0x409A0B22A05E4AE0)
%23 = load double, double* %3
%24 = call double @llvm.fmuladd.f64(double %22, double %23, double 0x40A03EAB81C54010)
%25 = load double, double* %3
%26 = call double @llvm.fmuladd.f64(double %24, double %25, double 0x408C0649ACC176F5)
%27 = fdiv double %16, %26
store double %27, double* %4
%28 = load double, double* %4
%29 = load double, double* %2
%30 = fmul double %28, %29
ret double %30
}

LLVM IR (-O2):
define double @xatan(double %0) {
%2 = fmul double %0, %0
%3 = fadd double %2, 0x404D7A7E027680C6
%4 = insertelement <2 x double> poison, double %2, i64 0
%5 = insertelement <2 x double> %4, double %3, i64 1
%6 = insertelement <2 x double> <double 0x40302755093F2ECA, double poison>, double %2, i64 1
%7 = call <2 x double> @llvm.fmuladd.v2f64(<2 x double> %5, <2 x double> %6, <2 x double> <double 0x4070C6CEC62A9EF6, double 0x4080C21F7C6B8A35>)
%8 = shufflevector <2 x double> %4, <2 x double> poison, <2 x i32> zeroinitializer
%9 = call <2 x double> @llvm.fmuladd.v2f64(<2 x double> %7, <2 x double> %8, <2 x double> <double 0x4092041E0E5489F8, double 0x409A0B22A05E4AE0>)
%10 = call <2 x double> @llvm.fmuladd.v2f64(<2 x double> %9, <2 x double> %8, <2 x double> <double 0x409BD1A0116A41AF, double 0x40A03EAB81C54010>)
%11 = call <2 x double> @llvm.fmuladd.v2f64(<2 x double> %10, <2 x double> %8, <2 x double> <double 0x408C0649ACC176F5, double 0x408C0649ACC176F5>)
%12 = extractelement <2 x double> %11, i64 0
%13 = extractelement <2 x double> %11, i64 1
%14 = fdiv double %12, %13
%15 = fmul double %14, %0
ret double %15
}