[cfe-dev] Passing StructType arguments directly

[John McCall]

On Sep 20, 2011, at 11:38 PM, Chris Lattner wrote:
> On Sep 20, 2011, at 4:03 AM, David Chisnall wrote:
>> On 20 Sep 2011, at 06:34, David Meyer wrote:
>>> * Front-ends would no longer need to implement the ABIs for each
>>> target architecture to get full ABI compliance. They would generate
>>> high-level bitcode, and the ABI lowering knowledge would be contained
>>> in LLVM.
>> 
>> I'd consider this to be a major benefit all by itself.  Not only is the ABI-dependence of the IR a major layering violation, it's also incredibly badly documented.  For example, I know that FreeBSD's x86 ABI returns small structures in registers, but I have no idea how I am supposed to know that this means that {float, float} is returned as an i64 (or why anyone thinks that's even a remotely sane representation in the IR of 'two floats in float registers').
> 
> My read of this thread is that there are two independent things being discussed:
> 
> 1. The utility of a target independent "IR ABI" that nacl wants, and 
> 2. Whether first class aggregates are the way to lower structs.
> 
> #1 is clearly essential for native client, and potentially really interesting for other projects.

Yeah, to be clear, I think this is a great goal.  I would love it if we could get frontends out of the business of doing bizarre ABI lowering around calls.

John.