Erlang -- Compiler Release Notes

Compiler

Release Notes

Version 7.2

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### Chapters

- Compiler Release Notes
  - Top of chapter
  - Compiler 7.2
  - Compiler 7.1.5
  - Compiler 7.1.4
  - Compiler 7.1.3
  - Compiler 7.1.2
  - Compiler 7.1.1
  - Compiler 7.1
  - Compiler 7.0.4.1
  - Compiler 7.0.4
  - Compiler 7.0.3
  - Compiler 7.0.2
  - Compiler 7.0.1
  - Compiler 7.0
  - Compiler 6.0.3.1
  - Compiler 6.0.3
  - Compiler 6.0.2
  - Compiler 6.0.1
  - Compiler 6.0
  - Compiler 5.0.4
  - Compiler 5.0.3
  - Compiler 5.0.2
  - Compiler 5.0.1
  - Compiler 5.0
  - Compiler 4.9.4
  - Compiler 4.9.3
  - Compiler 4.9.2
  - Compiler 4.9.1
  - Compiler 4.9
  - Compiler 4.8.2
  - Compiler 4.8.1
  - Compiler 4.8
  - Compiler 4.7.5
  - Compiler 4.7.4
  - Compiler 4.7.3
  - Compiler 4.7.2
  - Compiler 4.7.1
  - Compiler 4.7
  - Compiler 4.6.5
  - Compiler 4.6.4
  - Compiler 4.6.3
  - Compiler 4.6.2
  - Compiler 4.6.1
  - Compiler 4.6.0.1
  - Compiler 4.6
  - Compiler 4.5.5
  - Compiler 4.5.4
  - Compiler 4.5.3
  - Compiler 4.5.2.1
  - Compiler 4.5.2
  - Compiler 4.5.1.1
  - Compiler 4.5.1
  - Compiler 4.5
  - Compiler 4.4.5
  - Compiler 4.4.4
  - Compiler 4.4.3
  - Compiler 4.4.2.1
  - Compiler 4.4.2
  - Compiler 4.4.1
  - Compiler 4.4
  - Compiler 4.3.12
  - Compiler 4.3.11
  - Compiler 4.3.10
  - Compiler 4.3.9
  - Compiler 4.3.8
  - Compiler 4.3.7
  - Compiler 4.3.6
  - Compiler 4.3.5
  - Compiler 4.3.4
  - Compiler 4.3.3
  - Compiler 4.3.2
  - Compiler 4.3.1

# 1 Compiler Release Notes

This document describes the changes made to the Compiler application.

### 1.1 Compiler 7.2

#### Fixed Bugs and Malfunctions

- Fixed an error in an optimization pass that caused impossible tuple matching.

  Own Id: OTP-14855 Aux Id: ERL-549

- The exception thrown when a list comprehension was given a non-list term was not always correct.

  Own Id: OTP-14992 Aux Id: ERL-572

- The compiler could produce incorrect code in rare circumstances when the [{inline,F/A}] option was used.

  Own Id: OTP-15115 Aux Id: PR-1831

#### Improvements and New Features

- Changed the default behaviour of .erlang loading: .erlang is no longer loaded from the current directory. c:erlangrc(PathList) can be used to search and load an .erlang file from user specified directories.

  escript, erlc, dialyzer and typer no longer load an .erlang at all.

  *** POTENTIAL INCOMPATIBILITY ***

  Own Id: OTP-14439

- Support for "tuple calls" have been removed from the run-time system. Tuple calls was an undocumented and unsupported feature which allowed the module argument for an apply operation to be a tuple: Var = dict:new(), Var:size(). This "feature" frequently caused confusion, especially when such call failed. The stacktrace would point out functions that don't exist in the source code.

  For legacy code that need to use parameterized modules or tuple calls for some other reason, there is a new compiler option called tuple_calls. When this option is given, the compiler will generate extra code that emulates the old behavior for calls where the module is a variable.

  *** POTENTIAL INCOMPATIBILITY ***

  Own Id: OTP-14497

- In code such as example({ok, Val}) -> {ok, Val}. a tuple would be built. The compiler will now automatically rewrite the code to example({ok,Val}=Tuple) -> Tuple. which will reduce code size, execution time, and remove GC pressure.

  Own Id: OTP-14505

- The optimization of case expression where only one of the case arms can execute successfully has been improved.

  Own Id: OTP-14525

- Some uses of binary matching has been slightly improved, eliminating unnecessary register shuffling.

  Own Id: OTP-14594 Aux Id: ERL-444

- There is a new {compile_info,Info} option for the compiler that allows BEAM-based languages such as Elixir and LFE to add their own compiler versions.

  Own Id: OTP-14615 Aux Id: PR-1558

- Loaded BEAM code in a 64-bit system requires less memory because of better packing of operands for instructions.

  These memory savings were achieved by major improvements to the beam_makeops scripts used when building the run time system and BEAM compiler. There is also new for documentation for beam_makeops that describes how new BEAM instructions and loader transformations can be implemented. The documentation is found in here in a source directory or git repository: erts/emulator/internal_doc/beam_makeops.md. An online version can be found here: https://github.com/erlang/otp/blob/master/erts/emulator/internal_doc/beam_makeops.md

  Own Id: OTP-14626

- Size calculations for binary constructions has been somewhat optimized, producing smaller code.

  Own Id: OTP-14654

- When the value returned from a 'catch' expression is ignored, no stacktrace will be built if an exception is caught. That will save time and produce less garbage. There are also some minor optimizations of 'try/catch' both in the compiler and run-time system.

  Own Id: OTP-14683

- There is a new syntax in 'try/catch' for retrieving the stacktrace without calling 'erlang:get_stacktrace/0'. See the reference manual for a description of the new syntax. The 'erlang:get_stacktrace/0' BIF is now deprecated.

  Own Id: OTP-14692

- The following is an internal change in the compiler, that is not noticeable for normal use of the compiler: The module v3_life has been removed. Its functionality has been simplified and integrated into v3_codegen.

  Own Id: OTP-14712

- The optimization of binary matching that delays creation of sub binaries (see the Efficiency Guide) could be thwarted by the argument order and could be necessary to change the argument order. The compiler has now become smarter and can handle any argument order.

  Own Id: OTP-14774

- When the compiler was faced with complex case expressions it would unnecessarily allocate stack elements and shuffle data between x and y registers. Improved code generation to only allocate a stack frame when strictly necessary.

  Own Id: OTP-14808 Aux Id: ERL-514

- There is a new option 'makedep_side_effect' for the compiler and -MMD for 'erlc' that generates dependencies and continues to compile as normal.

  Own Id: OTP-14830

- When compiling modules with huge functions, the compiler would generate a lot of atoms for its internal, sometimes so many that the atom table would overflow. The compiler has been rewritten to generate far less internal atoms to avoid filling the atom table.

  Own Id: OTP-14968 Aux Id: ERL-563

- External funs with literal values for module, name, and arity (e.g. erlang:abs/1) are now treated as literals. That means more efficient code that produces less garbage on the heap.

  Own Id: OTP-15003

- Two new guards BIFs operating on maps have been added: map_get/2 and is_map_key/2. They do the same as maps:get/2 and maps:is_key/2, respectively, except that they are allowed to be used in guards.

  Own Id: OTP-15037 Aux Id: PR-1784, PR-1802

- A call or apply of a literal external fun will be replaced with a direct call.

  Own Id: OTP-15044 Aux Id: ERL-614

- Part of EEP-44 has been implemented.

  There is a new predefined macro called OTP_RELEASE which is an integer indicating the OTP release number (its value is 21 in this release).

  There are new preprocessor directives -if(Condition). and -elif(Condition).. The if/elif supports the builtin function defined(Symbol).

  Own Id: OTP-15087 Aux Id: PR-1810

### 1.2 Compiler 7.1.5

#### Fixed Bugs and Malfunctions

- The internal compiler pass (beam_validator) that validates the generated code has been strengthened.

  When compiling from BEAM assembly code, the beam_type optimizer pass could make the code unsafe. Corrected.

  Own Id: OTP-14863

- Corrected optimizations of integers matched out from binaries and used in bit operations.

  Own Id: OTP-14898

### 1.3 Compiler 7.1.4

#### Fixed Bugs and Malfunctions

- The 'deterministic' option was not recognized when given in a -compile() attribute in the source code.

  Own Id: OTP-14773 Aux Id: ERL-498

### 1.4 Compiler 7.1.3

#### Fixed Bugs and Malfunctions

- The compiler could issue an incorrect internal consistency failure diagnostic for some complicated bit syntax maches.

