path: root/lib/compiler/doc/src/notes.xml

<?xml version="1.0" encoding="latin1" ?>
<!DOCTYPE chapter SYSTEM "chapter.dtd">

<chapter>
  <header>
    <copyright>
      <year>2004</year><year>2010</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
      compliance with the License. You should have received a copy of the
      Erlang Public License along with this software. If not, it can be
      retrieved online at http://www.erlang.org/.

      Software distributed under the License is distributed on an "AS IS"
      basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
      the License for the specific language governing rights and limitations
      under the License.

    </legalnotice>

    <title>Compiler Release Notes</title>
    <prepared>otp_appnotes</prepared>
    <docno>nil</docno>
    <date>nil</date>
    <rev>nil</rev>
    <file>notes.xml</file>
  </header>
  <p>This document describes the changes made to the Compiler
    application.</p>

<section><title>Compiler 4.7</title>

    <section><title>Fixed Bugs and Malfunctions</title>
      <list>
        <item>
          <p>
	    Several problems in the inliner have been fixed.</p>
          <p>
	    Own Id: OTP-8552</p>
        </item>
      </list>
    </section>


    <section><title>Improvements and New Features</title>
      <list>
        <item>
          <p>
	    The module binary from EEP31 (and EEP9) is implemented.</p>
          <p>
	    Own Id: OTP-8217</p>
        </item>
        <item>
	    <p>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:</p>
	    <list><item><p>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</p></item>
	    <item><p>Explicitly importing a function having a name
	    clashing with the name of an autoimported BIF that was
	    present (and autoimported) before OTP R14A</p></item>
	    <item><p>Using any form of the old compiler directive
	    <c>nowarn_bif_clash</c></p></item> </list> <p>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,</p> <p>To resolve clashes, you
	    can either use the explicit module name <c>erlang</c> to
	    call the BIF, or you can remove the auto-import of that
	    specific BIF by using the new compiler directive
	    <c>-compile({no_auto_import,[F/A]}).</c>, which makes all
	    calls to the local or imported function without explicit
	    module name pass without warnings or errors.</p> <p>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 <c>nowarn_bif_clash</c> compiler
	    directive, might need changing to be accepted by the
	    compiler.</p>
          <p>
	    *** POTENTIAL INCOMPATIBILITY ***</p>
          <p>
	    Own Id: OTP-8579</p>
        </item>
        <item>
	    <p>The undocumented, unsupport, and deprecated function
	    <c>lists:flat_length/1</c> has been removed.</p>
          <p>
	    Own Id: OTP-8584</p>
        </item>
        <item>
	    <p>Nested records can now be accessed without
	    parenthesis. See the Reference Manual for examples.
	    (Thanks to YAMASHINA Hio and Tuncer Ayaz.)</p>
          <p>
	    Own Id: OTP-8597</p>
        </item>
        <item>
	    <p>It is now possible to suppress the warning in code
	    such as "<c>list_to_integer(S), ok</c>" by assigning the
	    ignored value "_" like this: "<c>_ = list_to_integer(S),
	    ok</c>".</p>
          <p>
	    Own Id: OTP-8602</p>
        </item>
        <item>
	    <p><c>receive</c> 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
	    <c>gen_server:call()</c>. (See <c>gen:do_call/4</c> for
	    an example of a receive statement that will be
	    optimized.)</p>
          <p>
	    Own Id: OTP-8623</p>
        </item>
        <item>
	    <p>The compiler optimizes record operations better.</p>
          <p>
	    Own Id: OTP-8668</p>
        </item>
      </list>
    </section>

</section>

<section><title>Compiler 4.6.5</title>

    <section><title>Fixed Bugs and Malfunctions</title>
      <list>
        <item>
          <p>
	    Using complex boolean expressions in ifs could cause the
	    compiler to either crash or teminate with an internal
	    error. (Thanks to Simon Cornish.)</p>
          <p>
	    Own Id: OTP-8338</p>
        </item>
        <item>
	    <p>Bit string comprehensions can now be used in
	    parameterized modules. (Thanks to Jebu Ittiachen.)</p>
          <p>
	    Own Id: OTP-8447</p>
        </item>
      </list>
    </section>


    <section><title>Improvements and New Features</title>
      <list>
        <item>
          <p>
	    The expected return value for an on_load function has
	    been changed. (See the section about code loading in the
	    Reference manual.)</p>
          <p>
	    *** POTENTIAL INCOMPATIBILITY ***</p>
          <p>
	    Own Id: OTP-8339</p>
        </item>
        <item>
          <p>
	    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.)</p>
          <p>
	    Own Id: OTP-8378</p>
        </item>
        <item>
          <p>
	    The <c>-Werror</c> option for <c>erlc</c> and the
	    compiler option <c>warnings_as_errors</c> will cause
	    warnings to be treated as errors. (Thanks to Christopher
	    Faulet.)</p>
          <p>
	    Own Id: OTP-8382</p>
        </item>
        <item>
	    <p>Macros overloading has been implemented. (Thanks to
	    Christopher Faulet.)</p>
          <p>
	    Own Id: OTP-8388</p>
        </item>
      </list>
    </section>

