void rkFehlbergStep(double (*f)(double, double), double (*fy)(double, double),
                    double t0, double y0, double h, int i, double *t,
                    double *y) {
  double k1, k2, k3, k4, k5, k6;
  k1 = h * (*f)(t0, y0);
  k2 = h * (*f)(t0 + 1.0 / 4.0 * h, y0 + 1.0 / 4.0 * h * (*fy)(t0, y0) * k1);
  k3 = h * (*f)(t0 + 3.0 / 8.0 * h,
                y0 + 3.0 / 32.0 * h * k1 + 9.0 / 32.0 * h * (*fy)(t0, y0) * k2);
  k4 = h * (*f)(t0 + 12.0 / 13.0 * h,
                y0 + 1932.0 / 2197.0 * h * k1 - 7200.0 / 2197.0 * h * k2 +
                    7296.0 / 2197.0 * h * (*fy)(t0, y0) * k4);
  k5 = h * (*f)(t0 + 1.0 * h, y0 + 439.0 / 216.0 * h * k1 - 8.0 * h * k2 +
                                  3680.0 / 513.0 * h * k3 -
                                  845 / 4104 * h * (*fy)(t0, y0) * k4);
  k6 = h * (*f)(t0 - 1.0 / 2.0 * h, y0 - 8.0 / 27.0 * h * k1 + 2.0 * h * k2 -
                                        3544.0 / 2565.0 * h * k3 +
                                        1859.0 / 4104.0 * h * k4 -
                                        11.0 / 40.0 * h * (*fy)(t0, y0) * k5);
  *t = t0 + h * i;
  *y = y0 + 25.0 / 216.0 * k1 + 0.0 * k2 + 1408.0 / 2565.0 * k3 +
       2197.0 / 4104.0 * k4 - 1.0 / 5.0 * k5 + 0.0 * k6;
}


x86 assembly (clang, -O0):
<rkFehlbergStep>:
push   %rbp
mov    %rsp,%rbp
sub    $0x140,%rsp
mov    %rdi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
movsd  %xmm0,-0x18(%rbp)
movsd  %xmm1,-0x20(%rbp)
movsd  %xmm2,-0x28(%rbp)
mov    %edx,-0x2c(%rbp)
mov    %rcx,-0x38(%rbp)
mov    %r8,-0x40(%rbp)
movsd  -0x28(%rbp),%xmm0
movsd  %xmm0,-0x140(%rbp)
ff
mov    -0x8(%rbp),%rax
movsd  -0x18(%rbp),%xmm0
movsd  -0x20(%rbp),%xmm1
call   *%rax
movaps %xmm0,%xmm1
movsd  -0x140(%rbp),%xmm0
ff
mulsd  %xmm1,%xmm0
movsd  %xmm0,-0x48(%rbp)
movsd  -0x28(%rbp),%xmm0
movsd  %xmm0,-0x118(%rbp)
ff
mov    -0x8(%rbp),%rax
mov    %rax,-0x128(%rbp)
movsd  -0x18(%rbp),%xmm1
movsd  -0x28(%rbp),%xmm0
movsd  0xf18(%rip),%xmm2
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  %xmm0,-0x120(%rbp)
ff
movsd  -0x20(%rbp),%xmm0
movsd  %xmm0,-0x130(%rbp)
ff
movsd  0xef3(%rip),%xmm0
mulsd  -0x28(%rbp),%xmm0
movsd  %xmm0,-0x138(%rbp)
ff
mov    -0x10(%rbp),%rax
movsd  -0x18(%rbp),%xmm0
movsd  -0x20(%rbp),%xmm1
call   *%rax
movsd  -0x138(%rbp),%xmm1
ff
movsd  -0x130(%rbp),%xmm2
ff
mov    -0x128(%rbp),%rax
movaps %xmm0,%xmm3
movsd  -0x120(%rbp),%xmm0
ff
mulsd  %xmm3,%xmm1
movsd  -0x48(%rbp),%xmm3
mulsd  %xmm3,%xmm1
addsd  %xmm2,%xmm1
call   *%rax
movaps %xmm0,%xmm1
movsd  -0x118(%rbp),%xmm0
ff
mulsd  %xmm1,%xmm0
movsd  %xmm0,-0x50(%rbp)
movsd  -0x28(%rbp),%xmm0
movsd  %xmm0,-0xf0(%rbp)
ff
mov    -0x8(%rbp),%rax
mov    %rax,-0x100(%rbp)
movsd  -0x18(%rbp),%xmm1
movsd  -0x28(%rbp),%xmm0
movsd  0xe5b(%rip),%xmm2
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  %xmm0,-0xf8(%rbp)
ff
movsd  -0x20(%rbp),%xmm1
movsd  0xe36(%rip),%xmm0
