This file is indexed.

/usr/share/doc/gcc-8-riscv64-linux-gnu-base/NEWS.html is in gcc-8-riscv64-linux-gnu 8-20180414-1ubuntu2cross1.

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
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
<?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="stylesheet" type="text/css" href="gcc.css" />
  
 <title>
GCC 7 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 7 Release Series<br />Changes, New Features, and Fixes</h1>

<p>
This page is a brief summary of some of the huge number of improvements in GCC 7.
For more information, see the
<a href="porting_to.html">Porting to GCC 7</a> page and the
<a href="../onlinedocs/index.html#current">full GCC documentation</a>.
</p>

<!-- .................................................................. -->
<h2>Disclaimer: GCC 7 has not been released yet, so this document is
a work-in-progress.</h2>

<!-- .................................................................. -->
<h2>Caveats</h2>
<ul>
  <li>GCC now uses <a href="https://gcc.gnu.org/wiki/LRAIsDefault">LRA (a
      new local register allocator) by default</a> for new targets.</li>

  <li>The non-standard C++0x type traits
      <code>has_trivial_default_constructor</code>,
      <code>has_trivial_copy_constructor</code> and
      <code>has_trivial_copy_assign</code> have been removed.</li>
  <li>The libstdc++
      <a href="https://gcc.gnu.org/onlinedocs/libstdc++/manual/profile_mode.html">Profile
      Mode</a> has been deprecated and will be removed in a future version.
  </li>

  <li>The Cilk+ extensions to the C and C++ languages have been deprecated.</li>
</ul>

<!-- .................................................................. -->
<h2 id="general">General Optimizer Improvements</h2>
<ul>
  <li>GCC 7 can determine the return value or range of return values of
    some calls to the <code>sprintf</code> family of functions and make
    it available to other optimization passes.  Some calls to the
    <code>snprintf</code> function with a zero size argument can be folded
    into constants.  This optimization is included in <code>-O1</code>
    and can be selectively controlled by the
    <code>-fprintf-return-value</code> option.</li>
  <li>A new store merging pass has been added.  It merges constant stores to
  adjacent memory locations into fewer, wider, stores.
  It is enabled by the <code>-fstore-merging</code> option and at the
  <code>-O2</code> optimization level or higher (and <code>-Os</code>).</li>

  <li>A new code hoisting optimization has been added to the partial
  redundancy elimination pass.  It attempts to move evaluation of
  expressions executed on all paths to the function exit as early as
  possible, which helps primarily for code size, but can be useful for
  speed of generated code as well.  It is enabled by the
  <code>-fcode-hoisting</code> option and at the <code>-O2</code>
  optimization level or higher (and <code>-Os</code>).</li>

  <li>A new interprocedural bitwise constant propagation optimization
  has been added, which propagates knowledge about which bits of variables
  are known to be zero (including pointer alignment information) across
  the call graph.  It is enabled by the <code>-fipa-bit-cp</code>
  option if <code>-fipa-cp</code> is enabled as well, and is enabled
  at the <code>-O2</code> optimization level and higher (and
  <code>-Os</code>).  This optimization supersedes interprocedural
  alignment propagation of GCC 6, and therefore the
  option <code>-fipa-cp-alignment</code> is now deprecated and
  ignored.</li>

  <li>A new interprocedural value range propagation optimization has been
  added, which propagates integral ranges that variable values can be proven
  to be within across the call graph.  It is enabled by the
  <code>-fipa-vrp</code> option and at the <code>-O2</code> optimization
  level and higher (and <code>-Os</code>).</li>

  <li>A new loop splitting optimization pass has been added.  It splits
  certain loops if they contain a condition that is always true on one
  side of the iteration space and always false on the other into two
  loops where each of the new two loops iterates just on one of the sides
  of the iteration space and the condition does not need to be checked
  inside of the loop.  It is enabled by the <code>-fsplit-loops</code>
  option and at the <code>-O3</code> optimization level or higher.</li>

  <li>The shrink-wrapping optimization can now separate portions of
  prologues and epilogues to improve performance if some of the
  work done traditionally by prologues and epilogues is not needed
  on certain paths.  This is controlled by the
  <code>-fshrink-wrap-separate</code> option, enabled by default.
  It requires target support, which is currently only implemented in the
  PowerPC and AArch64 ports.</li>

  <li>AddressSanitizer gained a new sanitization option, <code>-fsanitize-address-use-after-scope</code>,
      which enables sanitization of variables whose address is taken and used after a scope where the
      variable is defined:
  <blockquote><pre>
int
main (int argc, char **argv)
{
  char *ptr;
    {
      char my_char;
      ptr = &amp;my_char;
    }

  *ptr = 123;
  return *ptr;
}

<span class="boldred">==28882==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7fffb8dba990 at pc 0x0000004006d5 bp 0x7fffb8dba960 sp 0x7fffb8dba958</span>
<span class="boldblue">WRITE of size 1 at 0x7fffb8dba990 thread T0</span>
    #0 0x4006d4 in main /tmp/use-after-scope-1.c:10
    #1 0x7f9c71943290 in __libc_start_main (/lib64/libc.so.6+0x20290)
    #2 0x400739 in _start (/tmp/a.out+0x400739)

<span class="boldlime">Address 0x7fffb8dba990 is located in stack of thread T0 at offset 32 in frame</span>
    #0 0x40067f in main /tmp/use-after-scope-1.c:3

  This frame has 1 object(s):
    [32, 33) 'my_char' <span class="boldlime">&lt;== Memory access at offset 32 is inside this variable</span>
  </pre></blockquote>

  The option is enabled by default with <code>-fsanitize=address</code> and disabled
  by default with <code>-fsanitize=kernel-address</code>.
  Compared to the LLVM compiler, where the option already exists,
  the implementation in the GCC compiler has couple of improvements and advantages:
  <ul>
      <li>A complex usage of gotos and case labels are properly handled and should not
          report any false positive or false negatives.
      </li>
      <li>C++ temporaries are sanitized.</li>
      <li>Sanitization can handle invalid memory stores that are optimized out
      by the LLVM compiler when using an optimization level.</li>
  </ul>

  </li>

  <li>The <code>-fsanitize=signed-integer-overflow</code> suboption of the
  UndefinedBehavior Sanitizer now diagnoses arithmetic overflows even on
  arithmetic operations with generic vectors.</li>

  <li>Version 5 of the <a
  href="http://www.dwarfstd.org/Download.php">DWARF</a> debugging
  information standard is supported through the <code>-gdwarf-5</code>
  option.  The DWARF version 4 debugging information remains the
  default until debugging information consumers are adjusted.</li>

</ul>

<!-- .................................................................. -->
<h2 id="languages">New Languages and Language specific improvements</h2>
<!--
<ul>
  <li> -->
    OpenACC support in C, C++, and Fortran continues to be maintained and
    improved.
    See the <a href="https://gcc.gnu.org/wiki/OpenACC">OpenACC</a>
    and <a href="https://gcc.gnu.org/wiki/Offloading">Offloading</a> wiki pages
    for further information.
<!--  </li>
</ul>
-->