</section>

<section><title>Compiler 4.6.4</title>

    <section><title>Fixed Bugs and Malfunctions</title>
      <list>
        <item>
	    <p>The compiler's 'E' option now works with modules with
	    types and specifications.</p>
          <p>
	    Own Id: OTP-8238 Aux Id: OTP-8150 </p>
        </item>
        <item>
          <p>
	    Certain uses of binary matching in a
	    <c>begin</c>-<c>end</c> in a list comprehension could
	    cause the compiler to crash or generate incorrect code.</p>
          <p>
	    Own Id: OTP-8271</p>
        </item>
      </list>
    </section>


    <section><title>Improvements and New Features</title>
      <list>
        <item>
          <p>
	    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.</p>
          <p>
	    Own Id: OTP-8201</p>
        </item>
        <item>
          <p>
	    The compiler could crash if invalid calls to is_record/2
	    was used in (for example) a list comprehension. (Thanks
	    to Tobias Lindahl.)</p>
          <p>
	    Own Id: OTP-8269</p>
        </item>
        <item>
	    <p>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.</p>
          <p>
	    Own Id: OTP-8295</p>
        </item>
      </list>
    </section>

</section>

<section><title>Compiler 4.6.3</title>

    <section><title>Improvements and New Features</title>
      <list>
        <item>
	    <p>Corrected liveness optimization to eliminate a
	    compiler crash that could occur when compiling bit syntax
	    construction code. (Thanks to Mikage Sawatari.)</p>
	    <p>Calling BIFs such as <c>length/1</c> in guard context
	    in a try/catch block could cause a compiler crash.
	    (Thanks to Paul Fisher.)</p>
	    <p>Using filter expressions containing <c>andalso</c> or
	    <c>orelse</c> in a list comprehension could cause a
	    compiler crash. (Thanks to Martin Engstr�m.)</p>
          <p>
	    Own Id: OTP-8054</p>
        </item>
        <item>
          <p>
	    A guard with nested 'not' operators could cause the
	    compiler to crash. (Thanks to Tuncer Ayaz.)</p>
          <p>
	    Own Id: OTP-8131</p>
        </item>
      </list>
    </section>

</section>

<section><title>Compiler 4.6.2</title>

    <section><title>Fixed Bugs and Malfunctions</title>
      <list>
        <item>
          <p>
	    The compiler would crash while compiling certain complex
	    function bodies containing <c>receive after</c> 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.)</p>
          <p>
	    Own Id: OTP-7980</p>
        </item>
      </list>
    </section>

</section>

<section><title>Compiler 4.6.1</title>

    <section><title>Fixed Bugs and Malfunctions</title>
      <list>
        <item>
          <p>
	    Miscellaneous minor bugs fixed.</p>
          <p>
	    Own Id: OTP-7937</p>
        </item>
      </list>
    </section>


    <section><title>Improvements and New Features</title>
      <list>
        <item>
          <p>
	    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.</p>
          <p>
	    Own Id: OTP-7924</p>
        </item>
        <item>
	    <p>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.</p>
          <p>
	    Own Id: OTP-7927</p>
        </item>
      </list>
    </section>

</section>

<section><title>Compiler 4.6.0.1</title>

    <section><title>Fixed Bugs and Malfunctions</title>
      <list>
        <item>
            <p>Using <c>andalso</c>/<c>orelse</c> or record access in
            a <c>try</c>...<c>catch</c> could cause a compiler
            crash.</p>
            <p>Som large and complex functions could require
            extremely long compilation times (hours or days).</p>
          <p>
            Own Id: OTP-7905</p>
        </item>
      </list>
    </section>

</section>

<section><title>Compiler 4.6</title>

    <section><title>Fixed Bugs and Malfunctions</title>
      <list>
        <item>
          <p>
	    For some complex guards which used
	    <c>andalso</c>/<c>orelse</c>, the compiler would crash.
	    (Thanks to Hunter Morris.)</p>
          <p>
	    Own Id: OTP-7679</p>
        </item>
        <item>
          <p>
	    Code that (incorrectly) used the the value of nested
	    applications of <c>setelement/3</c> in bit syntax
	    construction could crash the compiler.</p>
          <p>
	    Own Id: OTP-7690</p>
        </item>
        <item>
	    <p>Modules containing huge integers (consisting of
	    several hundreds of thousands of digits or more) could be
	    slow to compile. This problem has been corrected.</p>
          <p>
	    Own Id: OTP-7707 Aux Id: seq11129 </p>
        </item>
        <item>
	    <p>If the generator in a list comprehension is given a
	    non-list term, there will now be <c>function_clause</c>
	    exception instead of a <c>case_clause</c> exception (as
	    it was in all releases before R12B).</p>
          <p>
	    Own Id: OTP-7844</p>
        </item>
      </list>
    </section>