  Own Id: OTP-14640 Aux Id: ERL-490

### 1.5 Compiler 7.1.2

#### Fixed Bugs and Malfunctions

- Fail labels on guard BIFs weren't taken into account during an optimization pass, and a bug in the validation pass sometimes prevented this from being noticed when a fault occurred.

  Own Id: OTP-14522 Aux Id: ERIERL-48

- When compiling from Core Erlang, an 'apply' with a nested apply in the function position would be treated as an invalid call. Corrected. (Thanks to Mikael Pettersson for reporting this bug.)

  Own Id: OTP-14526

- Fixed checking of binary matching in the beam_validator module to ensure that potential compiler bugs are found at compile-time instead as emulator crash at run-time.

  Own Id: OTP-14591

- There could be false warnings for erlang:get_stacktrace/0 being used outside of a try block when using multiple catch clauses.

  Own Id: OTP-14600 Aux Id: ERL-478

#### Improvements and New Features

- The Erlang code linter no longer checks that the functions mentioned in nowarn_deprecated_function options are declared in the module.

  Own Id: OTP-14378

### 1.6 Compiler 7.1.1

#### Fixed Bugs and Malfunctions

- Fail labels on guard BIFs weren't taken into account during an optimization pass, and a bug in the validation pass sometimes prevented this from being noticed when a fault occurred.

  Own Id: OTP-14522 Aux Id: ERIERL-48

### 1.7 Compiler 7.1

#### Fixed Bugs and Malfunctions

- For many releases, it has been legal to override a BIF with a local function having the same name. However, calling a local function with the same name as guard BIF as filter in a list comprehension was not allowed.

  Own Id: OTP-13690

- compile:forms/2 would not return the module name as documented when one of the options 'from_core', 'from_asm', or 'from_beam' was given. Also, the compiler would crash if one of those options was combined with 'native'.

  Own Id: OTP-14408 Aux Id: ERL-417

#### Improvements and New Features

- Optimized test for tuples with an atom as first element.

  Own Id: OTP-12148

- Compilation of modules with huge literal binary strings is now much faster.

  Own Id: OTP-13794

- Replaced usage of deprecated symbolic time unit representations.

  Own Id: OTP-13831 Aux Id: OTP-13735

- The undocumented and unsupported module sys_pre_expand has been removed. As a partial replacement for the functionality, there is a new function erl_internal:add_predefined_functions/1 and erl_expand_records will now add a module prefix to calls to BIFs and imported functions.

  Own Id: OTP-13856

- The internal compiler passes now start all generated variables with "@" to avoid any conflicts with variables in languages such as Elixir or LFE.

  Own Id: OTP-13924

- The function fmod/2 has been added to the math module.

  Own Id: OTP-14000

- Code generation for complicated guards have been improved.

  Own Id: OTP-14042

- The compiler has new warnings for repeated identical map keys.

  A map expression such as,

  #{'a' => 1, 'b' => 2, 'a' => 3}.

  will produce a warning for the repeated key 'a'.

  Own Id: OTP-14058

- By default, there will now be a warning when export_all is used. The warning can be disabled using nowarn_export_all.

  Own Id: OTP-14071

- Optimize maps pattern matching by only examining the common keys in each clause first instead of all keys. This will reduce the number of lookups of each key in maps pattern matching.

  Own Id: OTP-14072

- There is a new 'deterministic' option to omit 'source' and 'options' tuples in the BEAM file.

  Own Id: OTP-14087

- Analyzing modules with binary construction with huge strings is now much faster. The compiler also compiles such modules slightly faster.

  Own Id: OTP-14125 Aux Id: ERL-308

- Atoms may now contain arbitrary Unicode characters.

  Own Id: OTP-14178

- compile:file/2 now accepts the option extra_chunks to include extra chunks in the BEAM file.

  Own Id: OTP-14221

- The format of debug information that is stored in BEAM files (when debug_info is used) has been changed. The purpose of the change is to better support other BEAM-based languages such as Elixir or LFE.

  All tools included in OTP (dialyzer, debugger, cover, and so on) will handle both the new format and the previous format. Tools that retrieve the debug information using beam_lib:chunk(Beam, [abstract_code]) will continue to work with both the new and old format. Tools that call beam_lib:chunk(Beam, ["Abst"]) will not work with the new format.

  For more information, see the description of debug_info in the documentation for beam_lib and the description of the {debug_info,{Backend,Data}} option in the documentation for compile.

  Own Id: OTP-14369 Aux Id: PR-1367

- In a future release, erlang:get_stacktrace/0 will probably only work when called from within a 'try' expression (otherwise it will return [].

  To help prepare for that change, the compiler will now by default warn if 'get_stacktrace/0' is used in a way that will not work in the future. Note that the warning will not be issued if 'get_stacktrace/0' is used in a function that uses neither 'catch' nor 'try' (because that could be a legal use if the function is called from within a 'try'.

  Own Id: OTP-14401

### 1.8 Compiler 7.0.4.1

#### Fixed Bugs and Malfunctions

- Fail labels on guard BIFs weren't taken into account during an optimization pass, and a bug in the validation pass sometimes prevented this from being noticed when a fault occurred.

  Own Id: OTP-14522 Aux Id: ERIERL-48

### 1.9 Compiler 7.0.4

#### Fixed Bugs and Malfunctions

- Minor internal changes. A typo in the documentation was also fixed.

  Own Id: OTP-14240

### 1.10 Compiler 7.0.3

#### Fixed Bugs and Malfunctions

- Fixed a compiler crash when maps were matched.

  Own Id: OTP-13931 Aux Id: ERL-266

- Fixed a compiler crash having to with the delayed sub-creation optimization. (Thanks to Jose Valim for reporting this bug.)

  Own Id: OTP-13947 Aux Id: ERL-268

- The compiler option inline_list_funcs accidentally turned off some other optimizations.

  Own Id: OTP-13985

- The compiler could sometimes generate spurious warnings when inlining was enabled.

  Own Id: OTP-14040 Aux Id: ERL-301

### 1.11 Compiler 7.0.2

#### Fixed Bugs and Malfunctions

- If the compiler fails to write the BEAM file, it will now report the reason of the error for the write operation.

  Own Id: OTP-13701

- Fixed an internal compiler error. (Thanks to Svilen Ivanov for reporting this bug.)

  Own Id: OTP-13780 Aux Id: ERL-202

- The compiler could crash when trying to compile a complicated expression with multiple catches all on one line . (Thanks to Thomas Arts for reporting this bug.)

  Own Id: OTP-13804 Aux Id: ERL-209

- Eliminated a few internal compiler failures.

  Own Id: OTP-13863

### 1.12 Compiler 7.0.1

#### Fixed Bugs and Malfunctions

- A literal binary matching regression was introduced in 19.0 where a match could fail to resolve to the right clause. This has now been fixed.

  Own Id: OTP-13738

### 1.13 Compiler 7.0

#### Fixed Bugs and Malfunctions

- compile:forms/1,2 would crash when used in a working directory that had been deleted by another process.

  Own Id: OTP-13430 Aux Id: ERL-113

- Dialyzer no longer crashes when there is an invalid function call such as 42(7) in a module being analyzed. The compiler will now warn for invalid function calls such as X = 42, x(7).

  Own Id: OTP-13552 Aux Id: ERL-138

#### Improvements and New Features

- Optimization of tuple matching has been slightly improved.

  Own Id: OTP-12951

- Five deprecated and undocumented functions in the module core_lib have been removed. The functions are: get_anno/{1,2}, is_literal/1, is_literal_list/1, and literal_value. Use the appropriate functions in the cerl module instead.

  Own Id: OTP-12979

- The pre-processor can now expand the ?FUNCTION_NAME and ?FUNCTION_ARITY macros.

  Own Id: OTP-13059

- The function mapfold/4 has been added to the cerl_trees module.

  Own Id: OTP-13280

- Bitstring comprehensions have been generalized to allow arbitrary expressions in the construction part.

  Own Id: OTP-13289

- The compiler will now produce warnings for binary patterns that will never match (example: <<-1/unsigned>> = Bin).

  Own Id: OTP-13374 Aux Id: ERL-44

- The compiler will no longer put the compilation date and time into BEAM files. That means that two BEAM files compiled on the same computer from the same source code and compilation options will be identical.

  Note: If you want to find out whether a BEAM file on disk is different from the loaded code, compared the MD5 value obtained from Mod:module_info(md5) with the MD5 value obtained from beam_lib:md5(BeamFileForMod)

  .

  *** POTENTIAL INCOMPATIBILITY ***

  Own Id: OTP-13504

- The function compile:env_compiler_options/0 has been added to allow tools to pick up the same default compiler options as the compiler itself.

