fixes to PPC version of cas(), from David Kirkman <email@example.com>
From David's email: The problem is that the inline assembler code was placing the result of an operation in a register that is used as input later in the code. At the bottom of this message I've extracted a short short code fragment that you can run through gcc (on a powerpc machine) to see the generated assembly output. The changes to fix the problem are fairly simple. The first adds an ampersand to the output list of the assembly fragment ("=r" (result) --> "=&r" (result)) The ampersand just tells gcc that result can not be placed in a register used for any of the input parameters (o, n, or p). Otherwise, it feels free to place output parameters in the same registers used by the inputs -- but because of the flow of control here we need everything in a distinct register. This change fixes the TVar program above. The second change adds a clobber list (the :"cc", "memory"). This tells gcc that the condition code (due to the compare) and memory (due to the store) might be changed during the asm execution. The lack of a clobber list did not seem to be causing any trouble, but without it gcc is free to assume that no state is changed during the execution.
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