    <section><title>Improvements and New Features</title>
      <list>
        <item>
          <p>
	    The compiler could crash if the size for a binary segment
	    in matching was a complex literal such as binary or
	    tuple.</p>
          <p>
	    Own Id: OTP-7650</p>
        </item>
        <item>
          <p>
	    The compiler generates more compact and faster code for
	    matching of complex constants (such as constant lists and
	    tuples).</p>
          <p>
	    Own Id: OTP-7655</p>
        </item>
        <item>
          <p>
	    The undocumented, unsupported, and deprecated guard BIF
	    <c>is_constant/1</c> has been removed.</p>
          <p>
	    *** INCOMPATIBILITY with R12B ***</p>
          <p>
	    Own Id: OTP-7673</p>
        </item>
        <item>
	    <p>The compiler generates better code for many guard
	    expressions, and especially for guards that use
	    <c>andalso</c>/<c>orelse</c> or record fields.</p>
	    <p>(In technical terms, <c>andalso</c>/<c>orelse</c> 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.)</p>
          <p>
	    Own Id: OTP-7718</p>
        </item>
        <item>
	    <p>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.</p>
          <p>
	    Own Id: OTP-7737</p>
        </item>
        <item>
	    <p>The short-circuit operators <c>andalso</c> and
	    <c>orelse</c> no longer guarantees that their second
	    argument is either <c>true</c> or <c>false</c>. As a
	    consequence, <c>andalso</c>/<c>orelse</c> are now
	    tail-recursive.</p>
          <p>
	    *** POTENTIAL INCOMPATIBILITY ***</p>
          <p>
	    Own Id: OTP-7748</p>
        </item>
        <item>
	    <p>The compiler will refuse to a compile file where the
	    module name in the file differs from the output file
	    name.</p>
	    <p>When compiling using <c>erlc</c>, the current working
	    directory will no be included in the code path (unless
	    explicitly added using "-pa .").</p>
          <p>
	    *** POTENTIAL INCOMPATIBILITY ***</p>
          <p>
	    Own Id: OTP-7793</p>
        </item>
        <item>
	    <p>There will no longer be any warnings for list
	    comprehensions without generators, as such list
	    comprehension have turned out to be useful.</p>
          <p>
	    Own Id: OTP-7846</p>
        </item>
        <item>
	    <p>Warnings for obsolete guard tests are now turned on.
	    (That is, writing <c>list(L)</c> in a guard instead of
	    <c>is_list(L)</c> will generate a warning.)</p>
	    <p>The warnings can be turned off using the
	    <c>nowarn_obsolete_guard</c> option.</p>
          <p>
	    Own Id: OTP-7850</p>
        </item>
        <item>
	    <p>The copyright notices have been updated.</p>
          <p>
	    Own Id: OTP-7851</p>
        </item>
        <item>
	    <p>If a module contains an exported function with the
	    same name as an auto-imported BIF (such as
	    <c>length/1</c>), any calls to the BIF must have an
	    explicit <c>erlang:</c> prefix, or there will be a
	    compilation error (such calls would only generate a
	    warning in previous releases).</p>
	    <p>(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.)</p>
          <p>
	    *** POTENTIAL INCOMPATIBILITY ***</p>
          <p>
	    Own Id: OTP-7873</p>
        </item>
      </list>
    </section>

</section>

<section><title>Compiler 4.5.5</title>

    <section><title>Fixed Bugs and Malfunctions</title>
      <list>
        <item>
	    <p>Matching on a zero-width segment in the bit syntax
	    would crash the compiler. (Thanks to Will.)</p>
          <p>
	    Own Id: OTP-7591</p>
        </item>
      </list>
    </section>


    <section><title>Improvements and New Features</title>
      <list>
        <item>
          <p>
	    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.</p>
          <p>
	    Own Id: OTP-7556</p>
        </item>
        <item>
	    <p>In user-defined attributes, <c>Name/Arity</c> is now
	    allowed and will be translated to <c>{Name,Arity}</c>.
	    (An implementation of EEP-24 by Richard O'Keefe.)</p>
	    <p>The <c>module_info/{0,1}</c> functions automatically
	    inserted into each compiled modules are now documented in
	    the Modules section in the Reference Manual.</p>
          <p>
	    Own Id: OTP-7586</p>
        </item>
      </list>
    </section>

</section>

<section><title>Compiler 4.5.4</title>

    <section><title>Improvements and New Features</title>
      <list>
        <item>
          <p>
	    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.)</p>
          <p>
	    Own Id: OTP-7498</p>
        </item>
      </list>
    </section>

</section>

<section><title>Compiler 4.5.3</title>

    <section><title>Improvements and New Features</title>
      <list>
        <item>
          <p>
	    New option <c>warn_export_all</c> to warn for a module
	    using <c>export_all</c>. (Thanks to Richard Carlsson.)</p>
          <p>
	    Own Id: OTP-7392</p>
        </item>
      </list>
    </section>

</section>

<section><title>Compiler 4.5.2.1</title>

    <section><title>Fixed Bugs and Malfunctions</title>
      <list>
        <item>
          <p>
            In rare circumstances, the length/1 BIF (and a few other
            guard BIFs) would seem to return an incorrect value (of
            any type).</p>
          <p>
            Own Id: OTP-7345 Aux Id: seq10962 </p>
        </item>
      </list>
    </section>

