/usr/src/gcc-4.4/debian/NEWS.gcc is in gcc-4.4-source 4.4.7-1ubuntu2.
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 | GCC 4.4 Release Series -- Changes, New Features, and Fixes
==========================================================
Caveats
=======
- __builtin_stdarg_start has been completely removed from GCC.
Support for <varargs.h> had been deprecated since GCC 4.0. Use
__builtin_va_start as a replacement.
- Some of the errors issued by the C++ front end that could be
downgraded to warnings in previous releases by using -fpermissive
are now warnings by default. They can be converted into errors by
using -pedantic-errors.
- Use of the cpp assertion extension will now emit a warning when
-Wdeprecated or -pedantic is used. This extension has been
deprecated for many years, but never warned about.
- Packed bit-fields of type char were not properly bit-packed on many
targets prior to GCC 4.4. On these targets, the fix in GCC 4.4
causes an ABI change. For example there is no longer a 4-bit
padding between field a and b in this structure:
struct foo
{
char a:4;
char b:8;
} __attribute__ ((packed));
There is a new warning to help identify fields that are affected:
foo.c:5: note: Offset of packed bit-field 'b' has changed in GCC 4.4
The warning can be disabled with -Wno-packed-bitfield-compat.
- On ARM EABI targets, the C++ mangling of the va_list type has been
changed to conform to the current revision of the EABI. This does
not affect the libstdc++ library included with GCC.
- The SCOUNT and POS bits of the MIPS DSP control register are now
treated as global. Previous versions of GCC treated these fields as
call-clobbered instead.
- The MIPS port no longer recognizes the h asm constraint. It was
necessary to remove this constraint in order to avoid generating
unpredictable code sequences.
One of the main uses of the h constraint was to extract the high
part of a multiplication on 64-bit targets. For example:
asm ("dmultu\t%1,%2" : "=h" (result) : "r" (x), "r" (y));
You can now achieve the same effect using 128-bit types:
typedef unsigned int uint128_t __attribute__((mode(TI)));
result = ((uint128_t) x * y) >> 64;
- The second sequence is better in many ways. For example, if x and y
are constants, the compiler can perform the multiplication at
compile time. If x and y are not constants, the compiler can
schedule the runtime multiplication better than it can schedule an
asm statement.
- Support for a number of older systems and recently unmaintained or
untested target ports of GCC has been declared obsolete in GCC 4.4.
Unless there is activity to revive them, the next release of GCC
will have their sources permanently removed.
- The following ports for individual systems on particular
architectures have been obsoleted:
- Generic a.out on IA32 and m68k (i[34567]86-*-aout*, m68k-*-aout*)
- Generic COFF on ARM, H8300, IA32, m68k and SH (arm-*-coff*,
armel-*-coff*, h8300-*-*, i[34567]86-*-coff*, m68k-*-coff*,
sh-*-*). This does not affect other more specific targets using
the COFF object format on those architectures, or the more
specific H8300 and SH targets (h8300-*-rtems*, h8300-*-elf*,
sh-*-elf*, sh-*-symbianelf*, sh-*-linux*, sh-*-netbsdelf*,
sh-*-rtems*, sh-wrs-vxworks).
- 2BSD on PDP-11 (pdp11-*-bsd)
- AIX 4.1 and 4.2 on PowerPC (rs6000-ibm-aix4.[12]*,
powerpc-ibm-aix4.[12]*)
- Tuning support for Itanium1 (Merced) variants. Note that code
tuned for Itanium2 should also run correctly on Itanium1.
- The protoize and unprotoize utilities have been obsoleted and will
be removed in GCC 4.5. These utilities have not been installed by
default since GCC 3.0.
- Support has been removed for all the configurations obsoleted in
GCC 4.3.
- Unknown -Wno-* options are now silently ignored by GCC if no other
diagnostics are issued. If other diagnostics are issued, then GCC
warns about the unknown options.
- More information on porting to GCC 4.4 from previous versions of GCC
can be found in the porting guide for this release.
General Optimizer Improvements
==============================
- A new command-line switch -findirect-inlining has been added. When
turned on it allows the inliner to also inline indirect calls that
are discovered to have known targets at compile time thanks to
previous inlining.
