5 ms·

GCC 4.9 Release Series – Changes, New Features, and Fixes

134 points by beatbrokedown 12y ago

jevinskie 12y ago
libstdc++ finally supports C++11's <regex>! My team will be able to ditch boost regex once GCC 4.9 hits a stable version of Ubuntu. It is also nice to see more parity with Clang when it comes to diagnostics and ASan/UBSan.
- nly 12y ago
  Still not a fully optimised DFA solution though (although neither is Boost.Regex afaik)
jey 12y ago
Only six months since 4.8 was released. Is GCC moving to a more regular release schedule?
- nly 12y ago
  What's wrong with every every 6 months? It's not like bug fix releases aren't dropped in the meantime.
  - mpyne 12y ago
    I think that was the point... every 6 months being better than every 6+dx months as seemed the case before. I don't personally notice a change though, IMHO releases have been fairly consistently released since the 4.0 timeframe.
  - deleted 12y ago
    [deleted]
- 0x09 12y ago
  That was a point release. 4.8.0 was released over a year ago.
- agwa 12y ago
  4.8.0 was actually released in March 2013. GCC has been on a yearly major release schedule for several years now (since at least GCC 4.5.0 in 2010). This year 4.9.0 will be about a month late.
anotherfadjs 12y ago
It's 2014, we can now have colored output! Will error and warning messages get unique id's with explanatory/accompanying documentation in 2034?
_pmf_ 12y ago
Seems like competition from clang led to some really practical improvements.
- dfc 12y ago
  I use whatever compiler is defined in the makefile or called for in a README. Needless to say I do not really follow developments in either camp closely. I am curious what improvements are the result of "competition" from clang?
  - nly 12y ago
    I might be doing GCC a disservice but I'm pretty sure the various sanitization work has come from LLVM/Clang.
    - gillianseed 12y ago
      Actually the sanitizers where added to LLVM by Google who also added them to GCC as they are actively working on both compiler toolchains.
_stephan 12y ago
GCC 4.9 hasn't yet been released (and won't be until after Easter). Currently there's only a release candidate. See http://permalink.gmane.org/gmane.comp.gcc.devel/135470 http://permalink.gmane.org/gmane.comp.gcc.devel/135470
- beatbrokedown 12y ago
  Interesting the main page http://gcc.gnu.org/ http://gcc.gnu.org/ lists 4.9 as the current release as opposed to Development release.
  - pygy_ 12y ago
    If you follow the 4.9 link, you get to http://gcc.gnu.org/gcc-4.9/ http://gcc.gnu.org/gcc-4.9/ which states: > As of this time no releases of GCC 4.9 have yet been made.
krakensden 12y ago
> Memory usage building Firefox with debug enabled was reduced from 15GB to 3.5GB; link time from 1700 seconds to 350 seconds. This is huge- you can now do this on a laptop
- supergauntlet 12y ago
  well, you could do it on a laptop before, you just needed a much beefier laptop. But that's really impressive, how did they cut the resource usage to a quarter of previous usage?
  - alok-g 12y ago
    I am very curious too. Such drastic improvements often indicates something wrong before (either in design or implementation) that got fixed.
    - Denvercoder9 12y ago
      I bet it is caused by these two optimizations: > Early removal of virtual methods reduces the size of object files and improves link-time memory usage and compile time. > Function bodies are now loaded on-demand and released early improving overall memory usage at link time.
- deleted 12y ago
  [deleted]
- nly 12y ago
  15 GB was presumably with LTO enabled, you could always build it on a fairly average laptop with it disabled. This is great news though, as LTO is pretty awesome.
  - hf 12y ago
    For the uninitiated: LTO stands for Link-time optimization and happens when the compiler merges/links all separately-compiled object files into one (executable or library). Although it seems obvious that this might be a good idea, why would it 1) use exorbitant amounts of memory; and 2) be "pretty awesome" instead of, say, mildly useful? edit: And both questions satisfactorily answered in the time it took me to peruse the preamble of https://en.wikipedia.org/wiki/Interprocedural_optimization https://en.wikipedia.org/wiki/Interprocedural_optimization Thank you!
jonalmeida 12y ago
I like the addition of color the compile log. It's might be easier reading compile failures now.
dfc 12y ago
I wish latex/lualatex/xelatex would colorize their logs.
- michaelhoffman 12y ago
  I wish LaTeX would just limit their logs to information I need to see.
twic 12y ago
The things that caught my eye were both related to IBM hardware features. Firstly, apparently IBM chips have hardware transactional memory now: PowerPC / PowerPC64 / RS6000 GCC now supports Power ISA 2.07, which includes support for Hardware Transactional Memory (HTM) S/390, System z Support for the Transactional Execution Facility included with the IBM zEnterprise zEC12 processor has been added. That's pretty cool. Also on the 390: S/390, System z 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 -mhotpatch for a compilation unit or can be enabled per function using the hotpatch attribute. I guess if you're doing high availability the mainframe way, you don't get to restart your apps to patch them. That's terrifying, but again, pretty cool.
- revelation 12y ago
  Windows system DLLs have pointless "mov edi, edi" instructions in function prologues to enable hotpatching. It's not just mainframes ;)
  - maximilianburke 12y ago
    Yes, MSVC does this when the /hotpatch command line option is provided.
  - jodrellblank 12y ago
    Which I recently read about on Raymond Chen's blog. Link: http://blogs.msdn.com/b/oldnewthing/archive/2011/09/21/10214405.aspx http://blogs.msdn.com/b/oldnewthing/archive/2011/09/21/10214...
- gsnedders 12y ago
  One of the large design-constraints of Erlang is being able to hotpatch, given the uptime requirements for telephone switching.
- apaprocki 12y ago
asveikau 12y ago
> A new C extension __auto_type provides a subset of the functionality of C++11 auto in GNU C. I wonder if anyone is working to standardize something like this? It would be way more useful than all those _s() functions they added to C11.
- PySlice 12y ago
  Yes, bounds checking are unnecessary, you don't need those _s() functions - NSA director
  - asveikau 12y ago
    The problem isn't bounds-checking, the problem is that most of the _s() functions that deal with bounds-checking already have pre-C11 equivalents that check boundaries. I also disagree with some of the interface choices, for example when strlcpy() fails it tells you how many characters you needed, not simply "error" as in strcpy_s. Also the use case for memcpy_s() is extremely limited. It just seems like the _s() functions were rushed and stuck in there without regard for what makes sense.
knweiss 12y ago
Support for the CPU code names in -march is a simple but really useful change: -march=nehalem, westmere, sandybridge, ivybridge, haswell, bonnell, broadwell, silvermont Also this: -mtune=intel can now be used to generate code running well on the most current Intel processors, which are Haswell and Silvermont for GCC 4.9.
shurcooL 12y ago
Did anyone notice "GCC 4.9 provides a complete implementation of the Go 1.2.1 release."? Isn't that pretty big.

