This file is indexed.

/usr/share/doc/gcc-4.9-base/NEWS.html is in gcc-4.9 4.9.2-10+deb8u1.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
<?xml version="1.0" encoding="utf-8"?>
  <!DOCTYPE html
            PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
            "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 


 










     <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
  
  
   <head>
 
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <link rev="made" href="mailto:gcc@gcc.gnu.org" />
    <link rel="shortcut icon" href="http://gcc.gnu.org/favicon.ico" />
    <link rel="stylesheet" type="text/css" href="http://gcc.gnu.org/gcc.css" />
  
 <title>
GCC 4.9 Release Series &mdash; Changes, New Features, and Fixes
- GNU Project - Free Software Foundation (FSF)</title>
   </head>
 

<!-- GCC maintainers, please do not hesitate to update/contribute entries
     concerning those part of GCC you maintain!  2002-03-23, Gerald.
-->

<body>



<h1>GCC 4.9 Release Series<br />Changes, New Features, and Fixes</h1>


<h2>Caveats</h2>

  <ul>
    <li><p>The mudflap run time checker has been removed.  The mudflap
    options remain, but do nothing.</p></li>

    <li><p>Support for a number of older systems and recently
    unmaintained or untested target ports of GCC has been declared
    obsolete in GCC 4.9.  Unless there is activity to revive them, the
    next release of GCC will have their sources permanently
    <strong>removed</strong>.</p>

    <p>The following ports for individual systems on
    particular architectures have been obsoleted:</p>

    <ul>
	  <li>Solaris 9 (*-*-solaris2.9).  Details can be found in the
	  <a href="http://gcc.gnu.org/ml/gcc-patches/2013-05/msg00728.html">
	      announcement</a>.</li>
    </ul>
    </li>
  </ul>

  <p>
    More information on porting to GCC 4.9 from previous versions
    of GCC can be found in
    the <a href="http://gcc.gnu.org/gcc-4.9/porting_to.html">porting
    guide</a> for this release.
  </p>


<h2>General Optimizer Improvements</h2>

  <ul>
    <li>AddressSanitizer, a fast memory error detector, is now available on ARM.
    </li>
    <li>UndefinedBehaviorSanitizer (ubsan), a fast undefined behavior detector,
        has been added and can be enabled via <code>-fsanitize=undefined</code>.
	Various computations will be instrumented to detect undefined behavior
	at runtime.  UndefinedBehaviorSanitizer is currently available for the C
	and C++ languages.
    </li>
    <li>Link-time optimization (LTO) improvements:
    <ul>
      <li>Type merging was rewritten. The new implementation is significantly faster
      and uses less memory.</li>
      <li>Better partitioning algorithm resulting in less streaming during
	  link time.</li>
      <li>Early removal of virtual methods reduces the size of object files and
	  improves link-time memory usage and compile time.</li>
      <li>Function bodies are now loaded on-demand and released early improving
	  overall memory usage at link time.</li>
      <li>C++ hidden keyed methods can now be optimized out.</li>
      <li>When using a linker plugin, compiling with the <code>-flto</code>
          option now generates slim objects files (<code>.o</code>) which only
          contain intermediate language representation for LTO. Use
          <code>-ffat-lto-objects</code> to create files which contain
          additionally the object code.  To generate static libraries suitable
          for LTO processing, use <code>gcc-ar</code> and
         <code>gcc-ranlib</code>; to list symbols from a slim object file use
         <code>gcc-nm</code>. (Requires that <code>ar</code>,
         <code>ranlib</code> and <code>nm</code> have been compiled with
         plugin support.)</li>
    </ul>
    Memory usage building Firefox with debug enabled was reduced from 15GB to
    3.5GB; link time from 1700 seconds to 350 seconds.
    </li>
    <li>Inter-procedural optimization improvements:
    <ul>
      <li>New type inheritance analysis module improving devirtualization.
	  Devirtualization now takes into account anonymous name-spaces and the
	  C++11 <code>final</code> keyword.</li>
      <li>New speculative devirtualization pass (controlled by
	  <code>-fdevirtualize-speculatively</code>.</li>
      <li>Calls that were speculatively made direct are turned back to indirect
	  where direct call is not cheaper.</li>
      <li>Local aliases are introduced for symbols that are known to be
	  semantically equivalent across shared libraries improving dynamic
	  linking times.</li>
    </ul></li>
    <li>Feedback directed optimization improvements:
    <ul>
      <li>Profiling of programs using C++ inline functions is now more reliable.</li>
      <li>New time profiling determines typical order in which functions are
	  executed.</li>
      <li>A new function reordering pass (controlled by
	  <code>-freorder-functions</code>) significantly reduces
	  startup time of large applications.  Until binutils support is
 	  completed, it is effective only with link-time optimization.</li>
      <li>Feedback driven indirect call removal and devirtualization now handle
	  cross-module calls when link-time optimization is enabled.</li>
    </ul></li>
  </ul>

