#3193 gbz80 regression test failures

[Philipp Klaus Krause]

Current [r12125] sdcc is failing ucgbz80 regression tests, if the gbz80 library has been compiled with an SDCC that does not use the treedec library. It does not matter what SDCC is used to compile the tests themselves.

I do not know if this is due to my recent changes or those of Sebastian.

[Sergey Belyashov]

Can you recheck it?

[Philipp Klaus Krause]

At the moment, I see too many other failures in the z80-related ports to check for this specific one.

[Sebastian Riedel]

Is this still a problem? And what's treedec?

[Philipp Klaus Krause]

treedec is a library for computing tree-decompositions, which are used in register allocation (and two other optimizations) by SDCC.
When treedec is not installed, configure uses the old SDCC builtin Thorup's heuristic to compute tree-decompositions instead.
Typically, with treedec we get a better compilation time / code quality trade-off.
For details, see "The tree-width of C" by Krause, Larisch and Saalfelder.

For bugs, the main aspect is: You might get a different register allocation result with treedec vs. without it, so some bugs in later stages, e.g. code generation might only be reproducible with or without treedec.

[Philipp Klaus Krause]

Passes for current sdcc, and has been passing for a while.