ARM compiler update

Since my last shootout,  all the tested vendors have updated their compilers. Here is a quick update on each of them.

Both the 4.3 and 4.4 branches of FSF GCC have had bugfix releases, bringing them to 4.3.4 and 4.4.2, respectively. Neither update contains anything particularly noteworthy.

The CodeSourcery 2009q3 release sees an update to a GCC 4.4 base, a significant change from the 4.3 base used in 2009q1. The update is a mixed blessing. In fact, it is mostly a curse and hardly a blessing at all. On the bright side, the floating-point speed regressions in 2009q1 are gone, 2009q3 being a few per cent faster even than 2007q3. Unfortunately, this improvement is completely overshadowed by a major speed regression on integer code, a whopping 24% in one case. This ties in with the slowdown previously observed with FSF GCC 4.4 compared to 4.3.

ARM RVCT 4.0 is now at Build 697. This update fixes some bugs and introduces others. Notably, it no longer builds FFmpeg correctly. The issue has been reported to ARM.

Texas Instruments, finally, have made a formal release, v4.6.1, of their TMS470 compiler incorporating various fixes allowing it to build a moderately patched FFmpeg. The performance remains somewhere between GCC and RVCT on average.

In light of the above, my recommendations remain unchanged:

  • For a free compiler, choose CodeSourcery 2009q1. It beats GCC 4.3.4 by 5-10% in most cases.
  • GNU purists are best served by GCC 4.3.4, which is up to 20% faster than 4.4.2 and rarely slower.
  • When price is not a concern, ARM RCVT is a good option, outperforming GCC by up to a factor 2.
  • In all cases, disable any auto-vectorisation features.

Regardless of which compiler is chosen, I cannot overstress the importance of testing. All compilers are crawling with bugs, and even the most innocent-looking code change can trigger one of them. When using a compiler other than GCC, extra caution is advised considering a lot of code is developed using only GCC and may thus fall prey to bugs unique to said other compiler.

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2 Responses to ARM compiler update

  1. funman says:

    What about adding code size comparison of compilers ?

    It can affect cache usage, and in the case of rockbox every bit is very precious as it saves battery life when using hard disks.

    Not sure if the difference would be very noticeable though.

    Do some compilers generate thumb code even if not explicitely requested?

    • Mans says:

      When optimising for speed, I got these sizes for the .text section in the final ffmpeg executable:

      CS 2007q3 4.41 MB
      CS 2009q1 4.50 MB
      CS 2009q3 6.05 MB
      4.3.4 4.48 MB
      4.4.2 5.22 MB
      RVCT 3.77 MB
      TMS470 3.79 MB

      Compilers should never generate Thumb code when not asked to.

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