[cfe-dev] [RFC][OpenCL] Rename OpenCL opaque types in LLVM IR from opencl.* to __opencl_*

Wed Jul 27 12:46:28 PDT 2016

Clang does not allow casting OpenCL opaque types to any other types. For example,

$ cat test3.cl
void f(sampler_t s) {
  void *q = (void*) s;
  char *p = (char*) s;
}

$ bin/clang -cc1 test3.cl
test3.cl:2:21: error: operand of type 'sampler_t' where arithmetic or pointer type is required
  void *q = (void*) s;
                    ^
test3.cl:3:21: error: operand of type 'sampler_t' where arithmetic or pointer type is required
  char *p = (char*) s;
                    ^
2 errors generated.

That makes sense since allowing OpenCL opaque types to be casted to other types potentially can cause lots of issues and needs more checks.

Then I don't know how representing OpenCL opaque type as a non-struct type would work.

On the other hand, any type can be easily packaged in a struct type. What we need is a struct name that can be used by a common OpenCL source code.

Sam

From: Anastasia Stulova [mailto:Anastasia.Stulova at arm.com]
Sent: Wednesday, July 27, 2016 2:39 PM
To: Liu, Yaxun (Sam) <Yaxun.Liu at amd.com>; Bader, Alexey <alexey.bader at intel.com>; cfe-dev (cfe-dev at lists.llvm.org) <cfe-dev at lists.llvm.org>
Cc: Sumner, Brian <Brian.Sumner at amd.com>; Pan, Xiuli <xiuli.pan at intel.com>; nd <nd at arm.com>
Subject: RE: [RFC][OpenCL] Rename OpenCL opaque types in LLVM IR from opencl.* to __opencl_*

Right, what I mean is that OpenCL types are now generated by Clang as unknown opaque types identified by their name in LLVM.  Unfortunately LLVM is missing proper type support for OpenCL, therefore we have this issue. But adding "struct." prefix might imply that this has to be a struct.  Clang uses "struct." prefix as a naming convention for generated C struct types in LLVM.

Implementation should however have freedom to use OpenCL opaque types differently to struct (we don't force it to be anything). I don't think adding a struct prefix to the OpenCL opaque type names in LLVM is a good idea as it adds some confusion about their representation.

Cheers,
Anastasia

From: Liu, Yaxun (Sam) [mailto:Yaxun.Liu at amd.com]
Sent: 27 July 2016 18:58
To: Anastasia Stulova; Bader, Alexey; cfe-dev (cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>)
Cc: Sumner, Brian; Pan, Xiuli; nd
Subject: RE: [RFC][OpenCL] Rename OpenCL opaque types in LLVM IR from opencl.* to __opencl_*

In LLVM, the OpenCL opaque types are already represented as an opaque struct type since only struct types can have name. This proposal does not change that, it only changes the name of the struct type to be accessible in the OpenCL source code.

Besides, Clang does not allow OpenCL opaque types such as sampler and image types to be explicitly casted to other types.

Sam

From: Anastasia Stulova [mailto:Anastasia.Stulova at arm.com]
Sent: Wednesday, July 27, 2016 1:08 PM
To: Liu, Yaxun (Sam) <Yaxun.Liu at amd.com<mailto:Yaxun.Liu at amd.com>>; Bader, Alexey <alexey.bader at intel.com<mailto:alexey.bader at intel.com>>; cfe-dev (cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>) <cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>>
Cc: Sumner, Brian <Brian.Sumner at amd.com<mailto:Brian.Sumner at amd.com>>; Pan, Xiuli <xiuli.pan at intel.com<mailto:xiuli.pan at intel.com>>; nd <nd at arm.com<mailto:nd at arm.com>>
Subject: RE: [RFC][OpenCL] Rename OpenCL opaque types in LLVM IR from opencl.* to __opencl_*

In this case I am not sure it's generic enough to assume that those types are always mapped to some struct.

Perhaps, we should stay with the conversion?