<h2 id="languages">New Languages and Language specific improvements</h2>

  <ul>
    <li>Version 4.0 of the <a href="http://openmp.org/wp/openmp-specifications/"
	>OpenMP specification</a> is now supported for the C and C++ compilers.
	The new <code>-fopenmp-simd</code> option can be used to enable OpenMP's
	SIMD directives, while ignoring other OpenMP directives. The new <a
	href="http://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Optimize-Options.html#index-fsimd-cost-model-908"
	><code>-fsimd-cost-model=</code></a> option permits to tune the
	vectorization cost model for loops annotated with OpenMP and Cilk
	Plus <code>simd</code> directives; <code>-Wopenmp-simd</code> warns when
	the current costmodel overrides simd directives set by the user.</li>
    <li>The <code>-Wdate-time</code> option has been added for the C, C++ and
	Fortran compilers, which warns when the <code>__DATE__</code>,
	<code>__TIME__</code> or <code>__TIMESTAMP__</code> macros are used.
	Those macros might prevent bit-wise-identical reproducible
	compilations.</li>
  </ul>

<h3 id="ada">Ada</h3>

  <ul>
    <li>GNAT switched to Ada 2012 instead of Ada 2005 by default.</li>
  </ul>

<h3 id="c-family">C family</h3>

  <ul>
    <li>Support for colorizing diagnostics emitted by GCC has been added.
    The <code><a
    href="http://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Language-Independent-Options.html#index-fdiagnostics-color-252"
    >-fdiagnostics-color=auto</a></code> will enable it when
    outputting to terminals, <code>-fdiagnostics-color=always</code>
    unconditionally.  The <code>GCC_COLORS</code> environment variable
    can be used to customize the colors or disable coloring.
    If <code>GCC_COLORS</code> variable is present in the environment,
    the default is <code>-fdiagnostics-color=auto</code>, otherwise
    <code>-fdiagnostics-color=never</code>.<br/>
    Sample diagnostics output:<br/>
    <pre>
    $ g++ -fdiagnostics-color=always -S -Wall test.C
    <b>test.C:</b> In function &lsquo;<b>int foo()</b>&rsquo;:
    <b>test.C:1:14:</b> <b style='color:magenta'>warning:</b> no return statement in function returning non-void [-Wreturn-type]
     int foo () { }
                  <b style='color:lime'>^</b>
    <b>test.C:2:46:</b> <b style='color:red'>error:</b> template instantiation depth exceeds maximum of 900 (use -ftemplate-depth= to increase the maximum) instantiating &lsquo;<b>struct X&lt;100&gt;</b>&rsquo;
     template &lt;int N&gt; struct X { static const int value = X&lt;N-1&gt;::value; }; template struct X&lt;1000&gt;;
                                                  <b style='color:lime'>^</b>
    <b>test.C:2:46:</b>   recursively required from &lsquo;<b>const int X&lt;999&gt;::value</b>&rsquo;
    <b>test.C:2:46:</b>   required from &lsquo;<b>const int X&lt;1000&gt;::value</b>&rsquo;
    <b>test.C:2:88:</b>   required from here

    <b>test.C:2:46:</b> <b style='color:red'>error:</b> incomplete type &lsquo;<b>X&lt;100&gt;</b>&rsquo; used in nested name specifier
    </pre></li>

    <li>With the new <a
    href="http://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Loop-Specific-Pragmas.html"
    ><code>#pragma GCC ivdep</code></a>, the user can assert that there are no
    loop-carried dependencies which would prevent concurrent execution of
    consecutive iterations using SIMD (single instruction multiple data)
    instructions.</li>