  Own Id: OTP-13654

### 1.14 Compiler 6.0.3.1

#### Fixed Bugs and Malfunctions

- Fail labels on guard BIFs weren't taken into account during an optimization pass, and a bug in the validation pass sometimes prevented this from being noticed when a fault occurred.

  Own Id: OTP-14522 Aux Id: ERIERL-48

### 1.15 Compiler 6.0.3

#### Fixed Bugs and Malfunctions

- An complicated guard expression in a function call could crash the compiler. (Thanks to Thomas Arts for reporting this bug.)

  Own Id: OTP-13208

- Constructing a map in a guard in a catch could crash the compiler. (Thanks to Thomas Arts for reporting this bug.)

  Own Id: OTP-13223

- Updating a fun as if it were a map would cause the compiler to crash. (Thanks to Thomas Arts for reporting this bug.)

  Own Id: OTP-13231

- Fix pretty printing of Core Maps

  Literal maps could cause Dialyzer to crash when pretty printing the results.

  Own Id: OTP-13238

- A complex combination of bit syntax matching operations would cause an internal consistency check failure during compilation. (Thanks to Jose Valim for reporting this bug.)

  Own Id: OTP-13309

### 1.16 Compiler 6.0.2

#### Fixed Bugs and Malfunctions

- Fix cerl_trees:label/2 bug with map K/V swap

  Own Id: OTP-13091

- Warnings produced when the 'bin_opt_info' option was given could sometimes lack filenames and line numbers. (Thanks to José Valim for reporting this bug.)

  Own Id: OTP-13113

### 1.17 Compiler 6.0.1

#### Fixed Bugs and Malfunctions

- Fix get_map_elements register corruption

  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 if we copy one register and then jump.

  Own Id: OTP-12967

### 1.18 Compiler 6.0

#### Fixed Bugs and Malfunctions

- The compiler optimizes away building of terms that are never actually used. As a result, the compiler in OTP 18 may produce more warnings for terms that are built but not used than the compiler in OTP 17.

  Own Id: OTP-12453

- Using a map could incorrectly suppress warnings for unused variables.

  Own Id: OTP-12515

- The compiler now properly reports unknown parse transforms. That is, undef exceptions coming from the parse transform itself is reported differently from the absence of the parse transform.

  Own Id: OTP-12723

- Allow for 'creation of sub binary delayed' optimization if maps instructions are in a clause.

  Own Id: OTP-12758

#### Improvements and New Features

- The cerl and cerl_trees modules in the Compiler application are now documented.

  Own Id: OTP-11978

- The deprecated 'asm' option has been removed.

  *** POTENTIAL INCOMPATIBILITY ***

  Own Id: OTP-12100

- Support variables as Map keys in expressions and patterns

  Erlang will accept any expression as keys in Map expressions and it will accept literals or bound variables as keys in Map patterns.

  Own Id: OTP-12218

- Infer Map type information in beam_type compiler optimization pass.

  Own Id: OTP-12253

- Compiler optimizations have been improved.

  Own Id: OTP-12393

- Five undocumented functions in the module core_lib have been deprecated and will be removed in the next major release. The functions are: get_anno/{1,2}, is_literal/1, is_literal_list/1, and literal_value. Use the appropriate functions in the cerl module instead.

  Own Id: OTP-12497

- Change some internal data structures to Maps in order to speed up compilation time. Measured speed up is around 10%-15%.

  Own Id: OTP-12774

- Fix beam_bool pass for Maps instruction get_map_elements

  Before beam_split the get_map_elements instruction is still in blocks and the helper function in beam_jump did not reflect this.

  Own Id: OTP-12844 Aux Id: 17

### 1.19 Compiler 5.0.4

#### Fixed Bugs and Malfunctions

- Matching out a map from a record and then updating the record could cause a 'badarg' exception at run-time. (Thanks to Dmitry Aleksandrov for reporting this bug.)

  Own Id: OTP-12402

- The compiler would crash when compiling some complex, nonsensical guards such as:

  ... when {{X}}, -X...

  Own Id: OTP-12410

- In rare circumstances, using binary pattern in the value part of a map pattern would cause the compiler to crash.

  Own Id: OTP-12414

- Case expressions where a map was wrapped in a tuple or list such as:

  case {a,Map} of
  {a,#{k:=_}}=Tuple -> Tuple
  end.

  would be unsafely "optimized" to either cause an exception at run-time or would return an empty map.

  Own Id: OTP-12451

- When a variable was compared to a literal map using the '==' operator, the compiler would change the operator to '=:=' since it is more efficient. However, this optimization is not safe if the map literal has numeric keys or values. The compiler will now only do the optimization if all keys and values are non-numeric.

  Own Id: OTP-12456

### 1.20 Compiler 5.0.3

#### Fixed Bugs and Malfunctions

- Named funs with the same name and arity could get mixed up with each other.

  Own Id: OTP-12262

- Coalesce map keys in dialyzer mode

  This fixes a regression introduced in commit 805f9c89fc01220bc1bb0f27e1b68fd4eca688ba The problem occurred with compounded map keys compiled with dialyzer option turned on, '+dialyzer'.

  Reported by: Ivan Uemlianin

  Own Id: OTP-12347

### 1.21 Compiler 5.0.2

#### Fixed Bugs and Malfunctions

- Corrected a bug with incorrect code generation when inlining was turned on.

  Own Id: OTP-12132

### 1.22 Compiler 5.0.1

#### Fixed Bugs and Malfunctions

- A Dialyzer crash involving analysis of Map types has now been fixed.

  Own Id: OTP-11947

- The compiler would fail to compile a file with a latin-1 character in the false branch of an -ifdef or -indef.

  Own Id: OTP-11987

### 1.23 Compiler 5.0

#### Fixed Bugs and Malfunctions

- Line numbers would not be correct when a binary construction such as '<<Bin/binary,...>>' fails. (Thanks to Stanislav Seletskiy for reporting this bug.)

  Own Id: OTP-11572

- The compiler now properly annotates the code in value in the 'after' clause for a 'try' so that Dialyzer no longer generates a false warning for an unmatched return.

  Own Id: OTP-11580

- Some case statements where no clause would match could cause an internal error in the compiler. (Thanks to Erik Soe Sorensen for reporting this bug.)

  Own Id: OTP-11610

- With --Wunmatched_returns, dialyzer will no longer warn when the value of a list comprehension is ignored, provided that the each value in the list would be an atomic value (such as integer or atoms, as opposed to tuples and lists). Example: ignoring '[io:format(...) || ...]' will not cause a warning, while ignoring '[file:close(Fd) || ...]' will.

  Own Id: OTP-11626

- Matching out a binary and applying the binary as if it were a fun would crash the run-time system. (Thanks to Loïc Hoguin.)

  Own Id: OTP-11672

- Some local implementations of removing the last element from a list are replaced by lists:droplast/1. Note that this requires at least stdlib-2.0, which is the stdlib version delivered in OTP 17.0. (Thanks to Hans Svensson)

  Own Id: OTP-11678

- Allow all auto imports to be suppressed at once. Introducing the no_auto_import attribute: -compile(no_auto_import). Useful for code generation tools that always use the qualified function names and want to avoid the auto imported functions clashing with local ones. (Thanks to José Valim.)

  Own Id: OTP-11682

- Application upgrade (appup) files are corrected for the following applications:

  asn1, common_test, compiler, crypto, debugger, dialyzer, edoc, eldap, erl_docgen, et, eunit, gs, hipe, inets, observer, odbc, os_mon, otp_mibs, parsetools, percept, public_key, reltool, runtime_tools, ssh, syntax_tools, test_server, tools, typer, webtool, wx, xmerl

  A new test utility for testing appup files is added to test_server. This is now used by most applications in OTP.

  (Thanks to Tobias Schlager)

  Own Id: OTP-11744

- Adapt 'asm' deprecation message to new version scheme. (Thanks to Tuncer Ayaz)

  Own Id: OTP-11751

- A number of compiler errors where unusual or nonsensical code would crash the compiler have been reported by Ulf Norell and corrected by Anthony Ramine.

  Own Id: OTP-11770

#### Improvements and New Features

- Compilation times for modules with a huge number for record accesses using the dot operator has been improved.

  Own Id: OTP-10652

- The compiler can generate somewhat better code by moving let expressions into sequences. (Thanks to Anthony Ramine.)

  Own Id: OTP-11056

- Forbid unsized fields in patterns of binary generators and simplified v3_core's translation of bit string generators. (Thanks to Anthony Ramine.)

  Own Id: OTP-11186

- Funs can now be a given a name. Thanks to to Richard O'Keefe for the idea (EEP37) and to Anthony Ramine for the implementation.

  Own Id: OTP-11537

- Using the from_asm option to produce a BEAM file starting from BEAM assembly code would often fail because early optimization passes would not understand instructions that later optimization passes would introduce. (Thanks to Anthony Ramine.)

