Inline assembly with “jmp 0f” or “b 0f” at the beginning-Collection of common programming errors

updated

Changed the 2nd line of assembly to the mnemonic actually being used (mflr) and added more info at the bottom.

I ran across some code (using gcc) resembling the following (paraphrased):

#define SOME_MACRO( someVar ) \
do {                          \
  __asm__ (                   \
    "    b 0f\n"              \
    "0:  mflr %0\n"           \
    : "=r"( someVar )         \
  );                          \
} while(0)

… where the b instruction (ppc) is a short jmp and mflr is getting the contents of the ‘link register’ — which is similar to the program counter in some respects. I’ve seen this sort of thing for intel code as well (cf. the accepted answer in this question).

The branch acts as a no-op … my question: what purpose does this serve?

I’m guessing it has something to do with branch prediction stuff, but so far I’ve only found people’s code using this idiom while searching.

It looks like I was wrong on the branch prediction guess. mflr grabs the contents of the link register.

So, my question boils down to: why is the branch necessary.