    <li>Support for <a href="https://www.cilkplus.org/">Cilk Plus</a> has been
    added and can be enabled with the <code>-fcilkplus</code> option.  Cilk Plus
    is an extension to the C and C++ languages to support data and task
    parallelism.  The present implementation follows ABI version 1.2; all
    features but <code>_Cilk_for</code> have been implemented.</li>
  </ul>           

<h3>C</h3>
<ul>
  <li>ISO C11 atomics (the <code>_Atomic</code> type specifier and
  qualifier and the <code>&lt;stdatomic.h&gt;</code> header) are now
  supported.</li>

  <li>ISO C11 generic selections (<code>_Generic</code> keyword) are
  now supported.</li>

  <li>ISO C11 thread-local storage (<code>_Thread_local</code>,
  similar to GNU C <code>__thread</code>) is now supported.</li>

  <li>ISO C11 support is now at a similar level of completeness to ISO
  C99 support: substantially complete modulo bugs, extended
  identifiers (supported except for corner cases
  when <code>-fextended-identifiers</code> is used), floating-point
  issues (mainly but not entirely relating to optional C99 features
  from Annexes F and G) and the optional Annexes K (Bounds-checking
  interfaces) and L (Analyzability).</li>

  <li>A new C extension <code>__auto_type</code> provides a subset of
  the functionality of C++11 <code>auto</code> in GNU C.</li>
</ul>

<h3 id="cxx">C++</h3>
<ul>
  <li>
    The G++ implementation of <a href="../projects/cxx1y.html">C++1y</a> return type deduction for normal
    functions has been updated to conform to
    <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3638.html">N3638</a>, 
    the proposal accepted into the working paper.  Most notably, it adds <tt>decltype(auto)</tt> for
    getting <tt>decltype</tt> semantics rather than the template argument deduction semantics of plain <tt>auto</tt>:
<blockquote><pre>
int&amp; f();
         auto  i1 = f(); // int
decltype(auto) i2 = f(); // int&amp;
</pre></blockquote>
  </li>
  <li>
    G++ supports <a href="../projects/cxx1y.html">C++1y</a> lambda capture initializers:
<blockquote><pre>
[x = 42]{ ... };
</pre></blockquote>
Actually, they have been accepted since GCC 4.5, but now the compiler doesn't
warn about them with <tt>-std=c++1y</tt>, and supports parenthesized and
brace-enclosed initializers as well.
  </li>
  <li>
    G++ supports <a href="../projects/cxx1y.html">C++1y</a> variable length
    arrays.  G++ has supported GNU/C99-style VLAs for a long time, but now
    additionally supports initializers and lambda capture by reference.  In
    C++1y mode G++ will complain about VLA uses that are not permitted by
    the draft standard, such as forming a pointer to VLA type or
    applying <tt>sizeof</tt> to a VLA variable.  Note that it now appears
    that VLAs will not be part of C++14, but will be part of a separate
    document and then perhaps C++17.
<blockquote><pre>
void f(int n) {
  int a[n] = { 1, 2, 3 }; // throws std::bad_array_length if n &lt; 3
  [&amp;a]{ for (int i : a) { cout &lt;&lt; i &lt;&lt; endl; } }();
  &amp;a; // error, taking address of VLA
}
</pre></blockquote>
  </li>
  <li>
    G++ supports the <a href="../projects/cxx1y.html">C++1y</a> [[deprecated]]
    attribute modulo bugs in the underlying [[gnu::deprecated]] attribute.  Classes
    and functions can be marked deprecated and a diagnostic message added:
<blockquote><pre>
class A;
int bar(int n);
#if __cplusplus &gt; 201103
class [[deprecated("A is deprecated in C++14; Use B instead")]] A;
[[deprecated("bar is unsafe; use foo() instead")]]
int bar(int n);

int foo(int n);
class B;
#endif
A aa; // warning: 'A' is deprecated : A is deprecated in C++14; Use B instead
int j = bar(2); // warning: 'int bar(int)' is deprecated : bar is unsafe; use foo() instead
</pre></blockquote>
  </li>
  <li>
    G++ supports <a href="../projects/cxx1y.html">C++1y</a> digit separators.
    Long numeric literals can be subdivided with a single quote ' to enhance readability:
<blockquote><pre>
int i = 1048576;
int j = 1'048'576;
int k = 0x10'0000;
int m = 0'004'000'000;
int n = 0b0001'0000'0000'0000'0000'0000;

double x = 1.602'176'565e-19;
double y = 1.602'176'565e-1'9;
</pre></blockquote>
  </li>
  <li>
    G++ supports <a href="../projects/cxx1y.html">C++1y</a> polymorphic lambdas.
<blockquote><pre>
// a functional object that will increment any type
auto incr = [](auto x) { return x++; };
</pre></blockquote>
  </li>
</ul>