mulsd  -0x28(%rbp),%xmm0
movsd  -0x48(%rbp),%xmm2
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  %xmm0,-0x108(%rbp)
ff
movsd  0xe0c(%rip),%xmm0
mulsd  -0x28(%rbp),%xmm0
movsd  %xmm0,-0x110(%rbp)
ff
mov    -0x10(%rbp),%rax
movsd  -0x18(%rbp),%xmm0
movsd  -0x20(%rbp),%xmm1
call   *%rax
movsd  -0x110(%rbp),%xmm1
ff
movsd  -0x108(%rbp),%xmm2
ff
mov    -0x100(%rbp),%rax
movaps %xmm0,%xmm3
movsd  -0xf8(%rbp),%xmm0
ff
mulsd  %xmm3,%xmm1
movsd  -0x50(%rbp),%xmm3
mulsd  %xmm3,%xmm1
addsd  %xmm2,%xmm1
call   *%rax
movaps %xmm0,%xmm1
movsd  -0xf0(%rbp),%xmm0
ff
mulsd  %xmm1,%xmm0
movsd  %xmm0,-0x58(%rbp)
movsd  -0x28(%rbp),%xmm0
movsd  %xmm0,-0xc8(%rbp)
ff
mov    -0x8(%rbp),%rax
mov    %rax,-0xd8(%rbp)
movsd  -0x18(%rbp),%xmm1
movsd  -0x28(%rbp),%xmm0
movsd  0xd74(%rip),%xmm2
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  %xmm0,-0xd0(%rbp)
ff
movsd  -0x20(%rbp),%xmm0
movsd  0xd4f(%rip),%xmm1
mulsd  -0x28(%rbp),%xmm1
movsd  -0x48(%rbp),%xmm2
mulsd  %xmm2,%xmm1
addsd  %xmm0,%xmm1
movsd  0xd2d(%rip),%xmm0
mulsd  -0x28(%rbp),%xmm0
movsd  -0x50(%rbp),%xmm2
movq   %xmm0,%rax
movabs $0x8000000000000000,%rcx
xor    %rcx,%rax
movq   %rax,%xmm0
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  %xmm0,-0xe0(%rbp)
ff
movsd  0xcec(%rip),%xmm0
mulsd  -0x28(%rbp),%xmm0
movsd  %xmm0,-0xe8(%rbp)
ff
mov    -0x10(%rbp),%rax
movsd  -0x18(%rbp),%xmm0
movsd  -0x20(%rbp),%xmm1
call   *%rax
movsd  -0xe8(%rbp),%xmm1
ff
movsd  -0xe0(%rbp),%xmm2
ff
mov    -0xd8(%rbp),%rax
movaps %xmm0,%xmm3
movsd  -0xd0(%rbp),%xmm0
ff
mulsd  %xmm3,%xmm1
movsd  -0x60(%rbp),%xmm3
mulsd  %xmm3,%xmm1
addsd  %xmm2,%xmm1
call   *%rax
movaps %xmm0,%xmm1
movsd  -0xc8(%rbp),%xmm0
ff
mulsd  %xmm1,%xmm0
movsd  %xmm0,-0x60(%rbp)
movsd  -0x28(%rbp),%xmm0
movsd  %xmm0,-0xa0(%rbp)
ff
mov    -0x8(%rbp),%rax
mov    %rax,-0xb0(%rbp)
movsd  -0x18(%rbp),%xmm1
movsd  -0x28(%rbp),%xmm0
addsd  %xmm1,%xmm0
movsd  %xmm0,-0xa8(%rbp)
ff
movsd  -0x20(%rbp),%xmm1
movsd  0xc43(%rip),%xmm0
mulsd  -0x28(%rbp),%xmm0
movsd  -0x48(%rbp),%xmm2
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  0xc21(%rip),%xmm1
mulsd  -0x28(%rbp),%xmm1
movsd  -0x50(%rbp),%xmm2
movq   %xmm1,%rax
movabs $0x8000000000000000,%rcx
xor    %rcx,%rax
movq   %rax,%xmm1
mulsd  %xmm2,%xmm1
addsd  %xmm0,%xmm1
movsd  0xbe8(%rip),%xmm0
mulsd  -0x28(%rbp),%xmm0
movsd  -0x58(%rbp),%xmm2
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  %xmm0,-0xb8(%rbp)
ff
xorps  %xmm0,%xmm0
mulsd  -0x28(%rbp),%xmm0
movsd  %xmm0,-0xc0(%rbp)
ff
mov    -0x10(%rbp),%rax
movsd  -0x18(%rbp),%xmm0
movsd  -0x20(%rbp),%xmm1
call   *%rax
movsd  -0xc0(%rbp),%xmm1
ff
movsd  -0xb8(%rbp),%xmm2
ff
mov    -0xb0(%rbp),%rax
movaps %xmm0,%xmm3
movsd  -0xa8(%rbp),%xmm0
ff
mulsd  %xmm3,%xmm1
movsd  -0x60(%rbp),%xmm3
movq   %xmm1,%rcx
movabs $0x8000000000000000,%rdx
xor    %rdx,%rcx
movq   %rcx,%xmm1
mulsd  %xmm3,%xmm1
addsd  %xmm2,%xmm1
call   *%rax