134 points by beatbrokedown 12y ago

libstdc++ finally supports C++11's <regex>! My team will be able to ditch boost regex once GCC 4.9 hits a stable version of Ubuntu. It is also nice to see more parity with Clang when it comes to diagnostics and ASan/UBSan.

nly 12y ago
Still not a fully optimised DFA solution though (although neither is Boost.Regex afaik)

jey 12y ago

Only six months since 4.8 was released. Is GCC moving to a more regular release schedule?

nly 12y ago
What's wrong with every every 6 months? It's not like bug fix releases aren't dropped in the meantime.
- mpyne 12y ago
  I think that was the point... every 6 months being better than every 6+dx months as seemed the case before. I don't personally notice a change though, IMHO releases have been fairly consistently released since the 4.0 timeframe.
- deleted 12y ago
  [deleted]
0x09 12y ago
That was a point release. 4.8.0 was released over a year ago.
agwa 12y ago
4.8.0 was actually released in March 2013. GCC has been on a yearly major release schedule for several years now (since at least GCC 4.5.0 in 2010). This year 4.9.0 will be about a month late.

anotherfadjs 12y ago

It's 2014, we can now have colored output! Will error and warning messages get unique id's with explanatory/accompanying documentation in 2034?

_pmf_ 12y ago

Seems like competition from clang led to some really practical improvements.

dfc 12y ago
I use whatever compiler is defined in the makefile or called for in a README. Needless to say I do not really follow developments in either camp closely. I am curious what improvements are the result of "competition" from clang?
- nly 12y ago
  I might be doing GCC a disservice but I'm pretty sure the various sanitization work has come from LLVM/Clang.
  - gillianseed 12y ago
    Actually the sanitizers where added to LLVM by Google who also added them to GCC as they are actively working on both compiler toolchains.