<h3 id="ada">Ada</h3>
<ul>
  <li>On mainstream native platforms, Ada programs no longer require the stack
      to be made executable in order to run properly.</li>
</ul>

<h3 id="brig">BRIG (HSAIL)</h3>

<p>Support for processing BRIG 1.0 files was added in this release.
BRIG is a binary format for HSAIL (Heterogeneous System Architecture
Intermediate Language). The BRIG frontend can be used for implementing
HSAIL "finalizers" (compilation of HSAIL to a native ISA) for gcc-supported
targets. An implementation of an HSAIL runtime library, libhsail-rt is
also included.</p>

<h3 id="c-family">C family</h3>
<ul>
<li>New command-line options have been added for the C and C++ compilers:
  <ul>
    <li><code>-Wimplicit-fallthrough</code> warns when a switch case falls
        through.  This warning has five different levels.  The compiler is
	able to parse a wide range of fallthrough comments, depending on
	the level.  It also handles control-flow statements, such as ifs.
	It's possible to suppres the warning by either adding a fallthrough
	comment, or by using a null statement: <code>__attribute__
	((fallthrough));</code> (C, C++), or <code>[[fallthrough]];</code>
        (C++17), or <code>[[gnu::fallthrough]];</code> (C++11/C++14).
        This warning is enabled by <code>-Wextra</code>.</li>
    <li><code>-Wpointer-compare</code> warns when a pointer is compared with
        a zero character constant.  Such code is now invalid in C++11 and
	GCC rejects it.  This warning is enabled by default.</li>
    <li><code>-Wduplicated-branches</code> warns when an if-else has identical
        branches.</li>
    <li><code>-Wrestrict</code> warns when an argument passed to a
        <code>restrict</code>-qualified parameter aliases with another
	argument.</li>
    <li><code>-Wmemset-elt-size</code> warns for <code>memset</code> calls,
        when the first argument references an array, and the third argument is
	a number equal to the number of elements of the array, but not the size
	of the array.  This warning is enabled by <code>-Wall</code>.</li>
    <li><code>-Wint-in-bool-context</code> warns about suspicious uses of
        integer values where boolean values are expected.  This warning is
	enabled by <code>-Wall</code>.</li>
    <li><code>-Wswitch-unreachable</code> warns when a <code>switch</code>
	statement has statements between the controlling expression and the
	first case label which will never be executed.  This warning is enabled
	by default.</li>
    <li><code>-Wexpansion-to-defined</code> warns when <code>defined</code> is
        used outside <code>#if</code>.  This warning is enabled by
	<code>-Wextra</code> or <code>-Wpedantic</code>.</li>
    <li><code>-Wregister</code> warns about uses of the <code>register</code>
        storage specifier.  In C++17 this keyword has been removed and for C++17
	this is a pedantic warning enabled by default.  The warning is not
	emitted for the GNU Explicit Register Variables extension.</li>
    <li><code>-Wvla-larger-than=N</code> warns about unbounded uses of
        variable-length arrays, and about bounded uses of variable-length
	arrays whose bound can be larger than <code>N</code> bytes.</li>
    <li><code>-Wduplicate-decl-specifier</code> warns when a declaration
        has duplicate <code>const</code>, <code>volatile</code>,
	<code>restrict</code> or <code>_Atomic</code> specifier. This warning
	is enabled by <code>-Wall</code>.</li>
  </ul>
</li>
  <li>GCC 6's C and C++ frontends were able to offer suggestions for
      misspelled field names:
      <blockquote><pre>
<b>spellcheck-fields.cc:52:13:</b> <span class="boldred">error:</span> <b>'struct s'</b> has no member named <b>'colour'</b>; did you mean <b>'color'</b>?
   return ptr-&gt;<span class="boldred">colour</span>;
               <span class="boldred">^~~~~~</span>
</pre></blockquote>
      GCC 7 greatly expands the scope of these suggestions.  Firstly, it
      adds fix-it hints to such suggestions:
<blockquote><pre>
<b>spellcheck-fields.cc:52:13:</b> <span class="boldred">error:</span> <b>'struct s'</b> has no member named <b>'colour'</b>; did you mean <b>'color'</b>?
   return ptr-&gt;<span class="boldred">colour</span>;
               <span class="boldred">^~~~~~</span>
               <span class="green">color</span>
</pre></blockquote>
      The suggestions now cover many other things, such as misspelled
      function names:
<blockquote><pre>
<b>spellcheck-identifiers.c:11:3:</b> <span class="boldmagenta">warning:</span> implicit declaration of function <b>'gtk_widget_showall'</b>; did you mean <b>'gtk_widget_show_all'</b>? [<span class="boldmagenta">-Wimplicit-function-declaration</span>]
   <span class="boldmagenta">gtk_widget_showall</span> (w);
   <span class="boldmagenta">^~~~~~~~~~~~~~~~~~</span>
   <span class="green">gtk_widget_show_all</span>
</pre></blockquote>
      misspelled macro names and enum values:
<blockquote><pre>
<b>spellcheck-identifiers.cc:85:11:</b> <span class="boldred">error:</span> <b>'MAX_ITEM'</b> undeclared here (not in a function); did you mean <b>'MAX_ITEMS'</b>?
 int array[<span class="boldred">MAX_ITEM</span>];
           <span class="boldred">^~~~~~~~</span>
           <span class="green">MAX_ITEMS</span>
</pre></blockquote>
      misspelled type names:
<blockquote><pre>
<b>spellcheck-typenames.c:7:14:</b> <span class="boldred">error:</span> unknown type name <b>'singed'</b>; did you mean <b>'signed'</b>?
 void test (<span class="boldred">singed</span> char e);
            <span class="boldred">^~~~~~</span>
            <span class="green">signed</span>
</pre></blockquote>
      and, in the C frontend, named initializers:
<blockquote><pre>
<b>test.c:7:20:</b> <span class="boldred">error:</span> <b>'struct s'</b> has no member named <b>'colour'</b>; did you mean <b>'color'</b>?
 struct s test = { .<span class="boldred">colour</span> = 3 };
                    <span class="boldred">^~~~~~</span>
                    <span class="green">color</span>
</pre></blockquote></li>
  <li>The preprocessor can now offer suggestions for misspelled
      directives, e.g.: 
<blockquote><pre>
<b>test.c:5:2:</b> <span class="boldred">error:</span>invalid preprocessing directive #endfi; did you mean #endif?
 #<span class="boldred">endfi</span>
  <span class="boldred">^~~~~</span>
  <span class="green">endif</span>
</pre></blockquote></li>
  <li>Warnings about format strings now underline the pertinent part of
    the string, and can offer suggested fixes.  In some cases, the
    pertinent argument is underlined.
<blockquote><pre>
<b>test.c:51:29:</b> <span class="boldmagenta">warning:</span> format <b>'%s'</b> expects argument of type <b>'char *'</b>, but argument 3 has type <b>'int'</b> [<span class="boldmagenta">-Wformat=</span>]
   printf ("foo: %d  bar: <span class="boldmagenta">%s</span> baz: %d", 100, <span class="boldmagenta">i + j</span>, 102);
                          <span class="boldmagenta">~^</span>                <span class="boldmagenta">~~~~~</span>
                          <span class="green">%d</span>
</pre></blockquote></li>

