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During compilation, the bs_save2 and bs_restore2 instructions contain a match
context reference. That reference is the variable name that holds the match context.
beam_clean assumes that the reference always is an atom, which is not a safe assumption
since integers are legal variable names in Core Erlang.
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1a029efd1ad47f started to run the beam_block pass a second time,
but it did not attempt to combine adjacent blocks.
Combining adjacent blocks leads to many more opportunities for
optimizations.
After doing some diffing in generated code, it turns out that
there is no benefit for beam_split to split out line instructions
from blocks. It seems that the only reason it was done was to
slightly simplify the implementation of the no_line_info option
in beam_clean.
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There is an optimization in beam_clean that will remove values
having the same label as the failure label in a select_val
instruction. Conceptually, this optimization is in the wrong
module since ideally beam_clean is a mandatory pass that should
not do optimizations. Furthermore, this part of beam_clean is
called three times (from beam_dead, beam_peep, and as a compiler
pass from the 'compile' module), but it only does useful one of
the times it is called.
Therefore, move this optimization to the beam_peep pass.
The same optimization is done in beam_dead, but unfortunately it
misses some opportunities for optimization because the code sharing
optimization in beam_jump (share/1) runs after beam_dead. It would
be more satisfactory to have this optimization only in beam_dead,
but it turned out not to be trivial. If we try to run
beam_jump:share/1 before beam_dead, some optimizations will no
longer work in beam_dead because fallthroughs have been eliminated.
For the moment, the possible solutions to this problem seems to
involve more work and more complicated code than the gain from
eliminating the duplicated optimization would gain.
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In 45f469ca0890, the BEAM loader started to use x(1023) as scratch
register for some instructions. Therefore we should not allow
x(1023) to be used in code emitted by the compiler.
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The actual bs_match_string instruction has four operands:
bs_match_string {f,Lbl} Ctxt NumBits {string,ListOfBytes}
However, v3_codegen emits a more compact representation where
the bits to match are packaged in a bitstring:
bs_match_string {f,Lbl} Ctxt Bitstring
Currently, beam_clean:clean_labels/1 will rewrite the compact
representation to the final representation. That is unfortunate
since clean_labels/1 is called by beam_dead, which means that
the less compact representation will be introduced long before
it is actually needed by beam_asm. It will also complicate any
optimizations that we might want to do.
Move the rewriting of bs_match_string from beam_clean:clean_labels/1
to the beam_z pass, which is the last pass executed before
beam_validator and beam_asm.
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Commits b44f86b7 and 97953704 introduced translations of instructions
in beam_a and beam_z, but forgot to remove the handling of them in
beam_clean.
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* Combine multiple get values with one instruction
* Combine multiple check keys with one instruction
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To make it possible to build the entire OTP system, also define
dummys for the instructions in ops.tab.
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files as delimiters.
While working on a tool that processes Erlang code and testing it against this repo,
I found out about those little sneaky 0xff. I thought it may be of help to other
people build such tools to remove non-conforming-to-standard characters.
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Somewhat reduce the code bloat by eliminating special cases.
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Eliminate some code bloat.
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Rewrite the five binary creation instructions to a bs_init
instruction, in order to somewhat reduce code bloat.
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We can remove some code bloat by handling the special instructions
as BIF instructions in the optimization passes. Also note that
bs_utf*_size was not handled by beam_utils:check_liveness/3
(meaning the conservative answer instead of the correct answer
would be returned).
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Seven bs_put_* instructions can be combined into one generic bs_put
instruction to avoid some code bloat. That will also improve some
optimizations (such as beam_trim) that did not handle all bs_put*
variants.
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Also update the r12 and r13 options so that they imply no_line_info.
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