rtl_loop_init vs try_redirect_by_replacing_jump vs simple jumps

[Andrew Pinski]

> 
> On 5/23/06, DJ Delorie <dj@redhat.com> wrote:
> >
> > > You're misunderstanding how this code works.  In cfglayout mode,
> > > there is no "order" in the basic blocks such that
> > > BLOCK_FOR_INSN(NEXT_INSN(BB_END(BB)) ) == BB->next_bb. This means
> > > that you can fall through to other blocks than next_bb.
> >
> > Thanks for the tip, I figured out what was really happening.  Which
> > leads to the next question: What's the right way to keep an asm() from
> > being loop invariant?  I've got a case where an inline asm() is passed
> > a pointer (the pointer is invariant) but internally dereferences it
> > (the pointed-at memory is *not* invariant).  However, loop-invariant.c
> > is pulling it out of the loop anyway.
> 
> Sounds like you need a memory clobber constraint on the asm... ?

Or mark the memory as read like so:

asm ( "....." : .... : ... , "m" (*pointer) );

-- Pinski