Minor cleanups and bug fixes of the compiler #1965
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The purpose of beam_flatten is to eliminate the blocks created by
beam_block, but it also does a few optimizations because at the
time the optimizations were added, beam_flatten was the most
convenient place.
Move the optimization that places `{move,Something,{x,0}}` before
`call` instructions from beam_flatten to beam_ssa_codegen.
This change will very slightly improve compilation times, and it
will also apply the optimization in more places. In particular,
a `{move,Literal,{x,0}}` would never be moved passed a `trim`
instruction before this change. Now it will.
Continuing the simplification of beam_flatten, move the optimization that eliminates a test_heap instruction following a binary construction by incorporating the allocation of the heap space into the bs_init* instruction itself. This change does not change the generated code in any way. Also remove beam_utils:combine_heap_needs/2, because beam_flatten was the last user of it.
It is not necessary to combine get_hd and get_tl instruction to a get_list instruction. It will be done in beam_z. After this change, beam_flatten does nothing more than eliminating the blocks.
Using maps and cerl_sets instead of dict and sets will slightly speed up the beam_clean pass for modules with many functions and/or calls to local functions.
The source map for `get_map_element` is not supposed to be a literal,
and the sanitization code is supposed to ensure that.
The sanitization incorrectly translated this code:
Map = get_tuple_element literal {ok,#{key=>value}}, literal 1
Var = get_map_element Map, literal {a,key}
To this code:
Var = get_map_element literal #{key=>value}, literal {a,key}
Make sure to substitute the arguments for `get_map_element` before
looking for a literal source map.
Disallow a literal map source for get_map_elements. There is currently runtime support for get_map with a literal map source, but by forbidding it in OTP 22, the runtime support could be removed in a future release (perhaps OTP 24). Also verify that the source arguments for get_list, get_hd, get_tl, and get_tuple_element are not literals. Literals are not supported for those instructions in the runtime system; verifying it in beam_validator is a convenience so that this kind of bug will be detected already during compilation.
The only caller of bif_to_test/3 is beam_ssa_codegen.
Moving away this optimization makes beam_block do one thing and one thing only -- creating blocks.
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This pull request introduces several minor cleanups, bug fixes, and improvements in the compiler. See the individual commit messages for details.