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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}
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.
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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regressions_SUITE will have code snippets which previously crashed the compiler.
This commits includes a test for Maps crash in beam_bool.
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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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* bjorn/compiler/doc:
Update compiler documentation
(Sneaking in OTP-12769 here which is a release note for syntax_tools.
Sorry about that.)
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Language cleaned up by the technical writer tmanevik from
Combitech. Proofreading and corrections by Björn Gustavsson.
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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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In a5d724cf240a, a debug option for running eprof on a specific
compiler pass was added. That commit added a direct call to the eprof
module in the tools application, and therefore the test case
otp_SUITE:runtime_dependencies/1 would fail because xref would find a
call to the tools application, but tools is not listed as a runtime
dependency in compiler.app.
Since the 'eprof' option is only likely to be used by compiler
maintainers, we don't want a real dependency to the tools application.
Therefore, use c:appcall/4 to hide the call to the eprof module (and
to report the error nicely if the tools application is missing).
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Allows for 'creation of sub binary delayed' optimization if
map instructions are in a clause.
Reported-by: José Valim
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The optimization introduced in 0a0d39d351fc would cause spurious
warnings of the type: "a term is constructed, but never used".
To avoid the warning, we must mark not only tuples and lists as
compiler_generated, but also each element. We must also propagate
compiler_generated annotations in lets. For example, if we have:
let <X -| ['compiler_generated']> = 42 in X + 1
we must propagate the compiler_generated annotation to the literal
when do constant propagation:
42 -| ['compiler_generated'] + 1
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This reverts commit e09dd66dc4d89c62ddfd8c19791f9678d5d787c6.
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* nox/compiler/parse_transform-undef/OTP-12723:
Properly report unknown parse transforms
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* bjorn/compiler/misc:
test_lib: Simplify uniq/0
beam_dict: Correct comparison in opcode/2
beam_utils: Re-use the local helper function drop_labels/1
beam_asm: Speed up encoding of large numbers
compilation_SUITE: Speed up the self_compile test cases
beam_listing: Optimize writing of .S files
v3_core, v3_codegen: Eliminate old-style catches
cerl_inline: Replace old-style 'catch' with 'try'...'catch'
sys_core_fold: Suppress warnings better
beam_utils: Teach check_liveness/3 to understand get_map_elements
Teach beam_trim to handle map instructions
beam_utils: Be less conservative about liveness for exit instructions
beam_validator: Stop validating the 'aligned' flag for binaries
beam_validator: Clean up updating of types for y register
beam_validator: Remove support for removed BIF fault/1,2
beam_validator: Correct merging of states
beam_validator: Correct merging of y registers
sys_pre_expand: Remove unused fields in #expand{} record
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Simplify the uniq/0 function by using erlang:unique_integer/1.
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The intention of the comparison is to avoid unnecessary updates of the
">=" instead of ">". With the ">" comparison, typically every line
instruction would cause the #asm{} record to be updated.
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In 8470558, the drop_labels/1 function was added to beam_utils
as a minor optimization. Since the function is already available,
we might as well use it in index_label/3 too.
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The misc_SUITE:integer_encoding/1 test case is annoyingly slow.
Rewrite the encoding of integers in beam_asm to use the
binary:encode_unsigned/1 BIF.
Also tweak the test case itself. Scale the down the maximum
size of the numbers being generated, but also add test of
numbers around boundaries of power of two (which are the numbers
most likely to expose bugs in the encoding).
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It is not necessary to compile the compile three times. After the
second compilation, we compare the generated .beam files with the
.beam files that were used when compiling them. Doing one more
round will not find more bugs.
While we are it, remove the ?line macros and the unused make_current/1
function.
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The test suites generates listing files, so we can slightly speed
up running of test suites (especially when running 'cover') by
optimizing writing of .S files.
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