movaps %xmm0,%xmm1
movsd  -0xa0(%rbp),%xmm0
ff
mulsd  %xmm1,%xmm0
movsd  %xmm0,-0x68(%rbp)
movsd  -0x28(%rbp),%xmm0
movsd  %xmm0,-0x78(%rbp)
mov    -0x8(%rbp),%rax
mov    %rax,-0x88(%rbp)
movsd  -0x18(%rbp),%xmm1
movsd  -0x28(%rbp),%xmm0
movsd  0xb1f(%rip),%xmm2
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  %xmm0,-0x80(%rbp)
movsd  -0x20(%rbp),%xmm0
movsd  0xafd(%rip),%xmm1
mulsd  -0x28(%rbp),%xmm1
movsd  -0x48(%rbp),%xmm2
movq   %xmm1,%rax
movabs $0x8000000000000000,%rcx
xor    %rcx,%rax
movq   %rax,%xmm1
mulsd  %xmm2,%xmm1
addsd  %xmm0,%xmm1
movsd  0xac4(%rip),%xmm0
mulsd  -0x28(%rbp),%xmm0
movsd  -0x50(%rbp),%xmm2
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  0xaa2(%rip),%xmm1
mulsd  -0x28(%rbp),%xmm1
movsd  -0x58(%rbp),%xmm2
movq   %xmm1,%rax
movabs $0x8000000000000000,%rcx
xor    %rcx,%rax
movq   %rax,%xmm1
mulsd  %xmm2,%xmm1
addsd  %xmm0,%xmm1
movsd  0xa69(%rip),%xmm0
mulsd  -0x28(%rbp),%xmm0
movsd  -0x60(%rbp),%xmm2
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  %xmm0,-0x90(%rbp)
ff
movsd  0xa3f(%rip),%xmm0
mulsd  -0x28(%rbp),%xmm0
movsd  %xmm0,-0x98(%rbp)
ff
mov    -0x10(%rbp),%rax
movsd  -0x18(%rbp),%xmm0
movsd  -0x20(%rbp),%xmm1
call   *%rax
movsd  -0x98(%rbp),%xmm1
ff
movsd  -0x90(%rbp),%xmm2
ff
mov    -0x88(%rbp),%rax
movaps %xmm0,%xmm3
movsd  -0x80(%rbp),%xmm0
mulsd  %xmm3,%xmm1
movsd  -0x68(%rbp),%xmm3
movq   %xmm1,%rcx
movabs $0x8000000000000000,%rdx
xor    %rdx,%rcx
movq   %rcx,%xmm1
mulsd  %xmm3,%xmm1
addsd  %xmm2,%xmm1
call   *%rax
movaps %xmm0,%xmm1
movsd  -0x78(%rbp),%xmm0
mulsd  %xmm1,%xmm0
movsd  %xmm0,-0x70(%rbp)
movsd  -0x18(%rbp),%xmm1
movsd  -0x28(%rbp),%xmm0
cvtsi2sdl -0x2c(%rbp),%xmm2
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
mov    -0x38(%rbp),%rax
movsd  %xmm0,(%rax)
movsd  -0x20(%rbp),%xmm0
movsd  -0x48(%rbp),%xmm1
movsd  0x98f(%rip),%xmm2
mulsd  %xmm2,%xmm1
addsd  %xmm0,%xmm1
movsd  -0x50(%rbp),%xmm0
xorps  %xmm2,%xmm2
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  -0x58(%rbp),%xmm1
movsd  0x962(%rip),%xmm2
mulsd  %xmm2,%xmm1
addsd  %xmm0,%xmm1
movsd  -0x60(%rbp),%xmm0
movsd  0x945(%rip),%xmm2
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  -0x68(%rbp),%xmm1
movsd  0x928(%rip),%xmm2
mulsd  %xmm2,%xmm1
addsd  %xmm0,%xmm1
movsd  -0x70(%rbp),%xmm0
xorps  %xmm2,%xmm2
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
mov    -0x40(%rbp),%rax
movsd  %xmm0,(%rax)
add    $0x140,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<rkFehlbergStep>:
push   %rbp
push   %r15
push   %r14
push   %r12
push   %rbx
sub    $0x50,%rsp
mov    %r8,%r14
mov    %rcx,%r15
mov    %edx,%r12d
movsd  %xmm2,(%rsp)
movsd  %xmm1,0x18(%rsp)
movsd  %xmm0,0x30(%rsp)
mov    %rsi,%rbp
mov    %rdi,%rbx
call   *%rdi
movsd  (%rsp),%xmm1
mulsd  %xmm1,%xmm0
movsd  %xmm0,0x38(%rsp)
movsd  0xebb(%rip),%xmm0
mulsd  %xmm1,%xmm0
movsd  %xmm0,0x10(%rsp)
movapd %xmm0,%xmm1
movsd  0x30(%rsp),%xmm0
