The expansion of record field updates, when more than one field is updated, but not a majority of the fields, will create a sequence of calls to `erlang:setelement(Index, Value, Tuple)` where Tuple in the first call is the original record tuple, and in the subsequent calls Tuple is the result of the previous call. Furthermore, all Index values are constant positive integers, and the first call to `setelement` will have the greatest index. Thus all the following calls do not actually need to test at run-time whether Tuple has type tuple, nor that the index is within the tuple bounds. Since OTP R7, the `sys_core_dsetel` pass, run as the very last Core Erlang pass, has optimized this sequence of `setelement` calls to use a special destructive version of `setelement` (called `set_tuple_element`) for all but the very first `setelement` in the sequence. It turns out that the presence of the `set_tuple_element` in SSA code is awkward and can prevent or complicate type analysis and aggressive optimizations. Therefore, this commit removes the `sys_core_dsetel` pass and reimplements it for SSA code. The optimization will be done in the `beam_ssa_pre_codegen` pass (that is, just before code generation and after running all other SSA code optimization passes). In most cases, the resulting BEAM code is identical to previous code. For a few modules, the BEAM code is actually slightly better, with smaller stack frames.
This serves as a base for the upcoming module-level type optimization, but may come in handy for other passes like beam_ssa_funs and beam_ssa_bsm that have their own ad-hoc implementations.
Do the optimizations of bs_put* instructions in beam_ssa_opt and remove the beam_bs pass. This can lead to a slight improvement of compilation times.
Share code for semantically equivalent blocks referred to to by `br` and `switch` instructions. A similar optimization is done in `beam_jump`, but doing it here as well is beneficial as it may enable other optimizations. Also, if there are many semantically equivalent clauses, this optimization can substanstially decrease compilation times.
If a fun is defined locally and only used for calls, it can be replaced with direct calls to the relevant function. This greatly speeds up "named functions" (which rely on make_fun to recreate themselves) and macros that wrap their body in a fun.
This commit improves the bit-syntax match optimization pass, leveraging the new SSA intermediate format to perform much more aggressive optimizations. Some highlights: * Watch contexts can be reused even after being passed to a function or being used in a try block. * Sub-binaries are no longer eagerly extracted, making it far easier to keep "happy paths" free from binary creation. * Trivial wrapper functions no longer disable context reuse.
Most of the optimizations in beam_dead have been superseded by the optimizations in beam_ssa_dead. The forward/1 pass of beam_dead has been moved to beam_jump. The beam_split pass splits blocks that contain instructions with non-zero labels. Because there are no optimizations left that optimize instructions within blocks, beam_block never needs to put such instructions into blocks in the first place. beam_split also moved 'move' instructions out block to help beam_dead. That is no longer necessary since beam_dead no longer exists.
Add beam_ssa_dead to perform the main optimizations done by beam_dead: * Shortcut branches that jump to another block with a branch. If it can be seen that the second branch will always branch to a specific block, replace the target of the first branch. * Combined nested sequences of '=:=' tests and switch instructions operating on the same variable to a single switch. Diffing the compiler output, it seems that beam_ssa_dead finds many more opportunities for optimizations than beam_dead, although it does not find all opportunities that beam_dead does. In total, beam_ssa_dead is such improvement over beam_dead that there is no reason to keep beam_dead as well as beam_ssa_dead. Note that beam_ssa_dead does not attempt to optimize away redundant bs_context_binary instructions, because that instruction will be superseded by new instructions in the near future.