GCC 4.9 Release Series – Changes, New Features, and Fixes (opens in new tab)

(gcc.gnu.org)

134 pointsbeatbrokedown12y ago39 comments

39 comments

34 comments · 11 top-level

krakensden12y ago· 6 in thread

> 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

nly12y 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.

hf12y 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

Thank you!

2 more replies

frozenport12y ago

As a Gentoo user, we always did it on our laptop. Build time was about 30 minutes.

bgirard12y ago

Firefox recently (Trunk as of December) started using Unified Sources so builds are now typically 7-9 minutes on laptops now for non Windows platforms.

supergauntlet12y 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-g12y ago

I am very curious too. Such drastic improvements often indicates something wrong before (either in design or implementation) that got fixed.

1 more reply

twic12y ago· 5 in thread

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.

revelation12y ago

Windows system DLLs have pointless "mov edi, edi" instructions in function prologues to enable hotpatching. It's not just mainframes ;)

jodrellblank12y ago

Which I recently read about on Raymond Chen's blog. Link: http://blogs.msdn.com/b/oldnewthing/archive/2011/09/21/10214...

maximilianburke12y ago

Yes, MSVC does this when the /hotpatch command line option is provided.

apaprocki12y ago

You can read quick slides about the POWER8 transactional memory and general feature comparison here:

https://www-950.ibm.com/events/wwe/grp/grp030.nsf/vLookupPDF...

gsnedders12y ago

One of the large design-constraints of Erlang is being able to hotpatch, given the uptime requirements for telephone switching.

jey12y ago· 4 in thread

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

agwa12y 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.

0x0912y ago

That was a point release. 4.8.0 was released over a year ago.

nly12y ago

What's wrong with every every 6 months? It's not like bug fix releases aren't dropped in the meantime.

mpyne12y 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.

_stephan12y ago· 2 in thread

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

beatbrokedownOP12y ago

Interesting the main page 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/ which states:

> As of this time no releases of GCC 4.9 have yet been made.

_pmf_12y ago· 2 in thread

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

dfc12y 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?

nly12y ago

I might be doing GCC a disservice but I'm pretty sure the various sanitization work has come from LLVM/Clang.

1 more reply

asveikau12y ago· 2 in thread

> 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.

PySlice12y ago

Yes, bounds checking are unnecessary, you don't need those _s() functions - NSA director

asveikau12y 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.

jevinskie12y ago· 1 in thread

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.

nly12y ago

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

dfc12y ago· 1 in thread

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

michaelhoffman12y ago

I wish LaTeX would just limit their logs to information I need to see.

shurcooL12y ago

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

knweiss12y 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.

jonalmeida12y ago

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

j / k navigate · click thread line to collapse

39 comments

34 comments · 11 top-level

krakensden12y ago· 6 in thread

> 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

nly12y 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.

hf12y 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

Thank you!

2 more replies

frozenport12y ago

As a Gentoo user, we always did it on our laptop. Build time was about 30 minutes.

bgirard12y ago

Firefox recently (Trunk as of December) started using Unified Sources so builds are now typically 7-9 minutes on laptops now for non Windows platforms.

supergauntlet12y 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-g12y ago

I am very curious too. Such drastic improvements often indicates something wrong before (either in design or implementation) that got fixed.

1 more reply

twic12y ago· 5 in thread

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.

revelation12y ago

Windows system DLLs have pointless "mov edi, edi" instructions in function prologues to enable hotpatching. It's not just mainframes ;)

jodrellblank12y ago

Which I recently read about on Raymond Chen's blog. Link: http://blogs.msdn.com/b/oldnewthing/archive/2011/09/21/10214...

maximilianburke12y ago

Yes, MSVC does this when the /hotpatch command line option is provided.

apaprocki12y ago

You can read quick slides about the POWER8 transactional memory and general feature comparison here:

https://www-950.ibm.com/events/wwe/grp/grp030.nsf/vLookupPDF...

gsnedders12y ago

One of the large design-constraints of Erlang is being able to hotpatch, given the uptime requirements for telephone switching.

jey12y ago· 4 in thread

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

agwa12y 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.

0x0912y ago

That was a point release. 4.8.0 was released over a year ago.

nly12y ago

What's wrong with every every 6 months? It's not like bug fix releases aren't dropped in the meantime.

mpyne12y 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.

_stephan12y ago· 2 in thread

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

beatbrokedownOP12y ago

Interesting the main page 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/ which states:

> As of this time no releases of GCC 4.9 have yet been made.

_pmf_12y ago· 2 in thread

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

dfc12y ago

nly12y ago

I might be doing GCC a disservice but I'm pretty sure the various sanitization work has come from LLVM/Clang.

1 more reply

asveikau12y ago· 2 in thread

> 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.

PySlice12y ago

Yes, bounds checking are unnecessary, you don't need those _s() functions - NSA director

asveikau12y 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.

jevinskie12y ago· 1 in thread

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.

nly12y ago

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

dfc12y ago· 1 in thread

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

michaelhoffman12y ago

I wish LaTeX would just limit their logs to information I need to see.

shurcooL12y ago

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

knweiss12y 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.

jonalmeida12y ago

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

j / k navigate · click thread line to collapse