<li>The new <code>-Wdangling-else</code> command-line option has been split
out of <code>-Wparentheses</code> and warns about dangling <code>else</code>.</li>
<li><p>The <code>-Wshadow</code> warning has been split into three
variants. <code>-Wshadow=global</code> warns for any shadowing.  This
is the default when using <code>-Wshadow</code> without any
argument.  <code>-Wshadow=local</code> only warns for a local variable
shadowing another local variable or
parameter. <code>-Wshadow=compatible-local</code> only warns for a
local variable shadowing another local variable or parameter whose
type is compatible (in C++ compatible means that the type of the
shadowing variable can be converted to that of the shadowed variable).</p>

<p>The following example shows the different kinds of shadow
warnings:</p>

<blockquote><pre>
enum operation { add, count };
struct container { int nr; };

int
container_count (struct container c, int count)
{
  int r = 0;
  for (int count = 0; count > 0; count--)
    {
      struct container count = c;
      r += count.nr;
    }
  return r;
}</pre></blockquote>

<p><code>-Wshadow=compatible-local</code> will warn for the parameter being
shadowed with the same type:</p>

<blockquote><pre>
<b>warn-test.c:8:12:</b> <span class="boldmagenta">warning:</span> declaration of '<b>count</b>' shadows a parameter [<span class="boldmagenta">-Wshadow=compatible-local</span>]
   for (int <span class="boldmagenta">count</span> = 0; count > 0; count--)
            <span class="boldmagenta">^~~~~</span>
<b>warn-test.c:5:42:</b> <span class="boldcyan">note:</span> shadowed declaration is here
 container_count (struct container c, int <span class="boldcyan">count</span>)
                                          <span class="boldcyan">^~~~~</span></pre></blockquote>

<p><code>-Wshadow=local</code> will warn for the above and for the shadowed
declaration with incompatible type:</p>

<blockquote><pre>
<b>warn-test.c:10:24:</b> <span class="boldmagenta">warning:</span> declaration of '<b>count</b>' shadows a previous local [<span class="boldmagenta">-Wshadow=local</span>]
       struct container <span class="boldmagenta">count</span> = c;
                        <span class="boldmagenta">^~~~~</span>
<b>warn-test.c:8:12:</b> <span class="boldcyan">note:</span> shadowed declaration is here
   for (int <span class="boldcyan">count</span> = 0; count > 0; count--)
            <span class="boldcyan">^~~~~</span></pre></blockquote>

<p><code>-Wshadow=global</code> will warn for all of the above and the shadowing
of the global declaration:</p>

<blockquote><pre>
<b>warn-test.c:5:42:</b> <span class="boldmagenta">warning:</span> declaration of '<b>count</b>' shadows a global declaration [<span class="boldmagenta">-Wshadow</span>]
 container_count (struct container c, int <span class="boldmagenta">count</span>)
                                          <span class="boldmagenta">^~~~~</span>
<b>warn-test.c:1:23:</b> <span class="boldcyan">note:</span> shadowed declaration is here
 enum operation { add, <span class="boldcyan">count</span> };
                       <span class="boldcyan">^~~~~</span></pre></blockquote>
</li>
<li>GCC 7 contains a number of enhancements that help detect buffer overflow
  and other forms of invalid memory accesses.
  <ul>
    <li><p>The <code>-Walloc-size-larger-than=<i>size</i></code> option
	detects calls to standard and user-defined memory allocation
	functions decorated with attribute <code>alloc_size</code> whose
	argument exceeds the specified <code><i>size</i></code>
	(<code>PTRDIFF_MAX</code> by default).  The option also detects
	arithmetic overflow in the computation of the size in two-argument
	allocation functions like <code>calloc</code> where the total size
	is the product of the two arguments.  Since calls with an excessive
	size cannot succeed they are typically the result of programming
	errors.  Such bugs have been known to be the source of
	security vulnerabilities and a target of exploits.
      <code>-Walloc-size-larger-than=PTRDIFF_MAX</code> is included
      in <code>-Wall</code>.</p>
      <p>For example, the following call to <code>malloc</code> incorrectly
	tries to avoid passing a negative argument to the function and
	instead ends up unconditionally invoking it with an argument less
	than or equal to zero.  Since after conversion to the type of
	the argument of the function (<code>size_t</code>) a negative
	argument results in a value in excess of the maximum
	<code>PTRDIFF_MAX</code> the call is diagnosed.</p>
      <blockquote><pre>
void* f (int n)
{
  return malloc (n &gt; 0 ? 0 : n);
}

<span class="boldmagenta">warning: </span>argument 1 range [2147483648, 4294967295] exceeds maximum object size 2147483647 [<span class="boldmagenta">-Walloc-size-larger-than=</span>]</pre></blockquote></li>
    <li>The <code>-Walloc-zero</code> option detects calls to standard
      and user-defined memory allocation functions decorated with attribute
      <code>alloc_size</code> with a zero argument.  <code>-Walloc-zero</code>
      is not included in either <code>-Wall</code> or <code>-Wextra</code>
      and must be explicitly enabled.</li>
    <li>The <code>-Walloca</code> option detects all calls to the
      <code>alloca</code> function in the program.  <code>-Walloca</code>
      is not included in either <code>-Wall</code> or <code>-Wextra</code>
      and must be explicitly enabled.</li>
    <li><p>The <code>-Walloca-larger-than=<i>size</i></code> option detects
	calls to the <code>alloca</code> function whose argument either may
	exceed the specified <code><i>size</i></code>, or that is not known
	to be sufficiently constrained to avoid exceeding it.
	<code>-Walloca-larger-than</code> is not included in either
	<code>-Wall</code> or <code>-Wextra</code> and must be explicitly
	enabled.</p>
      <p>For example, compiling the following snippet with
	<code>-Walloca-larger-than=1024</code> results in a warning because
	even though the code appears to call <code>alloca</code> only with
	sizes of 1kb and less, since <code>n</code> is signed, a negative
	value would result in a call to the function well in excess of
	the limit.</p>
	<blockquote><pre>
void f (int n)
{
  char *d;
  if (n &lt; 1025)
    d = alloca (n);
  else
    d = malloc (n);
  &hellip;
}

