llvm-project

12769aa7 - [Offload] Introduce ATTACH map-type support for pointer attachment. (#149036)

[Offload] Introduce ATTACH map-type support for pointer attachment. (#149036) This patch introduces libomptarget support for the ATTACH map-type, which can be used to implement OpenMP conditional compliant pointer attachment, based on whether the pointer/pointee is newly mapped on a given construct. For example, for the following: ```c int *p; #pragma omp target enter data map(p[1:10]) ``` The following maps can be emitted by clang: ``` (A) &p[0], &p[1], 10 * sizeof(p[1]), TO | FROM &p, &p[1], sizeof(p), ATTACH ``` Without this map-type, these two possible maps could be emitted by clang: ``` (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, which are both incorrect. In terms of implementation, maps with the ATTACH map-type are handled after all other maps have been processed, as it requires knowledge of which new allocations happened as part of the construct. As per OpenMP 5.0, an attachment should happen only when either the pointer or the pointee was newly mapped while handling the construct. Maps with ATTACH map-type-bit do not increase/decrease the ref-count. With OpenMP 6.1, `attach(always/never)` can be used to force/prevent attachment. For `attach(always)`, the compiler will insert the ALWAYS map-type, which would let libomptarget bypass the check about one of the pointer/pointee being new. With `attach(never)`, the ATTACH map will not be emitted at all. The size argument of the ATTACH map-type can specify values greater than `sizeof(void*)` which can be used to support pointer attachment on Fortran descriptors. Note that this also requires shadow-pointer tracking to also support them. That has not been implemented in this patch. This was worked upon in coordination with Ravi Narayanaswamy, who has since retired. Happy retirement, Ravi! --------- Co-authored-by: Alex Duran <alejandro.duran@intel.com>