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From: Jon Harrop <jonathandeanharrop@googlemail.com>
To: <caml-list@inria.fr>
References: <036001cb9a0c$725acef0$57106cd0$@com>	<20101212175524.73a8e285@deb0>	<9264BEE6-DBAE-4523-93AC-4560615D2AC5@googlemail.com>	<4D05DCB6.2060100@frisch.fr> <85AB623B-0278-41F0-9C70-8E8814C0A16F@googlemail.com>
In-Reply-To: <85AB623B-0278-41F0-9C70-8E8814C0A16F@googlemail.com>
Subject: RE: Value types (Was: [Caml-list] ocamlopt LLVM support)
Date: Wed, 15 Dec 2010 13:15:26 -0000
Organization: Flying Frog Consultancy
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X-Spam: no; 0.00; ocamlopt:01 fwiw:01 structs:01 structs:01 recursion:01 unboxed:01 cheers:01 polymorphic:01 wrote:01 caml-list:01 tuples:01 tuples:01 library:03 let:03 let:03 

Benedikt wrote:
> Nice. But it would be even better to avoid the dummy, in your example
> 
>   let x = u in
>   let y = v in
>   if b then x <- v; y <- u
> 
> This does not only avoid the dummy, but would also allow lowering to
> "cmovcc" instructions in the backend selector (atleast for x86-32/64).

FWIW, when you're using LLVM (as a library!) to generate equivalent code
then you can just represent the tuples as structs (value types) and LLVM
will take care of all of this for you. Again, it generates really efficient
code with minimal effort.

The latest example front-end for HLVM represents tuples as structs so it
gets this for free. However, polymorphic recursion is *much* harder to
implement with that design choice. Also, there is the question of when boxed
vs unboxed tuples are more efficient.

Cheers,
Jon.