- A new command-line switch -ftree-switch-conversion has been added.
This new pass turns simple initializations of scalar variables in
switch statements into initializations from a static array, given
that all the values are known at compile time and the ratio between
the new array size and the original switch branches does not exceed
the parameter --param switch-conversion-max-branch-ratio (default is
eight).
- A new command-line switch -ftree-builtin-call-dce has been added.
This optimization eliminates unnecessary calls to certain builtin
functions when the return value is not used, in cases where the
calls can not be eliminated entirely because the function may set
errno. This optimization is on by default at -O2 and above.
- A new command-line switch -fconserve-stack directs the compiler to
minimize stack usage even if it makes the generated code slower.
This affects inlining decisions.
- When the assembler supports it, the compiler will now emit unwind
information using assembler .cfi directives. This makes it possible
to use such directives in inline assembler code. The new option
-fno-dwarf2-cfi-asm directs the compiler to not use .cfi directives.
- The Graphite branch has been merged. This merge has brought in a
new framework for loop optimizations based on a polyhedral
intermediate representation. These optimizations apply to all the
languages supported by GCC. The following new code transformations
are available in GCC 4.4:
- -floop-interchange performs loop interchange transformations on
loops. Interchanging two nested loops switches the inner and
outer loops. For example, given a loop like:
DO J = 1, M
DO I = 1, N
A(J, I) = A(J, I) * C
ENDDO
ENDDO
loop interchange will transform the loop as if the user had written:
DO I = 1, N
DO J = 1, M
A(J, I) = A(J, I) * C
ENDDO
ENDDO
which can be beneficial when N is larger than the caches, because
in Fortran, the elements of an array are stored in memory
contiguously by column, and the original loop iterates over rows,
potentially creating at each access a cache miss.
- -floop-strip-mine performs loop strip mining transformations on
loops. Strip mining splits a loop into two nested loops. The
outer loop has strides equal to the strip size and the inner loop
has strides of the original loop within a strip. For example,
given a loop like:
DO I = 1, N
A(I) = A(I) + C
ENDDO
loop strip mining will transform the loop as if the user had written:
DO II = 1, N, 4
DO I = II, min (II + 3, N)
A(I) = A(I) + C
ENDDO
ENDDO
- -floop-block performs loop blocking transformations on loops.
Blocking strip mines each loop in the loop nest such that the
memory accesses of the element loops fit inside caches. For
example, given a loop like:
DO I = 1, N
DO J = 1, M
A(J, I) = B(I) + C(J)
ENDDO
ENDDO
loop blocking will transform the loop as if the user had written:
DO II = 1, N, 64
DO JJ = 1, M, 64
DO I = II, min (II + 63, N)
DO J = JJ, min (JJ + 63, M)
A(J, I) = B(I) + C(J)
ENDDO
ENDDO
ENDDO
ENDDO
which can be beneficial when M is larger than the caches, because
the innermost loop will iterate over a smaller amount of data that
can be kept in the caches.
- A new register allocator has replaced the old one. It is called
integrated register allocator (IRA) because coalescing, register
live range splitting, and hard register preferencing are done
on-the-fly during coloring. It also has better integration with the
reload pass. IRA is a regional register allocator which uses modern
Chaitin-Briggs coloring instead of Chow's priority coloring used in
the old register allocator. More info about IRA internals and
options can be found in the GCC manuals.
- A new instruction scheduler and software pipeliner, based on the
selective scheduling approach, has been added. The new pass
performs instruction unification, register renaming, substitution
through register copies, and speculation during scheduling. The
software pipeliner is able to pipeline non-countable loops. The new
pass is targeted at scheduling-eager in-order platforms. In GCC 4.4
it is available for the Intel Itanium platform working by default as
the second scheduling pass (after register allocation) at the -O3
optimization level.
- When using -fprofile-generate with a multi-threaded program, the
profile counts may be slightly wrong due to race conditions. The
new -fprofile-correction option directs the compiler to apply
heuristics to smooth out the inconsistencies. By default the
compiler will give an error message when it finds an inconsistent
profile.
- The new -fprofile-dir=PATH option permits setting the directory
where profile data files are stored when using -fprofile-generate
and friends, and the directory used when reading profile data files
using -fprofile-use and friends.