<span class="boldmagenta">warning: </span>argument to '<b>alloca</b> may be too large due to conversion from '<b>int</b>' to '<b>long unsigned int</b>' [<span class="boldmagenta">-Walloca-larger-than=</span>]</pre></blockquote>
      <p>In contrast, a call to <code>alloca</code> that isn't bounded at all
	such as in the following function will elicit the warning below
	regardless of the <code><i>size</i></code> argument to the option.</p>
      <blockquote><pre>
void f (size_t n)
{
  char *d = alloca (n);
  &hellip;
}

<span class="boldmagenta">warning: </span>unbounded use of '<b>alloca</b>' [<span class="boldmagenta">-Walloca-larger-than=</span>]</pre></blockquote></li>
    <li><p>The <code>-Wformat-overflow=<i>level</i></code> option detects
	certain and likely buffer overflow in calls to the <code>sprintf</code>
	family of formatted output functions.  Although the option is enabled
	even without optimization it works best with <code>-O2</code> and
	higher.</p>
      <p>For example, in the following snippet the call to
	<code>sprintf</code> is diagnosed because even though its
	output has been constrained using the modulo operation it could
	result in as many as three bytes if <code>mday</code> were negative.
	The solution is to either allocate a larger buffer or make sure
	the argument is not negative, for example by changing
	<code>mday</code>'s type to <code>unsigned</code> or by making
	the type of the second operand of the modulo expression
	<code>unsigned</code>: <code>100U</code>.</p>
      <blockquote><pre>
void* f (int mday)
{
  char *buf = malloc (3);
  sprintf (buf, "%02i", mday % 100);
  return buf;
}

<span class="boldmagenta">warning: </span>'<b>sprintf</b> may write a terminating nul past the end of the destination [<span class="boldmagenta">-Wformat-overflow=</span>]
<span class="boldcyan">note: </span>'<b>sprintf</b>' output between 3 and 4 bytes into a destination of size 3</pre></blockquote></li>
    <li><p>The <code>-Wformat-truncation=<i>level</i></code> option detects
	certain and likely output truncation in calls to the
	<code>snprintf</code> family of formatted output functions.
	<code>-Wformat-truncation=1</code> is included in <code>-Wall</code>
	and enabled without optimization but works best with <code>-O2</code>
	and higher.</p>
      <p>For example, the following function attempts to format an integer
	between 0 and 255 in hexadecimal, including the <code>0x</code>
	prefix, into a buffer of four charactars.  But since the function
	must always terminate output by the null character (<code>'\0'</code>)
	such a buffer is only big enough to fit just one digit plus the prefix.
	Therefore the <code>snprintf</code> call is diagnosed.  To avoid
	the warning either use a bigger buffer or handle the function's
	return value which indicates whether or not its output has
	been truncated.</p>
      <blockquote><pre>
void f (unsigned x)
{
  char d[4];
  snprintf (d, sizeof d, "%#02x", x &amp; 0xff);
  &hellip;
}

<span class="boldmagenta">warning: </span>'<b>snprintf</b>' output may be truncated before the last format character [<span class="boldmagenta">-Wformat-truncation=</span>]
<span class="boldcyan">note: </span>'<b>snprintf</b>' output between 3 and 5 bytes into a destination of size 4</pre></blockquote></li>
    <li>The <code>-Wnonnull</code> option has been enhanced to detect
      a broader set of cases of passing null pointers to functions that
      expect a non-null argument (those decorated with attribute
      <code>nonnull</code>).  By taking advantage of optimizations the
      option can detect many more cases of the problem than in prior GCC
      versions.</li>
    <li><p>The <code>-Wstringop-overflow=<i>type</i></code> option detects
	buffer overflow in calls to string handling functions like
	<code>memcpy</code> and <code>strcpy</code>.  The option relies on
	<a href="https://gcc.gnu.org/onlinedocs/gcc/Object-Size-Checking.html">
	  Object Size Checking</a> and has an effect similar to defining
	the <code>_FORTIFY_SOURCE</code> macro.
	<code>-Wstringop-overflow=2</code> is enabled by default.</p>
      <p>For example, in the following snippet, because the call to
	<code>strncat</code> specifies a maximum that allows the function to
	write past the end of the destination, it is diagnosed.  To correct
	the problem and avoid the overflow the function should be called
	with a size of at most <code>sizeof d - strlen(d) - 1</code>.</p>
      <blockquote><pre>
void f (const char *fname)
{
  char d[8];
  strncpy (d, "/tmp/", sizeof d);
  strncat (d, fname, sizeof d);
  &hellip;
}

<span class="boldmagenta">warning: </span>specified bound 8 equals the size of the destination [<span class="boldmagenta">-Wstringop-overflow=</span>]</pre>
    </blockquote></li>
  </ul>
</li>
<li>The <code>&lt;limits.h&gt;</code> header provided by GCC defines
  macros such as <code>INT_WIDTH</code> for the width in bits of
  integer types, if <code>__STDC_WANT_IEC_60559_BFP_EXT__</code> is
  defined before the header is included.
  The <code>&lt;stdint.h&gt;</code> header defines such macros
  as <code>SIZE_WIDTH</code> and <code>INTMAX_WIDTH</code> for the
  width of some standard <code>typedef</code> names for integer types,
  again if <code>__STDC_WANT_IEC_60559_BFP_EXT__</code> is defined
  before the header is included; note that GCC's implementation of
  this header is only used for freestanding compilations, not hosted
  compilations, on most systems.  These macros come from ISO/IEC TS
  18661-1:2014.</li>
<li>The <code>&lt;float.h&gt;</code> header provided by GCC defines
  the macro <code>CR_DECIMAL_DIG</code>, from ISO/IEC TS 18661-1:2014,
  if <code>__STDC_WANT_IEC_60559_BFP_EXT__</code> is defined before
  the header is included.  This represents the number of decimal
  digits for which conversions between decimal character strings and
  binary formats, in both directions, are correctly rounded, and
  currently has the value of <code>UINTMAX_MAX</code> on all systems,
  reflecting that GCC's compile-time conversions are correctly rounded
  for any number of digits.</li>
<li><p>New <code>__builtin_add_overflow_p</code>,
  <code>__builtin_sub_overflow_p</code>,
  <code>__builtin_mul_overflow_p</code> built-in functions have been added.
  These work similarly to their siblings without the
  <code>_p</code> suffix, but do not actually store the result of the
  arithmetics anywhere, just return whether the operation would overflow.
  Calls to these built-ins with integer constant arguments evaluate to
  integer constants expressions.</p>
  <p>For example, in the following, <code>c</code> is assigned the result
    of <code>a * b</code> only if the multiplication does not overflow,
    otherwise it is assigned the value zero.  The multiplication is
    performed at compile-time and without triggering
    a <code>-Woverflow</code> warning.</p>
  <blockquote><pre>enum {
  a = 12345678,
  b = 87654321,
  c = __builtin_mul_overflow_p (a, b, a) ? 0 : a * b
};</pre></blockquote></li>

