mirrors/arti.git/crates/hashx/src/compiler, branch ios-sqlite-hacks

hashx: Cleanup around Instruction and NUM_INSTRUCTIONS

2023-08-25T20:14:24Z

This patch tries to make some of the expressions around NUM_INSTRUCTIONS more convenient. We can import it directly where it's needed, but most uses are replaced by new type aliases for InstructionArray and InstructionVec. No change to any hashx_cachegrind iai benchmarks

hashx: Avoid memcpy in Assembler::finalize()

2023-08-25T19:46:44Z

This is a very simple change, just passing 'self' by reference instead of value. The by-value version generates a memcpy of the entire temporary program buffer which doesn't optimize out like I expected it would. The juicy impact here is a much lower cache footprint for compilation, since we avoid having yet another temporary storage location for the program data. generate_compiled_1000x Instructions: 271682605 (-0.627292%) L1 Accesses: 341834751 (-0.813903%) L2 Accesses: 56420 (-39.48365%) RAM Accesses: 618 (-20.25806%) Estimated Cycles: 342138481 (-0.867660%)

Rustfmt

2023-08-25T17:12:56Z

RFC: hashx: Make Architecture::compile take an array ref

2023-08-25T17:12:56Z

generate_interp_1000x Instructions: 219216169 (No change) L1 Accesses: 278017243 (-0.000441%) L2 Accesses: 1257 (+4389.286%) RAM Accesses: 415 (-0.479616%) Estimated Cycles: 278038053 (+0.001744%) generate_interp_1000x_c Instructions: 272748034 (No change) L1 Accesses: 349932964 (No change) L2 Accesses: 76 (-1.298701%) RAM Accesses: 411 (+0.243902%) Estimated Cycles: 349947729 (+0.000009%) generate_compiled_1000x Instructions: 256896028 (+0.175731%) L1 Accesses: 342543838 (+0.131802%) L2 Accesses: 149273 (-10.34924%) RAM Accesses: 810 (-0.246305%) Estimated Cycles: 343318553 (+0.106328%) generate_compiled_1000x_c Instructions: 281855218 (No change) L1 Accesses: 362569035 (-0.000001%) L2 Accesses: 88 (+1.149425%) RAM Accesses: 473 (+0.211864%) Estimated Cycles: 362586030 (+0.000010%) interp_u64_hash_1000x Instructions: 13450926 (No change) L1 Accesses: 16622561 (+0.000024%) L2 Accesses: 28 (No change) RAM Accesses: 390 (-1.015228%) Estimated Cycles: 16636351 (-0.000817%) interp_8b_hash_1000x_c Instructions: 8618541 (No change) L1 Accesses: 12316160 (-0.000008%) L2 Accesses: 80 (No change) RAM Accesses: 433 (+0.231481%) Estimated Cycles: 12331715 (+0.000276%) compiled_u64_hash_100000x Instructions: 87311792 (+0.000520%) L1 Accesses: 94396598 (+0.000463%) L2 Accesses: 215 (+2.380952%) RAM Accesses: 774 (-0.641849%) Estimated Cycles: 94424763 (+0.000304%) compiled_8b_hash_100000x_c Instructions: 91547640 (No change) L1 Accesses: 98838166 (-0.000007%) L2 Accesses: 137 (+3.007519%) RAM Accesses: 488 (+0.618557%) Estimated Cycles: 98855931 (+0.000119%)

hashx: Assembly buffer sizing and tidying

2023-08-21T22:27:28Z

I was looking for ways to optimize out the many redundant capacity checks in the Assembler. I didn't find any promising approaches, but I also saw no evidence that it was an important bottleneck. (A simple unsafe fix didn't improve any important metrics) While I was in there, I tightened up the buffer size definitions for both x86_64 and aarch64, and added assertions to test the limits we set for the size of prologue, epilogue, and single instructions. I kept some of the inlining and data type tweaks, even though benchmarks show no difference. They seem like a step in the right direction, from the disassembly at least. Signed-off-by: Micah Elizabeth Scott

hashx: avoid surprising overhead of enum code() method

2023-08-21T22:27:28Z

This is a very simple change that avoids a surprising performance pitfall: using the code() method on an enum from another crate caused a non-inlined function call in code where we otherwise expect a high level of compiler optimization. Replacing code() with a cast to u8 avoids this function call and allows more intensive optimization at the call site. Signed-off-by: Micah Elizabeth Scott

hashx: New approach to avoid memcpy in Program

2023-08-21T22:27:28Z

I was trying to eliminate all the places where we copied a Program (about 4100 bytes) except for the one final copy into a Box; but that approach was proving too annoying. Even returning a Program via Result will cause multiple unnecessary copies that don't optimize out. This patch switches approaches, and instead allocates a Vec presized to the correct capacity. This allocation is made as early as possible and retained for the lifetime of the program if necessary. This means we'll never avoid a heap allocation, but we can always avoid extra copies and we don't need a separate Box for interpreted programs. Performance effects are subtle. Overall wallclock time doesn't change much. Cachegrind shows some accesses moving up from RAM to L2 cache. Using GDB to probe memcpy sizes shows that large (>1024b) memcpy are now totally gone in the generate-interp test. Signed-off-by: Micah Elizabeth Scott

hashx: Rewrite RegisterSet again to reduce CPU frontend stalls

2023-08-21T22:27:28Z

Closer inspection of the CPU counters showed that the branching in RegisterSet::index() was a big problem, contributing to the overall CPU frontend stall bottleneck in program generation. This new version is less general, and closer to the appraoch used by the original C implementation. We store a sorted ArrayVec of in-set registers, and most operations construct the RegisterSet only once using a combined filter predicate. Choosing a register from a set is now cheaper in branches, instructions, and L1 cache space. We now very rarely manipulate an entire RegisterSet in any way other than by selecting a register randomly. (Just for the register R5 special case.) Wallclock time benchmarks: generate-interp improves, -7.0% generate-x86_64 improves, -7.2% Cachegrind benchmarks: generate_interp_1000x, more total instructions run but a large decrease in frontend cache misses. +4.6% instructions, +11% L1 accesses, -99% L2 access, -40% RAM access. generate_compiled_100x, +4.0% instructions, +9.4% L1 access. cache miss improvements: -57% L2 access, -25% RAM access. Signed-off-by: Micah Elizabeth Scott

equix, hashx: Additional comment tweaks

2023-07-27T20:17:23Z

More review feedback. Thanks nickm! Signed-off-by: Micah Elizabeth Scott

tor-hspow, equix, hashx: Comment tweaks

2023-07-27T14:20:14Z

Making a few comment tweaks suggested in review feedback. Signed-off-by: Micah Elizabeth Scott