fib in Dylan and the LLVM backend

fib.dylan

define function fib (n :: <integer>) => (fib :: <integer>)
  if (n < 2)
    n
  else
    fib(n - 1) + fib(n - 2)
  end if
end;

format-out("%d ", fib(50))

fib.ll

define fastcc %struct.MV @KfibVfibI(i8* %nF1, i8* %.next, i8* %.function) {
bb.entry:
  call void @llvm.dbg.value(metadata !{i8* %nF1}, i64 0, metadata !23) #0, !dbg !24
  %0 = ptrtoint i8* %nF1 to i64, !dbg !25
  %1 = icmp slt i64 %0, 9, !dbg !25
  %2 = select i1 %1, i8* bitcast (%KLbooleanGVKd* @KPtrueVKi to i8*), i8* bitcast (%KLbooleanGVKd* @KPfalseVKi to i8*), !dbg !25
  %3 = icmp ne i8* %2, bitcast (%KLbooleanGVKd* @KPfalseVKi to i8*), !dbg !25
  br i1 %3, label %4, label %5, !dbg !25

; <label>:4                                       ; preds = %bb.entry
  br label %34, !dbg !26

; <label>:5                                       ; preds = %bb.entry
  %6 = call { i64, i1 } @llvm.ssub.with.overflow.i64(i64 %0, i64 4) #0, !dbg !27
  %7 = extractvalue { i64, i1 } %6, 0, !dbg !27
  %8 = extractvalue { i64, i1 } %6, 1, !dbg !27
  br i1 %8, label %9, label %11, !dbg !27

; <label>:9                                       ; preds = %5
  %10 = tail call fastcc %struct.MV @Kmachine_word_overflowVKmI(i8* undef, i8* undef), !dbg !27
  unreachable, !dbg !27

; <label>:11                                      ; preds = %5
  %12 = inttoptr i64 %7 to i8*, !dbg !27
  %13 = call fastcc %struct.MV @KfibVfibI(i8* %12, i8* undef, i8* undef), !dbg !27
  %14 = extractvalue %struct.MV %13, 0, !dbg !27
  %15 = call { i64, i1 } @llvm.ssub.with.overflow.i64(i64 %0, i64 8) #0, !dbg !27
  %16 = extractvalue { i64, i1 } %15, 0, !dbg !27
  %17 = extractvalue { i64, i1 } %15, 1, !dbg !27
  br i1 %17, label %18, label %20, !dbg !27

; <label>:18                                      ; preds = %11
  %19 = tail call fastcc %struct.MV @Kmachine_word_overflowVKmI(i8* undef, i8* undef), !dbg !27
  unreachable, !dbg !27

; <label>:20                                      ; preds = %11
  %21 = inttoptr i64 %16 to i8*, !dbg !27
  %22 = call fastcc %struct.MV @KfibVfibI(i8* %21, i8* undef, i8* undef), !dbg !27
  %23 = extractvalue %struct.MV %22, 0, !dbg !27
  %24 = ptrtoint i8* %14 to i64, !dbg !27
  %25 = ptrtoint i8* %23 to i64, !dbg !27
  %26 = xor i64 %25, 1, !dbg !27
  %27 = call { i64, i1 } @llvm.sadd.with.overflow.i64(i64 %24, i64 %26) #0, !dbg !27
  %28 = extractvalue { i64, i1 } %27, 0, !dbg !27
  %29 = extractvalue { i64, i1 } %27, 1, !dbg !27
  br i1 %29, label %30, label %32, !dbg !27

; <label>:30                                      ; preds = %20
  %31 = tail call fastcc %struct.MV @Kmachine_word_overflowVKmI(i8* undef, i8* undef), !dbg !27
  unreachable, !dbg !27

; <label>:32                                      ; preds = %20
  %33 = inttoptr i64 %28 to i8*, !dbg !27
  br label %34, !dbg !27

; <label>:34                                      ; preds = %32, %4
  %35 = phi i8* [ %nF1, %4 ], [ %33, %32 ], !dbg !27
  %36 = insertvalue %struct.MV undef, i8* %35, 0, !dbg !24
  %37 = insertvalue %struct.MV %36, i8 1, 1, !dbg !24
  ret %struct.MV %37, !dbg !24
}

fib.S

libfib.dylib`KfibVfibI:
    0x100003e40 <+0>:  pushq  %rbp
    0x100003e41 <+1>:  movq   %rsp, %rbp
    0x100003e44 <+4>:  pushq  %r14
    0x100003e46 <+6>:  pushq  %rbx
    0x100003e47 <+7>:  movq   %rdi, %rbx
    0x100003e4a <+10>: cmpq   $0x9, %rbx
    0x100003e4e <+14>: jl     0x100003e7b               ; <+59> at fib.dylan:10
    0x100003e50 <+16>: movq   %rbx, %rdi
    0x100003e53 <+19>: subq   $0x4, %rdi
    0x100003e57 <+23>: jo     0x100003e85               ; <+69> at fib.dylan:10
    0x100003e59 <+25>: callq  0x100003e40               ; <+0> at fib.dylan:6
->  0x100003e5e <+30>: movq   %rax, %r14
    0x100003e61 <+33>: subq   $0x8, %rbx
    0x100003e65 <+37>: jo     0x100003e85               ; <+69> at fib.dylan:10
    0x100003e67 <+39>: movq   %rbx, %rdi
    0x100003e6a <+42>: callq  0x100003e40               ; <+0> at fib.dylan:6
    0x100003e6f <+47>: xorq   $0x1, %rax
    0x100003e73 <+51>: addq   %rax, %r14
    0x100003e76 <+54>: jo     0x100003e85               ; <+69> at fib.dylan:10
    0x100003e78 <+56>: movq   %r14, %rbx
    0x100003e7b <+59>: movb   $0x1, %dl
    0x100003e7d <+61>: movq   %rbx, %rax
    0x100003e80 <+64>: popq   %rbx
    0x100003e81 <+65>: popq   %r14
    0x100003e83 <+67>: popq   %rbp
    0x100003e84 <+68>: retq
    0x100003e85 <+69>: callq  0x100003ee2               ; symbol stub for: Kmachine_word_overflowVKmI
    0x100003e8a <+74>: nopw   (%rax,%rax)