Performance issue re: simple loop

The runtime of the following code actually decreases if the number 2147483647 (2^31^-1) is increased to 2147483648 (2^31^). In addition, adding "module Main where" at the top of the file improves performance to the fast case regardless of what number is picked.

f n = go 1 0 where
  go i c = if i == n then c + i else go (i+1) (c+i)

main = print $ f (2147483647 :: Int) 

I've attached two dumps from ghc-core, core7 is the 2147483647 case and core8 is the 2147483648 case, however the main differences are below:

2147483647 case:

_c3Qg:
	cmpq $2147483647,%r14
	jne _c3Q9
_c3Qa:
	leaq 2147483647(%rsi),%rbx
	jmp *(%rbp)
_c3Q9:
	addq %r14,%rsi
	incq %r14
	jmp _c3Qg

2147483648 case:

_c3Qg:
	movl $2147483648,%eax
	cmpq %rax,%r14
	jne _c3Q9
_c3Qa:
	movl $2147483648,%eax
	movq %rsi,%rbx
	addq %rax,%rbx
	jmp *(%rbp)
_c3Q9:
	addq %r14,%rsi
	incq %r14
	jmp _c3Qg

Despite the extra instructions, the latter approach seems faster for my PC.