</section>
<section><title>Compiler 4.5.2</title>

    <section><title>Fixed Bugs and Malfunctions</title>
      <list>
        <item>
	    <p>A bug in the old inliner has been fixed. Some
	    undocumented functionality has been removed.</p>
          <p>
	    Own Id: OTP-7223</p>
        </item>
        <item>
	    <p>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 '='.</p>
          <p>
	    Own Id: OTP-7227</p>
        </item>
        <item>
	    <p>Complex combinations of record operations and binary
	    matching could cause the compiler to crash. (Thanks to
	    Vladimir Klebansky.)</p>
          <p>
	    Own Id: OTP-7233</p>
        </item>
        <item>
          <p>
	    In rare circumstances, mixing binary matching clauses
	    with clauses matching other data types, the compiler
	    could crash.</p>
          <p>
	    Own Id: OTP-7240 Aux Id: seq10916 </p>
        </item>
      </list>
    </section>

</section>

<section><title>Compiler 4.5.1.1</title>

    <section><title>Fixed Bugs and Malfunctions</title>
      <list>
        <item>
          <p>
	    Corrected a compiler bug that could cause a complex
	    binary matching operation to fail when it shouldn't.
	    (Thanks to Tomas Stejskal.)</p>
          <p>
	    Own Id: OTP-7188</p>
        </item>
        <item>
          <p>
	    In unusual circumstances, the environment for a fun could
	    bind wrong values.</p>
          <p>
	    Own Id: OTP-7202 Aux Id: seq10887 </p>
        </item>
        <item>
	    <p>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
	    '<c>[...||...]++Expr</c>', <c>Expr</c> is now evaluated
	    before the list comprehension. This change <em>is</em>
	    backwards compatible (see the following note about
	    evaluation order if you have doubts).</p>
	    <p>Note about evaluation order: The Reference manual says
	    that subexpressions are evaluated <em>in any order</em>
	    before the expression itself. Therefore, in an expression
	    such as '<c>LeftExpr++RightExpr</c>', you should not
	    depend on <c>LeftExpr</c> being evaluated before
	    <c>RightExpr</c> 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 <c>ets</c> operations.</p>
          <p>
	    Own Id: OTP-7206</p>
        </item>
      </list>
    </section>

</section>


<section><title>Compiler 4.5.1</title>

    <section><title>Fixed Bugs and Malfunctions</title>
      <list>
        <item>
          <p>
	    A match expression inside a function call could cause a
	    false "a term is constructed but never used" warning.</p>
          <p>
	    Own Id: OTP-7018 Aux Id: seq10824 </p>
        </item>
        <item>
	    <p>The compiler could crash if a binary tail was matched
	    out, and then used in a binary append operation. (Thanks
	    to Oleg Avdeev.)</p>
	    <p>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.) </p>
          <p>
	    Own Id: OTP-7022</p>
        </item>
        <item>
          <p>
	    Matching an empty binary in a record and then using the
	    same record again could cause a compiler crash. (Thanks
	    to Fredrik Thulin.)</p>
          <p>
	    Own Id: OTP-7029</p>
        </item>
        <item>
	    <p>In rare circumstances, constants containing floating
	    points and integers could be confused. Example:</p>
	    <p><c>f(a) -> [1]; f(b) -> [1.0].</c></p>
	    <p>Both <c>f(a)</c> and <c>f(b)</c> would return
	    <c>[1]</c>.</p>
          <p>
	    Own Id: OTP-7073</p>
        </item>
        <item>
	    <p>Some bit syntax code such as</p>
	    <p><c>matching d(_,&lt;$lt;$gt;$gt;) -> one; d(0,&lt;$lt;D$gt;$gt;)
	    ->two.</c></p>
	    <p>could crash the compiler. (Thanks to Simon
	    Cornish.)</p>
          <p>
	    Own Id: OTP-7094</p>
        </item>
        <item>
          <p>
	    In unusual circumstances, a call to a fun could fail due
	    to an unsafe optimization. (Thanks to Simon Cornish.)</p>
          <p>
	    Own Id: OTP-7102</p>
        </item>
        <item>
          <p>
	    Bit syntax matching with a guard containing two or more
	    uses of andalso/orelse could cause the compiler to crash.
	    (Thanks to Mateusz Berezecki.)</p>
          <p>
	    Own Id: OTP-7113</p>
        </item>
        <item>
          <p>
	    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
	    <c>erlang:'$lt;'(erlang:length(L), 2)</c> as case expression
	    into a guard, which would change the semantics. (Thanks
	    to Robert Virding.)</p>
          <p>
	    Own Id: OTP-7117</p>
        </item>
      </list>
    </section>


    <section><title>Improvements and New Features</title>
      <list>
        <item>
          <p>
	    The compiler could generate suboptimal code for record
	    updates if the record update code consisted of multiple
	    source code lines.</p>
          <p>
	    Own Id: OTP-7101</p>
        </item>
      </list>
    </section>

</section>

<section><title>Compiler 4.5</title>

    <section><title>Fixed Bugs and Malfunctions</title>
      <list>
        <item>
	    <p>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,
	    <c><![CDATA[<<B/binary,EmptyBinary/binary>> = Bin]]></c>
	    used to compile, but now the compilation will fail with
	    an an error message.</p>
	    <p>Also, it is now longer permitted to give a literal
	    string in a binary pattern a type or a size; for
	    instance, <c><![CDATA[<<"abc"/binary>> = Bin]]></c> will
	    no longer compile. (In previous releases, there would
	    always be a <c>badmatch</c> exception at run-time.)</p>
          <p>
	    Own Id: OTP-6885</p>
        </item>
      </list>
    </section>