</ul>

<h3 id="c">C</h3>
<ul>
  <li><p>The C front end now supports type
  names <code>_Float<i>N</i></code> for floating-point types with IEEE
  interchange formats and <code>_Float<i>N</i>x</code> for
  floating-point types with IEEE extended formats.  These type names
  come from ISO/IEC TS 18661-3:2015.</p>
  <p>The set of types supported depends on the target for which GCC is
  configured.  Most targets
  support <code>_Float32</code>, <code>_Float32x</code>
  and <code>_Float64</code>.  <code>_Float128</code> is supported on
  targets where IEEE binary128 encoding was already supported
  as <code>long double</code>
  or <code>__float128</code>.  <code>_Float64x</code> is supported on
  targets where a type with either binary128 or Intel extended
  precision format is available.</p>
  <p>Constants with these types are supported using
  suffixes <code>f<i>N</i></code>, <code>F<i>N</i></code>,
  <code>f<i>N</i>x</code> and <code>F<i>N</i>x</code>
  (e.g., <code>1.2f128</code> or <code>2.3F64x</code>).  Macros such
  as <code>FLT128_MAX</code> are defined
  in <code>&lt;float.h&gt;</code>
  if <code>__STDC_WANT_IEC_60559_TYPES_EXT__</code> is defined before
  it is included.</p>
  <p>These new types are always distinct from each other and
  from <code>float</code>, <code>double</code> and <code>long
  double</code>, even if they have the same encoding.  Complex types
  such as <code>_Complex _Float128</code> are also supported.</p>
  <p>Type-generic built-in functions such
  as <code>__builtin_isinf</code> support the new types, and the
  following type-specific built-in functions have versions
  (suffixed <code>f<i>N</i></code> or <code>f<i>N</i>x</code>) for the
  new
  types: <code>__builtin_copysign</code>, <code>__builtin_fabs</code>, <code>__builtin_huge_val</code>, <code>__builtin_inf</code>, <code>__builtin_nan</code>, <code>__builtin_nans</code>.</p></li>
  <li>Compilation with <code>-fopenmp</code> is now compatible with the
  C11 <code>_Atomic</code> keyword.</li>
</ul>

<h3 id="cxx">C++</h3>
<ul>
  <li>The C++ front end has experimental support for all of the current C++17
    draft with the <code>-std=c++1z</code> or <code>-std=gnu++1z</code> flags,
    including <tt>if constexpr</tt>, class template argument
    deduction, <code>auto</code> template parameters, and structured bindings.
    For a full list of new features,
    see <a href="https://gcc.gnu.org/projects/cxx-status.html#cxx1z">the C++
      status page</a>.</li>
  <li>C++17 support for <code>new</code> of over-aligned types can be enabled
    in other modes with the <code>-faligned-new</code> flag.</li>
  <li>The C++17 evaluation order requirements can be selected in other modes
    with the <code>-fstrong-eval-order</code> flag, or disabled in C++17 mode
    with <code>-fno-strong-eval-order</code>.</li>
  <li>The default semantics of inherited constructors has changed in all modes,
    following <a href="http://wg21.link/p0136">P0136</a>.  Essentially,
    overload resolution happens as if calling the inherited constructor
    directly, and the compiler fills in construction of the other bases and
    members as needed.  Most uses should not need any changes.  The old
    behavior can be restored with <code>-fno-new-inheriting-ctors</code>,
    or <code>-fabi-version</code> less than 11.</li>
  <li>The resolution of DR 150 on matching of template template parameters,
    allowing default template arguments to make a template match a parameter,
    is currently enabled by default in C++17 mode only.  The default can be
    overridden with <code>-f{no-,}new-ttp-matching</code>.</li>
  <li>The C++ front end will now provide fix-it hints for some missing
    semicolons, allowing for automatic fixes by IDEs:
<blockquote><pre>
<b>test.cc:4:11:</b> <span class="boldred">error:</span> expected <b>';'</b> after class definition
 class a {} 
           <span class="boldred">^</span>
           <span class="green">;</span>
</pre></blockquote></li>
  <li><code>-Waligned-new</code> has been added to the C++ front end.  It warns
      about <code>new</code> of type with extended alignment without
      <code>-faligned-new</code>.</li>
</ul>

<h4 id="libstdcxx">Runtime Library (libstdc++)</h4>
<ul>
  <li>
    The type of exception thrown by iostreams,
    <code>std::ios_base::failure</code>, now uses the
    <a href="https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html"><code>cxx11</code>
    ABI</a>.
  </li>
  <li>Experimental support for C++17, including the following new features:
  <ul>
    <li>
      <code>std::string_view</code>;
    </li>
    <li>
      <code>std::any</code>, <code>std::optional</code>,
      and <code>std::variant</code>;
    </li>
    <li>
      <code>std::invoke</code>, <code>std::is_invocable</code>,
      <code>std::is_nothrow_invocable</code>, and <code>invoke_result</code>;
    </li>
    <li>
      <code>std::is_swappable</code>,
      and <code>std::is_nothrow_swappable</code>;
    </li>
    <li>
      <code>std::apply</code>,
      and <code>std::make_from_tuple</code>;
    </li>
    <li>
      <code>std::void_t</code>, <code>std::bool_constant</code>,
      <code>std::conjunction</code>, <code>std::disjunction</code>,
      and <code>std::negation</code>;
    </li>
    <li>Variable templates for type traits;</li>
    <li>Mathematical Special Functions;</li>
    <li>
      <code>std::chrono::floor</code>, <code>std::chrono::ceil</code>,
      <code>std::chrono::round</code>, and <code>std::chrono::abs</code>;
    </li>
    <li>
      <code>std::clamp</code>, <code>std::gcd</code>, <code>std::lcm</code>,
      3-dimensional <code>std::hypot</code>;
    </li>
    <li>
      <code>std::scoped_lock</code>, <code>std::shared_mutex</code>,
      <code>std::atomic&lt;T&gt;::is_always_lock_free</code>;
    </li>
    <li>
      <code>std::sample</code>, <code>std::default_searcher</code>,
      <code>std::boyer_moore_searcher</code> and
      <code>std::boyer_moore_horspool_searcher</code>;
    </li>
    <li>
      Extraction and re-insertion of map and set nodes, <code>try_emplace</code>
      members for maps, and functions for accessing containers
      <code>std::size</code>, <code>std::empty</code>, and
      <code>std::data</code>;
    </li>
    <li>
      <code>std::shared_ptr</code> support for arrays,
      <code>std::shared_ptr&lt;T&gt;::weak_type</code>,
      <code>std::enable_shared_from_this&lt;T&gt;::weak_from_this()</code>,
      and <code>std::owner_less&lt;void&gt;</code>;
    </li>
    <li><code>std::byte</code>;</li>
    <li><code>std::as_const</code>, <code>std::not_fn</code>,
      <code>std::has_unique_object_representations</code>,
      constexpr <code>std::addressof</code>.
    </li>
  </ul>
  Thanks to Daniel Kr&uuml;gler, Tim Shen, Edward Smith-Rowland, and Ville Voutilainen for
  work on the C++17 support.
  </li>
  <li>
    A new power-of-two rehashing policy for use with the
    <code>_Hashtable</code> internals, thanks to Fran&ccedil;ois Dumont.
  </li>
</ul>

