[llvm-dev] RFC: Adding argument allocas

Philip Reames via llvm-dev llvm-dev at lists.llvm.org
Fri Dec 9 11:56:04 PST 2016

On 12/09/2016 08:45 AM, Reid Kleckner via llvm-dev wrote:
> On Thu, Dec 8, 2016 at 5:37 PM, Mehdi Amini <mehdi.amini at apple.com 
> <mailto:mehdi.amini at apple.com>> wrote:
>     So IIUC basically the *only* reason for this IR change is that we
>     don’t want to pattern match in debug build?
>     I don't understand right now why we wouldn’t want to do this?
> If we need to pattern match such a basic construct, it suggests to me 
> that we have the wrong representation, and we should instead make our 
> representation more accurately model reality. To me, it feels like 
> this representation allows several good things to just "fall out" 
> without any additional work, and that suggests it's a good representation.
I'm concerned by this response on multiple levels.  I agree Mehdi that 
the proposed IR change seems to be solving a (relatively minor) 
optimization problem with an IR change.  We generally expect our IR 
changes to be well justified and this doesn't even come close to me.  
More than that, I'm really concerned about the assumption that the IR 
should be a close fit *for a particular frontend* in a *particular mode 
of operation*.  We have tried very hard to keep the IR generic enough to 
be useful by many language frontends and this would seem to give up on 
that goal.  That is deeply concerning  to me.

As it stands right now, based on what I've seen to date in discussion, I 
would be strongly opposed to this proposal.

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