RFR: 8326135: Enhance adlc to report unused operands [v4]

[Vladimir Ivanov]

On Thu, 22 Feb 2024 03:44:16 GMT, kuaiwei <duke at openjdk.org> wrote:

>> 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.
>
> kuaiwei has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix copyright header and comment

Nice feature!

src/hotspot/share/adlc/archDesc.cpp line 27:

> 25: 
> 26: // archDesc.cpp - Internal format for architecture definition
> 27: #include <unordered_set>

Even though it's not hotspot code per se (but a tool used during build), it'll be the first usage of C++ STL in the hotspot code base.

HotSpot Coding Style [1] clearly states "Avoid using the C++ Standard Library." 

@kimbarrett what are your thoughts on it?

[1] https://github.com/openjdk/jdk/blob/master/doc/hotspot-style.md

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PR Review: https://git.openjdk.org/jdk/pull/17910#pullrequestreview-1894861637
PR Review Comment: https://git.openjdk.org/jdk/pull/17910#discussion_r1498615515