[llvm-dev] Clang for the PlayStation 2

[Dan Ravensloft via llvm-dev]

Hello,

I'm part of the (sadly fairly small) community of PS2 hackers. The current
cross-toolchain for the PS2 is based on GCC 3.2.3, an outdated and buggy
compiler, which I have personally gotten tired of working with, so I would
like to port Clang as a newer cross-compiler for the PS2.

However, the PS2 has some notable quirks which make this a non-trivial task
for the current compiler. It has two main CPUs, the "Emotion Engine" (EE),
which controls the main operating system, and the "I/O Processor" (IOP),
which is used for PS1 compatibility and for I/O.

The EE is based on a custom chip called the R5900, which implements most of
MIPS III (except the ll and sc instructions, which make little sense on a
single-core CPU), as well as some instructions from MIPS IV (pref,
movz/movn, rsqrt.s), and a set of SIMD instructions known as Multimedia
Instructions (MMI). It also contains a non-IEEE 754 single-precision FPU
(which has provided a lot of headaches). It was later re-used by Toshiba as
the TX79, along with a proper FPU.

The IOP is based on the MIPS I R3051A, and was also used as the PS1 CPU.

I'd like to go through some of the issues I've had so far.

I've tried to use `mips64el` as a target, but it would invoke the system
GCC with obvious bad results, so I have used the `mips64el-img-linux`
target to generate ELF files which the PS2 BIOS can load (is there a better
solution to generate bare-metal ELF?).

I then tried to compile newlib 3.0.0-20180802, as newlib is used as the
standard C library for the PS2, and hit multiple asserts, which I have
attached below.

I don't mind trying to fix these myself, but I would appreciate some
pointers.
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