New warning options
===================
- The new -Wframe-larger-than=NUMBER option directs GCC to emit a
warning if any stack frame is larger than NUMBER bytes. This may be
used to help ensure that code fits within a limited amount of stack
space.
- The new -Wno-mudflap option disables warnings about constructs which
can not be instrumented when using -fmudflap.
New Languages and Language specific improvements
================================================
- Version 3.0 of the OpenMP specification is now supported for the C,
C++, and Fortran compilers.
C family
--------
- A new optimize attribute was added to allow programmers to change
the optimization level and particular optimization options for an
individual function. You can also change the optimization options
via the GCC optimize pragma for functions defined after the pragma.
The GCC push_options pragma and the GCC pop_options pragma allow you
temporarily save and restore the options used. The GCC
reset_options pragma restores the options to what was specified on
the command line.
- Uninitialized warnings do not require enabling optimization anymore,
that is, -Wuninitialized can be used together with -O0.
Nonetheless, the warnings given by -Wuninitialized will probably be
more accurate if optimization is enabled.
- -Wparentheses now warns about expressions such as (!x | y) and (!x & y).
Using explicit parentheses, such as in ((!x) | y), silences this warning.
- -Wsequence-points now warns within if, while,do while and for
conditions, and within for begin/end expressions.
- A new option -dU is available to dump definitions of preprocessor
macros that are tested or expanded.
C++
---
- Improved experimental support for the upcoming ISO C++ standard,
C++0x. Including support for auto, inline namespaces, generalized
initializer lists, defaulted and deleted functions, new character
types, and scoped enums.
- Those errors that may be downgraded to warnings to build legacy code
now mention -fpermissive when -fdiagnostics-show-option is enabled.
- -Wconversion now warns if the result of a static_cast to enumeral
type is unspecified because the value is outside the range of the
enumeral type.
- -Wuninitialized now warns if a non-static reference or non-static
const member appears in a class without constructors.
- G++ now properly implements value-initialization, so objects with an
initializer of () and an implicitly defined default constructor will
be zero-initialized before the default constructor is called.
Runtime Library (libstdc++)
---------------------------
- Improved experimental support for the upcoming ISO C++ standard,
C++0x, including:
- Support for <chrono>, <condition_variable>, <cstdatomic>,
<forward_list>, <initializer_list>, <mutex>, <ratio>,
<system_error>, and <thread>.
- unique_ptr, <algorithm> additions, exception propagation, and
support for the new character types in <string> and <limits>.
- Existing facilities now exploit initializer lists, defaulted and
deleted functions, and the newly implemented core C++0x features.
- The standard containers are more efficient together with stateful
allocators.
- Experimental support for non-standard pointer types in containers.
The long standing libstdc++/30928 has been fixed for targets running
glibc 2.10 or later.
- As usual, many small and larger bug fixes, in particular quite a few
corner cases in <locale>.
Fortran
-------
- GNU Fortran now employs libcpp directly instead of using cc1 as an
external preprocessor. The -cpp option was added to allow manual
invocation of the preprocessor without relying on filename
extensions.
- The -Warray-temporaries option warns about array temporaries
generated by the compiler, as an aid to optimization.
- The -fcheck-array-temporaries option has been added, printing a
notification at run time, when an array temporary had to be created
for an function argument. Contrary to -Warray-temporaries the
warning is only printed if the array is noncontiguous.
- Improved generation of DWARF debugging symbols
- If using an intrinsic not part of the selected standard (via -std=
and -fall-intrinsics) gfortran will now treat it as if this
procedure were declared EXTERNAL and try to link to a user-supplied
procedure. -Wintrinsics-std will warn whenever this happens. The
now-useless option -Wnonstd-intrinsic was removed.
- The flag -falign-commons has been added to control the alignment of
variables in COMMON blocks, which is enabled by default in line with
previous GCC version. Using -fno-align-commons one can force commons
to be contiguous in memory as required by the Fortran standard,
however, this slows down the memory access. The option
-Walign-commons, which is enabled by default, warns when padding
bytes were added for alignment. The proper solution is to sort the
common objects by decreasing storage size, which avoids the
alignment problems.
- Fortran 2003 support has been extended:
- Wide characters (ISO 10646, UCS-4, kind=4) and UTF-8 I/O is now
supported (except internal reads from/writes to wide strings).
