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GCC 5.2 released
- the8472 11y ago> Write-only variables are now detected and optimized out. That's probably something one should keep in mind when writing micro-benchmarks.
- nitrogen 11y agoThere should be a warning for this enabled in every C project.
- JoshTriplett 11y agoGCC has a warning for that, and yes, it should be.
- deleted 11y ago[deleted]
- ot 11y agohttps://github.com/facebook/folly/blob/master/folly/Benchmark.h#L244 https://github.com/facebook/folly/blob/master/folly/Benchmar...
- spacehome 11y agoI'm appalled that this wasn't taken care of 20 years ago. It seems like such low-hanging fruit.
- greglindahl 11y agoThis is a standard compiler feature, yes -- lots of real code out there has a lot of dead writes, such as debugging code that has been only partly removed or disabled. Historically, it's been a significant win for some of the SPECcpu benchmarks.
- anon4 11y agoHistorically, it's been a significant win for some of the SPECcpu benchmarks. But doesn't it mean that you're not really executing the full benchmark then?
- greglindahl 11y agoNo, because no one ever reads the dead data. These are not microbenchmarks that get broken by optimizations like this; SPECcpu programs have answers, and the goal is to output the answer. The answer is tested. Anything you can delete from the program is fair game.
- astrange 11y agoIt's standard to remove local variables that are write-only, but globals aren't always defined to be unused even when you want them to be. If you're building a shared library and you exported the symbol, it has to leave it in as part of the API. Link-time optimization can delete a lot more stuff when you're building a program directly, since it only has to keep main()… as long as you didn't go and use things like function pointers. This is one reason I try to use '-fvisibility=hidden' in libraries, because it prevents anything from being part of the API unless you go back and specifically export it.
- pcwalton 11y agoI assume it means globals, which is significantly less trivial. Any SSA-based compiler, which GCC has been for years and years, trivially does this for locals.
- lifeisstillgood 11y agoIt's worth celebrating (well, noting in an approving manner) this release. GCC is a foundation stone project for, well, a huge amount of the world's wealth. It is a healthy project (even with CLang etc), and with the heartbleed post mortem on our minds we should probably ask what can be done to keep it and others healthy - auditing, foundation status etc. So thank you GCC developers, for making sure I do not need to worry about something.
- digital-rubber 11y agoBit strange comment; there are still plenty of bugs in GCC to worry about.
- tosseraccount 11y agoAny benchmarks? How does this compare with previous versions of gcc?
- Meai 11y agoDoes GCC support modules? http://clang.llvm.org/docs/Modules.html http://clang.llvm.org/docs/Modules.html
- RoboSeldon 11y agogfortran which is part of GCC supports modules (this is because Fortran the language supports modules). If you meant modules for C or C++, no (as far as I know), probably because C and C++ have no standard for modules. In a recent talk Bjarne Stroustroup talks about his hope that C++17 will include support for modules https://www.youtube.com/watch?v=2egL4y_VpYg https://www.youtube.com/watch?v=2egL4y_VpYg
- cozzyd 11y agoIt probably will once the C++ committee figures out how they want to do it...
- agwa 11y agoIt's worth noting that, due to GCC's new and esoteric version numbering scheme[1], this is a bugfix-only release on the 5.x branch. The bigger news was when GCC 5.1 (a major stable release) was released in April. That said, GCC 5.2 fixes a pretty serious bug that I was hitting so I'm happy to hear about it! [1] https://gcc.gnu.org/develop.html#num_scheme https://gcc.gnu.org/develop.html#num_scheme
- rst 11y agoThey switched the default C compilation mode from --std=gnu89 to --std=gnu11 in a bugfix-only release?
- 3JPLW 11y agoWoah, new and esoteric indeed! X.0.0 is experimental development X.0.1 is pre-release stabilization stage X.1.0 is the stable release X.1.1 is development of release branch (fixes and backports) X.2.0 is the second stable release It looks like only X.1.0, X.2.0, etc uniquely tag a single point in the development history. Are all the others just moving labels?
- ademarre 11y agoWith this release the golang frontend catches up it'so Go version 1.4.2. EDIT: I'm wrong. That was GCC 5.1.
- sajal83 11y agoNopes. Go 1.4.2 was released with GCC 5.1 (April 22, 2015). This release is just bugfixes.
- ademarre 11y agoThanks; you're right. I read the 5 series general release notes as if it were for 5.2.
- bsdetector 11y agoI'm more interested in why GCC still doesn't have a D frontend. Back when people were criticizing Google for acquiring GCC developers and then adding their own Go language I think they promised to add D in like 4.6 or something like that.
- jlarocco 11y agoI don't know anything about that, but there's already a D front end for GCC: http://gdcproject.org http://gdcproject.org
- minot 11y agoHi guys, any idea when we might get this on mingw?
- rossy 11y agoIf you're using MSYS2 to get your MinGW compilers, the package has been updated, but you won't see builds on the mirrors until all the other packages have been rebuilt for GCC 5.1/5.2 (due to the ABI change.) https://github.com/Alexpux/MINGW-packages/commit/a6a16a3 https://github.com/Alexpux/MINGW-packages/commit/a6a16a3
- anon3_ 11y agoWhere is GCC's place in the world now that there is LLVM/Clang? Does the LLVM+Clang combo make GCC obsolete?