• Simon Marlow's avatar
    fixes to PPC version of cas(), from David Kirkman <dkirkman@gmail.com> · 7adc29e8
    Simon Marlow authored
    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.
    7adc29e8
SMP.h 4.25 KB