Re: [tree-ssa Too many edges in CFG

[Jason Merrill <jason at redhat dot com>]

On Thu, 08 May 2003 09:18:20 -0600, law@redhat.com wrote:

> In message <20030508151341.GA14715@tornado.toronto.redhat.com>, Diego Novillo w
> rites:
>  >On Wed, May 07, 2003 at 02:25:20PM -0700, Richard Henderson wrote:
>  >> On Tue, May 06, 2003 at 08:50:06PM -0600, law@redhat.com wrote:
>  >> > +       /* Some calls are known not to return.  For such calls we need to
>  >> > + 	 add an edge to the exit block.  No fall thru edge is needed
>  >> > + 	 as these calls can not return in the normal sense.  */
>  >> 
>  >> Why do you need an edge to the exit block?
>  >> 
>  >I don't think we use that for anything right now.  In the future,
>  >the predecessor blocks of EXIT_BLOCK_PTR will be the blocks where
>  >we want to put copy-out operations for globals and statics.

> But for a non-returning function the edge to the exit block can never
> execute.

But a call to a non-returning function does in fact exit the function, just
not by returning to the caller.  IIUC, the optimizers assume that any
non-dead code will be on some path between the entry and exit blocks.  And,
as Diego says, if we've deferred copy-out operations we need to insert them
here, as a non-returning function can still refer to globals, and might do
a longjmp or throw to get back to our caller.

It would probably make sense to model it as an abnormal edge from the call,
much like EH.

Jason