<h3 id="fortran">Fortran</h3>
<ul>

  <li>
    Support for a number of extensions for compatibility with legacy code
    with new flags:
  <ul>
    <li>
      <code>-fdec-structure</code>
      Support for DEC <code>STRUCTURE</code> and <code>UNION</code>
    </li>
    <li>
      <code>-fdec-intrinsic-ints</code>
      Support for new integer intrinsics with B/I/J/K prefixes such as
      <code>BABS</code>, <code>JIAND</code>...
    </li>
    <li>
      <code>-fdec-math</code>
      Support for additional math intrinsics, including <code>COTAN</code> and
      degree-valued trigonometric functions such as <code>TAND</code>,
      <code>ASIND</code>...
    </li>
    <li>
      <code>-fdec</code>
      Enable the <code>-fdec-*</code> family of extensions.
    </li>
  </ul>
  </li>

  <li>
    New flag <code>-finit-derived</code> to allow default initialization of
    derived-type variables.
  </li>

  <li>
    Improved <code>DO</code> loops with step equal to 1 or -1, generates faster
    code without a loop preheader.  A new warning, <code>-Wundefined-do-loop</code>, 
    warns when a loop iterates either to <code>HUGE(i)</code> (with step equal
    to 1), or to <code>-HUGE(i)</code> (with step equal to -1). Invalid behavior
    can be caught at run time with <code>-fcheck=do</code> enabled:
    <blockquote><pre>
program test
  implicit none
  integer(1) :: i
  do i = -HUGE(i)+10, -HUGE(i)-1, -1
    print *, i
  end do
end program test

At line 8 of file do_check_12.f90
Fortran runtime error: Loop iterates infinitely</pre></blockquote>
  </li>
  <li>Version 4.5 of the <a href="http://www.openmp.org/specifications/"
      >OpenMP specification</a> is now partially supported also in the
      Fortran compiler; the largest missing item is structure element
      mapping.</li>
      
  <li>User-defined derived-type input/output (UDTIO) is added.</li>
  
  <li>Derived type coarrays with allocable and pointer components
      is partially supported.</li>

  <li>Non-constant stop codes and error stop codes (Fortran 2015 feature).</li>
  
  <li>Derived types with allocatable components of recursive type.</li>
  
  <li>Intrinsic assignment to polymorphic variables.</li>
  
  <li>Improved submodule support.</li>
  
  <li>Improved diagnostics (polymorphic results in pure functions).</li>
</ul>

<h3 id="go">Go</h3>
<ul>
  <li>GCC 7 provides a complete implementation of the Go 1.8.1
    user packages.</li>

  <li>Compared to the Go 1.8.1 toolchain, the garbage collector is more
    conservative and less concurrent.</li>

  <li>Escape analysis is available for experimental use via
    the <code>-fgo-optimize-allocs</code> option.
    The <code>-fgo-debug-escape</code> prints information useful for
    debugging escape analysis choices.</li>

</ul>

<h3 id="java">Java (GCJ)</h3>

<p>The GCC Java frontend and associated libjava runtime library have been
removed from GCC.</p>

<!-- .................................................................. -->
<h2 id="jit">libgccjit</h2>

<p>The libgccjit API gained support for marking calls as requiring
tail-call optimization via a new entrypoint:
<a href="https://gcc.gnu.org/onlinedocs/jit/topics/expressions.html#gcc_jit_rvalue_set_bool_require_tail_call">gcc_jit_rvalue_set_bool_require_tail_call</a>.</p>

<p>libgccjit performs numerous checks at the API boundary, but
if these succeed, it previously ignored errors and other diagnostics emitted
within the core of GCC, and treated the compile of a gcc_jit_context
as having succeeded.  As of GCC 7 it now ensures that if any diagnostics are
emitted, they are visible from the libgccjit API, and that the the context is
flagged as having failed.</p>

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

<h3 id="aarch64">AArch64</h3>
   <ul>
     <li>
       The ARMv8.3-A architecture is now supported.  It can be used by
       specifying the <code>-march=armv8.3-a</code> option.
     </li>
     <li>
       The option <code>-msign-return-address=</code> is supported to enable
       return address protection using ARMv8.3-A Pointer Authentication
       Extensions.  For more information on the arguments accepted by this
       option, please refer to
	<a href="https://gcc.gnu.org/onlinedocs/gcc/AArch64-Options.html#AArch64-Options">
	AArch64-Options</a>.
     </li>
     <li>
       The ARMv8.2-A architecture and the ARMv8.2-A 16-bit Floating-Point
       Extensions are now supported.  They can be used by specifying the
       <code>-march=armv8.2-a</code> or <code>-march=armv8.2-a+fp16</code>
       options.
       The 16-bit Floating-Point Extensions introduce new half-precision data
       processing floating-point instructions.
     </li>
     <li>
       Support has been added for the following processors
       (GCC identifiers in parentheses):
       ARM Cortex-A73 (<code>cortex-a73</code>),
       Broadcom Vulcan (<code>vulcan</code>),
       Cavium ThunderX CN81xx (<code>thunderxt81</code>),
       Cavium ThunderX CN83xx (<code>thunderxt83</code>),
       Cavium ThunderX CN88xx (<code>thunderxt88</code>),
       Cavium ThunderX CN88xx pass 1.x (<code>thunderxt88p1</code>),
       Cavium ThunderX 2 CN99xx (<code>thunderx2t99</code>),
       Qualcomm Falkor (<code>falkor</code>).
       The GCC identifiers can be used
       as arguments to the <code>-mcpu</code> or <code>-mtune</code> options,
       for example: <code>-mcpu=cortex-a73</code> or
       <code>-mtune=vulcan</code> or as arguments to the equivalent target
       attributes and pragmas.
     </li>
   </ul>

<h3 id="arc">ARC</h3>
   <ul>
     <li>
       Add support for ARC HS and ARC EM processors.
     </li>
     <li>
       Add support for ARC EM variation found in Intel QuarkSE SoCs.
     </li>
     <li>
       Add support for NPS400 ARC700 based CPUs.
     </li>
     <li>
       Thread Local Storage is now supported by ARC CPUs.
     </li>
     <li>
       Fix errors for ARC600 when using 32x16 multiplier option.
     </li>
     <li>
       Fix PIE for ARC CPUs.
     </li>
     <li>
       New CPU templates are supported via multilib.
     </li>
   </ul>

