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When the bit syntax is used to match a single binary literal, the bit
syntax instructions will be replaced with a comparison to a binary
literal. The only problem is that the bs_context_to_binary instruction
will not be eliminated.
Example:
f(<<"string">>) ->
ok.
This function would be translated to:
{function, f, 1, 2}.
{label,1}.
{line,...}.
{func_info,...}.
{label,2}.
{test,is_eq_exact,{f,3},[{x,0},{literal,<<"string">>}]}.
{move,{atom,ok},{x,0}}.
return.
{label,3}.
{bs_context_to_binary,{x,0}}.
{jump,{f,1}}.
The bs_context_to_binary instruction serves no useful purpose,
since {x,0} can never be a match context. Eliminating the
instruction, the resulting code will be:
{function, f, 1, 2}.
{label,1}.
{line,...}.
{func_info,...}.
{label,2}.
{test,is_eq_exact,{f,1},[{x,0},{literal,<<"string">>}]}.
{move,{atom,ok},{x,0}}.
return.
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In a select_val instruction, values associated with a label
which is the same as the failure label can be removed. We
already do this optimization in beam_clean, but it is better
do this sort of optimization before the beam_jump pass.
Also rewrite a select_val instruction with a single value
to is_eq_exact instruction followed by a jump instruction.
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In the future we might want to add more bit syntax optimizations,
but beam_block is already sufficiently complicated. Therefore, move
the bit syntax optimizations out of beam_block into a separate
compiler pass called beam_bs.
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Knowing that a BIF returns an integer makes it possible to
replace '==' with the cheaper '=:=' test.
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Consider the following function:
f(Bin, Bool) ->
case Bin of
<<Val:16/binary,_/binary>> when Bool ->
Val
end.
Simplified, the generated code looks like:
bs_start_match2 Fail Live Bin => Bin
bs_get_integer2 Fail Live Bin size=Sz unit=1 => Val
bs_skip_bits2 Fail Bin size=all unit=8
is_eq_exact Fail Bool true
The code generator will replace the bs_skip_bits2 instruction with
a bs_test_unit instruction if it can be clearly seen that the
context register will not be used again. In this case, it is not
obvious without looking at the code at the Fail label.
However, it turns out that bs_test_unit instruction is always
safe beacuse of the way v3_kernel compiles pattern matching.
It doesn't matter whether the match context will be used again.
If it will be used again, the position in it will *not* be used.
Instead, a bs_restore2 instruction will restore one of the saved
instructions.
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d0784035ab fixed a problem with register corruption. Because of
that, opt_moves/2 will never be asked to optimize instructions with
more than two destination registers. Therefore, to regain full
coverage of beam_block, remove the final clause in opt_moves/2.
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* bjorn/compiler/remove-deprecated/OTP-12979:
core_lib: Remove previously deprecated functions
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* c-rack/fix-typo3:
Fix typo in call_last/3 spec
Fix typo
Fix typo: message to send is in x(1) not x(0)
Fix another small typo
Fix typo
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Instruction get_map_elements might destroy target registers when the fail-label is taken.
Only seen for patterns with two, and only two, target registers.
Specifically: we copy one register, and then jump.
foo(A,#{a := V1, b := V2}) -> ...
foo(A,#{b := V}) -> ...
call foo(value, #{a=>whops, c=>42}).
corresponding assembler:
{test,is_map,{f,5},[{x,1}]}.
{get_map_elements,{f,7},{x,1},{list,[{atom,a},{x,1},{atom,b},{x,2}]}}.
%% if 'a' exists but not 'b' {x,1} is overwritten, jump {f,7}
{move,{integer,1},{x,0}}.
{call_only,3,{f,10}}.
{label,7}.
{get_map_elements,{f,8},{x,1},{list,[{atom,b},{x,2}]}}.
%% {x,1} (src) is read with a corrupt value
{move,{x,0},{x,1}}.
{move,{integer,2},{x,0}}.
{call_only,3,{f,10}}.
The fix is to remove 'opt_moves' pass for get_map_elements instruction
in the case of two or more destinations.
Reported-by: Valery Tikhonov
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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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When translating guards to Core Erlang, it is sometimes necessary
to add an is_boolean/1 guard test. Here is an example when it is
necessary:
o(A, B) when A or B ->
ok.
That would be translated to something like:
o(A, B) when ((A =:= true) or (B =:= true)) and
is_boolean(A) and is_boolean(B) ->
ok.
The is_boolean/1 tests are necessary to ensure that the guard
fails for calls such as:
o(true, not_boolean)
However, because of a bug in v3_core, is_boolean/1 tests were
added when they were not necessary. Here is an example:
f(B) when not B -> ok.
That would be translated to:
f(B) when (B =:= false) and is_boolean(B) -> ok.
The following translation will work just as well.
f(B) when B =:= false -> ok.
Correct the bug to suppress those unnecessary is_boolean/1 tests.
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We can rewrite more instances of select_val to is_boolean because
it is not necessary that a particular label follows the select_val.
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Put 'try' instructions inside block to improve the optimization
of allocation instructions. Currently, the compiler only looks
at initialization of y registers inside blocks when determining
which y registers that will be "naturally" initialized.