  Own Id: OTP-11544

- The .core and .S extensions are now documented in the erlc documentation, and the 'from_core' and 'from_asm' options are now documented in the compiler documentation. (Thanks to Tuncer Ayaz.)

  Own Id: OTP-11547

- Optimization of case expressions that build tuples or lists have been improved.

  Own Id: OTP-11584

- EEP43: New data type - Maps

  With Maps you may for instance:

    M0 = #{ a => 1, b => 2}, % create associations
    M1 = M0#{ a := 10 }, % update values
    M2 = M1#{ "hi" => "hello"}, % add new associations
    #{ "hi" := V1, a := V2, b := V3} = M2. % match keys with values

  For information on how to use Maps please see Map Expressions in the Reference Manual.

  The current implementation is without the following features:

    No variable keys
    No single value access
    No map comprehensions

  Note that Maps is experimental during OTP 17.0.

  Own Id: OTP-11616

- Some function specs are corrected or moved and some edoc comments are corrected in order to allow use of edoc. (Thanks to Pierre Fenoll)

  Own Id: OTP-11702

- Thanks to Anthony Ramine for several improvements to the optimizations in the BEAM compiler and for cleaning up the code the code that transforms list and binary comprehensions to Core Erlang.

  Own Id: OTP-11720

- The default encoding for Erlang source files is now UTF-8. As a temporary measure to ease the transition from the old default of latin-1, if the compiler encounters byte sequences that are not valid UTF-8 sequences, the compiler will re-try the compilation in latin-1 mode. This workaround will be removed in a future release.

  Own Id: OTP-11791

### 1.24 Compiler 4.9.4

#### Fixed Bugs and Malfunctions

- Typo fix ambigous -> ambiguous. Thanks to Leo Correa.

  Own Id: OTP-11455

#### Improvements and New Features

- Lift 'after' blocks to zeroary functions. Thanks to Anthony Ramine.

  Own Id: OTP-11267

### 1.25 Compiler 4.9.3

#### Fixed Bugs and Malfunctions

- Expressions such as 'B = is_integer(V), if B and B -> ok end' would crash the compiler.

  Own Id: OTP-11240

- compile:file2/2 with the option report_errors could return ErrorInfo tuples with only two elements, while the documentation says that the ErrorInfo tuple always has three elements. Also updated the documentation to add that the first element may be 'none' if no line number is applicable.

  Own Id: OTP-11304 Aux Id: seq12412

#### Improvements and New Features

- Fix matching of floating point middle-endian machines. Thanks to Johannes Weissl.

  Own Id: OTP-11201

- Restrict inlining of local fun references. Thanks to Anthony Ramine.

  Own Id: OTP-11211

- Silence a misleading warning with some comprehensions. Thanks to Anthony Ramine.

  Own Id: OTP-11212

- Forbid returning a match context in beam_validator. Thanks to Anthony Ramine.

  Own Id: OTP-11247

### 1.26 Compiler 4.9.2

#### Fixed Bugs and Malfunctions

- Compiling functions with complex boolean operations in guards could be very slow. (Thanks to Magnus Muller for reporting this issue.)

  Own Id: OTP-10939

- Certain guard expressions used in a receive statement could cause the compiler to crash.

  Own Id: OTP-11119 Aux Id: seq12342

#### Improvements and New Features

- Fix optimization of some binary comprehensions. Thanks to Anthony Ramine.

  Own Id: OTP-11005

- Use a set to store ref registers in beam_receive. Thanks to Anthony Ramine.

  Own Id: OTP-11069

- Fix renaming of bs_put_string instructions. Thanks to Anthony Ramine.

  Own Id: OTP-11129

### 1.27 Compiler 4.9.1

#### Fixed Bugs and Malfunctions

- The compiler would crash attempting to compile expressions such as "element(2, not_tuple)".

  Own Id: OTP-10794

- Forbid multiple values in Core Erlang sequence arguments. Thanks to José Valim and Anthony Ramine.

  Own Id: OTP-10818

- An unsafe optimization would cause the compiler to crash with an internal error for certain complex code sequences.

  Own Id: OTP-10825 Aux Id: seq12247

#### Improvements and New Features

- Integers in expression that will give a floating point result (such as "X / 2" will now be converted to floating point at compile-time. (Suggested by Richard O'Keefe.)

  Identical floating points constans in a module will now be coalesced to one entry in the constant pool.

  Own Id: OTP-10788

### 1.28 Compiler 4.9

#### Improvements and New Features

- The compiler optimizations have been polished, so that the code quality will be slightly better in some cases.

  Own Id: OTP-10193

- Support for Unicode has been implemented.

  Own Id: OTP-10302

- Where necessary a comment stating encoding has been added to Erlang files. The comment is meant to be removed in Erlang/OTP R17B when UTF-8 becomes the default encoding.

  Own Id: OTP-10630

- Fix some wrong warnings triggered by the option inline_list_funcs. Thanks to Anthony Ramine.

  Own Id: OTP-10690

- Forbid local fun variables in Core Erlang guards. Thanks to Anthony Ramine.

  Own Id: OTP-10706

- Binary syntax matches could cause an internal consistency error in in the compiler. (Thanks to Viktor Sovietov for reporting this bug.)

  Own Id: OTP-10724

### 1.29 Compiler 4.8.2

#### Fixed Bugs and Malfunctions

- Modules with very many functions would compile very slowly.

  Own Id: OTP-10123

- compile:forms/2 will now use a {source,SourceFilePath} to set the source returned by module_info(compile) (Thanks to José Valim)

  Own Id: OTP-10150

- A process which had enabled trap_exit would receive EXIT messages after calling the compiler. (Thanks to Jeremy Heater.)

  Own Id: OTP-10171

- Fix messages ordering with column numbers

  Own Id: OTP-10183

- sys_pre_expand: Fix BASE never being set

  Commit a612e99fb5aaa934fe5a8591db0f083d7fa0b20a turned module attributes from 2-tuples to 3-tuples but forgot to update get_base/1, breaking BASE for parametric modules.

  Own Id: OTP-10184

- The compiler will now issue a warning if literal tuple funs are used. For example, {erlang,is_tuple}(X) will now generate a warning.

  Own Id: OTP-10185

- The compiler will now warn for illegal sizes for segments in binary construction. For example, <<X:(2.5)>> will now cause the compiler to issue a warning.

  Own Id: OTP-10197

- Fix the erlc -MP flag

  Because of a copy-and-paste error in erlc.c, the -MP flag had the same effect as -MG. As a workaround, you had to pass +makedep_phony to enable the MP option. This patch makes -MP work as intended.

  Own Id: OTP-10211

### 1.30 Compiler 4.8.1

#### Fixed Bugs and Malfunctions

- In rare circumstance, the compiler could crash when compiling a case statement. (Thanks to Hakan Mattsson.)

  Own Id: OTP-9842

- Calling a guard test (such as is_list/1) from the top-level in a guard, would cause a compiler crash if there was a local definition with the same name. Corrected to reject the program with an error message.

  Own Id: OTP-9866

- Using get/1 in a try block could in some cases cause an internal compiler error. (Thanks to Eric Merritt.)

  Own Id: OTP-9867

- An unexported on_load function would not get run if the module was compiled with the inline option. (Thanks to Yiannis Tsiouris.)

  Own Id: OTP-9910

- Fixed a discrepancy in compile_info

  The BEAM disassembler used the atom 'none' to signify the absence of a compile_info chunk in a .beam file. This clashed with the type declaration of the compile_info field of a #beam_file{} record as containing a list. Now [] signifies the absence of this chunk. This simplifies the code and avoids a dialyzer warning.

  Own Id: OTP-9917

- Fix typo in `compile' doc: unmatched parenthesis (Thanks to Ricardo Catalinas Jiménez)

  Own Id: OTP-9919

- In a try...catch statement that always returned false, the compiler would remove calls to BIFs that could not cause an exception (such as put/2). Example of such code: try put(K, V), false catch _:_ -> false end.

  Own Id: OTP-9982

### 1.31 Compiler 4.8

#### Fixed Bugs and Malfunctions

- Add '-callback' attributes in stdlib's behaviours

  Replace the behaviour_info(callbacks) export in stdlib's behaviours with -callback' attributes for all the callbacks. Update the documentation with information on the callback attribute Automatically generate 'behaviour_info' function from '-callback' attributes

  'behaviour_info(callbacks)' is a special function that is defined in a module which describes a behaviour and returns a list of its callbacks.