  <h4>Runtime Library (libstdc++)</h4>

  <ul>
    <li><a href="http://gcc.gnu.org/onlinedocs/libstdc++/manual/status.html#status.iso.2011">
       Improved support for C++11</a>, including:
       <ul>
         <li> support for <code>&lt;regex&gt;</code>;</li>
         <li> The associative containers in <code>&lt;map&gt;</code> and
              <code>&lt;set&gt;</code> and the unordered associative containers
              in <code>&lt;unordered_map&gt;</code> and <code>&lt;unordered_set&gt;</code>
              meet the allocator-aware container requirements; </li>
       </ul>
    </li>
    <li><a href="http://gcc.gnu.org/onlinedocs/libstdc++/manual/status.html#status.iso.2014">
       Improved experimental support for the upcoming ISO C++ standard, C++14</a>,
       including:
      <ul>
        <li> fixing <code>constexpr</code> member functions without <code>const</code>; </li>
        <li> implementation of the <code>std::exchange()</code> utility function; </li>
        <li> addressing tuples by type; </li>
        <li> implemention of <code>std::make_unique</code>; </li>
        <li> implemention of <code>std::shared_lock</code>; </li>
        <li> making <code>std::result_of</code> SFINAE-friendly; </li>
        <li> adding <code>operator()</code> to <code>integral_constant</code>; </li>
        <li> adding user-defined literals for standard library types
             <code>std::basic_string</code>, <code>std::chrono::duration</code>,
             and <code>std::complex</code>; </li>
        <li> adding two range overloads to non-modifying sequence oprations
             <code>std::equal</code> and <code>std::mismatch</code>; </li>
        <li> adding IO manipulators for quoted strings; </li>
        <li> adding <code>constexpr</code> members to <code>&lt;utility&gt;</code>,
             <code>&lt;complex&gt;</code>, <code>&lt;chrono&gt;</code>, and some containers; </li>
        <li> adding compile-time <code>std::integer_sequence</code>; </li>
        <li> adding cleaner transformation traits; </li>
        <li> making <code>&lt;functional&gt;</code>s operator functors easier to use
             and more generic; </li>
      </ul>
    </li>
    <li>An implementation of <code>std::experimental::optional</code>.</li>
    <li>An implementation of <code>std::experimental::string_view</code>.</li>
    <li>The non-standard function <code>std::copy_exception</code> has been deprecated
        and will be removed in a future version. <code>std::make_exception_ptr</code>
        should be used instead.
    </li>
  </ul>