addsd  %xmm0,%xmm1
movsd  %xmm1,0x28(%rsp)
movsd  0x18(%rsp),%xmm1
call   *%rbp
movsd  0x10(%rsp),%xmm1
mulsd  %xmm0,%xmm1
mulsd  0x38(%rsp),%xmm1
addsd  0x18(%rsp),%xmm1
movsd  0x28(%rsp),%xmm0
call   *%rbx
movsd  (%rsp),%xmm2
mulsd  %xmm2,%xmm0
movsd  %xmm0,0x28(%rsp)
movsd  0xe68(%rip),%xmm1
mulsd  %xmm2,%xmm1
movsd  0x30(%rsp),%xmm0
addsd  %xmm0,%xmm1
movsd  %xmm1,0x10(%rsp)
movsd  0xe54(%rip),%xmm3
mulsd  %xmm2,%xmm3
mulsd  0x38(%rsp),%xmm3
movsd  0x18(%rsp),%xmm1
addsd  %xmm1,%xmm3
movsd  %xmm3,0x8(%rsp)
movsd  0xe3a(%rip),%xmm3
mulsd  %xmm2,%xmm3
movsd  %xmm3,0x20(%rsp)
call   *%rbp
movsd  0x20(%rsp),%xmm1
mulsd  %xmm0,%xmm1
mulsd  0x28(%rsp),%xmm1
addsd  0x8(%rsp),%xmm1
movsd  0x10(%rsp),%xmm0
call   *%rbx
movsd  (%rsp),%xmm1
mulsd  %xmm1,%xmm0
movsd  %xmm0,0x10(%rsp)
movsd  0xe01(%rip),%xmm2
mulsd  %xmm1,%xmm2
movsd  0x30(%rsp),%xmm0
addsd  %xmm0,%xmm2
movsd  %xmm2,0x8(%rsp)
movsd  0x18(%rsp),%xmm1
call   *%rbp
movsd  0xde5(%rip),%xmm1
movsd  0x8(%rsp),%xmm0
call   *%rbx
movsd  (%rsp),%xmm3
mulsd  %xmm3,%xmm0
movsd  %xmm0,0x8(%rsp)
movsd  0x30(%rsp),%xmm0
movapd %xmm0,%xmm1
addsd  %xmm3,%xmm1
movsd  %xmm1,0x20(%rsp)
movsd  0xdba(%rip),%xmm4
mulsd  %xmm3,%xmm4
mulsd  0x38(%rsp),%xmm4
movsd  0x18(%rsp),%xmm1
addsd  %xmm1,%xmm4
movsd  0xda6(%rip),%xmm2
mulsd  %xmm3,%xmm2
mulsd  0x28(%rsp),%xmm2
addsd  %xmm4,%xmm2
movsd  0xd98(%rip),%xmm4
mulsd  %xmm3,%xmm4
mulsd  0x10(%rsp),%xmm4
addsd  %xmm2,%xmm4
movsd  %xmm4,0x40(%rsp)
call   *%rbp
movsd  0xd82(%rip),%xmm1
mulsd  (%rsp),%xmm1
mulsd  %xmm0,%xmm1
mulsd  0x8(%rsp),%xmm1
addsd  0x40(%rsp),%xmm1
movsd  0x20(%rsp),%xmm0
call   *%rbx
movsd  (%rsp),%xmm2
mulsd  %xmm2,%xmm0
movsd  %xmm0,0x20(%rsp)
movsd  0xd56(%rip),%xmm1
mulsd  %xmm2,%xmm1
movsd  0x30(%rsp),%xmm0
addsd  %xmm0,%xmm1
movsd  %xmm1,0x40(%rsp)
movsd  0xd42(%rip),%xmm4
mulsd  %xmm2,%xmm4
mulsd  0x38(%rsp),%xmm4
movsd  0x18(%rsp),%xmm1
addsd  %xmm1,%xmm4
movapd %xmm2,%xmm3
movapd %xmm2,%xmm5
addsd  %xmm2,%xmm3
mulsd  0x28(%rsp),%xmm3
addsd  %xmm4,%xmm3
movsd  0xd18(%rip),%xmm2
mulsd  %xmm5,%xmm2
mulsd  0x10(%rsp),%xmm2
addsd  %xmm3,%xmm2
movsd  0xd0a(%rip),%xmm3
mulsd  %xmm5,%xmm3
mulsd  0x8(%rsp),%xmm3
addsd  %xmm2,%xmm3
movsd  %xmm3,0x48(%rsp)
call   *%rbp
movsd  0xcf4(%rip),%xmm1
mulsd  (%rsp),%xmm1
mulsd  %xmm0,%xmm1
mulsd  0x20(%rsp),%xmm1
addsd  0x48(%rsp),%xmm1
movsd  0x40(%rsp),%xmm0
call   *%rbx
movsd  (%rsp),%xmm2
mulsd  %xmm2,%xmm0
xorps  %xmm1,%xmm1
cvtsi2sd %r12d,%xmm1
mulsd  %xmm2,%xmm1
addsd  0x30(%rsp),%xmm1
movsd  %xmm1,(%r15)
movsd  0x38(%rsp),%xmm1
mulsd  0xcb1(%rip),%xmm1
addsd  0x18(%rsp),%xmm1
movapd %xmm1,%xmm2
xorpd  %xmm1,%xmm1
movsd  0x28(%rsp),%xmm3
mulsd  %xmm1,%xmm3
addsd  %xmm2,%xmm3
movsd  0x10(%rsp),%xmm2
mulsd  0xc8f(%rip),%xmm2
movsd  0x8(%rsp),%xmm4
mulsd  0xc89(%rip),%xmm4
addsd  %xmm3,%xmm2
addsd  %xmm2,%xmm4
movsd  0x20(%rsp),%xmm2
mulsd  0xc7b(%rip),%xmm2
addsd  %xmm4,%xmm2
