I tried to install GCC on Irix, but it did not work. I tried to install Code::Blocks on Irix, and it did not work. The GCC gave me parse errors in iostream.h and streambuf.h, and NetScape does not support the HTML format that the sourceforge website has. What is the best IDE that I can use for an IRIX computer that was originally designed for IRIX?
SGI was one of the leading vendors to put a modern touch around X/Motif. IRIX came with ViewKit and OpenInventor, plus some SGI-specific libraries to handle desktop integration, all part of SGI's DeveloperMagic development environment. To enable developers to build a fully IRIX-Integrated application, SGI provided a whole landscape of C++ libraries and development tools to developers.
SGI RapidApp was one of the first fully integrated interface builders /code generators and (sort of) IDEs in the Unix/X/Motif world. It is not exactly what you would expect from a modern IDE, but is an interface designer including callback editors and a build system. It knows about all the SGI extensions to Motif, and generates ViewKit code. If you want the real deal, RapidApp is the way to go. You might, however, encounter some problems in finding the complete toolset on free download sites. I didn't check the license status of DeveloperMagic (I seem to recall that at least ViewKit was owned, maintained and sold by ICS for some time after SGI went bust).
Beyond that, as IRIX is a relatively modern system, you should be able to build most modern IDEs (maybe in some older versions) for Unix on an SGI machine. But that would neglect a lot of the SGI-specific fun you can have. If you want something halfway modern, you could do worse than to look here (Retrogeeks, I think there's an SGI Eclipse IDE)