RFR: 8360192: C2: Make the type of count leading/trailing zero nodes more precise [v9]

[Qizheng Xing]

> The result of count leading/trailing zeros is always non-negative, and the maximum value is integer type's size in bits. In previous versions, when C2 can not know the operand value of a CLZ/CTZ node at compile time, it will generate a full-width integer type for its result. This can significantly affect the efficiency of code in some cases.
> 
> This patch makes the type of CLZ/CTZ nodes more precise, to make C2 generate better code. For example, the following implementation runs ~115% faster on x86-64 with this patch:
> 
> 
> public static int numberOfNibbles(int i) {
>   int mag = Integer.SIZE - Integer.numberOfLeadingZeros(i);
>   return Math.max((mag + 3) / 4, 1);
> }
> 
> 
> Testing: tier1, IR test

Qizheng Xing has updated the pull request incrementally with two additional commits since the last revision:

 - Add microbench
 - Add missing test method declarations

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25928/files
  - new: https://git.openjdk.org/jdk/pull/25928/files/ce5f8695..b4b9b643

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25928&range=08
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25928&range=07-08

  Stats: 78 lines in 2 files changed: 74 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/25928.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25928/head:pull/25928

PR: https://git.openjdk.org/jdk/pull/25928