Since we weren't assigning region counters until we were emitting
function bodies, we would crash while walking the expressions in
default arguments. This assigns the counters earlier and fixes up the
ASTWalker to expect that.
Swift SVN r25445
This adds the -profile-coverage-mapping option to swift, and teaches
SILGenProfiling to generate mappings from source ranges to counters.
Swift SVN r25266
This adds the -profile-generate flag, which enables LLVM's
instrumentation based profiling. It implements the instrumentation
for basic control flow, such as if statements, loops, and closures.
Swift SVN r25155
