vaivaswatha
commented
1 year ago When I worked on #4592, without local_copy_prop_prememcpy, the test u256_ops_test wouldn't compile. That was because, the new optimization inserted instructions at the beginning of the block, when the use was actually much later, thus increasing register pressure. With #4628 however, this issue is solved. u256_ops_test compiles fine now when local_copy_prop_prememcpy is removed. So we just need to benchmark and if the change is acceptable, remove it.
anton-trunov
The optimization pass was written during the IR refactor of #4336, and uses an ad-hoc algorithm. A much more systematic (data-flow based, but not a fully data-flow analysis) algorithm was later implemented in #4592. But that does not seem to cover everything that the ad-hoc algorithm did. This needs to be investigated and the function then removed, ensuring correctness and no penalty in generated code sizes.
The algorithm implemented in #4592, to optimize a sequence of
memcpys, does so by optimizing pairs in a loop. This is inefficient, and can probably be done in one go.