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Minor cleanups and bug fixes of the compiler #1965

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merged 9 commits into from Oct 1, 2018

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@bjorng bjorng commented Sep 26, 2018

This pull request introduces several minor cleanups, bug fixes, and improvements in the compiler. See the individual commit messages for details.

bjorng added 9 commits Sep 20, 2018
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.
@bjorng bjorng self-assigned this Sep 26, 2018
@bjorng bjorng added the testing label Sep 27, 2018
@bjorng bjorng merged commit ba7e9c3 into erlang:master Oct 1, 2018
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@bjorng bjorng deleted the bjorng:bjorn/compiler/misc-cleanups branch Oct 1, 2018
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