mulsd  %xmm1,%xmm0
addsd  %xmm2,%xmm0
movsd  %xmm0,(%r14)
add    $0x50,%rsp
pop    %rbx
pop    %r12
pop    %r14
pop    %r15
pop    %rbp
ret

LLVM IR (-O0):
define void @rkFehlbergStep(double (double, double)* %0, double (double, double)* %1, double %2, double %3, double %4, i32 %5, double* %6, double* %7) {
%9 = alloca double (double, double)*
%10 = alloca double (double, double)*
%11 = alloca double
%12 = alloca double
%13 = alloca double
%14 = alloca i32
%15 = alloca double*
%16 = alloca double*
%17 = alloca double
%18 = alloca double
%19 = alloca double
%20 = alloca double
%21 = alloca double
%22 = alloca double
store double (double, double)* %0, double (double, double)** %9
store double (double, double)* %1, double (double, double)** %10
store double %2, double* %11
store double %3, double* %12
store double %4, double* %13
store i32 %5, i32* %14
store double* %6, double** %15
store double* %7, double** %16
%23 = load double, double* %13
%24 = load double (double, double)*, double (double, double)** %9
%25 = load double, double* %11
%26 = load double, double* %12
%27 = call double %24(double %25, double %26)
%28 = fmul double %23, %27
store double %28, double* %17
%29 = load double, double* %13
%30 = load double (double, double)*, double (double, double)** %9
%31 = load double, double* %11
%32 = load double, double* %13
%33 = call double @llvm.fmuladd.f64(double 2.500000e-01, double %32, double %31)
%34 = load double, double* %12
%35 = load double, double* %13
%36 = fmul double 2.500000e-01, %35
%37 = load double (double, double)*, double (double, double)** %10
%38 = load double, double* %11
%39 = load double, double* %12
%40 = call double %37(double %38, double %39)
%41 = fmul double %36, %40
%42 = load double, double* %17
%43 = call double @llvm.fmuladd.f64(double %41, double %42, double %34)
%44 = call double %30(double %33, double %43)
%45 = fmul double %29, %44
store double %45, double* %18
%46 = load double, double* %13
%47 = load double (double, double)*, double (double, double)** %9
%48 = load double, double* %11
%49 = load double, double* %13
%50 = call double @llvm.fmuladd.f64(double 3.750000e-01, double %49, double %48)
%51 = load double, double* %12
%52 = load double, double* %13
%53 = fmul double 9.375000e-02, %52
%54 = load double, double* %17
%55 = call double @llvm.fmuladd.f64(double %53, double %54, double %51)
%56 = load double, double* %13
%57 = fmul double 2.812500e-01, %56
%58 = load double (double, double)*, double (double, double)** %10
%59 = load double, double* %11
%60 = load double, double* %12
%61 = call double %58(double %59, double %60)
%62 = fmul double %57, %61
%63 = load double, double* %18
%64 = call double @llvm.fmuladd.f64(double %62, double %63, double %55)
%65 = call double %47(double %50, double %64)
%66 = fmul double %46, %65
store double %66, double* %19
%67 = load double, double* %13