    <section><title>Improvements and New Features</title>
      <list>
        <item>
          <p>
	    Bitstrings (bit-level) binaries and binary comprehensions
	    are now part of the language. See the Reference Manual.</p>
          <p>
	    Own Id: OTP-6558</p>
        </item>
        <item>
          <p>
	    The '<c>compressed</c>' option for the compiler has been
	    documented.</p>
          <p>
	    Own Id: OTP-6801</p>
        </item>
        <item>
	    <p>If the value of a list comprehension is not used, such
	    as in '<c>[do_something(X) || X &lt;- List], ok</c>', a
	    result list will no longer be built. For more details,
	    see the Efficiency Guide.</p>
	    <p>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: '<c>self(),ok</c>' and
	    '<c>{error,Reason},ok</c>'.</p>
          <p>
	    Own Id: OTP-6824</p>
        </item>
        <item>
          <p>
	    Three new functions have been added to the <c>compile</c>
	    module: <c>noenv_file/2</c>, <c>noenv_forms/2</c>, and
	    <c>noenv_output_generated/1</c>.</p>
          <p>
	    Own Id: OTP-6829</p>
        </item>
        <item>
	    <p>Many bit syntax operations, both construction and
	    matching, are faster. For further information, see the
	    Efficiency Guide.</p>
          <p>
	    Own Id: OTP-6838</p>
        </item>
        <item>
	    <p>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.</p>
	    <p>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.</p>
	    <p>Example 1: In the expression <c>element(BitNum-1,
	    {1,2,4,8,16,32,64,128})</c>, 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.</p>
	    <p>Example 2: Literal strings, such as <c>"abc"</c>, 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
	    <c>[$a,$b,$c]</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,
	    <c>&lt;&lt;"abc"&lt;&lt;</c>) instead of string literals for
	    infrequently used long strings (such as error
	    messages).</p>
          <p>
	    Own Id: OTP-6850</p>
        </item>
        <item>
          <p>
	    Recursive calls now usually consume less stack than in
	    R11B. See the Efficiency Guide.</p>
          <p>
	    Own Id: OTP-6862 Aux Id: seq10746 </p>
        </item>
        <item>
	    <p>Two new guard BIFs have been introduced as a
	    recommended replacement for <c>size/1</c>. (The
	    <c>size/1</c> BIF will be removed no earlier than in
	    R14B.) The BIFs are <c>tuple_size/1</c> to calculate the
	    size of a tuple and <c>byte_size/1</c> 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).</p>
	    <p>There is also a new <c>bit_size/1</c> BIF that returns
	    the exact number of bits that a binary or bitstring
	    contains.</p>
          <p>
	    Own Id: OTP-6902</p>
        </item>
        <item>
          <p>
	    The two internal functions <c>erl_bifs:is_bif/3</c> and
	    <c>erl_bifs:is_guard/3</c> have been removed. They were
	    unsupported, undocumented, and unmaintained.</p>
          <p>
	    Own Id: OTP-6966</p>
        </item>
      </list>
    </section>

</section>

  <section>
    <title>Compiler 4.4.5</title>

    <section>
      <title>Fixed Bugs and Malfunctions</title>
      <list type="bulleted">
        <item>
          <p>The compiler would crash if you tried to combine to
            non-list literals with '<c><![CDATA[++]]></c>' (for instance,
            <c><![CDATA[an_atom++"string"]]></c>).</p>
          <p>Own Id: OTP-6630 Aux Id: seq10635 </p>
        </item>
      </list>
    </section>

    <section>
      <title>Improvements and New Features</title>
      <list type="bulleted">
        <item>
          <p>Minor Makefile changes.</p>
          <p>Own Id: OTP-6689</p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.4.4</title>

    <section>
      <title>Fixed Bugs and Malfunctions</title>
      <list type="bulleted">
        <item>
          <p>Incorrect code could be generated for bit syntax matching
            if the old inliner was used with aggressive settings.</p>
          <p>Own Id: OTP-6461</p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.4.3</title>

    <section>
      <title>Fixed Bugs and Malfunctions</title>
      <list type="bulleted">
        <item>
          <p>The R10B compiler could generate unsafe
            <c><![CDATA[bs_save/bs_restore]]></c> 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
            <c><![CDATA[bs_save/bs_restore]]></c> 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.)</p>
          <p>Own Id: OTP-6386</p>
        </item>
      </list>
    </section>

    <section>
      <title>Improvements and New Features</title>
      <list type="bulleted">
        <item>
          <p>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.</p>
          <p>Own Id: OTP-5344</p>
        </item>
        <item>
          <p>Minor improvements in code generation for some guards
            expression involving boolean expressions.</p>
          <p>Own Id: OTP-6347</p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.4.2.1</title>

    <section>
      <title>Fixed Bugs and Malfunctions</title>
      <list type="bulleted">
        <item>
          <p>The compiler could generate incorrect code for bit syntax
            matching consisting of several clauses.</p>
          <p>Own Id: OTP-6392 Aux Id: seq10539 </p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.4.2</title>

