swift234

Print list of uses for each SIL basic block argument.

SILPrinter was printing uses for all SIL values, except for SIL basic blocks arguments. Fill the gap and print uses for BB arguments as well. This makes reading and analyzing SIL easier.

Basic blocks may have multiple arguments, therefore print uses of each BB argument on separate lines - one line per BB argument.

The comment containing information about uses of a BB argument is printed on the line just above the basic block name, following the approach used for function_ref and other kinds of instructions, which have additional information printed on the line above the actual instruction.

The output now looks like:
// %0                                             // user: %3
// %1                                             // user: %9
bb0(%0 : $Int32, %1 : $UnsafeMutablePointer<UnsafeMutablePointer<Int8>>):

rdar://23336589