%68 = load double (double, double)*, double (double, double)** %9
%69 = load double, double* %11
%70 = load double, double* %13
%71 = call double @llvm.fmuladd.f64(double 0x3FED89D89D89D89E, double %70, double %69)
%72 = load double, double* %12
%73 = load double, double* %13
%74 = fmul double 0x3FEC23E39189614C, %73
%75 = load double, double* %17
%76 = call double @llvm.fmuladd.f64(double %74, double %75, double %72)
%77 = load double, double* %13
%78 = fmul double 0x400A37B2A108BD3C, %77
%79 = load double, double* %18
%80 = fneg double %78
%81 = call double @llvm.fmuladd.f64(double %80, double %79, double %76)
%82 = load double, double* %13
%83 = fmul double 0x400A912FE408DB10, %82
%84 = load double (double, double)*, double (double, double)** %10
%85 = load double, double* %11
%86 = load double, double* %12
%87 = call double %84(double %85, double %86)
%88 = fmul double %83, %87
%89 = load double, double* %20
%90 = call double @llvm.fmuladd.f64(double %88, double %89, double %81)
%91 = call double %68(double %71, double %90)
%92 = fmul double %67, %91
store double %92, double* %20
%93 = load double, double* %13
%94 = load double (double, double)*, double (double, double)** %9
%95 = load double, double* %11
%96 = load double, double* %13
%97 = call double @llvm.fmuladd.f64(double 1.000000e+00, double %96, double %95)
%98 = load double, double* %12
%99 = load double, double* %13
%100 = fmul double 0x4000425ED097B426, %99
%101 = load double, double* %17
%102 = call double @llvm.fmuladd.f64(double %100, double %101, double %98)
%103 = load double, double* %13
%104 = fmul double 8.000000e+00, %103
%105 = load double, double* %18
%106 = fneg double %104
%107 = call double @llvm.fmuladd.f64(double %106, double %105, double %102)
%108 = load double, double* %13
%109 = fmul double 0x401CB1A72C69CB1A, %108
%110 = load double, double* %19
%111 = call double @llvm.fmuladd.f64(double %109, double %110, double %107)
%112 = load double, double* %13
%113 = fmul double 0.000000e+00, %112
%114 = load double (double, double)*, double (double, double)** %10
%115 = load double, double* %11
%116 = load double, double* %12
%117 = call double %114(double %115, double %116)
%118 = fmul double %113, %117
%119 = load double, double* %20
%120 = fneg double %118
%121 = call double @llvm.fmuladd.f64(double %120, double %119, double %111)
%122 = call double %94(double %97, double %121)
%123 = fmul double %93, %122
store double %123, double* %21
%124 = load double, double* %13
%125 = load double (double, double)*, double (double, double)** %9
%126 = load double, double* %11
%127 = load double, double* %13
%128 = call double @llvm.fmuladd.f64(double -5.000000e-01, double %127, double %126)
%129 = load double, double* %12
%130 = load double, double* %13
%131 = fmul double 0x3FD2F684BDA12F68, %130
%132 = load double, double* %17
%133 = fneg double %131
