[LLVMdev] Broke my tail (call)

[Arnold Schwaighofer]

Hello Jon,

Yes you are right tail call optimization breaks for i1.

It breaks for the same reason it breaks when structs are returned.

Simple example

define fastcc i1 @i1test(i32, i32, i32, i32) {
  entry:
  %4 = tail call fastcc i1 @i1test( i32 %0, i32 %1, i32 %2, i32 %3)
  ret i1 %4
}

In the intermediate representation, the SelectionDAG, there is a node
that converts the result of i1test from a i8 to a i1. This should not
hinder tail call optimization. But since i don't detect this case
correctly tail calls are turned off.

A fix for this bug and the struct return bug is in svn (revision 67934).

regards
arnold
On Sat, Mar 28, 2009 at 6:16 AM, Jon Harrop <jon at ffconsultancy.com> wrote:
> I just noticed that altering my representation of the unit type also seems to
> break tail calls. Specifically, if I return the i1 or i8 types. Is that
> expected to break tail calls as well as returning structs? If so, when
> exactly can tail calls be relied upon?

Whenever i did not miss something ;). Sorry!