    <section>
      <title>Fixed Bugs and Malfunctions</title>
      <list type="bulleted">
        <item>
          <p>Defining a fun itself containing a fun in an
            <c><![CDATA[after]]></c> block of a <c><![CDATA[try]]></c> would cause the
            compiler to crash or generate incorrect code. (Thanks to
            Tim Rath.)</p>
          <p>Shorter compilation times for modules containing with
            an extreme number of functions (10000 functions or more).</p>
          <p>(The compiled could generate deprecated instructions
            for certain bit syntax matching operations.)</p>
          <p>Own Id: OTP-6212 Aux Id: seq10446 </p>
        </item>
        <item>
          <p>Fixed several bugs that would cause warnings to be shown
            without file name and line number.</p>
          <p>Own Id: OTP-6260 Aux Id: seq10461 </p>
        </item>
      </list>
    </section>

    <section>
      <title>Improvements and New Features</title>
      <list type="bulleted">
        <item>
          <p>The <c><![CDATA[strict_record_tests]]></c> option is now default;
            that is, reading a field from a record using the
            <c><![CDATA[Record#record_tag.field]]></c> syntax will fail if
            <c><![CDATA[Record]]></c> is not a record of the correct type.</p>
          <p>If necessary, the record tests can be turned off by
            giving the <c><![CDATA[no_strict_record_tests]]></c> option. To avoid
            editing Makefiles, the environment variable
            <c><![CDATA[ERL_COMPILER_OPTIONS]]></c> can be set to
            "<c><![CDATA[no_strict_record_tests]]></c>".</p>
          <p>The <c><![CDATA[no_strict_record_tests]]></c> option will probably
            be removed in the R12B release.</p>
          <p>*** POTENTIAL INCOMPATIBILITY ***</p>
          <p>Own Id: OTP-6294</p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.4.1</title>

    <section>
      <title>Fixed Bugs and Malfunctions</title>
      <list type="bulleted">
        <item>
          <p>The compiler used to crash if a module contained code
            similar to '<c><![CDATA[fun(1=0) -> ok end]]></c>'. (Thanks to
            Richard Carlsson.)</p>
          <p>The compiler would spend really long time compiling
            bit syntax expressions such as
            '<c><![CDATA[<<1:(50*1024*1024)>>]]></c>' and produce a huge .beam
            file. Corrected.</p>
          <p>The compiler would compile list comprehensions with
            many generators really, really slow. (Thanks to Thomas
            Raes.)</p>
          <p>Module attributes would be stored in reverse order
            compared to the order in the source code. (Thus,
            <c><![CDATA[M:module_info(attributes)]]></c> would also return the
            attributes in reversed order.)</p>
          <p>Defining a fun in an <c><![CDATA[after]]></c> block of a
            <c><![CDATA[try]]></c> would cause the compiler to crash or generate
            incorrect code. (Thanks to Martin Bjorklund.)</p>
          <p>The combination of binary pattern and a guard with
            andalso/orelse could cause the compiler to crash.</p>
          <p>Own Id: OTP-6121 Aux Id: seq10400 </p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.4</title>

    <section>
      <title>Fixed Bugs and Malfunctions</title>
      <list type="bulleted">
        <item>
          <p>When a <c><![CDATA[.hrl]]></c> file is included using
            <c><![CDATA[-include_lib]]></c>, the include path is temporarily
            updated to include the directory the <c><![CDATA[.hrl]]></c> file was
            found in, which will allow that <c><![CDATA[.hrl]]></c> file to itself
            include files from the same directory using
            <c><![CDATA[-include]]></c>. (Thanks to Richard Carlsson.)</p>
          <p>Own Id: OTP-5944</p>
        </item>
      </list>
    </section>

    <section>
      <title>Improvements and New Features</title>
      <list type="bulleted">
        <item>
          <p>The <c><![CDATA[andalso]]></c> and <c><![CDATA[orelse]]></c> operators are
            now allowed to be used in guards. That also applies to
            match specifications.</p>
          <p>Own Id: OTP-5894 Aux Id: OTP-5149 </p>
        </item>
        <item>
          <p>When given the new option
            <c><![CDATA[strict_record_tests]]></c>, the compiler will generate
            code that verifies the record type for
            <c><![CDATA[R#record.field]]></c> operations in guards. Code that
            verifies record types in bodies has already been
            generated since R10B, but in this release there will be a
            <c><![CDATA[{badrecord,RecordTag}]]></c> instead of a
            <c><![CDATA[badmatch]]></c> if the record verification test fails.
            See <c><![CDATA[compile(3)]]></c> for more information.</p>
          <p>The Erlang shell always applies strict record tests.</p>
          <p>Own Id: OTP-5915 Aux Id: OTP-5714 </p>
        </item>
        <item>
          <p>The BIF <c><![CDATA[is_record/3]]></c> can now be used in guards.
            Also, <c><![CDATA[is_record/3]]></c> can now be called without an
            <c><![CDATA[erlang:]]></c> module prefix for consistency with the other
            <c><![CDATA[is_*]]></c> functions.</p>
          <p>Own Id: OTP-5916</p>
        </item>
        <item>
          <p>The compiler options <c><![CDATA[ignore_try]]></c> and
            <c><![CDATA[ignore_cond]]></c>, which allowed code that used
            unquoted <c><![CDATA[try]]></c> or <c><![CDATA[cond]]></c> as atoms or record
            tags, has been removed. Old code that depended on the
            options need to be revised to have occurrences of
            <c><![CDATA[try]]></c> or <c><![CDATA[cond]]></c> as atom or record tags
            single-quoted. (Note: Although <c><![CDATA[cond]]></c> is a reserved
            keyword, there is no <c><![CDATA[cond]]></c> statement. It might be
            introduced in a future release.)</p>
          <p>*** POTENTIAL INCOMPATIBILITY ***</p>
          <p>Own Id: OTP-6058</p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.3.12</title>

