1fbf33cd40
This adds support for using `ATTACH` map-type for proper pointer-attachment when mapping list-items that have base-pointers. For example, for the following: ```c int *p; #pragma omp target enter data map(p[1:10]) ``` The following maps are now emitted by clang: ``` (A) &p[0], &p[1], 10 * sizeof(p[1]), TO | FROM &p, &p[1], sizeof(p), ATTACH ``` Previously, the two possible maps emitted by clang were: ``` (B) &p[0], &p[1], 10 * sizeof(p[1]), TO | FROM (C) &p, &p[1], 10 * sizeof(p[1]), TO | FROM | PTR_AND_OBJ ```` (B) does not perform any pointer attachment, while (C) also maps the pointer p, both of which are incorrect. ----- With this change, we are using ATTACH-style maps, like `(A)`, for cases where the expression has a base-pointer. For example: ```cpp int *p, **pp; S *ps, **pps; ... map(p[0]) ... map(p[10:20]) ... map(*p) ... map(([20])p) ... map(ps->a) ... map(pps->p->a) ... map(pp[0][0]) ... map(*(pp + 10)[0]) ``` #### Grouping of maps based on attach base-pointers We also group mapping of clauses with the same base decl in the order of the increasing complexity of their base-pointers, e.g. for something like: ``` S **spp; map(spp[0][0], spp[0][0].a), // attach-ptr: spp[0] map(spp[0]), // attach-ptr: spp map(spp), // attach-ptr: N/A ``` We first map `spp`, then `spp[0]` then `spp[0][0]` and `spp[0][0].a`. This allows us to also group "struct" allocation based on their attach pointers. This resolves the issues of us always mapping everything from the beginning of the symbol `spp`. Each group is mapped independently, and at the same level, like `spp[0][0]` and its member `spp[0][0].a`, we still get map them together as part of the same contiguous struct `spp[0][0]`. This resolves issue #141042. #### use_device_ptr/addr fixes The handling of `use_device_ptr/addr` was updated to use the attach-ptr information, and works for many cases that were failing before. It has to be done as part of this series because otherwise, the switch from ptr_to_obj to attach-style mapping would have caused regressions in existing use_device_ptr/addr tests. #### Handling of attach-pointers that are members of implicitly mapped structs: * When a struct member-pointer, like `p` below, is a base-pointer in a `map` clause on a target construct (like `map(p[0:1])`, and the base of that struct is either the `this` pointer (implicitly or explicitly), or a struct that is implicitly mapped on that construct, we add an implicit `map(p)` so that we don't implicitly map the full struct. ```c struct S { int *p; void f1() { #pragma omp target map(p[0:1]) // Implicitly map this->p, to ensure // that the implicit map of `this[:]` does // not map the full struct printf("%p %p\n", &p, p); } ``` #### Scope for improvement: * We may be able to compute attach-ptr expr while collecting component-lists in Sema. * But we cache the computation results already, and `findAttachPtrExpr` is fairly simple, and fast. * There may be a better way to implement semantic expr comparison. #### Needs future work: * Attach-style maps not yet emitted for declare mappers. * Mapping of class member references: We are still using PTR_AND_OBJ maps for them. We will likely need to change that to handle `ref_ptr/ref_ptee`, and `attach` map-type-modifier on them. * Implicit capturing of "this" needs to map the full `this[0:1]` unless there is an explicit map on one of the members, or a map with a member as its base-pointer. * Implicit map added for capturing a class member pointer needs to also add a zero-length-array-section map. * `use_device_addr` on array-sections-on-pointers need further improvements (documented using FIXMEs) #### Why a large PR While it's unfortunate that this PR has gotten large and difficult to review, the issue is that all the functional changes have to be made together, to prevent regressions from partially implemented changes. For example, the changes to capturing were previously done separately (#145454), but they would still cause stability issues in absence of full attach-mapping. And attach-mapping needs those changes to be able to launch kernels. We extracted the utilities and functions, like those for finding attach-ptrs, or comparing exprs, out as a separate NFC PR that doesn't call those functions, just adds them (#155625). Maybe the change that adds a new error message for use_device_addr on array-sections with non-var base-pointers could have been extracted out too (but that would have had to be a follow-up change in that case, and we would get comp-fails with this PR when the erroneous case was not caught/diagnosed). --------- Co-authored-by: Alex Duran <alejandro.duran@intel.com>
The LLVM/Offload Subproject
The Offload subproject aims at providing tooling, runtimes, and APIs that allow users to execute code on accelerators or other "co-processors" that may or may not match the architecture of their "host". In the long run, all kinds of targets are in scope of this effort, including but not limited to: CPUs, GPUs, FPGAs, AI/ML accelerators, distributed resources, etc.
For OpenMP offload users, the project is ready and fully usable. The final API design is still under development. More content will show up here and on our webpage soon. In the meantime, people are encouraged to participate in our meetings (see below) and check our development board as well as the discussions on Discourse.
Meetings
Every second Wednesday, 7:00 - 8:00am PT, starting Jan 24, 2024. Alternates with the OpenMP in LLVM meeting. invite.ics Meeting Minutes and Agenda