<h3 id="arm">ARM</h3>
   <ul>
     <li>
       Support for the ARMv5 and ARMv5E architectures has been deprecated
       (which have no known implementations) and will be removed in a future
       GCC release.  Note that ARMv5T, ARMv5TE and ARMv5TEJ architectures
       remain supported.
       The values <code>armv5</code> and <code>armv5e</code> of
       <code>-march</code> are thus deprecated.
     </li>
     <li>
       The ARMv8.2-A architecture and the ARMv8.2-A 16-bit Floating-Point
       Extensions are now supported.  They can be used by specifying the
       <code>-march=armv8.2-a</code> or <code>-march=armv8.2-a+fp16</code>
       options.
       The 16-bit Floating-Point Extensions introduce new half-precision data
       processing floating-point instructions.
     </li>
     <li>
       The ARMv8-M architecture is now supported in its two architecture
       profiles: ARMv8-M Baseline and ARMv8-M Mainline with its DSP and
       Floating-Point Extensions.  They can be used by specifying the
       <code>-march=armv8-m.base</code>, <code>armv8-m.main</code> or
       <code>armv8-m.main+dsp</code> options.
     </li>
     <li>
       Support has been added for the following processors
       (GCC identifiers in parentheses): ARM Cortex-A73
       (<code>cortex-a73</code>), ARM Cortex-M23 (<code>cortex-m23</code>) and
       ARM Cortex-M33 (<code>cortex-m33</code>).
       The GCC identifiers can be used
       as arguments to the <code>-mcpu</code> or <code>-mtune</code> options,
       for example: <code>-mcpu=cortex-a73</code> or
       <code>-mtune=cortex-m33</code>.
     </li>
     <li>
       A new command-line option <code>-mpure-code</code> has been added.
       It does not allow constant data to be placed in code sections.
       This option is only available when generating non-pic code for ARMv7-M
       targets.
     </li>
     <li>
      Support for the ACLE Coprocessor Intrinsics has been added. This enables
      the generation of coprocessor instructions through the use of intrinsics
      such as <code>cdp</code>, <code>ldc</code>, and others.
    </li>
     <li>
      The configure option <code>--with-multilib-list</code> now accepts the
      value <code>rmprofile</code> to build multilib libraries for a range of
      embedded targets.  See our
      <a href="https://gcc.gnu.org/install/configure.html">installation
      instructions</a> for details.
    </li>
   </ul>

<h3 id="avr">AVR</h3>
<ul>
  <li>On the reduced Tiny cores, the <code>progmem</code>
    <a href="https://gcc.gnu.org/onlinedocs/gcc/AVR-Variable-Attributes.html">variable
      attribute</a>
    is now properly supported.  Respective read-only variables are located
    in flash memory in section <code>.progmem.data</code>.  No special
    code is needed to access such variables; the compiler automatically
    adds an offset of <code>0x4000</code> to all addresses, which is needed
    to access variables in flash memory.  As opposed to ordinary cores
    where it is sufficient to specify the <code>progmem</code> attribute
    with definitions, on the reduced Tiny cores the attribute also has to
    be specified with (external) declarations:
    <blockquote><pre>
extern const int array[] __attribute__((__progmem__));

int get_value2 (void)
{
  /* Access via addresses array + 0x4004 and array + 0x4005. */
  return array[2];
}

const int* get_address (unsigned idx)
{
  /* Returns array + 0x4000 + 2 * idx. */
  return &amp;array[idx];
}</pre></blockquote></li>
  <li>A new command-line option <code>-Wmisspelled-isr</code> has been added.
    It turns off &mdash; or turns into errors &mdash;
    warnings that are reported for interrupt service routines (ISRs)
    which don't follow AVR-LibC's naming convention of prefixing
    ISR names with <code>__vector</code>.</li>
  <li><code>__builtin_avr_nops(<i>n</i>)</code> is a new
    <a href="https://gcc.gnu.org/onlinedocs/gcc/AVR-Built-in-Functions.html">built-in
      function</a>
    that inserts <i>n</i> <code>NOP</code> instructions into
    the instruction stream. <i>n</i> must be a value known at
    compile time.</li>
</ul>

<!-- <h3 id="hsa">Heterogeneous Systems Architecture</h3> -->

<h3 id="x86">IA-32/x86-64</h3>
<ul>
  <li>Support for the AVX-512 Fused Multiply Accumulation Packed Single precision
  (4FMAPS), AVX-512 Vector Neural Network Instructions Word variable precision
  (4VNNIW), AVX-512 Vector Population Count (VPOPCNTDQ) and Software
  Guard Extensions (SGX) ISA extensions has been added.</li>
</ul>

<!-- <h3 id="mips">MIPS</h3> -->

<!-- <h3 id="mep">MeP</h3> -->

<!-- <h3 id="msp430">MSP430</h3> -->

<!-- <h3 id="nds32">NDS32</h3> -->

<h3 id="nvptx">NVPTX</h3>
<ul>
  <li>OpenMP target regions can now be offloaded to NVidia PTX GPGPUs.
  See the <a href="https://gcc.gnu.org/wiki/Offloading">Offloading Wiki</a>
  on how to configure it.</li>
</ul>

<h3 id="powerpc">PowerPC / PowerPC64 / RS6000</h3>
<ul>
  <li>The PowerPC port now uses LRA by default.</li>
  <li>GCC now diagnoses inline assembly that clobbers register r2.
    This has always been invalid code, and is no longer quietly
    tolerated.</li>
  <li>The PowerPC port's support for ISA 3.0 (<code>-mcpu=power9</code>)
    has been enhanced to generate more of the new instructions by default, and
    to provide more built-in functions to generate code for other new
    instructions.</li>
  <li>The configuration option <code>--enable-gnu-indirect-function</code>
    is now enabled by default on PowerPC GNU/Linux builds.</li>
  <li>The PowerPC port will now allow 64-bit and 32-bit integer types to be
    allocated to the VSX vector registers (ISA 2.06 and above).  In addition,
    on ISA 3.0, 16-bit and 8-bit integer types can be allocated in the vector
    registers.  Previously, only 64-bit integer types were allowed in the
    traditional floating point registers.</li>
  <li>New options <code>-mstack-protector-guard=global</code>,
    <code>-mstack-protector-guard=tls</code>,
    <code>-mstack-protector-guard-reg=</code>, and
    <code>-mstack-protector-guard-offset=</code> change how the stack
    protector gets the value to use as canary.</li>
</ul>

<!-- <h3 id="s390">S/390, System z, IBM z Systems</h3> -->

<h3 id="riscv">RISC-V</h3>
<ul>
  <li>Support for the RISC-V instruction set has been added.</li>
</ul>

<!-- <h3 id="rx">RX</h3> -->

<!-- <h3 id="sh">SH</h3> -->

<h3 id="sparc">SPARC</h3>
<ul>
  <li>The SPARC port now uses LRA by default.</li>
  <li>Support for the new Subtract-Extended-with-Carry instruction
      available in SPARC M7 (Niagara 7) has been added.</li>
</ul>

<!-- .................................................................. -->
<h2 id="os">Operating Systems</h2>

<h3 id="aix">AIX</h3>
  <ul>
    <li>Visibility support has been enabled for AIX 7.1 and above.</li>
  </ul>

