[PATCH] D37822: [OpenCL] Clean up and add missing fields for block struct

[Anastasia Stulova via Phabricator via cfe-commits]

Anastasia added a comment.

In https://reviews.llvm.org/D37822#872446, @yaxunl wrote:

> In https://reviews.llvm.org/D37822#872291, @Anastasia wrote:
>
> > Could you please explain a bit more why the alignment have to be put explicitly in the struct? I am just not very convinced this is general enough.
>
>
> The captured variables are fields of the block literal struct. Due to alignment requirement of these fields, there is alignment requirement of
>  the block literal struct. The ISA of the block invoke function is generated with the assumption of these alignments. If the block literal is
>  allocated at a memory address not satisfying the alignment requirement, the kernel behavior is undefined.
>
> Generally, __enqueue_kernel library function needs to prepare the kernel argument before launching the kernel. It usually does this by copying
>  the block literal to some buffer then pass the address of the buffer to the kernel. Then the address of the buffer has to satisfy the alignment
>  requirement.
>
> If this block literal struct is not general enough, how about add another field as target reserved size, and leave the remaining space of header for
>  target specific use. And add a target hook to allow target fill the reserved space, e.g.
>
>   struct __opencl_block_literal {
>     int total_size;
>     int align;
>     __generic void *invoke;
>     int target_reserved_size; /* round up to 4 bytes */
>     int target_reserved[];
>     /* captures */
>   };
>


I like the idea of the target reserved part actually. But not sure how it could be used without adding any target specific methods?

However, I am still not clear why the alignment of this struct has to be different from any other struct Clang produces. Normally the alignment of objects have to be known during IR generation to put them correctly in the attributes of generated alloca, store and loads. But as a field inside struct I don't know how it can be useful. I would imagine `enqueue_kernel` would just operate on the block as if it would be an arbitrary buffer of data. Also would size of the struct not account for any padding to make sure the alignment can be deduced based on it correctly?



================
Comment at: lib/CodeGen/CGOpenCLRuntime.cpp:108
+llvm::PointerType *CGOpenCLRuntime::getGenericVoidPointerType() {
+  return llvm::IntegerType::getInt8PtrTy(
+      CGM.getLLVMContext(),
----------------
Should we put an assert of LangOpts.OpenCL?


================
Comment at: test/CodeGen/blocks-opencl.cl:1
 // RUN: %clang_cc1 -O0 %s -ffake-address-space-map -emit-llvm -o - -fblocks -triple x86_64-unknown-unknown | FileCheck %s
+// RUN: %clang_cc1 -O0 %s -emit-llvm -o - -fblocks -triple amdgcn | FileCheck %s
----------------
Btw, do you think we need this test any more? And if yes, could this be moved to CodeGenOpenCL?


https://reviews.llvm.org/D37822