LLVM wizardry

generated_llvm

julia> code_llvm(g, (Int,))

define i64 @julia_g_20191(i64) {
top:
  %1 = icmp sgt i64 %0, 0, !dbg !8
  br i1 %1, label %L.preheader, label %L3, !dbg !8

L.preheader:                                      ; preds = %top
  %2 = add i64 %0, -1, !dbg !8
  %3 = zext i64 %2 to i65
  %4 = add i64 %0, -2, !dbg !8
  %5 = zext i64 %4 to i65
  %6 = mul i65 %3, %5, !dbg !8
  %7 = add i64 %0, -3, !dbg !8
  %8 = zext i64 %7 to i65
  %9 = mul i65 %6, %8, !dbg !8
  %10 = lshr i65 %9, 1, !dbg !8
  %11 = trunc i65 %10 to i64
  %12 = mul i64 %11, 6148914691236517206, !dbg !8
  %13 = mul i64 %0, 6, !dbg !8
  %14 = add i64 %12, %13, !dbg !8
  %15 = lshr i65 %6, 1, !dbg !8
  %16 = trunc i65 %15 to i64
  %17 = mul i64 %16, 6, !dbg !8
  %18 = add i64 %14, %17, !dbg !8
  %19 = add i64 %18, -4, !dbg !8
  br label %L3

L3:                                               ; preds = %L.preheader, %top
  %tot.1 = phi i64 [ 0, %top ], [ %19, %L.preheader ]
  ret i64 %tot.1, !dbg !9
}

generated_machine_code

julia> code_native(g, (Int,))
	.text
Filename: none
Source line: 0
	push	rbp
	mov	rbp, rsp
	xor	eax, eax
Source line: 3
	test	rdi, rdi
	jle	72
	lea	rax, qword ptr [rdi - 1]
	lea	rcx, qword ptr [rdi - 2]
	mul	rcx
	mov	r8, rax
	mov	rsi, rdx
	lea	rdx, qword ptr [rdi - 3]
	mov	ecx, edx
	imul	ecx, esi
	mul	rdx
	add	edx, ecx
	shld	rdx, rax, 63
	movabs	rax, 6148914691236517206
	imul	rax, rdx
	lea	rcx, qword ptr [rdi + 2*rdi]
	lea	rax, qword ptr [rax + 2*rcx]
	shld	rsi, r8, 63
	lea	rcx, qword ptr [rsi + 2*rsi]
	lea	rax, qword ptr [rax + 2*rcx - 4]
Source line: 6
	pop	rbp
	ret

poc.jl

f(n) = n*n + n

function g(n)
    tot = zero(n)
    for i in 1:n
        tot += f(i)
    end
    tot
end

@time g(10000000) # wtf?

code_native(g, (Int,)) # How does it do this?