Data-structure splicing techniques, such as structure splitting, field reordering, and pointer inlining reorganize data structures to improve cache and translation look-aside buffer (TLB) utilization. Structure types are typically transformed globally in the program, requiring updates to all references to elements of a transformed type. These techniques often rely on instrumentation, tracing, or sampling to create models that guide their transformations. Furthermore, compilers often cannot prove that their transformations are legal and must rely on manual inspection and manual transformation. Applying data-layout transformations locally -- as opposed to globally -- to regions of code removes the need for expensive profiling and simplifies legality verification. This work introduces RebaseDL, a static analysis that finds profitable and legal region-based data layout transformation opportunities that improve access locality. These opportunities are found within code regions that exhibit data reuse. Going beyond structure splicing, RebaseDL also identifies transformation opportunities that do not involve structure types, that is, it identifies data packing transformations. The analysis is implemented in LLVM and it detects multiple transformation opportunities within the SPEC CPU benchmark suite, where the transformation obtains speedups of up to 1.34x for transformed regions.

Packing is an essential loop optimization for handcrafting a high-performance General Matrix Multiplication (GEMM). Packing copies a non-contiguous block of data to a contiguous block to reduce the number of TLB entries required to access it, avoiding expensive TLB misses. When copying data, packing can rearrange elements of the block to decrease the stride between consecutive accesses, improving spatial locality. Until now the use of packing has been limited to handcrafted GEMM implementations and to auto-tuning techniques. Existing loop optimizers, such as Polly and Pluto, either only apply packing to GEMM computations (Polly), or not at all (Pluto). This work proposes GPAT, a generalized packing analysis and code transformation that applies packing, when beneficial, to a generic input loop nest. GPAT is implemented in the Affine dialect of MLIR and evaluated on Polybench/C. GPAT applies packing to benchmarks beyond GEMM and obtains significant speedup compared to current loop optimizers that do not apply packing.