    <section>
      <title>Improvements and New Features</title>
      <list type="bulleted">
        <item>
          <p>The following code would crash the compiler: <c><![CDATA[case T of #r{s = ""} -> T #r{s = "x"} end]]></c>. (Thanks to
            Richard Carlsson.)</p>
          <p>The compiler could crash if binaries were constructed
            in certain guards involving boolean operators (including
            semicolon). (Thanks to Torbjorn Tornkvist.)</p>
          <p>Own Id: OTP-5872</p>
        </item>
        <item>
          <p>The compiler will now warn that the
            <c><![CDATA[megaco:format_versions/1]]></c> function is deprecated.</p>
          <p>Own Id: OTP-5976</p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.3.11</title>

    <section>
      <title>Improvements and New Features</title>
      <list type="bulleted">
        <item>
          <p>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.)</p>
          <p>Minor cleanups to eliminate Dialyzer warnings.</p>
          <p>Own Id: OTP-5791 Aux Id: seq10141 </p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.3.10</title>

    <section>
      <title>Fixed Bugs and Malfunctions</title>
      <list type="bulleted">
        <item>
          <p>When given the new option
            <c><![CDATA[strict_record_tests]]></c>, the compiler will generate
            code that verifies the record type for
            <c><![CDATA[R#record.field]]></c> operations (in body context only,
            not in guards). See the documentation for the
            <c><![CDATA[compile]]></c> module for more information.</p>
          <p>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.)</p>
          <p>Attributes containing binaries (such as -a(&lt;&lt;1,2,3&gt;&gt;))
            would crash the compiler. (Thanks to Roger Price.)</p>
          <p>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
            <c><![CDATA[application]]></c> and <c><![CDATA[supervisor]]></c> behaviours
            in the same module will NOT generate any warning, but
            using <c><![CDATA[gen_server]]></c> and <c><![CDATA[gen_fsm]]></c> will.</p>
          <p>Own Id: OTP-5714 Aux Id: seq10073 </p>
        </item>
        <item>
          <p>The pre-processor used to complain that the macro
            definition <c><![CDATA[-define(S(S), ??S).]]></c> was circular,
            which it isn't. (Thanks to Richard Carlsson.)</p>
          <p>Own Id: OTP-5777</p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.3.9</title>

    <section>
      <title>Fixed Bugs and Malfunctions</title>
      <list type="bulleted">
        <item>
          <p>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.
            <c><![CDATA[R#r{a="abc",b=1}]]></c>). (Thanks to Mikael Karlsson.)</p>
          <p>Unecessary tests (such as a 'case' with two case
            branches that were identical) could cause the compiler to
            crash. (Thanks to Fredrik Thulin.)</p>
          <p>The validation pass of the compiler could generate an
            error for correct code when floating point operations
            were used in try/catch statements.</p>
          <p>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.)</p>
          <p>Some complex guard expressions (such as <c><![CDATA[A#a.b==""; A#a.b==undefined]]></c>) would crash the compiler. (Thanks
            to Sean Hinde.)</p>
          <p>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).</p>
          <p>Own Id: OTP-5632 Aux Id: seq10057 </p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.3.8</title>

    <section>
      <title>Fixed Bugs and Malfunctions</title>
      <list type="bulleted">
        <item>
          <p>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.)</p>
          <p>Incorrect calls such as <c><![CDATA[M:42()]]></c> would crash the
            compiler. The compiler now generates a warning. (Thanks
            to Ulf Wiger.)</p>
          <p>Own Id: OTP-5553</p>
        </item>
      </list>
    </section>

    <section>
      <title>Improvements and New Features</title>
      <list type="bulleted">
        <item>
          <p>The new <c><![CDATA[fun M:F/A]]></c> construct creates a fun that
            refers to the latest version of <c><![CDATA[M:F/A]]></c>. This syntax is
            meant to replace tuple funs <c><![CDATA[{M,F}]]></c> which have many
            problems.</p>
          <p>The new type test <c><![CDATA[is_function(Fun, A)]]></c> (which may be
            used in guards) test whether <c><![CDATA[Fun]]></c> is a fun that can be
            applied with <c><![CDATA[A]]></c> arguments. (Currently, <c><![CDATA[Fun]]></c> can
            also be a tuple fun.)</p>
          <p>Own Id: OTP-5584</p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.3.7</title>

    <section>
      <title>Improvements and New Features</title>
      <list type="bulleted">
        <item>
          <p>Further improvements of encrypted debug info: New option
            <c><![CDATA[encrypt_debug_info]]></c> for compiler.</p>
          <p>Own Id: OTP-5541 Aux Id: seq9837 </p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.3.6</title>

    <section>
      <title>Fixed Bugs and Malfunctions</title>
      <list type="bulleted">
        <item>
          <p>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.</p>
          <p>Own Id: OTP-5481 Aux Id: seq9798 </p>
        </item>
      </list>
    </section>

