llvm-project

9871d708 - [mlir][acc] Introduce ACCImplicitDeclare pass for globals handling (#169720)

[mlir][acc] Introduce ACCImplicitDeclare pass for globals handling (#169720) This commit introduces the ACCImplicitDeclare pass to the OpenACC dialect, complementing ACCImplicitData by handling global variables referenced in OpenACC compute regions and routines. Overview: --------- The pass applies implicit `acc declare` actions to global variables referenced in OpenACC regions. While the OpenACC spec focuses on implicit data mapping (handled by ACCImplicitData), implicit declare is advantageous and required for specific cases: 1. Globals referenced in implicit `acc routine` - Since data mapping only applies to compute regions, globals in routines must use `acc declare`. 2. Compiler-generated globals - Type descriptors, runtime names, and error reporting strings introduced during compilation that wouldn't be visible for user-provided `acc declare` directives. 3. Constant globals - Constants like filename strings or initialization values benefit from being marked with `acc declare` rather than being mapped repeatedly (e.g., 1000 kernel launches shouldn't map the same constant 1000 times). Implementation: --------------- The pass performs this in two phases: 1. Hoisting: Non-constant globals in compute regions have their address-of operations hoisted out of the region when possible, allowing implicit data mapping instead of declare marking. 2. Declaration: Remaining that must be device available (constants, globals in routines, globals in recipe operations) are marked with the acc.declare attribute. The pass processes: - OpenACC compute constructs (parallel, kernels, serial) - Functions marked with acc routine - Private, firstprivate, and reduction recipes (when used) - Initialization regions of existing declared globals Requirements: ------------- The pass requires operations to implement: - acc::AddressOfGlobalOpInterface (for address-of ops) - acc::GlobalVariableOpInterface (for global definitions) - acc::IndirectGlobalAccessOpInterface (for indirect access)