[ARM][Asm] Debug trace for the processInstruction loop

In the Arm assembly parser, we first match an instruction, then call
processInstruction to possibly change it to a different encoding, to
match rules in the architecture manual which can't be expressed by the
table-generated matcher.

This adds debug printing so that this process is visible when using the
-debug option.

To support this, I've added a new overload of MCInst::dump_pretty which
takes the opcode name as a StringRef, since we don't have an InstPrinter
instance in the assembly parser. Instead, we can get the same
information directly from the MCInstrInfo.

Differential revision: https://reviews.llvm.org/D54852



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@348113 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed