[LLVMdev] Query on optimization and tail call.

[Eli Friedman]

On Tue, Jun 10, 2008 at 11:07 PM, Mahadevan R <mdevan.foobar at gmail.com> wrote:
> int sum(int n)
> {
>    return n + sum(n-1);
> }
>
> it generates this:
>
> define i32 @sum(i32 %n) nounwind  {
> entry:
>        %tmp2 = add i32 %n, -1          ; <i32> [#uses=1]
>        %tmp3 = tail call i32 @sum( i32 %tmp2 ) nounwind                ; <i32> [#uses=1]
>        %tmp5 = add i32 %tmp3, %n               ; <i32> [#uses=1]
>        ret i32 %tmp5
> }
>
> Why isn't llvm able to eliminate the tail call in this (simpler) case?

I haven't checked, but this is probably a case that wasn't worth
handling, since it's an infinite loop.

-Eli