    <section>
      <title>Improvements and New Features</title>
      <list type="bulleted">
        <item>
          <p>It is now possible to encrypt the debug information in
            Beam files, to help keep the source code secret. See the
            documentation for <c><![CDATA[compile]]></c> on how to provide the key
            for encrypting, and the documentation for <c><![CDATA[beam_lib]]></c>
            on how to provide the key for decryption so that tools such
            as the Debugger, Xref, or Cover can be used.</p>
          <p>The <c><![CDATA[beam_lib:chunks/2]]></c> functions now accepts an
            additional chunk type <c><![CDATA[compile_info]]></c> to retrieve
            the compilation information directly as a term. (Thanks
            to Tobias Lindahl.)</p>
          <p>Own Id: OTP-5460 Aux Id: seq9787 </p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.3.5</title>

    <section>
      <title>Fixed Bugs and Malfunctions</title>
      <list type="bulleted">
        <item>
          <p>Complex functions could cause the internal validator in
            the compiler to generate an internal error even though
            the generated code was correct.</p>
          <p>Own Id: OTP-5436 Aux Id: seq9781 </p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.3.4</title>

    <section>
      <title>Fixed Bugs and Malfunctions</title>
      <list type="bulleted">
        <item>
          <p>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.)</p>
          <p>Corrected a bug in in bit syntax matching where
            clauses could match in the wrong order. (Thanks to Ulf
            Wiger.)</p>
          <p>Own Id: OTP-5404 Aux Id: seq9767 </p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.3.3</title>

    <section>
      <title>Improvements and New Features</title>
      <list type="bulleted">
        <item>
          <p>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.)</p>
          <p>Matches such as
            <c><![CDATA[<<103133:64/float>> = <<103133:64/float>>]]></c>
            used to fail. Now they succeed.</p>
          <p>Shadowing of variables in bit syntax matches in fun heads
            such as in
            <c><![CDATA[L = 8, F = fun(<<L:L,B:L>>) -> B end]]></c> was
            handled incorrectly by the compiler. The fun used to be
            compiled as if it was written
            '<c><![CDATA[>fun(<<8:8,B:8>>)]]></c>, while it should be
            compiled in the same way as <c><![CDATA[fun(<<L:8,B:L>>)]]></c>.</p>
          <p>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
            <c><![CDATA[fun(<<L:L,B:L>>) -> B end]]></c> was handled
            incorrectly by the in the same way as
            <c><![CDATA[fun(<<L:8,B:L>>)]]></c>.</p>
          <p>A bug in the unknown_catch_try_state.</p>
          <p>Corrected a bug in the optimizer that would cause
            the compiler to crash. (Thanks to Peter-Henry Mander.)</p>
          <p>There are now warnings generated if a bit syntax
            construction will fail at run-time because of a type
            mismatch (e.g. <c><![CDATA[<<an_atom:8>>]]></c>).</p>
          <p>Own Id: OTP-5342 Aux Id: OTP-5118, OTP-5270, OTP-5323 </p>
        </item>
        <item>
          <p>Binary pattern matching such as
            <c><![CDATA[t(<<A:8>> = <<A:8>)]]></c> used to silently
            fail at runtime (i.e. never match). The compiler now
            generates an error for any such patterns.</p>
          <p>Own Id: OTP-5371</p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.3.2</title>

    <section>
      <title>Fixed Bugs and Malfunctions</title>
      <list type="bulleted">
        <item>
          <p>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.</p>
          <p>If a bit syntax construction failed within a catch,
            previously assigned variables could get the wrong value.</p>
          <p>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.</p>
          <p>Some corrections to the unsupported feature
            parameterized modules by Richard Carlsson (HiPE).</p>
          <p>Own Id: OTP-5247 Aux Id: OTP-5235 </p>
        </item>
      </list>
    </section>
  </section>

  <section>
    <title>Compiler 4.3.1</title>

    <section>
      <title>Fixed Bugs and Malfunctions</title>
      <list type="bulleted">
        <item>
          <p>Corrected the release note regarding <c><![CDATA[try/catch]]></c> below.
            <c><![CDATA[try/catch]]></c> DOES work in the initial R10B release.</p>
          <p>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.</p>
          <p>A debug printout (that could be seen in rare
            circumstances) has been removed.</p>
          <p><c><![CDATA[not record_test(not_a_tuple, RecordTag)]]></c> and
            similar expressions in a guard would fail.</p>
          <p>New options <c><![CDATA[basic_validation]]></c> and
            <c><![CDATA[strong_validation]]></c> to do a quick check of the code
            of a module.</p>
          <p>The <c><![CDATA[inline]]></c> option was not recognized if it
            appeared in a <c><![CDATA[-compile()]]></c> directive inside the
            module.</p>
          <p>Corrected some bugs in the undocumented feature
            "parameterized modules".</p>
          <p>Own Id: OTP-5198</p>
        </item>
        <item>
          <p>When the undocumented feature "parameterized modules" was
            used, the <c><![CDATA[?MODULE]]></c> macro did not work correctly.</p>
          <p>Own Id: OTP-5224</p>
        </item>
      </list>
    </section>
  </section>
</chapter>