-fbackslash now supports also \unnnn and \Unnnnnnnn to enter
Unicode characters.
- Asynchronous I/O (implemented as synchronous I/O) and the
decimal=, size=, sign=, pad=, blank=, and delim= specifiers are
now supported in I/O statements.
- Support for Fortran 2003 structure constructors and for array
constructor with typespec has been added.
- Procedure Pointers (but not yet as component in derived types and
as function results) are now supported.
- Abstract types, type extension, and type-bound procedures (both
PROCEDURE and GENERIC but not as operators). Note: As
CLASS/polymorphyic types are not implemented, type-bound
procedures with PASS accept as non-standard extension TYPE
arguments.
- Fortran 2008 support has been added:
- The -std=f2008 option and support for the file extensions .f2008
and .F2008 has been added.
- The g0 format descriptor is now supported.
- The Fortran 2008 mathematical intrinsics ASINH, ACOSH, ATANH, ERF,
ERFC, GAMMA, LOG_GAMMA, BESSEL_*, HYPOT, and ERFC_SCALED are now
available (some of them existed as GNU extension before). Note:
The hyperbolic functions are not yet supporting complex arguments
and the three- argument version of BESSEL_*N is not available.
- The bit intrinsics LEADZ and TRAILZ have been added.
Java (GCJ)
----------
Ada
---
- The Ada runtime now supports multilibs on many platforms including
x86_64, SPARC and PowerPC. Their build is enabled by default.
New Targets and Target Specific Improvements
============================================
ARM
---
- GCC now supports optimizing for the Cortex-A9, Cortex-R4 and
Cortex-R4F processors and has many other improvements to
optimization for ARM processors.
- GCC now supports the VFPv3 variant with 16 double-precision
registers with -mfpu=vfpv3-d16. The option -mfpu=vfp3 has been
renamed to -mfpu=vfpv3.
- GCC now supports the -mfix-cortex-m3-ldrd option to work around an
erratum on Cortex-M3 processors.
- GCC now supports the __sync_* atomic operations for ARM EABI GNU/Linux.
- The section anchors optimization is now enabled by default when
optimizing for ARM.
- GCC now uses a new EABI-compatible profiling interface for EABI
targets. This requires a function __gnu_mcount_nc, which is
provided by GNU libc versions 2.8 and later.
AVR
---
- The -mno-tablejump option has been deprecated because it has the
same effect as the -fno-jump-tables option.
- Added support for these new AVR devices:
- ATA6289
- ATtiny13A
- ATtiny87
- ATtiny167
- ATtiny327
- ATmega8C1
- ATmega16C1
- ATmega32C1
- ATmega8M1
- ATmega16M1
- ATmega32M1
- ATmega32U4
- ATmega16HVB
- ATmega4HVD
- ATmega8HVD
- ATmega64C1
- ATmega64M1
- ATmega16U4
- ATmega32U6
- ATmega128RFA1
- AT90PWM81
- AT90SCR100
- M3000F
- M3000S
- M3001B
IA-32/x86-64
------------
- Support for Intel AES built-in functions and code generation is
available via -maes.
- Support for Intel PCLMUL built-in function and code generation is
available via -mpclmul.
- Support for Intel AVX built-in functions and code generation is
available via -mavx.
- Automatically align the stack for local variables with alignment
requirement.
- GCC can now utilize the SVML library for vectorizing calls to a set
of C99 functions if -mveclibabi=svml is specified and you link to an
SVML ABI compatible library.
- A new target attribute was added to allow programmers to change the
target options like -msse2 or -march=k8 for an individual function.
You can also change the target options via the GCC target pragma for
functions defined after the pragma.
- GCC can now be configured with options --with-arch-32,
--with-arch-64, --with-cpu-32, --with-cpu-64, --with-tune-32 and
--with-tune-64 to control the default optimization separately for
32-bit and 64-bit modes.
