[PATCH] Canonicalize addrspacecast between different pointer types.

[Matt Arsenault]

On Nov 17, 2013, at 5:12 AM, Michele Scandale <michele.scandale at gmail.com> wrote:

> 
>  I would like to better understand the motivation of this patch: what are the benefit obtained doing a split between the change of address space and the pointer type within the new address space?
>  Being a bitcast just a reintepretation of the input value (no change in the bits) this behavior has been included in the addrspacecast instruction (nobody reported any objection on this).
> 

The addrspacecast instruction’s purpose is to only change the address space. Changing the type of the pointer is a logically separate operation. If separated out, the bitcast could potentially be combined with other instructions that use the value to simplify things. This is similar to how inttoptr / ptrtoint behave. You can use a different size integer than the pointer size, but instcombine splits it into the 2 logically steps of reinterpreting as an integer, and then extending or truncating to the real pointer size.