  This function is now automatically generated using the '-callback' specs. An error is returned by lint if user defines both '-callback' attributes and the behaviour_info/1 function. If no type info is needed for a callback use a generic spec for it. Add '-callback' attribute to language syntax

  Behaviours may define specs for their callbacks using the familiar spec syntax, replacing the '-spec' keyword with '-callback'. Simple lint checks are performed to ensure that no callbacks are defined twice and all types referred are declared.

  These attributes can be then used by tools to provide documentation to the behaviour or find discrepancies in the callback definitions in the callback module.

  Add callback specs into 'application' module in kernel Add callback specs to tftp module following internet documentation Add callback specs to inets_service module following possibly deprecated comments

  Own Id: OTP-9621

- The calculation of the 'uniq' value for a fun (see erlang:fun_info/1) was too weak and has been strengthened. It used to be based on the only the code for the fun body, but it is now based on the MD5 of the BEAM code for the module.

  Own Id: OTP-9667

#### Improvements and New Features

- Variables are now now allowed in 'fun M:F/A' as suggested by Richard O'Keefe in EEP-23.

  The representation of 'fun M:F/A' in the abstract format has been changed in an incompatible way. Tools that directly read or manipulate the abstract format (such as parse transforms) may need to be updated. The compiler can handle both the new and the old format (i.e. extracting the abstract format from a pre-R15 BEAM file and compiling it using compile:forms/1,2 will work). The syntax_tools application can also handle both formats.

  *** POTENTIAL INCOMPATIBILITY ***

  Own Id: OTP-9643

- filename:find_src/1,2 will now work on stripped BEAM files (reported by Per Hedeland). The HiPE compiler will also work on stripped BEAM files. The BEAM compiler will no longer include compilation options given in the source code itself in M:module_info(compile) (because those options will be applied anyway if the module is re-compiled).

  Own Id: OTP-9752

- Inlining binary matching could cause an internal compiler error. (Thanks to Rene Kijewski for reporting this bug.)

  Own Id: OTP-9770

### 1.32 Compiler 4.7.5

#### Fixed Bugs and Malfunctions

- Compiler options given in the source code using a -compile() attribute used to be included twice in Mod:module_info(compile). They are now only included once at the beginning of the list of options.

  Own Id: OTP-9534

- beam_disasm: Handle stripped BEAM files

  beam_disasm:file/1 would crash if asked to disassemble a stripped BEAM file without an "Attr" chunk. (Thanks to Haitao Li)

  Own Id: OTP-9571

### 1.33 Compiler 4.7.4

#### Fixed Bugs and Malfunctions

- If a variable is matched out in binary matching and used as the size for a binary element, it would seem to be unbound if used in a subsequent match operation. (Thanks to Bernard Duggan.)

  Own Id: OTP-9134

- Eliminate incorrect warning in sys_core_fold

  Own Id: OTP-9152

### 1.34 Compiler 4.7.3

#### Fixed Bugs and Malfunctions

- The -export_type() directive is no longer included among the attributes.

  Own Id: OTP-8998

#### Improvements and New Features

- The maximum number of allowed arguments for an Erlang function has been lowered from 256 to 255, so that the number of arguments can now fit in a byte.

  Own Id: OTP-9049

- Dependency generation for Makefiles has been added to the compiler and erlc. See the manual pages for compile and erlc. (Thanks to Jean-Sebastien Pedron.)

  Own Id: OTP-9065

### 1.35 Compiler 4.7.2

#### Fixed Bugs and Malfunctions

- Two compiler bugs (that would cause the compiler to terminate) reported by Christopher Williams have been fixed.

  Own Id: OTP-8949

#### Improvements and New Features

- The compiler would translate binary comprehensions containing tail segments in a way that would would confuse Dialyzer. For instance:

  [42 || <<_:8/integer, _/bits>> <= Bits]

  would produce a Dialyzer warning.

  Own Id: OTP-8864

- Code such as foo(A) -> <<A:0>> would crash the compiler.

  Own Id: OTP-8865

- The compiler could fail with an internal error when variables were exported from a receive block but the return value of the receive block were not used. (Thanks to Jim Engquist for reporting this error.)

  Own Id: OTP-8888

### 1.36 Compiler 4.7.1

#### Improvements and New Features

- Eliminated warnings for auto-imported BIF clashes.

  Own Id: OTP-8840

### 1.37 Compiler 4.7

#### Fixed Bugs and Malfunctions

- Several problems in the inliner have been fixed.

  Own Id: OTP-8552

#### Improvements and New Features

- The module binary from EEP31 (and EEP9) is implemented.

  Own Id: OTP-8217

- Local and imported functions now override the auto-imported BIFs when the names clash. The pre R14 behaviour was that auto-imported BIFs would override local functions. To avoid that old programs change behaviour, the following will generate an error:

  - Doing a call without explicit module name to a local function having a name clashing with the name of an auto-imported BIF that was present (and auto-imported) before OTP R14A

  - Explicitly importing a function having a name clashing with the name of an autoimported BIF that was present (and autoimported) before OTP R14A

  - Using any form of the old compiler directive nowarn_bif_clash

  If the BIF was added or auto-imported in OTP R14A or later, overriding it with an import or a local function will only result in a warning,

  To resolve clashes, you can either use the explicit module name erlang to call the BIF, or you can remove the auto-import of that specific BIF by using the new compiler directive -compile({no_auto_import,[F/A]})., which makes all calls to the local or imported function without explicit module name pass without warnings or errors.

  The change makes it possible to add auto-imported BIFs without breaking or silently changing old code in the future. However some current code ingeniously utilizing the old behaviour or the nowarn_bif_clash compiler directive, might need changing to be accepted by the compiler.

  *** POTENTIAL INCOMPATIBILITY ***

  Own Id: OTP-8579

- The undocumented, unsupport, and deprecated function lists:flat_length/1 has been removed.

  Own Id: OTP-8584

- Nested records can now be accessed without parenthesis. See the Reference Manual for examples. (Thanks to YAMASHINA Hio and Tuncer Ayaz.)

  Own Id: OTP-8597

- It is now possible to suppress the warning in code such as "list_to_integer(S), ok" by assigning the ignored value "_" like this: "_ = list_to_integer(S), ok".

  Own Id: OTP-8602

- receive statements that can only read out a newly created reference are now specially optimized so that it will execute in constant time regardless of the number of messages in the receive queue for the process. That optimization will benefit calls to gen_server:call(). (See gen:do_call/4 for an example of a receive statement that will be optimized.)

  Own Id: OTP-8623

- The compiler optimizes record operations better.

  Own Id: OTP-8668

### 1.38 Compiler 4.6.5

#### Fixed Bugs and Malfunctions

- Using complex boolean expressions in ifs could cause the compiler to either crash or teminate with an internal error. (Thanks to Simon Cornish.)

  Own Id: OTP-8338

- Bit string comprehensions can now be used in parameterized modules. (Thanks to Jebu Ittiachen.)

  Own Id: OTP-8447

#### Improvements and New Features

- The expected return value for an on_load function has been changed. (See the section about code loading in the Reference manual.)

  *** POTENTIAL INCOMPATIBILITY ***

  Own Id: OTP-8339

- In rare circumstances when using garbaging collecting guard BIFs, the validation pass (beam_validator) would signal that the code was unsafe, when it in fact was correct. (Thanks to Kiran Khaladkar.)

  Own Id: OTP-8378

- The -Werror option for erlc and the compiler option warnings_as_errors will cause warnings to be treated as errors. (Thanks to Christopher Faulet.)

  Own Id: OTP-8382

- Macros overloading has been implemented. (Thanks to Christopher Faulet.)

  Own Id: OTP-8388

### 1.39 Compiler 4.6.4

#### Fixed Bugs and Malfunctions

- The compiler's 'E' option now works with modules with types and specifications.

  Own Id: OTP-8238 Aux Id: OTP-8150

- Certain uses of binary matching in a begin-end in a list comprehension could cause the compiler to crash or generate incorrect code.

  Own Id: OTP-8271

#### Improvements and New Features

- The documentation is now built with open source tools (xsltproc and fop) that exists on most platforms. One visible change is that the frames are removed.

  Own Id: OTP-8201

- The compiler could crash if invalid calls to is_record/2 was used in (for example) a list comprehension. (Thanks to Tobias Lindahl.)

  Own Id: OTP-8269

- The -on_load() directive can be used to run a function when a module is loaded. It is documented in the section about code loading in the Reference Manual.

  Own Id: OTP-8295

### 1.40 Compiler 4.6.3

#### Improvements and New Features

- Corrected liveness optimization to eliminate a compiler crash that could occur when compiling bit syntax construction code. (Thanks to Mikage Sawatari.)

  Calling BIFs such as length/1 in guard context in a try/catch block could cause a compiler crash. (Thanks to Paul Fisher.)