<h3 id="fuchsia">Fuchsia</h3>
   <ul>
     <li>Support has been added for the
     <a href="https://fuchsia.googlesource.com/">Fuchsia OS</a>.</li>
   </ul>

<!-- <h3 id="dragonfly">DragonFly BSD</h3> -->

<!-- <h3 id="freebsd">FreeBSD</h3> -->

<!-- <h3 id="linux">Linux</h3> -->

<h3 id="rtems">RTEMS</h3>
   <ul>
     <li>The ABI changes on ARM so that no short enums are used by default.</li>
   </ul>

<!-- <h3 id="solaris">Solaris</h3> -->

<!-- <h3 id="vxmils">VxWorks MILS</h3> -->

<!-- <h3 id="windows">Windows</h3> -->

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

<!-- .................................................................. -->
<h2>Other significant improvements</h2>
<ul>
  <li><code>-fverbose-asm</code> previously emitted information on the
    meanings of assembly expressions.  This has been extended so that
    it now also prints comments showing the source lines that correspond
    to the assembly, making it easier to read the generated assembly
    (especially with larger functions).
    For example, given this C source file:
<blockquote><pre>
int test (int n)
{
  int i;
  int total = 0;

  for (i = 0; i &lt; n; i++)
    total += i * i;
  return total;
}
</pre></blockquote>
      <code>-fverbose-asm</code> now gives output similar to this for
      the function body (when compiling for x86_64, with
      <code>-Os</code>):
<blockquote><pre>
       .text
       .globl  test
       .type   test, @@function
test:
.LFB0:
       .cfi_startproc
# example.c:4:   int total = 0;
       xorl    %eax, %eax      # &lt;retval&gt;
# example.c:6:   for (i = 0; i &lt; n; i++)
       xorl    %edx, %edx      # i
.L2:
# example.c:6:   for (i = 0; i &lt; n; i++)
       cmpl    %edi, %edx      # n, i
       jge     .L5     #,
# example.c:7:     total += i * i;
       movl    %edx, %ecx      # i, tmp92
       imull   %edx, %ecx      # i, tmp92
# example.c:6:   for (i = 0; i &lt; n; i++)
       incl    %edx    # i
# example.c:7:     total += i * i;
       addl    %ecx, %eax      # tmp92, &lt;retval&gt;
       jmp     .L2     #
.L5:
# example.c:10: }
       ret
       .cfi_endproc
</pre></blockquote></li>
  <li id="printing-fix-it-hints">Two new options have been added for
    printing fix-it hints:
    <ul>
      <li><code>-fdiagnostics-parseable-fixits</code>
        allows for fix-it hints to be emitted in a machine-readable
        form, suitable for consumption by IDEs.  For example, given:
<blockquote><pre>
<b>spellcheck-fields.cc:52:13:</b> <span class="boldred">error:</span> <b>'struct s'</b> has no member named <b>'colour'</b>; did you mean <b>'color'</b>?
   return ptr-&gt;<span class="boldred">colour</span>;
               <span class="boldred">^~~~~~</span>
               <span class="green">color</span>
</pre></blockquote>
it will emit:
<blockquote><pre>
fix-it:"spellcheck-fields.cc":{52:13-52:19}:"color"
</pre></blockquote></li>
      <li><code>-fdiagnostics-generate-patch</code> will print
        a patch in "unified" format after any diagnostics are printed,
        showing the result of applying all fix-it hints.  For the above
        example it would emit:
<blockquote><pre>
<b>--- spellcheck-fields.cc</b>
<b>+++ spellcheck-fields.cc</b>
<span class="boldmagenta">@@ -49,5 +49,5 @@</span>

 color get_color(struct s *ptr)
 {
<span class="boldred">-  return ptr-&gt;colour;</span>
<span class="green">+  return ptr-&gt;color;</span>
 }
</pre></blockquote></li></ul></li>
  <li>The <code>gcc</code> and <code>g++</code> driver programs will now
    provide suggestions for misspelled arguments to command-line options.
<blockquote><pre>
$ gcc -c test.c -ftls-model=global-dinamic
gcc: <span class="boldred">error:</span> unknown TLS model <b>'global-dinamic'</b>
gcc: <span class="boldcyan">note:</span> valid arguments to <b>'-ftls-model='</b> are: global-dynamic initial-exec local-dynamic local-exec; did you mean <b>'global-dynamic'</b>?
</pre></blockquote></li>
  <li>The compiler will now provide suggestions for misspelled parameters.
<blockquote><pre>
$ gcc -c test.c --param max-early-inliner-iteration=3 
cc1: <span class="boldred">error:</span> invalid --param name <b>'max-early-inliner-iteration'</b>; did you mean <b>'max-early-inliner-iterations'</b>?
</pre></blockquote></li>

  <li>Profile-guided optimization (PGO) instrumentation, as well as test coverage (GCOV),
      can newly instrument constructors (functions marks with <code>__attribute__((constructor)))</code>,
      destructors and C++ constructors (and destructors) of classes that are used
      as a type of a global variable.
  </li>
  <li>A new option <code>-fprofile-update=atomic</code> prevents creation of corrupted
      profiles created during instrumentation run (<code>-fprofile=generate</code>)
      of an application.  Downside of the option is a speed penalty.  Providing
      <code>-pthread</code> on command line would result in selection of atomic
      profile updating (when supports by a target).
  </li>
  <li>
    <p>GCC's already extensive testsuite has gained some new
      capabilities, to further improve the reliability of the compiler:</p>
    <ul>
      <li>GCC now has has an internal unit testing API and a suite of tests
        for programmatic self-testing of subsystems.</li>
      <li>GCC's C frontend has been extended so that it can parse dumps of
        GCC's internal representations, allowing for DejaGnu tests
        that more directly exercise specific optimization passes.  This
        covers both the
        <a href="https://gcc.gnu.org/onlinedocs/gccint/GIMPLE-Tests.html">
        GIMPLE representation</a> (for testing higher-level
        optimizations) and the
        <a href="https://gcc.gnu.org/onlinedocs/gccint/RTL-Tests.html">
        RTL representation</a>, allowing for more direct testing of
        lower-level details, such as register allocation and instruction
        selection.</li>
    </ul>
  </li>
</ul>

<!-- <h2><a name="7.1">GCC 7.1</a></h2>

<p>This is the <a href="https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&amp;resolution=FIXED&amp;target_milestone=7.1">list
of problem reports (PRs)</a> from GCC's bug tracking system that are
known to be fixed in the 7.1 release. This list might not be
complete (that is, it is possible that some PRs that have been fixed
are not listed here).</p>
-->




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

<div class="copyright">

<address>For questions related to the use of GCC,
please consult these web pages and the
<a href="https://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="https://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>These pages are
<a href="https://gcc.gnu.org/about.html">maintained by the GCC team</a>.
Last modified 2017-05-01<!-- IGNORE DIFF
--><a href="http://validator.w3.org/check/referer">.</a></p>

</div>

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

</body>
     </html>