<h3 id="fortran">Fortran</h3>
  <ul>
    <li>Compatibility notice:
    <ul>
      <li>Module files: The version of the module files (<code>.mod</code>)
        has been incremented; additionally, module files are now compressed.
        Fortran <code>MODULE</code>s compiled by earlier GCC versions have
        to be recompiled, when they are <code>USE</code>d by files compiled
        with GCC 4.9, because GCC 4.9 is not able to read <code>.mod</code>
        files of earlier GCC versions; attempting to do so gives an error
        message. Note: The ABI of the produced assembler data itself has not
        changed: object files and libraries are fully compatible to older
        versions. (Except for the next items.)</li>
      <li>ABI changes:
      <ul>
        <li>Note that the <a
          href="http://gcc.gnu.org/onlinedocs/gcc-4.9.0/gfortran/Argument-passing-conventions.html"
          >argument passing ABI</a> has changed for scalar dummy
  	  arguments of type <code>INTEGER</code>, <code>REAL</code>,
	  <code>COMPLEX</code> and <code>LOGICAL</code>, which have
	  <em>both</em> the <code>VALUE</code> and the <code>OPTIONAL</code>
	  attribute.</li>
        <li>Due to the support of finalization, the virtual table associated
          with polymorphic variables has changed. Therefore, code containing
          <code>CLASS</code> should be recompiled, including all files which
          define derived types involved in the type definition used by
          polymorphic variables. (Note: Due to the incremented module version,
          trying to mix old code with new code will usually give an error
          message.)</li>
      </ul></li>
      <li>GNU Fortran no longer deallocates allocatable variables or
        allocatable components of variables declared in the main program. Since
        Fortran 2008, the standard explicitly states that variables declared
        in the Fortran main program automatically have the <code>SAVE</code>
        attribute.</li>
      <li>When opening files, the close-on-exec flag is set if the system
        supports such a feature. This is generally considered good practice
        these days, but if there is a need to pass file descriptors to child
        processes the parent process must now remember to clear the
        close-on-exec flag by calling <code>fcntl()</code>, e.g. via
        <code>ISO_C_BINDING</code>, before executing the child process.</li>
    </ul></li>
    <li>The deprecated command-line option <code>-fno-whole-file</code>
      has been removed. (<code>-fwhole-file</code> is the default since
      GCC 4.6.) <code>-fwhole-file</code>/<code>-fno-whole-file</code>
      continue to be accepted but do not influence the code generation.</li>
    <li>The compiler no longer unconditionally warns
      about <code>DO</code> loops with zero iterations.  This warning is now
      controlled by the <code>-Wzerotrips</code> option, which is implied by
      <code>-Wall</code>.</li>
    <li>The new <code>NO_ARG_CHECK</code> attribute of the <a
      href="http://gcc.gnu.org/onlinedocs/gcc-4.9.0/gfortran/GNU-Fortran-Compiler-Directives.html"
      ><code>!GCC$</code> directive</a> can be used to disable the
      type-kind-rank (TKR) argument check for a dummy argument. The feature
      is similar to ISO/IEC TS 29133:2012's <code>TYPE(*)</code>, except that
      it additionally also disables the rank check. Variables with
      <code>NO_ARG_CHECK</code> have to be dummy arguments and may only be
      used as argument to <code>ISO_C_BINDING</code>'s <code>C_LOC</code>
      and as actual argument to another <code>NO_ARG_CHECK</code> dummy
      argument; also the other constraints of <code>TYPE(*)</code> apply.
      The dummy arguments should be declared as scalar or assumed-size
      variable of type <code>type(*)</code> (recommended) &ndash; or of
      type <code>integer</code>, <code>real</code>, <code>complex</code>
      or <code>logical</code>. With <code>NO_ARG_CHECK</code>, a pointer
      to the data without further type or shape information is passed,
      similar to C's <code>void*</code>. Note that also TS 29113's
      <code>type(*),dimension(..)</code> accepts arguments of any type and
      rank; contrary to <code>NO_ARG_CHECK</code> assumed-rank arguments
      pass an array descriptor which contains the array shape and stride
      of the argument.</li>
    <li><a href="http://gcc.gnu.org/wiki/Fortran2003Status">Fortran 2003</a>:
    <ul>
      <li>Finalization is now supported. Note that finalization is currently
        only done for a subset of the situations in which it should occur.</li>
      <li>Experimental support for <em>scalar</em> character components with
        deferred length (i.e. allocatable string length) in derived types has
        been added. (Deferred-length character variables are supported since
        GCC 4.6.)</li>
    </ul></li>
    <li><a href="http://gcc.gnu.org/wiki/Fortran2008Status">Fortran 2008</a>:
    <ul>
      <li>When <code>STOP</code> or <code>ERROR STOP</code> is used to terminate
        the execution and any exception (but inexact) is signaling, a warning is
        printed to <code>ERROR_UNIT</code>, indicating which exceptions are
        signaling. The <code><a
        href="http://gcc.gnu.org/onlinedocs/gcc-4.9.0/gfortran/Debugging-Options.html"
        >-ffpe-summary=</a></code> command-line option can be used to fine-tune
        for which exception the warning should be shown.</li>
      <li>Rounding on input (<code>READ</code>) is now handled on systems where
        <code>strtod</code> honours the rounding mode. (For output, rounding is
        supported since GCC 4.5.) Note that for input, the
        <code>compatible</code> rounding mode is handled as <code>nearest</code>
        (i.e., for a tie, rounding to an even last significant
        [cf. IEC 60559:1989] &ndash; while <code>compatible</code> rounds away
        from zero for a tie).</li>
    </ul></li>
  </ul>

