[LLVMdev] [RFC] Upstreaming LLVM/SPIR-V converter

[罗勇刚(Yonggang Luo)]

2015-05-20 0:29 GMT+08:00 Chris Lattner <clattner at apple.com>:
>
>> On May 19, 2015, at 1:25 AM, Neil Henning <llvm at duskborn.com> wrote:
>>
>> The problem is - as Sean and Pete (and others before) have pointed out, from a users perspective they'll want to say 'clang make me SPIR-V'. There are things in SPIR-V that are not representable by the LLVM IR, so we'd have to add SPIR-V specific intrinsics for this (again making the case for having it as a target more palatable), and also there are things in the IR that won't be allowed when producing SPIR-V (off the top of my head, in a graphics shader with logical addressing mode a ton of pointer use is banned).
>>
>> I think what Sean suggested of having a very thin backend that satisfies what a user will want when producing SPIR-V + setting up the target specific intrinsics, and then the majority of the actual SPIR-V production code being in lib/SPIRV sounds like a good approach to me!
>
> There are two different things going on here:
>
> 1) Where the code lives in the llvm tree.
> 2) How clang and other tools expose it to users.
>
> Per #1, it is pretty clear to me that this is a serialization format and should be structured like the bitcode reader & writer.  It is not a target, though maybe it also need a minimal target (but not instruction selection tables etc) so that clang and other tools can generate code for it.
>
> Per #2, that is a discussion for the clang lists.
>
>From my points of view, there is two different of roles along with SPIR-V.
1, As a backend of clang, in this way, maybe we treat SPIR-V as a llvm
backend is the easiest way to implement, but that not agree with the
nature of SPIR-V, it's a IR(intermediate representation) , and Target
means the machine level abstraction. Anyway, we also have Asm.js and
CppBackend have same feature.
2, As a frontend IR, it's would first translate to LLVM IR, and then
translate to Target Machine.

So maybe we need to have two different kinds of target,
One is real target like x86, x64, arm and so on.

The other one is CppBackend, Asm.js SPIR-V, and maybe Java ByteCodes MSIL

> -Chris
>
>
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-- 
         此致
礼
罗勇刚
Yours
    sincerely,
Yonggang Luo