_stephan 12y ago

GCC 4.9 hasn't yet been released (and won't be until after Easter). Currently there's only a release candidate. See http://permalink.gmane.org/gmane.comp.gcc.devel/135470 http://permalink.gmane.org/gmane.comp.gcc.devel/135470

beatbrokedown 12y ago
Interesting the main page http://gcc.gnu.org/ http://gcc.gnu.org/ lists 4.9 as the current release as opposed to Development release.
- pygy_ 12y ago
  If you follow the 4.9 link, you get to http://gcc.gnu.org/gcc-4.9/ http://gcc.gnu.org/gcc-4.9/ which states: > As of this time no releases of GCC 4.9 have yet been made.

krakensden 12y ago

> Memory usage building Firefox with debug enabled was reduced from 15GB to 3.5GB; link time from 1700 seconds to 350 seconds. This is huge- you can now do this on a laptop

supergauntlet 12y ago
well, you could do it on a laptop before, you just needed a much beefier laptop. But that's really impressive, how did they cut the resource usage to a quarter of previous usage?
- alok-g 12y ago
  I am very curious too. Such drastic improvements often indicates something wrong before (either in design or implementation) that got fixed.
  - Denvercoder9 12y ago
    I bet it is caused by these two optimizations: > Early removal of virtual methods reduces the size of object files and improves link-time memory usage and compile time. > Function bodies are now loaded on-demand and released early improving overall memory usage at link time.
deleted 12y ago
[deleted]
nly 12y ago
15 GB was presumably with LTO enabled, you could always build it on a fairly average laptop with it disabled. This is great news though, as LTO is pretty awesome.
- hf 12y ago
  For the uninitiated: LTO stands for Link-time optimization and happens when the compiler merges/links all separately-compiled object files into one (executable or library). Although it seems obvious that this might be a good idea, why would it 1) use exorbitant amounts of memory; and 2) be "pretty awesome" instead of, say, mildly useful? edit: And both questions satisfactorily answered in the time it took me to peruse the preamble of https://en.wikipedia.org/wiki/Interprocedural_optimization https://en.wikipedia.org/wiki/Interprocedural_optimization Thank you!

jonalmeida 12y ago

I like the addition of color the compile log. It's might be easier reading compile failures now.

dfc 12y ago

I wish latex/lualatex/xelatex would colorize their logs.

michaelhoffman 12y ago
I wish LaTeX would just limit their logs to information I need to see.

twic 12y ago

The things that caught my eye were both related to IBM hardware features. Firstly, apparently IBM chips have hardware transactional memory now: PowerPC / PowerPC64 / RS6000 GCC now supports Power ISA 2.07, which includes support for Hardware Transactional Memory (HTM) S/390, System z Support for the Transactional Execution Facility included with the IBM zEnterprise zEC12 processor has been added. That's pretty cool. Also on the 390: S/390, System z 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 -mhotpatch for a compilation unit or can be enabled per function using the hotpatch attribute. I guess if you're doing high availability the mainframe way, you don't get to restart your apps to patch them. That's terrifying, but again, pretty cool.

revelation 12y ago
Windows system DLLs have pointless "mov edi, edi" instructions in function prologues to enable hotpatching. It's not just mainframes ;)
- maximilianburke 12y ago
  Yes, MSVC does this when the /hotpatch command line option is provided.
- jodrellblank 12y ago
  Which I recently read about on Raymond Chen's blog. Link: http://blogs.msdn.com/b/oldnewthing/archive/2011/09/21/10214405.aspx http://blogs.msdn.com/b/oldnewthing/archive/2011/09/21/10214...
gsnedders 12y ago
One of the large design-constraints of Erlang is being able to hotpatch, given the uptime requirements for telephone switching.
apaprocki 12y ago

asveikau 12y ago

> A new C extension __auto_type provides a subset of the functionality of C++11 auto in GNU C. I wonder if anyone is working to standardize something like this? It would be way more useful than all those _s() functions they added to C11.

PySlice 12y ago
Yes, bounds checking are unnecessary, you don't need those _s() functions - NSA director
- asveikau 12y ago
  The problem isn't bounds-checking, the problem is that most of the _s() functions that deal with bounds-checking already have pre-C11 equivalents that check boundaries. I also disagree with some of the interface choices, for example when strlcpy() fails it tells you how many characters you needed, not simply "error" as in strcpy_s. Also the use case for memcpy_s() is extremely limited. It just seems like the _s() functions were rushed and stuck in there without regard for what makes sense.

knweiss 12y ago

Support for the CPU code names in -march is a simple but really useful change: -march=nehalem, westmere, sandybridge, ivybridge, haswell, bonnell, broadwell, silvermont Also this: -mtune=intel can now be used to generate code running well on the most current Intel processors, which are Haswell and Silvermont for GCC 4.9.

shurcooL 12y ago

Did anyone notice "GCC 4.9 provides a complete implementation of the Go 1.2.1 release."? Isn't that pretty big.