llvm dev - Sep 2015 - Rerunning TailCallElim at a later stage

Hi

from what I have figured out, the pass "TailCallElim" is being done in
what I would call the "opt" phase of optimization. The
"StackColoring"
is being done in the "llc" phase. opt -> llc, so TailCallElim is
always
ahead.

Now I would like to add something (my reusealloca idea) in 
"StackColoring" to get rid of some allocas, which inhibit
"TailCallElim".

* Is it possible to rerun (if even possible at that stage) the 
"TailCallElim" at this stage ?

* Is it possible to make "StackColoring" into an "opt" pass
and try to
get it ahead of "TailCallElim" ? I guess not, though I can see how 
"RegisterColoring" is dependent on architecture, but I don't
really see
it for allocas.

Ciao
    Nat!

P.S. AU.addRequired<TailCallElim>(); would not work BTW.

No, this reordering is not possible. Stack coloring is part of codegen.
Passes that modify the IR cannot run as part of codegen.

Your best bet for enabling tail calls with your meta calling convention is
to write a custom pass that rewrites calls in the tail position to use the
incoming argument memory instead of a local alloca. It would be up to this
custom pass to determine exactly when this is legal.

On Thu, Sep 3, 2015 at 8:57 AM, Nat! via llvm-dev <llvm-dev at
lists.llvm.org>
wrote:
> Hi
>
> from what I have figured out, the pass "TailCallElim" is being
done in
> what I would call the "opt" phase of optimization. The
"StackColoring" is
> being done in the "llc" phase. opt -> llc, so TailCallElim is
always ahead.
>
> Now I would like to add something (my reusealloca idea) in
"StackColoring"
> to get rid of some allocas, which inhibit "TailCallElim".
>
> * Is it possible to rerun (if even possible at that stage) the
> "TailCallElim" at this stage ?
>
> * Is it possible to make "StackColoring" into an "opt"
pass and try to get
> it ahead of "TailCallElim" ? I guess not, though I can see how
> "RegisterColoring" is dependent on architecture, but I don't
really see it
> for allocas.
>
> Ciao
>    Nat!
>
> P.S. AU.addRequired<TailCallElim>(); would not work BTW.
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20150903/217d4d3c/attachment.html>

Reid Kleckner schrieb:
> Your best bet for enabling tail calls with your meta calling convention
> is to write a custom pass that rewrites calls in the tail position to
> use the incoming argument memory instead of a local alloca. It would be
> up to this custom pass to determine exactly when this is legal.

I assume that would be a pass that I would try to get, somehow, ahead of 
"TailCallElim" in the "opt" phase ?

Thanks for the help!

Ciao
    Nat!