  Using filter expressions containing andalso or orelse in a list comprehension could cause a compiler crash. (Thanks to Martin Engström.)

  Own Id: OTP-8054

- A guard with nested 'not' operators could cause the compiler to crash. (Thanks to Tuncer Ayaz.)

  Own Id: OTP-8131

### 1.41 Compiler 4.6.2

#### Fixed Bugs and Malfunctions

- The compiler would crash while compiling certain complex function bodies containing receive after due to a bug in the jump optimizer (a label that had only had backward references could still be removed). (Thanks to Vincent de Phily.)

  Own Id: OTP-7980

### 1.42 Compiler 4.6.1

#### Fixed Bugs and Malfunctions

- Miscellaneous minor bugs fixed.

  Own Id: OTP-7937

#### Improvements and New Features

- There will be more efficient code if there is a clause that matches the empty binary and no other clauses that matches non-empty binaries.

  Own Id: OTP-7924

- There is new option to allow a module to have a module name other than the filename. Do not use it unless you know what you are doing.

  Own Id: OTP-7927

### 1.43 Compiler 4.6.0.1

#### Fixed Bugs and Malfunctions

- Using andalso/orelse or record access in a try...catch could cause a compiler crash.

  Som large and complex functions could require extremely long compilation times (hours or days).

  Own Id: OTP-7905

### 1.44 Compiler 4.6

#### Fixed Bugs and Malfunctions

- For some complex guards which used andalso/orelse, the compiler would crash. (Thanks to Hunter Morris.)

  Own Id: OTP-7679

- Code that (incorrectly) used the the value of nested applications of setelement/3 in bit syntax construction could crash the compiler.

  Own Id: OTP-7690

- Modules containing huge integers (consisting of several hundreds of thousands of digits or more) could be slow to compile. This problem has been corrected.

  Own Id: OTP-7707 Aux Id: seq11129

- If the generator in a list comprehension is given a non-list term, there will now be function_clause exception instead of a case_clause exception (as it was in all releases before R12B).

  Own Id: OTP-7844

#### Improvements and New Features

- The compiler could crash if the size for a binary segment in matching was a complex literal such as binary or tuple.

  Own Id: OTP-7650

- The compiler generates more compact and faster code for matching of complex constants (such as constant lists and tuples).

  Own Id: OTP-7655

- The undocumented, unsupported, and deprecated guard BIF is_constant/1 has been removed.

  *** INCOMPATIBILITY with R12B ***

  Own Id: OTP-7673

- The compiler generates better code for many guard expressions, and especially for guards that use andalso/orelse or record fields.

  (In technical terms, andalso/orelse in a guard would case the creation of a stack frame and saving of all x registers that could potentially be alive after the guard and restoring all x registers before leaving the guard. For certain guards, far too many x registers were saved and subsequently restored. In this version of the compiler, no stack frame is created and no x registers are saved and restored.)

  Own Id: OTP-7718

- The default size for the resulting binary created by a binary comprehension was 64Kb in R12B (it would grow if needed). This was often far too much. In this release, the default is changed to 256 bytes. Furthermore, for most binary comprehensions without filters, the exact size of the resulting binary can be calculated beforehand and the compiler now generates code that does that calculation.

  Own Id: OTP-7737

- The short-circuit operators andalso and orelse no longer guarantees that their second argument is either true or false. As a consequence, andalso/orelse are now tail-recursive.

  *** POTENTIAL INCOMPATIBILITY ***

  Own Id: OTP-7748

- The compiler will refuse to a compile file where the module name in the file differs from the output file name.

  When compiling using erlc, the current working directory will no be included in the code path (unless explicitly added using "-pa .").

  *** POTENTIAL INCOMPATIBILITY ***

  Own Id: OTP-7793

- There will no longer be any warnings for list comprehensions without generators, as such list comprehension have turned out to be useful.

  Own Id: OTP-7846

- Warnings for obsolete guard tests are now turned on. (That is, writing list(L) in a guard instead of is_list(L) will generate a warning.)

  The warnings can be turned off using the nowarn_obsolete_guard option.

  Own Id: OTP-7850

- The copyright notices have been updated.

  Own Id: OTP-7851

- If a module contains an exported function with the same name as an auto-imported BIF (such as length/1), any calls to the BIF must have an explicit erlang: prefix, or there will be a compilation error (such calls would only generate a warning in previous releases).

  (The reason for the change is to avoid breaking code in a future major release, R14 or R15, in which we plan to make calls without a module prefix always call the local function in the same module even if there is an auto-imported BIF with the same name.)

  *** POTENTIAL INCOMPATIBILITY ***

  Own Id: OTP-7873

### 1.45 Compiler 4.5.5

#### Fixed Bugs and Malfunctions

- Matching on a zero-width segment in the bit syntax would crash the compiler. (Thanks to Will.)

  Own Id: OTP-7591

#### Improvements and New Features

- In bit syntax expressions which started with a binary segment, and was followed by at least two segments of variable size, too little space could be allocated for the binary, leading to memory corruption.

  Own Id: OTP-7556

- In user-defined attributes, Name/Arity is now allowed and will be translated to {Name,Arity}. (An implementation of EEP-24 by Richard O'Keefe.)

  The module_info/{0,1} functions automatically inserted into each compiled modules are now documented in the Modules section in the Reference Manual.

  Own Id: OTP-7586

### 1.46 Compiler 4.5.4

#### Improvements and New Features

- Certain complex bit syntax matching operations matching out binaries and having several clauses could give incorrect results (the matched out binaries were too short). (Thanks to Christian von Roques for bug report and correction.)

  Own Id: OTP-7498

### 1.47 Compiler 4.5.3

#### Improvements and New Features

- New option warn_export_all to warn for a module using export_all. (Thanks to Richard Carlsson.)

  Own Id: OTP-7392

### 1.48 Compiler 4.5.2.1

#### Fixed Bugs and Malfunctions

- In rare circumstances, the length/1 BIF (and a few other guard BIFs) would seem to return an incorrect value (of any type).

  Own Id: OTP-7345 Aux Id: seq10962

### 1.49 Compiler 4.5.2

#### Fixed Bugs and Malfunctions

- A bug in the old inliner has been fixed. Some undocumented functionality has been removed.

  Own Id: OTP-7223

- Matching several binary patterns in parallel using the '=' operator is not allowed (an implementation limitation), but the compiler did not reject all such attempts (depending on the patterns, the generated code might or might not work correctly). Now the compiler rejects all binary patterns joined by '='.

  Own Id: OTP-7227

- Complex combinations of record operations and binary matching could cause the compiler to crash. (Thanks to Vladimir Klebansky.)

  Own Id: OTP-7233

- In rare circumstances, mixing binary matching clauses with clauses matching other data types, the compiler could crash.

  Own Id: OTP-7240 Aux Id: seq10916

### 1.50 Compiler 4.5.1.1

#### Fixed Bugs and Malfunctions

- Corrected a compiler bug that could cause a complex binary matching operation to fail when it shouldn't. (Thanks to Tomas Stejskal.)

  Own Id: OTP-7188

- In unusual circumstances, the environment for a fun could bind wrong values.

  Own Id: OTP-7202 Aux Id: seq10887

- Long sequences of list comprehensions without generators joined by the '++' operator would cause a code expansion explosion, which could cause the compiler to run out of memory. To resolve this problem, in '[...||...]++Expr', Expr is now evaluated before the list comprehension. This change is backwards compatible (see the following note about evaluation order if you have doubts).

  Note about evaluation order: The Reference manual says that subexpressions are evaluated in any order before the expression itself. Therefore, in an expression such as 'LeftExpr++RightExpr', you should not depend on LeftExpr being evaluated before RightExpr or vice versa. The evaluation order is only important if the expressions contains and/or depends on operations with side-effects, such as message passing or ETS operations.

  Own Id: OTP-7206

### 1.51 Compiler 4.5.1

#### Fixed Bugs and Malfunctions

- A match expression inside a function call could cause a false "a term is constructed but never used" warning.

  Own Id: OTP-7018 Aux Id: seq10824

- The compiler could crash if a binary tail was matched out, and then used in a binary append operation. (Thanks to Oleg Avdeev.)

  Similarly, the compiler could crash if a binary tail was matched out, and then used (incorrectly) in binary construction in an integer field. (Thanks to Fredrik Svahn.) Or was incorrectly used in a float field. Or was used in a binary field with a given length. (Thanks to Chih - Wei Yu.)

  Own Id: OTP-7022

- Matching an empty binary in a record and then using the same record again could cause a compiler crash. (Thanks to Fredrik Thulin.)

  Own Id: OTP-7029

- In rare circumstances, constants containing floating points and integers could be confused. Example:

  f(a) -> [1]; f(b) -> [1.0].