<h3 id="go">Go</h3>
  <ul>
    <li>GCC 4.9 provides a complete implementation of the Go 1.2.1
      release.</li>
  </ul>

<!--
<h3>Java (GCJ)</h3>
-->

<h2 id="targets">New Targets and Target Specific Improvements</h2>

<h3 id="aarch64">AArch64</h3>
   <ul>
     <li> The ARMv8-A crypto and CRC instructions are now supported through
       intrinsics. These are enabled when the architecture supports these
       and are available through the <code>-march=armv8-a+crc</code>
       and <code>-march=armv8-a+crypto</code> options.
     </li>
     <li> Initial support for ILP32 has now been added to the
       compiler. This is now available through the command line option
       <code>-mabi=ilp32</code>. Support for ILP32 is
       considered experimental as the ABI specification is still beta.
     </li>
     <li> Coverage of more of the ISA including the SIMD extensions has
       been added. The Advanced SIMD intrinsics have also been improved.
     </li>
     <li> The new local register allocator (LRA) is now on by default
       for the AArch64 backend.
     </li>
     <li> The REE (Redundant extension elimination) pass has now been enabled
       by default for the AArch64 backend.
     </li>
     <li> Tuning for the Cortex-A53 and Cortex-A57 has been improved.
     </li>
     <li> Initial big.LITTLE tuning support for the combination of Cortex-A57
       and Cortex-A53 was added through the <code>-mcpu=cortex-a57.cortex-a53
       </code> option.
     </li>
     <li> A number of structural changes have been made to both the ARM
       and AArch64 backends to facilitate improved code-generation.
     </li>
   </ul>

