RFR: 8347555: [REDO] C2: implement optimization for series of Add of unique value [v3]

Kangcheng Xu kxu at openjdk.org
Thu Feb 27 16:14:22 UTC 2025


> [JDK-8347555](https://bugs.openjdk.org/browse/JDK-8347555) is a redo of [JDK-8325495](https://bugs.openjdk.org/browse/JDK-8325495) was [first merged](https://git.openjdk.org/jdk/pull/20754) then backed out due to a regression. This patch redos the feature and fixes the bit shift overflow problem. For more information please refer to the previous PR.
> 
> When constanlizing multiplications (possibly in forms on `lshifts`), the multiplier is upgraded to long and then later narrowed to int if needed. However, when a `lshift` operand is exactly `32`, overflowing an int, using long has an unexpected result. (i.e., `(1 << 32) = 1` and `(int) (1L << 32) = 0`)
> 
> The following was implemented to address this issue.
> 
> if (UseNewCode2) {
>     *multiplier = bt == T_INT
>         ? (jlong) (1 << con->get_int()) // loss of precision is expected for int as it overflows
>         : ((jlong) 1) << con->get_int();
> } else {
>     *multiplier = ((jlong) 1 << con->get_int());
> }
> 
> 
> Two new bitshift overflow tests were added.

Kangcheng Xu has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 49 commits:

 - Merge branch 'master' into arithmetic-canonicalization
 - added bit shift operations accept an explicit BasicType
 - use explicit argument types for overloaded java_shift_left()
 - use java_shift_left()
 - remove UseNewCode
 - Merge branch 'master' into arithmetic-canonicalization
 - fix serial addition regression
 - remove trailing empty comments
 - fix comment grammar
   
   Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
 - remove matching power-of-2 subtractions since it's already handled by Identity()
 - ... and 39 more: https://git.openjdk.org/jdk/compare/8323ddfe...0ffae804

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

Changes: https://git.openjdk.org/jdk/pull/23506/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23506&range=02
  Stats: 478 lines in 5 files changed: 478 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/23506.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23506/head:pull/23506

PR: https://git.openjdk.org/jdk/pull/23506


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