[ZooLib-dev] Fixing an optimization problem in ZByteSwap.h (PowerPC)

[Richard C. <rd_...@sb...>]

I ran into 2 problems making the asset compiler on Mac OS X: using the 
makefile, ZByteSwap fails while compiling the release version 
(optimization flag -O2):

{standard input}:1844:Parameter error: r0 not allowed for parameter 3 
(code as 0 not r0)
{standard input}:1869:Parameter error: r0 not allowed for parameter 3 
(code as 0 not r0)

Looking at the intermediate assembly file reveals the culprit:
stw r2, 0(r0)

The corresponding source looks like this:

inline void ZByteSwap_32(register void* iValueAddress)
	{
	register int32 temp;
	asm
		(
		"lwbrx %0, 0, %2\n"
		"stw %0, 0(%2)\n"
		: "=&r" (temp), "=m" (*(int32*)iValueAddress)
		: "r" (iValueAddress)
		: "cc"
		);
	}


But, if GCC optimizes iValueAddress into r0, the assembly will fail. 
(r0 gets special treatment in PPC assembly; it can't be used in the 
same way as the other GPRs.) We need to force gcc not to use that as a 
working register, and the easiest way is to force it is to make GCC use 
r0 for temp.

The fix: change
	register int32 temp;
to
	register int32 temp asm("r0");

in both inline void ZByteSwap_16(register void* iValueAddress) and 
inline void ZByteSwap_32(register void* iValueAddress)


(It helps that I used to teach PowerPC assembly development for Apple 
;))

  ...Richard