%134 = call double @llvm.fmuladd.f64(double %133, double %132, double %129)
%135 = load double, double* %13
%136 = fmul double 2.000000e+00, %135
%137 = load double, double* %18
%138 = call double @llvm.fmuladd.f64(double %136, double %137, double %134)
%139 = load double, double* %13
%140 = fmul double 0x3FF61B58BA0961B6, %139
%141 = load double, double* %19
%142 = fneg double %140
%143 = call double @llvm.fmuladd.f64(double %142, double %141, double %138)
%144 = load double, double* %13
%145 = fmul double 0x3FDCFD813F604FD8, %144
%146 = load double, double* %20
%147 = call double @llvm.fmuladd.f64(double %145, double %146, double %143)
%148 = load double, double* %13
%149 = fmul double 2.750000e-01, %148
%150 = load double (double, double)*, double (double, double)** %10
%151 = load double, double* %11
%152 = load double, double* %12
%153 = call double %150(double %151, double %152)
%154 = fmul double %149, %153
%155 = load double, double* %21
%156 = fneg double %154
%157 = call double @llvm.fmuladd.f64(double %156, double %155, double %147)
%158 = call double %125(double %128, double %157)
%159 = fmul double %124, %158
store double %159, double* %22
%160 = load double, double* %11
%161 = load double, double* %13
%162 = load i32, i32* %14
%163 = sitofp i32 %162 to double
%164 = call double @llvm.fmuladd.f64(double %161, double %163, double %160)
%165 = load double*, double** %15
store double %164, double* %165
%166 = load double, double* %12
%167 = load double, double* %17
%168 = call double @llvm.fmuladd.f64(double 0x3FBDA12F684BDA13, double %167, double %166)
%169 = load double, double* %18
%170 = call double @llvm.fmuladd.f64(double 0.000000e+00, double %169, double %168)
%171 = load double, double* %19
%172 = call double @llvm.fmuladd.f64(double 0x3FE190D13101190D, double %171, double %170)
%173 = load double, double* %20
%174 = call double @llvm.fmuladd.f64(double 0x3FE1216F485BD217, double %173, double %172)
%175 = load double, double* %21
%176 = call double @llvm.fmuladd.f64(double -2.000000e-01, double %175, double %174)
%177 = load double, double* %22
%178 = call double @llvm.fmuladd.f64(double 0.000000e+00, double %177, double %176)
%179 = load double*, double** %16
store double %178, double* %179
ret void
}

LLVM IR (-O2):
define void @rkFehlbergStep(double (double, double)* nocapture %0, double (double, double)* nocapture %1, double %2, double %3, double %4, i32 %5, double* nocapture writeonly %6, double* nocapture writeonly %7) {
%9 = tail call double %0(double %2, double %3)
%10 = fmul double %9, %4
%11 = tail call double @llvm.fmuladd.f64(double %4, double 2.500000e-01, double %2)
%12 = fmul double %4, 2.500000e-01
%13 = tail call double %1(double %2, double %3)
%14 = fmul double %12, %13
%15 = tail call double @llvm.fmuladd.f64(double %14, double %10, double %3)
%16 = tail call double %0(double %11, double %15)