<h3 id="arm">ARM</h3>
     <ul>
      <li> Use of Advanced SIMD (Neon) for 64-bit scalar computations has been
	disabled by default. This was found to generate better code in only
	a small number of cases. It can be turned back on with the
	<code>-mneon-for-64bits</code> option.
      </li>
     <li> Further support for the ARMv8-A architecture, notably implementing
       the restriction around IT blocks in the Thumb32 instruction set has
       been added. The <code>-mrestrict-it</code> option can be used with
       <code>-march=armv7-a</code> or the <code>-march=armv7ve</code> options
       to make code generation fully compatible with the deprecated instructions
       in ARMv8-A.
     </li>
     <li> Support has now been added for the ARMv7ve variant of the
       architecture. This can be used by the <code>-march=armv7ve</code> option.
     </li>
     <li> The ARMv8-A crypto and CRC instructions are now supported through
       intrinsics and are available through the <code>-march=armv8-a+crc</code>
       and <code>mfpu=crypto-neon-fp-armv8</code> options.
     </li>
     <li> LRA is now on by default for the ARM target. This can be turned off
       using the <code>-mno-lra</code> option. This option is purely
       transitionary command line option and will be removed in a future
       release. We are interested in any bug reports regarding functional and
       performance regressions with LRA.
     </li>
     <li> A new option <code>-mslow-flash-data</code> to improve performance
       of programs fetching data on slow flash memory has now been
       introduced for the ARMv7-M profile cores.
     </li>
     <li> A new option <code>-mpic-data-is-text-relative</code> for targets
       that allows data segments to be relative to text segments has
       been added. This is on by default for all targets except VxWorks RTP.
     </li>
     <li> A number of infrastructural changes have been made to both the ARM
       and AArch64 backends to facilitate improved code-generation.
     </li>
     <li> GCC now supports Cortex-A12 and the Cortex-R7 through the
       <code>-mcpu=cortex-a12</code> and <code>-mcpu=cortex-r7</code> options.
     </li>
     <li> GCC now has tuning for the Cortex-A57 and Cortex-A53
       through the <code>-mcpu=cortex-a57</code> and <code>-mcpu=cortex-a53
       </code> options.
     </li>
     <li> Initial big.LITTLE tuning support for the combination of Cortex-A57
       and Cortex-A53 was added through the <code>-mcpu=cortex-a57.cortex-a53
       </code> option. Similar support was added for the combination of
       Cortex-A15 and Cortex-A7 through the <code>-mcpu=cortex-a15.cortex-a7
       </code> option.
     </li>
     <li> Further performance optimizations for the Cortex-A15 and the
       Cortex-M4 have been added.
     </li>
     <li>A number of code generation improvements for Thumb2 to reduce code
       size when compiling for the M-profile processors.
     </li>
     </ul>
<h3 id="x86">IA-32/x86-64</h3>
  <ul>
    <li><code>-mfpmath=sse</code> is now implied by <code>-ffast-math</code>
	on all targets where SSE2 is supported.</li>
    <li>Intel AVX-512 support was added to GCC.  That includes inline
      assembly support, new registers and extending existing ones,
      new intrinsics (covered by corresponding testsuite), and basic
      autovectorization.  AVX-512 instructions are available via
      the following GCC switches: AVX-512 foundation instructions:
      <code>-mavx512f</code>, AVX-512 prefetch instructions: <code>-mavx512pf</code>,
      AVX-512 exponential and reciprocal instructions: <code>-mavx512er</code>,
      AVX-512 conflict detection instructions: <code>-mavx512cd</code>.
    </li>
    <li> It is now possible to call x86 intrinsics from select functions in
      a file that are tagged with the corresponding target attribute without
      having to compile the entire file with the <code>-mxxx</code> option.
      This improves the usability of x86 intrinsics and is particularly useful
      when doing <a
      href="http://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Function-Multiversioning.html"
      >Function Multiversioning</a>.
    </li>
    <li>GCC now supports the new Intel microarchitecture named Silvermont
      through <code>-march=silvermont</code>.
    </li>
    <li>GCC now supports the new Intel microarchitecture named Broadwell 
      through <code>-march=broadwell</code>.
    </li>
    <li>Optimizing for other Intel microarchitectures have been renamed
      to <code>-march=nehalem</code>, <code>westmere</code>,
      <code>sandybridge</code>, <code>ivybridge</code>,
      <code>haswell</code>, <code>bonnell</code>.
    </li>
    <li><code>-march=generic</code> has been retuned for better support of
      Intel core and AMD Bulldozer architectures.  Performance of AMD K7, K8,
      Intel Pentium-M, and Pentium4 based CPUs is no longer considered important
      for generic.
    </li>
    <li><code>-mtune=intel</code> can now be used to generate code running
      well on the most current Intel processors, which are Haswell
      and Silvermont for GCC 4.9.
    </li>
    <li>Support to encode 32-bit assembly instructions in 16-bit format
      is now available through the <code>-m16</code> command-line option.
    </li>
    <li>Better inlining of <code>memcpy</code> and <code>memset</code> 
	that is aware of value ranges and produces shorter alignment prologues.
    </li>
    <li><code>-mno-accumulate-outgoing-args</code> is now honored when unwind
      information is output.  Argument accumulation is also now turned off
      for portions of programs optimized for size.</li>
    <li>Support for new AMD family 15h processors (Excavator core)
        is now available through the <code>-march=bdver4</code> and
        <code>-mtune=bdver4</code> options.</li>
  </ul>
<h3 id="msp430">MSP430</h3>
  <ul>
    <li>A new command-line option <code>-mcpu=</code> has been added to the MSP430 backend.
    This option is used to specify the ISA to be used.  Accepted values are
    <code>msp430</code> (the default), <code>msp430x</code> and <code>msp430xv2</code>.  The ISA is no longer deduced
    from the <code>-mmcu=</code> option as there are far too many different MCU names.  The
    <code>-mmcu=</code> option is still supported, and this is still used to select linker
    scripts and generate a C preprocessor symbol that will be recognised by the
    <code>msp430.h</code> header file.</li>
  </ul>
<h3 id="nds32">NDS32</h3>
  <ul>
    <li> A new nds32 port supports the 32-bit architecture from Andes
      Technology Corporation.</li>
    <li> The port provides initial support for the V2, V3, V3m
      instruction set architectures.</li>
  </ul>
<h3 id="nios2">Nios II</h3>
  <ul>
    <li> A port for the Altera Nios II has been contributed by
      Mentor Graphics.</li>
  </ul>
<h3 id="powerpc">PowerPC / PowerPC64 / RS6000</h3>
  <ul>
    <li>GCC now supports Power ISA 2.07, which includes support for Hardware
    Transactional Memory (HTM), Quadword atomics and several VMX and VSX
    additions, including Crypto, 64-bit integer, 128-bit integer and
    decimal integer operations.</li>
    <li>Support for the POWER8 processor is now available through the
    <code>-mcpu=power8</code> and <code>-mtune=power8</code> options.</li>
    <li>The libitm library has been modified to add a HTM fastpath that
    automatically uses POWER's HTM hardware instructions when it is
    executing on a HTM enabled processor.</li>
    <li>Support for the new powerpc64le-linux platform has been added.
    It defaults to generating code that conforms to the ELFV2 ABI.</li>
</ul>
<h3>S/390, System z</h3>
  <ul>
    <li>Support for the Transactional Execution Facility included with
      the IBM zEnterprise zEC12 processor has been added.  A set of
      GCC style builtins as well as XLC style builtins are provided.
      The builtins are enabled by default when using
      the <code>-march=zEC12</code> option but can explicitly be
      disabled with <code>-mno-htm</code>.
      Using the GCC builtins also libitm supports hardware
      transactions on S/390.</li>
    <li>The hotpatch features allows to prepare functions for
      hotpatching.  A certain amount of bytes is reserved before the
      function entry label plus a NOP is inserted at its very
      beginning to implement a backward jump when applying a patch.
      The feature can either be enabled via command line
      option <code>-mhotpatch</code> for a compilation unit or can be
      enabled per function using the <code>hotpatch</code>
      attribute.</li>
    <li>The shrink wrap optimization is now supported on S/390 and
      enabled by default.</li>
    <li>A major rework of the routines to determine which registers
      need to be saved and restored in function prologue/epilogue now
      allow to use floating point registers as save slots.  This will
      happen for certain leaf function with <code>-march=z10</code>
      or higher.</li>
    <li>The LRA rtl pass replaces reload by default on S/390.</li>
  </ul>
<h3 id="rx">RX</h3>
  <ul>
    <li> The port now allows to specify the RX100, RX200, and RX600 processors
      with the command line options -mcpu=rx100, -mcpu=rx200 and -mcpu=rx600.
    </li>
  </ul>