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Simplify further optimizations by moving safe instructions to
before the 'try' or 'catch' instruction.
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When matching tuples, the pattern matching compiler would generate
code that would fetch all elements of the tuple that will ultimately
be used, *before* testing that (for example) the first element is the
correct record tag. For example:
is_tuple Fail {x,0}
test_arity Fail {x,0} 3
get_tuple_element {x,0} 0 {x,1}
get_tuple_element {x,0} 1 {x,2}
get_tuple_element {x,0} 2 {x,3}
is_eq_exact Fail {x,1} some_tag
If {x,2} and {x,3} are not used at label Fail, we can re-arrange the
code like this:
is_tuple Fail {x,0}
test_arity Fail {x,0} 3
get_tuple_element {x,0} 0 {x,1}
is_eq_exact Fail {x,1} some_tag
get_tuple_element {x,0} 1 {x,2}
get_tuple_element {x,0} 2 {x,3}
Doing that may be beneficial in two ways.
If the branch is taken, we have eliminated the execution of two
unnecessary instructions.
Even if the branch is never or rarely taken, there is the possibility
for more optimizations following the is_eq_exact instructions.
For example, imagine that the code looks like this:
get_tuple_element {x,0} 1 {x,2}
get_tuple_element {x,0} 2 {x,3}
move {x,2} {y,0}
move {x,3} {y,1}
Assuming that {x,2} and {x,3} have no further uses in the code
that follows, that can be rewritten to:
get_tuple_element {x,0} 1 {y,0}
get_tuple_element {x,0} 2 {y,1}
When should we perform this optimization?
At the very latest, it must be done before opt_blocks/1 in
beam_block which does the elimination of unnecessary moves.
Actually, we want do the optimization before the blocks have
been established, since moving instructions out of one block
into another is cumbersome.
Therefore, we will do the optimization in a new pass that is
run before beam_block. A new pass will make debugging easier,
and beam_block already has a fair number of sub passes.
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Here is an example of a move instruction that could not be optimized
away because the {x,2} register was not killed:
get_tuple_element Reg Pos {x,2}
.
.
.
move {x,2} {y,0}
put_list {x,2} nil Any
We can do the optimization if we replace all occurrences of the {x,2}
register as a source with {y,0}:
get_tuple_element Reg Pos {y,0}
.
.
.
put_list {y,0} nil Dst
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The 'move' optimization was relatively clean until GC BIFs
were introduced. Instead of re-thinking the implementation,
the existing code was fixed and patched.
The current code unsuccessfully attempts to eliminate 'move'
instructions across GC BIF and allocation instructions. We can
simplify the code if we give up as soon as we encounter any
instruction that allocates.
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opt_alloc/1 makes a redundant call to opt/1. It is redundant because
the opt/1 function has already been applied to the instruction
sequence prior to calling opt_alloc/1.
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Add the 'da' option to create a list after the beam_a pass. Seeing
how the code looks after beam_a, but before the blocks have been
established, is sometimes useful.
For symmetry, add the 'dz' option, even though it is just a synonym
for 'S'.
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Before beam_split the get_map_elements instruction is still in
blocks and the helper function in beam_jump did not reflect this.
Reported-by: Quviq twitter account
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* bjorn/compiler/spurious-warning:
sys_core_fold: Eliminate warnings for unused terms in effect context
sys_core_fold: Eliminate warnings for unused terms
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* egil/opt-compile-time/OTP-12774:
stdlib: Relax erl_anno_SUITE:is_anno/1 test
Update primary bootstrap
compiler: Use Maps as type information
compiler: Use Maps instead of dict in beam_jump
compiler: Use cerl_sets instead of gb_sets in beam_type
compiler: Use Maps instead of gb_trees in beam_dead
compiler: Use cerl_sets instead of gb_sets in beam_jump
compiler: Use cerl_sets instead of sets in v3_kernel
compiler: Use cerl_sets instead of gb_sets in sys_core_fold
compiler: Add cerl_sets module
compiler: Scope uses gb_sets not gb_trees
beam_dict: Use Maps to map function name indices
beam_dict: Use Maps to map line indices
beam_dict: Use Maps to map atom indices
v3_codegen: Use Maps to map local functions
v3_life: Refactor variable db
compiler: Use lc instead of map/1 in v3_codegen
stdlib: Optimize erl_anno:is_string/1
Conflicts:
bootstrap/lib/kernel/ebin/inet_dns.beam
bootstrap/lib/stdlib/ebin/erl_anno.beam
bootstrap/lib/stdlib/ebin/erl_lint.beam
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The optimization introduced in 0a0d39d351fc could cause spurious
warnings of the type: "a term is constructed, but never used".
That would happen for constructs in effect context.
To avoid those warnings, we will need to apply warning suppression
also in effect context.
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* egil/fix-compiler-beam_bsm/OTP-12758:
compiler: Add tests for beam_bsm get_map_elements
compiler: Teach beam_bsm get_map_elements instruction
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Using Maps as type information container speedups files like cow_http_hd.erl
by ~500ms. Previously spent ~60% of the time in orddict:store/3.
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A sets implementation based on maps.
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Small speed increase for large files.
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