Anastasia

From: Liu, Yaxun (Sam) [mailto:Yaxun.Liu at amd.com]
Sent: 27 July 2016 16:29
To: Bader, Alexey; Anastasia Stulova; cfe-dev (cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>)
Cc: Sumner, Brian; Pan, Xiuli; nd
Subject: RE: [RFC][OpenCL] Rename OpenCL opaque types in LLVM IR from opencl.* to __opencl_*

You are right. It should be struct.__opencl_ prefix.

Sam

From: Bader, Alexey [mailto:alexey.bader at intel.com]
Sent: Wednesday, July 27, 2016 10:56 AM
To: Anastasia Stulova <Anastasia.Stulova at arm.com<mailto:Anastasia.Stulova at arm.com>>; Liu, Yaxun (Sam) <Yaxun.Liu at amd.com<mailto:Yaxun.Liu at amd.com>>; cfe-dev (cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>) <cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>>
Cc: Sumner, Brian <Brian.Sumner at amd.com<mailto:Brian.Sumner at amd.com>>; Pan, Xiuli <xiuli.pan at intel.com<mailto:xiuli.pan at intel.com>>; nd <nd at arm.com<mailto:nd at arm.com>>
Subject: RE: [RFC][OpenCL] Rename OpenCL opaque types in LLVM IR from opencl.* to __opencl_*

Hi Sam,

I want to clarify the use case.
The intension is to allow library developer redefining OpenCL images types in a library written in OpenCL C and prefix starting with double underscore is supposed to protect the library image types definitions from redefinition by user.
The change you are proposing is to rename image opaque types in LLVM IR, without making them concrete.
Am I getting it right?

Wouldn't types defined by library developer prefixed with 'struct.'? Shouldn't clang create opaque types with 'struct.__opencl_' prefix instead to match the type names defined by library developer?

Thanks,
Alexey

From: Anastasia Stulova [mailto:Anastasia.Stulova at arm.com]
Sent: Monday, July 25, 2016 6:41 PM
To: Liu, Yaxun (Sam) <Yaxun.Liu at amd.com<mailto:Yaxun.Liu at amd.com>>; cfe-dev (cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>) <cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>>
Cc: Sumner, Brian <Brian.Sumner at amd.com<mailto:Brian.Sumner at amd.com>>; Bader, Alexey <alexey.bader at intel.com<mailto:alexey.bader at intel.com>>; Pan, Xiuli <xiuli.pan at intel.com<mailto:xiuli.pan at intel.com>>; nd <nd at arm.com<mailto:nd at arm.com>>
Subject: RE: [RFC][OpenCL] Rename OpenCL opaque types in LLVM IR from opencl.* to __opencl_*

Sounds good to me!

Thanks,

Anastasia

From: Liu, Yaxun (Sam) [mailto:Yaxun.Liu at amd.com]
Sent: 20 July 2016 18:49
To: cfe-dev (cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>)
Cc: Anastasia Stulova; Sumner, Brian; Bader, Alexey (alexey.bader at intel.com<mailto:alexey.bader at intel.com>); Pan, Xiuli
Subject: [RFC][OpenCL] Rename OpenCL opaque types in LLVM IR from opencl.* to __opencl_*

Currently OpenCL opaque types have name opencl.* in LLVM IR, which causes difficulty for library developers who need to implement the concrete types corresponding to the opaque types.

For example, read_only image2d_t type is translated to opencl.image2d_ro_t addrspace(1)* in LLVM IR. Ideally, a library developer would implement a concreate struct type with name opencl.image2d_ro_t and access its members. However, due to the '.', 'opencl.image2d_ro_t' is not a valid identifier in OpenCL C language, library developers cannot use it as the name of the concrete struct type for image2d_t. Bitcasts have to be introduced, which causes extra efforts in backends.

Due to this reason, we would like to propose renaming OpenCL opaque types in LLVM IR from opencl.* to __opencl_*.

This change will make the IR deviate from SPIR spec. However, considering there is simple rule to map this new name to SPIR defined name, and LLVM IR currently generated by Clang has already been deviated from SPIR spec, a SPIR consumer should be able to accommodate this change if it is able to accommodate existing deviations.

Your feedbacks are welcome. Thanks.

Sam

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