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72a8c9e7dc
Inspection of the generated assembly showed that before this commit, armcc 5 was optimizing away the successive reads to the volatile local variable that's used for double-checks. Inspection also reveals that inserting a call to an external function is enough to prevent it from doing that. The tested versions of ARM-GCC, Clang and Armcc 6 (aka armclang) all keep the double read, with our without a call to an external function in the middle. The inserted function can also be changed to insert a random delay if desired in the future, as it is appropriately places between the reads.