Presuming you have the IDO (Iris Development Option) installed,
  recent versions of gcc build reliably on IRIX without much 
  difficulty. Just read the INSTALL document and follow the
  directions.  A few hints:

  - Don't. Several people have already, and they'll let you have a
    copy.  Even if you must do it yourself, you can bootstrap from
    someone else's binary. Furthermore, their distribution may include
    notes on how they did it, if they didn't think it was obvious.  See
    "Where can I get software already compiled for SGIs?" above.

  - Don't forget to install the dev.cmplrs_hdr.internal (IRIX 4.0.x), 
    dev.hdr.lib (IRIX 5.x, 6.0.x, 6.1), or eoe.hdr.lib (IRIX 6.2+)
    subsystem, which contains needed headers and is not installed by
    default.

  - READ THE RELEASE NOTES! gcc (and gas, etc.) are updated too
    frequently for this FAQ to document every quirk of every release.
    The release notes often describe quirks that have not yet been
    fixed.

  The following advice applies if you do not have the IDO installed:

  If you're running any release of IRIX previous to 6.2, you will be 
  unable to build or use gcc, since you will be missing critical 
  header files and runtime libraries.  Of course if you buy IDO you'll 
  get SGI's compiler anyway; this is comp.sys.sgi.*'s most popular 
  Catch-22.

  IRIX 6.2 (or later) comes with a full set of headers. Before anything
  else - make sure you have all the SGI headers. They are not installed 
  by default, but are on the 6.2 CD in the subsystem eoe.hdr.lib.

  As of IRIX 6.5, support for gcc is much improved and includes the new
  ABIs (n32, 64). The SGI backend (including an assembler and linker
  supporting the n32 and 64 ABIs) plus all the bits and pieces needed
  for gcc (headers, libraries, runtime startup files, etc.) are included
  free with any IRIX 6.5 distribution on the 2 CDs titled "Development
  Foundation" and "Development Libraries" (in other words you don't need
  to have the SGI Developer's Option in order to use gcc.)
  In recent SGI releases, the SGI assembler and linker are in the
  subsystem compiler_dev.sw.base.

  Precompiled versions of gcc and g++ that were well-tested on 6.5
  and are known to work on IRIX 6.2 and up can be found in
  <http://reality.sgi.com/ariel/freeware> and will be available shortly
  on the SGI freeware site <http://freeware.sgi.com/>.