  Both f(a) and f(b) would return [1].

  Own Id: OTP-7073

- Some bit syntax code such as

  matching d(_,<$lt;$gt;$gt;) -> one; d(0,<$lt;D$gt;$gt;) ->two.

  could crash the compiler. (Thanks to Simon Cornish.)

  Own Id: OTP-7094

- In unusual circumstances, a call to a fun could fail due to an unsafe optimization. (Thanks to Simon Cornish.)

  Own Id: OTP-7102

- Bit syntax matching with a guard containing two or more uses of andalso/orelse could cause the compiler to crash. (Thanks to Mateusz Berezecki.)

  Own Id: OTP-7113

- This was only a problem if you generated or wrote your own Core Erlang code: The Core Erlang optimizer code could move nested calls such as erlang:'$lt;'(erlang:length(L), 2) as case expression into a guard, which would change the semantics. (Thanks to Robert Virding.)

  Own Id: OTP-7117

#### Improvements and New Features

- The compiler could generate suboptimal code for record updates if the record update code consisted of multiple source code lines.

  Own Id: OTP-7101

### 1.52 Compiler 4.5

#### Fixed Bugs and Malfunctions

- The compiler used to allow that a binary field without size could be used in other positions than at the end in bit syntax pattern. For instance, <<B/binary,EmptyBinary/binary>> = Bin used to compile, but now the compilation will fail with an an error message.

  Also, it is now longer permitted to give a literal string in a binary pattern a type or a size; for instance, <<"abc"/binary>> = Bin will no longer compile. (In previous releases, there would always be a badmatch exception at run-time.)

  Own Id: OTP-6885

#### Improvements and New Features

- Bitstrings (bit-level) binaries and binary comprehensions are now part of the language. See the Reference Manual.

  Own Id: OTP-6558

- The 'compressed' option for the compiler has been documented.

  Own Id: OTP-6801

- If the value of a list comprehension is not used, such as in '[do_something(X) || X <- List], ok', a result list will no longer be built. For more details, see the Efficiency Guide.

  If the value of an expression is not used, and the expression has no side effects except for possibly throwing an exception, a warning will be generated. Examples: 'self(),ok' and '{error,Reason},ok'.

  Own Id: OTP-6824

- Three new functions have been added to the compile module: noenv_file/2, noenv_forms/2, and noenv_output_generated/1.

  Own Id: OTP-6829

- Many bit syntax operations, both construction and matching, are faster. For further information, see the Efficiency Guide.

  Own Id: OTP-6838

- Literal lists, tuples, and binaries are no longer constructed at run-time as they used to be, but are stored in a per-module constant pool. Literals that are used more than once are stored only once.

  This is not a change to the language, only in the details of its implementation. Therefore, the implications of this change is described in the Efficiency Guide.

  Example 1: In the expression element(BitNum-1, {1,2,4,8,16,32,64,128}), the tuple used to be constructed every time the expression was executed, which could be detrimental to performance in two ways if the expression was executed in a loop: the time to build the tuple itself and the time spent in garbage collections because the heap filled up with garbage faster.

  Example 2: Literal strings, such as "abc", used to be stored in the compiled code compactly as a byte string and expanded to a list at run-time. Now all strings will be stored expanded to lists (such as [$a,$b,$c]) in the constant pool. That means that the string will be faster to use at run-time, but that it will require more space even when not used. If space is an issue, you might want to use binary literals (that is, <<"abc"<<) instead of string literals for infrequently used long strings (such as error messages).

  Own Id: OTP-6850

- Recursive calls now usually consume less stack than in R11B. See the Efficiency Guide.

  Own Id: OTP-6862 Aux Id: seq10746

- Two new guard BIFs have been introduced as a recommended replacement for size/1. (The size/1 BIF will be removed no earlier than in R14B.) The BIFs are tuple_size/1 to calculate the size of a tuple and byte_size/1 to calculate the number of bytes needed for the contents of the binary or bitstring (rounded up to the nearest number of bytes if necessary).

  There is also a new bit_size/1 BIF that returns the exact number of bits that a binary or bitstring contains.

  Own Id: OTP-6902

- The two internal functions erl_bifs:is_bif/3 and erl_bifs:is_guard/3 have been removed. They were unsupported, undocumented, and unmaintained.

  Own Id: OTP-6966

### 1.53 Compiler 4.4.5

#### Fixed Bugs and Malfunctions

- The compiler would crash if you tried to combine to non-list literals with '++' (for instance, an_atom++"string").

  Own Id: OTP-6630 Aux Id: seq10635

#### Improvements and New Features

- Minor Makefile changes.

  Own Id: OTP-6689

### 1.54 Compiler 4.4.4

#### Fixed Bugs and Malfunctions

- Incorrect code could be generated for bit syntax matching if the old inliner was used with aggressive settings.

  Own Id: OTP-6461

### 1.55 Compiler 4.4.3

#### Fixed Bugs and Malfunctions

- The R10B compiler could generate unsafe bs_save/bs_restore instructions that could cause memory corruption. (The R11B compiler does not have that problem.) The erlang emulator will now refuse to load R10B-compiled modules that contain such unsafe bs_save/bs_restore instructions. In addition, the beam_validator module in the compiler will also reject such instructions (in case it is used to validate R10B code). (Thanks to Matthew Reilly.)

  Own Id: OTP-6386

#### Improvements and New Features

- Directives for parse transforms that have been run are now removed from the abstract code stored when the debug_info option is given, to prevent the parse transforms to be run again.

  Own Id: OTP-5344

- Minor improvements in code generation for some guards expression involving boolean expressions.

  Own Id: OTP-6347

### 1.56 Compiler 4.4.2.1

#### Fixed Bugs and Malfunctions

- The compiler could generate incorrect code for bit syntax matching consisting of several clauses.

  Own Id: OTP-6392 Aux Id: seq10539

### 1.57 Compiler 4.4.2

#### Fixed Bugs and Malfunctions

- Defining a fun itself containing a fun in an after block of a try would cause the compiler to crash or generate incorrect code. (Thanks to Tim Rath.)

  Shorter compilation times for modules containing with an extreme number of functions (10000 functions or more).

  (The compiled could generate deprecated instructions for certain bit syntax matching operations.)

  Own Id: OTP-6212 Aux Id: seq10446

- Fixed several bugs that would cause warnings to be shown without file name and line number.

  Own Id: OTP-6260 Aux Id: seq10461

#### Improvements and New Features

- The strict_record_tests option is now default; that is, reading a field from a record using the Record#record_tag.field syntax will fail if Record is not a record of the correct type.

  If necessary, the record tests can be turned off by giving the no_strict_record_tests option. To avoid editing Makefiles, the environment variable ERL_COMPILER_OPTIONS can be set to "no_strict_record_tests".

  The no_strict_record_tests option will probably be removed in the R12B release.

  *** POTENTIAL INCOMPATIBILITY ***

  Own Id: OTP-6294

### 1.58 Compiler 4.4.1

#### Fixed Bugs and Malfunctions

- The compiler used to crash if a module contained code similar to 'fun(1=0) -> ok end'. (Thanks to Richard Carlsson.)

  The compiler would spend really long time compiling bit syntax expressions such as '<<1:(50*1024*1024)>>' and produce a huge .beam file. Corrected.

  The compiler would compile list comprehensions with many generators really, really slow. (Thanks to Thomas Raes.)

  Module attributes would be stored in reverse order compared to the order in the source code. (Thus, M:module_info(attributes) would also return the attributes in reversed order.)

  Defining a fun in an after block of a try would cause the compiler to crash or generate incorrect code. (Thanks to Martin Bjorklund.)

  The combination of binary pattern and a guard with andalso/orelse could cause the compiler to crash.

  Own Id: OTP-6121 Aux Id: seq10400

### 1.59 Compiler 4.4

#### Fixed Bugs and Malfunctions

- When a .hrl file is included using -include_lib, the include path is temporarily updated to include the directory the .hrl file was found in, which will allow that .hrl file to itself include files from the same directory using -include. (Thanks to Richard Carlsson.)

  Own Id: OTP-5944

#### Improvements and New Features

- The andalso and orelse operators are now allowed to be used in guards. That also applies to match specifications.

  Own Id: OTP-5894 Aux Id: OTP-5149

- When given the new option strict_record_tests, the compiler will generate code that verifies the record type for R#record.field operations in guards. Code that verifies record types in bodies has already been generated since R10B, but in this release there will be a {badrecord,RecordTag} instead of a badmatch if the record verification test fails. See compile(3) for more information.

  The Erlang shell always applies strict record tests.

  Own Id: OTP-5915 Aux Id: OTP-5714

- The BIF is_record/3 can now be used in guards. Also, is_record/3 can now be called without an erlang: module prefix for consistency with the other is_* functions.

