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Does anyone have any knowledge of why Ada isn't used over C? Specifically, it seems like Ada gives you a lot better tools when it comes to numerical overflows/underflows.

Also, what compiler does NASA use? Something like CompCert? What kind of compiler flags? Do they run it through an optimizer at all?

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See my post below - to reuse code cross platform. There's a diverse set of compiler toolchains, operating systems, architectures. Only ANSI C is supported by all of them. The compilers are specific to the target OS and hardware, and flags are unsurprisingly the strictest possible for C89.

i'd think that you can run ada generated code pretty much everywhere. even on obscure hardware that works in space.

As to what compiler NASA uses, their C Coding Standard [1] nominates a set of flags for GCC (page 8).

http://lars-lab.jpl.nasa.gov/JPL_Coding_Standard_C.pdf

Interesting, I'm curious if they have looked into CompCert, and if so what they think of it. Maybe it doesn't target the architecture they want. There is also vellvm which seems like something a space mission would care about. Although, I've never heard of a gcc compiler bug being the cause of a NASA mission failure so perhaps gcc is Good Enough?

CompCert does support PowerPC which RAD750 implements. On the other hand, compiler bugs are probably not the weakest link.

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