%17 = fmul double %16, %4
%18 = tail call double @llvm.fmuladd.f64(double %4, double 3.750000e-01, double %2)
%19 = fmul double %4, 9.375000e-02
%20 = tail call double @llvm.fmuladd.f64(double %19, double %10, double %3)
%21 = fmul double %4, 2.812500e-01
%22 = tail call double %1(double %2, double %3)
%23 = fmul double %21, %22
%24 = tail call double @llvm.fmuladd.f64(double %23, double %17, double %20)
%25 = tail call double %0(double %18, double %24)
%26 = fmul double %25, %4
%27 = tail call double @llvm.fmuladd.f64(double %4, double 0x3FED89D89D89D89E, double %2)
%28 = tail call double %1(double %2, double %3)
%29 = tail call double %0(double %27, double 0x7FF8000000000000)
%30 = fmul double %29, %4
%31 = fadd double %2, %4
%32 = fmul double %4, 0x4000425ED097B426
%33 = tail call double @llvm.fmuladd.f64(double %32, double %10, double %3)
%34 = fmul double %4, -8.000000e+00
%35 = tail call double @llvm.fmuladd.f64(double %34, double %17, double %33)
%36 = fmul double %4, 0x401CB1A72C69CB1A
%37 = tail call double @llvm.fmuladd.f64(double %36, double %26, double %35)
%38 = tail call double %1(double %2, double %3)
%39 = fmul double %4, -0.000000e+00
%40 = fmul double %39, %38
%41 = tail call double @llvm.fmuladd.f64(double %40, double %30, double %37)
%42 = tail call double %0(double %31, double %41)
%43 = fmul double %42, %4
%44 = tail call double @llvm.fmuladd.f64(double %4, double -5.000000e-01, double %2)
%45 = fmul double %4, 0xBFD2F684BDA12F68
%46 = tail call double @llvm.fmuladd.f64(double %45, double %10, double %3)
%47 = fmul double %4, 2.000000e+00
%48 = tail call double @llvm.fmuladd.f64(double %47, double %17, double %46)
%49 = fmul double %4, 0xBFF61B58BA0961B6
%50 = tail call double @llvm.fmuladd.f64(double %49, double %26, double %48)
%51 = fmul double %4, 0x3FDCFD813F604FD8
%52 = tail call double @llvm.fmuladd.f64(double %51, double %30, double %50)
%53 = tail call double %1(double %2, double %3)
%54 = fmul double %4, -2.750000e-01
%55 = fmul double %54, %53
%56 = tail call double @llvm.fmuladd.f64(double %55, double %43, double %52)
%57 = tail call double %0(double %44, double %56)
%58 = fmul double %57, %4
%59 = sitofp i32 %5 to double
%60 = tail call double @llvm.fmuladd.f64(double %4, double %59, double %2)
store double %60, double* %6
%61 = tail call double @llvm.fmuladd.f64(double %10, double 0x3FBDA12F684BDA13, double %3)
%62 = tail call double @llvm.fmuladd.f64(double %17, double 0.000000e+00, double %61)
%63 = tail call double @llvm.fmuladd.f64(double %26, double 0x3FE190D13101190D, double %62)
%64 = tail call double @llvm.fmuladd.f64(double %30, double 0x3FE1216F485BD217, double %63)
%65 = tail call double @llvm.fmuladd.f64(double %43, double -2.000000e-01, double %64)
%66 = tail call double @llvm.fmuladd.f64(double %58, double 0.000000e+00, double %65)
store double %66, double* %7
ret void
}