<h3 id="sh">SH</h3>
  <ul>
    <li>Minor improvements to code generated for integer arithmetic and code
    that involves the T bit.</li>

    <li>Added support for the SH2A <code>clips</code> and <code>clipu</code>
    instructions.  The compiler will now try to utilize them for min/max
    expressions such as <code>max (-128, min (127, x))</code>.</li>

    <li>Added support for the <code>cmp/str</code> instruction through built-in
    functions such as <code>__builtin_strlen</code>.  When not optimizing for
    size, the compiler will now expand calls to e.g. <code>strlen</code> as an
    inlined sequences which utilize the <code>cmp/str</code> instruction.</li>

    <li>Improved code generated around volatile memory loads and stores.</li>

    <li>The option <code>-mcbranchdi</code> has been deprecated.  Specifying it
    will result in a warning and will not influence code generation.</li> 

    <li>The option <code>-mcmpeqdi</code> has been deprecated.  Specifying it
    will result in a warning and will not influence code generation.</li> 
  </ul>

<!--
<h2>Documentation improvements</h2>
-->


<!--
<h2>Other significant improvements</h2>

-->




<!-- ==================================================================== -->

<div class="copyright">

<address style="margin-top:0;">For questions related to the use of GCC,
please consult these web pages and the
<a href="http://gcc.gnu.org/onlinedocs/">GCC manuals</a>. If that fails,
the <a href="mailto:gcc-help@gcc.gnu.org">gcc-help@gcc.gnu.org</a>
mailing list might help.
Comments on these web pages and the development of GCC are welcome on our
developer list at <a href="mailto:gcc@gcc.gnu.org">gcc@gcc.gnu.org</a>.
All of <a href="http://gcc.gnu.org/lists.html">our lists</a>
have public archives.
</address>

<p>Copyright (C)
<a href="http://www.fsf.org">Free Software Foundation, Inc.</a>
Verbatim copying and distribution of this entire article is
permitted in any medium, provided this notice is preserved.</p>

<p style="margin-bottom:0;">These pages are
<a href="http://gcc.gnu.org/about.html">maintained by the GCC team</a>.
Last modified 2014-04-22<!-- IGNORE DIFF
--><a href="http://validator.w3.org/check/referer">.</a></p>

</div>

<!-- ==================================================================== -->

</body>
     </html>