llvm-project

ef7de8d1 - [AMDGPU] Remove scope check in SIInsertWaitcnts::generateWaitcntInstBefore (#157821)

[AMDGPU] Remove scope check in SIInsertWaitcnts::generateWaitcntInstBefore (#157821) This change was motivated by CK where many VMCNT(0)'s were generated due to instructions lacking !alias.scope metadata. The two causes of this were: 1) LowerLDSModule not tacking on scope metadata on a single LDS variable 2) IPSCCP pass before inliner replacing noalias ptr derivative with a global value, which made inliner unable to track it back to the noalias ptr argument. However, it turns out that IPSCCP losing the scope information was largely ineffectual as ScopedNoAliasAA was able to handle asymmetric condition, where one MemLoc was missing scope, and still return NoAlias result. AMDGPU however was checking for existence of scope in SIInsertWaitcnts and conservatively treating it as aliasing all and inserted VMCNT(0) before DS_READs, forcing it to wait for all previous LDS DMA instructions. Since we know that ScopedNoAliasAA can handle asymmetry, we should also allow AA query to determine if two MIs may alias. Passed PSDB. Previous attempt to address the issue in IPSCCP, likely stalled: https://github.com/llvm/llvm-project/pull/154522 This solution may be preferrable over that as issue only affects AMDGPU.