Month: October 2007

New GCC hotness

I’ve been talking with Lance lately about setting up a good development machine, and GCC 4.3 (still unreleased) came up so I checked out its changes. Here’s a few I found particularly cool:

  • A new forward propagation pass on RTL was added. The new pass replaces several slower transformations, resulting in compile-time improvements as well as better code generation in some cases.
  • A new command-line switch -frecord-gcc-switches has been added to GCC, although it is only enabled for some targets. The switch causes the command line that was used to invoke the compiler to be recorded into the object file that is being created. The exact format of this recording is target and binary file format dependent, but it usually takes the form of a note section containing ASCII text. The switch is related to the -fverbose-asm switch, but that one only records the information in the assembler output file as comments, so the information never reaches the object file.
  • A new internal representation for GIMPLE statements has been contributed, resulting in compile-time memory savings.
  • A new command-line option -fdirectives-only has been added. It enables a special preprocessing mode which improves the performance of applications like distcc and ccache.
  • Experimental support for the upcoming ISO C++ standard, C++0x
  • Fortran: The -fexternal-blas option has been added, which generates calls to BLAS routines for intrinsic matrix operations such as matmul rather than using the built-in algorithms.
  • Fortran: Support to give a backtrace (compiler flag -fbacktrace or environment variable GFORTRAN_ERROR_BACKTRACE; on glibc systems only) or a core dump (-fdump-core, GFORTRAN_ERROR_DUMPCORE) when a run-time error occurred.
  • Java: libgcj now supports all 1.5 language features which require runtime support: foreach, enum, annotations, generics, and auto-boxing.
  • x86/amd64: Tuning for Intel Core 2 processors is available via -mtune=core2 and -march=core2.
  • x86/amd64: Code generation of block move (memcpy) and block set (memset) was rewritten. GCC can now pick the best algorithm (loop, unrolled loop, instruction with rep prefix or a library call) based on the size of the block being copied and the CPU being optimized for. A new option -minline-stringops-dynamically has been added. With this option string operations of unknown size are expanded such that small blocks are copied by in-line code, while for large blocks a library call is used. This results in faster code than -minline-all-stringops when the library implementation is capable of using cache hierarchy hints.
  • x86/amd64: Support for SSSE3 built-in functions and code generation are available via -mssse3.
  • x86/amd64: Both SSE4.1 and SSE4.2 support can be enabled via -msse4.
  • x86/amd64: GCC can now utilize the ACML library for vectorizing calls to a set of C99 functions on x86_64 if -mveclibabi=acml is specified and you link to an ACML ABI compatible library.
  • MIPS: libffi and libjava now support all three GNU/Linux ABIs: o32, n32 and n64. Every GNU/Linux configuration now builds these libraries by default.
  • The configure options –with-pkgversion and –with-bugurl have been added. These allow distributors of GCC to include a distributor-specific string in manuals and –version output and to specify the URL for reporting bugs in their versions of GCC.

I’m already using GCC 4.2, but I hadn’t really looked into its changes either until now:

  • OpenMP is now supported for the C, C++ and Fortran compilers.
  • A new command-line option -Waddress has been added to warn about suspicious uses of memory addresses as, for example, using the address of a function in a conditional expression, and comparisons against the memory address of a string literal. This warning is enabled by -Wall.
  • C++: -Wextra will produce warnings for if statements with a semicolon as the only body
  • C++/libstdc++: Enabled library-wide visibility control, allowing -fvisibility to be used.
  • x86/amd64: -mtune=generic can now be used to generate code running well on common x86 chips. This includes AMD Athlon, AMD Opteron, Intel Pentium-M, Intel Pentium 4 and Intel Core 2.
  • x86/amd64: -mtune=native and -march=native will produce code optimized for the host architecture as detected using the cpuid instruction.

Who made Gentoo Linux, and when? A commit analysis

LWN just published my story of this name as premium content. I ran a number of analyses on Gentoo’s CVS commit history, kindly provided by Robin Johnson, to look at what happened to our developers and our commits over time. If you want to know the results now (rather than waiting until the content becomes free), subscribe to LWN—the best Linux and open-source software news.

HOWTO make Gentoo great

Gentoo is good. How do we make it great?

Over the past year or so, I’ve read a few books, and I want to use those ideas to build a better Gentoo. The books:

I plan to write a short series of posts discussing the lessons in these books and how to apply them to Gentoo. In this post, I’m going to summarize the concepts of “Good to Great.” I’ll discuss how we can apply them to Gentoo in a later post. The book explains what it takes to transform a good company into a great one. It’s a comparison of companies that made a transition from good to great (thus the title) with companies that remained merely good. Jim Collins and his group reduced the differences to a remarkably small set:

  • Level 5 leadership: The leaders of great companies aren’t charismatic, big-name CEOs. They’re humble, and their ambition is for the company, not for themselves.
  • First, get the right people: Before you decide what to do and where to go, get the right people in the right spots. Otherwise, you’ve got the wrong people creating the wrong vision, strategy, etc., which the right people are then forced to implement. Concrete implementations:
    • “When in doubt, don’t hire—keep looking. (Corollary: A company should limit its growth based on its ability to attract enough of the right people.)”
    • “When you know you need to make a people change, act. (Corollary: First be sure you don’t simply have someone in the wrong seat.)”
    • “Put your best people on your biggest opportunities, not your biggest problems. (Corollary: If you sell off your problems, don’t sell off your best people.)”

    The right people have the right innate abilities and character traits, not necessarily the specific knowledge and skills. For example, look for work ethic, dedication, and problem-solving ability, not ebuild-writing skills and knowledge of bash.

  • Confront the brutal facts: Don’t deny reality, or you can’t make the right decisions. To do this, create an environment where everyone can be heard, so the truth can come out. Don’t lose faith that you will win eventually, but accept the reality of now.
  • The Hedgehog Concept: Only do things that overlap in the three circles:
    • You’re passionate about it
    • You can be the best in the world at it
    • It drives your resource engine

    The resource engine is a combination of time (how well we attract contributors), money and brand (how well we create a community), drawn from an accompanying monograph for the social sectors.

  • Build a culture of discipline: Create a culture of self-disciplined people who are “fanatically consistent with the three circles.” Bureaucracy arises to compensate for incompetence and poor discipline due to having the wrong people. If you’ve got the right people, you don’t need the bureaucracy.
  • Technology accelerators: If a new technology fits into your Hedgehog Concept, become a pioneer. If not, settle for decent, or drop it altogether if you can.
  • The flywheel and the doom loop: Transforming from good to great is not quick. It’s a flywheel, slowly building momentum. From outside, all people see is the breakthrough, but from inside there’s a prior buildup. Merely good companies couldn’t build momentum—they jumped around from focus to focus, never getting anywhere with any of them. You don’t need to spend effort getting people behind your idea. Show them the results, and they’ll follow you.