RFR: 8326135: Enhance adlc to report unused operands

[kuaiwei]

Some operands are defined in adfile but no one used them. But it's hard to find them manually. So I try to enhance adlc to report them after parsing the whole adfile.

I added a helper Form::forms_do to recursively visit child forms. After parsing, adlc will start from all instructions to mark all used forms. And report unvisited operands as unused. By this way, I can find 44 unused operands for aarch64, 12 for x86_64 and 4 for riscv64. The report is like

...
Warning: unused operand (vRegD_V28)
Warning: unused operand (vRegD_V29)
Warning: unused operand (vRegD_V30)
Warning: unused operand (vRegD_V31)
Warning: unused operand (lr_RegP)
Warning: unused operand (indOffI)
Warning: unused operand (indOffL)
Warning: unused operand (thread_anchor_pc)
-------Warning: total 44 unused operands


I tested and find they can be safely removed.

-------------

Commit messages:
 - 8326135: Enhance adlc to report unused operands

Changes: https://git.openjdk.org/jdk/pull/17910/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17910&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8326135
  Stats: 287 lines in 9 files changed: 287 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/17910.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17910/head:pull/17910

PR: https://git.openjdk.org/jdk/pull/17910