IA-32/IA64
----------
- Support for __float128 (TFmode) IEEE quad type and corresponding
TCmode IEEE complex quad type is available via the soft-fp library
on IA-32/IA64 targets. This includes basic arithmetic operations
(addition, subtraction, negation, multiplication and division) on
__float128 real and TCmode complex values, the full set of IEEE
comparisons between __float128 values, conversions to and from
float, double and long double floating point types, as well as
conversions to and from signed or unsigned integer, signed or
unsigned long integer and signed or unsigned quad (TImode, IA64
only) integer types. Additionally, all operations generate the full
set of IEEE exceptions and support the full set of IEEE rounding
modes.
M68K/ColdFire
-------------
- GCC now supports instruction scheduling for ColdFire V1, V3 and V4
processors. (Scheduling support for ColdFire V2 processors was
added in GCC 4.3.) GCC now supports the -mxgot option to support
programs requiring many GOT entries on ColdFire. The
m68k-*-linux-gnu target now builds multilibs by default.
MIPS
----
- MIPS Technologies have extended the original MIPS SVR4 ABI to
include support for procedure linkage tables (PLTs) and copy
relocations. These extensions allow GNU/Linux executables to use a
significantly more efficient code model than the one defined by the
original ABI.
GCC support for this code model is available via a new command-line
option, -mplt. There is also a new configure-time option,
--with-mips-plt, to make -mplt the default.
The new code model requires support from the assembler, the linker,
and the runtime C library. This support is available in binutils
2.19 and GLIBC 2.9.
- GCC can now generate MIPS16 code for 32-bit GNU/Linux executables
and 32-bit GNU/Linux shared libraries. This feature requires GNU
binutils 2.19 or above.
- Support for RMI's XLR processor is now available through the
-march=xlr and -mtune=xlr options.
- 64-bit targets can now perform 128-bit multiplications inline,
instead of relying on a libgcc function.
- Native GNU/Linux toolchains now support -march=native and
-mtune=native, which select the host processor.
- GCC now supports the R10K, R12K, R14K and R16K processors. The
canonical -march= and -mtune= names for these processors are r10000,
r12000, r14000 and r16000 respectively.
- GCC can now work around the side effects of speculative execution on
R10K processors. Please see the documentation of the
-mr10k-cache-barrier option for details.
- Support for the MIPS64 Release 2 instruction set has been added.
The option -march=mips64r2 enables generation of these instructions.
- GCC now supports Cavium Networks' Octeon processor. This support is
available through the -march=octeon and -mtune=octeon options.
- GCC now supports STMicroelectronics' Loongson 2E/2F processors. The
canonical -march= and -mtune= names for these processors are
loongson2e and loongson2f.
picochip
--------
Picochip is a 16-bit processor. A typical picoChip contains over 250
small cores, each with small amounts of memory. There are three
processor variants (STAN, MEM and CTRL) with different instruction
sets and memory configurations and they can be chosen using the -mae
option.
This port is intended to be a "C" only port.
Power Architecture and PowerPC
------------------------------
- GCC now supports the e300c2, e300c3 and e500mc processors.
- GCC now supports Xilinx processors with a single-precision FPU.
- Decimal floating point is now supported for e500 processors.
S/390, zSeries and System z9/z10
--------------------------------
- Support for the IBM System z10 EC/BC processor has been added. When
using the -march=z10 option, the compiler will generate code making
use of instructions provided by the General-Instruction-Extension
Facility and the Execute-Extension Facility.
VxWorks
-------
- GCC now supports the thread-local storage mechanism used on VxWorks.
Xtensa
------
- GCC now supports thread-local storage (TLS) for Xtensa processor
configurations that include the Thread Pointer option. TLS also
requires support from the assembler and linker; this support is
provided in the GNU binutils beginning with version 2.19.
Documentation improvements
==========================
Other significant improvements
==============================
------------------------------------------------------------------------------
Please send FSF & GNU inquiries & questions to gnu@gnu.org. There are
also other ways to contact the FSF.
These pages are maintained by the GCC team.
For questions related to the use of GCC, please consult these web
pages and the GCC manuals. If that fails, the gcc-help@gcc.gnu.org
mailing list might help. Please send comments on these web pages and
the development of GCC to our developer mailing list at gcc@gnu.org or
gcc@gcc.gnu.org. All of our lists have public archives.
Copyright (C) Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110, USA.
Verbatim copying and distribution of this entire article is
permitted in any medium, provided this notice is preserved.
Last modified 2009-04-21
|