  Own Id: OTP-5916

- The compiler options ignore_try and ignore_cond, which allowed code that used unquoted try or cond as atoms or record tags, has been removed. Old code that depended on the options need to be revised to have occurrences of try or cond as atom or record tags single-quoted. (Note: Although cond is a reserved keyword, there is no cond statement. It might be introduced in a future release.)

  *** POTENTIAL INCOMPATIBILITY ***

  Own Id: OTP-6058

### 1.60 Compiler 4.3.12

#### Improvements and New Features

- The following code would crash the compiler: case T of #r{s = ""} -> T #r{s = "x"} end. (Thanks to Richard Carlsson.)

  The compiler could crash if binaries were constructed in certain guards involving boolean operators (including semicolon). (Thanks to Torbjorn Tornkvist.)

  Own Id: OTP-5872

- The compiler will now warn that the megaco:format_versions/1 function is deprecated.

  Own Id: OTP-5976

### 1.61 Compiler 4.3.11

#### Improvements and New Features

- The compiler would assume that some patterns with aliases ('=') would not match if they were split into several lines. (Thanks to Peter Nagy/Mats Cronqvist.)

  Minor cleanups to eliminate Dialyzer warnings.

  Own Id: OTP-5791 Aux Id: seq10141

### 1.62 Compiler 4.3.10

#### Fixed Bugs and Malfunctions

- When given the new option strict_record_tests, the compiler will generate code that verifies the record type for R#record.field operations (in body context only, not in guards). See the documentation for the compile module for more information.

  The beam validator pass of the compiler could crash given in rare circumstances when given certain combinations of catches and record operations. (Thanks to Mats Cronqvist.)

  Attributes containing binaries (such as -a(<<1,2,3>>)) would crash the compiler. (Thanks to Roger Price.)

  Multiple behaviours in the same module will no longer generate a warning, unless one or more callbacks for the behaviours overlap. For instance, using both the application and supervisor behaviours in the same module will NOT generate any warning, but using gen_server and gen_fsm will.

  Own Id: OTP-5714 Aux Id: seq10073

- The pre-processor used to complain that the macro definition -define(S(S), ??S). was circular, which it isn't. (Thanks to Richard Carlsson.)

  Own Id: OTP-5777

### 1.63 Compiler 4.3.9

#### Fixed Bugs and Malfunctions

- Updating at least two fields of a record with a literal string could cause the compiler to generate dangerous code that could cause a crash at run-time (e.g. R#r{a="abc",b=1}). (Thanks to Mikael Karlsson.)

  Unecessary tests (such as a 'case' with two case branches that were identical) could cause the compiler to crash. (Thanks to Fredrik Thulin.)

  The validation pass of the compiler could generate an error for correct code when floating point operations were used in try/catch statements.

  In bit syntax construction, any field following a binary field would always be marked as "aligned" (which may or may not be correct). That would cause the hipe native compiler to generate incorrect code if the field was in fact unaligned. (Thanks to Per Gustafsson.)

  Some complex guard expressions (such as A#a.b==""; A#a.b==undefined) would crash the compiler. (Thanks to Sean Hinde.)

  Compilation speed has been increased for modules with many functions and/or atoms (such as modules generated by the Asn1 application or other code generators).

  Own Id: OTP-5632 Aux Id: seq10057

### 1.64 Compiler 4.3.8

#### Fixed Bugs and Malfunctions

- In some circumstances, having two try/catch constructs following each in a function body, would cause an internal error to be generated (when in fact the generated code was correct). (Thanks to Fredrik Thulin.)

  Incorrect calls such as M:42() would crash the compiler. The compiler now generates a warning. (Thanks to Ulf Wiger.)

  Own Id: OTP-5553

#### Improvements and New Features

- The new fun M:F/A construct creates a fun that refers to the latest version of M:F/A. This syntax is meant to replace tuple funs {M,F} which have many problems.

  The new type test is_function(Fun, A) (which may be used in guards) test whether Fun is a fun that can be applied with A arguments. (Currently, Fun can also be a tuple fun.)

  Own Id: OTP-5584

### 1.65 Compiler 4.3.7

#### Improvements and New Features

- Further improvements of encrypted debug info: New option encrypt_debug_info for compiler.

  Own Id: OTP-5541 Aux Id: seq9837

### 1.66 Compiler 4.3.6

#### Fixed Bugs and Malfunctions

- Fixed a bug in the validator of the generated code (beam_validator) which caused an internal compiler error even though the generated code was indeed correct.

  Own Id: OTP-5481 Aux Id: seq9798

#### Improvements and New Features

- It is now possible to encrypt the debug information in Beam files, to help keep the source code secret. See the documentation for compile on how to provide the key for encrypting, and the documentation for beam_lib on how to provide the key for decryption so that tools such as the Debugger, Xref, or Cover can be used.

  The beam_lib:chunks/2 functions now accepts an additional chunk type compile_info to retrieve the compilation information directly as a term. (Thanks to Tobias Lindahl.)

  Own Id: OTP-5460 Aux Id: seq9787

### 1.67 Compiler 4.3.5

#### Fixed Bugs and Malfunctions

- Complex functions could cause the internal validator in the compiler to generate an internal error even though the generated code was correct.

  Own Id: OTP-5436 Aux Id: seq9781

### 1.68 Compiler 4.3.4

#### Fixed Bugs and Malfunctions

- In rare circumstances, incorrect code for record or tuple access could be generated. The incorrect code would either trigger an internal error in the compiler or cause an exception at run time. (Thanks to Martin Bjorklund.)

  Corrected a bug in in bit syntax matching where clauses could match in the wrong order. (Thanks to Ulf Wiger.)

  Own Id: OTP-5404 Aux Id: seq9767

### 1.69 Compiler 4.3.3

#### Improvements and New Features

- Given bit syntax construction in certain complex contexts involving a catch, the compiler would either crash or terminate due to failure in an internal consistency check. (Thanks to Fredrik Thulin.)

  Matches such as <<103133:64/float>> = <<103133:64/float>> used to fail. Now they succeed.

  Shadowing of variables in bit syntax matches in fun heads such as in L = 8, F = fun(<<L:L,B:L>>) -> B end was handled incorrectly by the compiler. The fun used to be compiled as if it was written '>fun(<<8:8,B:8>>), while it should be compiled in the same way as fun(<<L:8,B:L>>).

  A bug in the validation pass has been corrected. It sometimes occurred when the compiler optimized by reusing code for causing an exception when the reused code was called from within catch or try-catch statements. Then the validator refused to approve the code and complained about fun(<<L:L,B:L>>) -> B end was handled incorrectly by the in the same way as fun(<<L:8,B:L>>).

  A bug in the unknown_catch_try_state.

  Corrected a bug in the optimizer that would cause the compiler to crash. (Thanks to Peter-Henry Mander.)

  There are now warnings generated if a bit syntax construction will fail at run-time because of a type mismatch (e.g. <<an_atom:8>>).

  Own Id: OTP-5342 Aux Id: OTP-5118, OTP-5270, OTP-5323

- Binary pattern matching such as t(<<A:8>> = <<A:8>) used to silently fail at runtime (i.e. never match). The compiler now generates an error for any such patterns.

  Own Id: OTP-5371

### 1.70 Compiler 4.3.2

#### Fixed Bugs and Malfunctions

- In rare cases, the code compiler code generate code for a tuple match that could crash the emulator if passed a term that was not a tuple.

  If a bit syntax construction failed within a catch, previously assigned variables could get the wrong value.

  The compiler now runs a validation pass on the generated code and aborts before writing a Beam file if any suspect code is found. In particular, the validation pass checks for incorrect code that may cause emulator crashes or other strange symptoms in the emulator.

  Some corrections to the unsupported feature parameterized modules by Richard Carlsson (HiPE).

  Own Id: OTP-5247 Aux Id: OTP-5235

### 1.71 Compiler 4.3.1

#### Fixed Bugs and Malfunctions

- Corrected the release note regarding try/catch below. try/catch DOES work in the initial R10B release.

  A few minor issues code generation issues were corrected. Although the generated code was correct, it was slightly slower and larger than it needed to be.

  A debug printout (that could be seen in rare circumstances) has been removed.

  not record_test(not_a_tuple, RecordTag) and similar expressions in a guard would fail.

  New options basic_validation and strong_validation to do a quick check of the code of a module.

  The inline option was not recognized if it appeared in a -compile() directive inside the module.

  Corrected some bugs in the undocumented feature "parameterized modules".

  Own Id: OTP-5198

- When the undocumented feature "parameterized modules" was used, the ?MODULE macro did not work correctly.

  Own Id: OTP-5224