On Fri, 23 Jan 2026 13:47:53 GMT, Volkan Yazici <[email protected]> wrote:
>> ## Issue >> >> This is a redo of [JDK-8361842](https://bugs.openjdk.org/browse/JDK-8361842) >> which was backed out by >> [JDK-8374210](https://bugs.openjdk.org/browse/JDK-8374210) due to C2-related >> regressions. The original change moved input validation checks for >> java.lang.StringCoding from the intrinsic to Java code (leaving the >> intrinsic check only with the `VerifyIntrinsicChecks` flag). Refer to the >> [original PR](https://github.com/openjdk/jdk/pull/25998) for details. >> >> This additional issue happens because, in some cases, for instance when the >> Java checking code is not inlined and we give an out-of-range constant as >> input, we fold the data path but not the control path and we crash in the >> backend. >> >> ## Causes >> >> The cause of this is that the out-of-range constant (e.g. -1) floats into >> the intrinsic and there (assuming the input is valid) we add a constraint to >> its type to positive integers (e.g. to compute the array address) which >> makes it top. >> >> ## Fix >> >> A possible fix is to introduce an opaque node (OpaqueGuardNode) similar to >> what we do in `must_be_not_null` for values that we know cannot be null: >> https://github.com/openjdk/jdk/blob/ce721665cd61d9a319c667d50d9917c359d6c104/src/hotspot/share/opto/graphKit.cpp#L1484 >> This will temporarily add the range check to ensure that C2 figures that >> out-of-range values cannot reach the intrinsic. Then, during macro >> expansion, we replace the opaque node with the corresponding constant >> (true/false) in product builds such that the actually unneeded guards are >> folded and do not end up in the emitted code. >> >> # Testing >> >> * Tier 1-3+ >> * 2 JTReg tests added >> * `TestRangeCheck.java` as regression test for the reported issue >> * `TestOpaqueGuardNodes.java` to check that opaque guard nodes are added >> when parsing and removed at macro expansion > > I'd like to provide some help for reviewers: > > 1. [JDK-8361842] (integrated in 655dc516c22) implemented changes for > `java.lang.StringCoding` > 2. [JDK-8374210] (integrated in 7e18de137c3) reported regressions against > JDK-8361842, and used as the BACKOUT issue. > 3. [JDK-8374582] (this PR) is the REDO of JDK-8361842, plus the fix for > regressions reported in JDK-8374210 > > That is, this PR starts with 3c466d372b7 (i.e, the revert of 7e18de137c3), > and continues with the fix, which is **the interesting part, and that can be > viewed by diff'ing 3c466d372b7...ff22857609d**. (ff22857609d is the last > commit as of date.) > > [JDK-8361842]: https://bugs.openjdk.org/browse/JDK-8361842 > [JDK-8374210]: https://bugs.openjdk.org/browse/JDK-8374210 > [JDK-8374582]: https://bugs.openjdk.org/browse/JDK-8374582 Thanks a lot for your reviews @vy @chhagedorn @TobiHartmann! ------------- PR Comment: https://git.openjdk.org/jdk/pull/29164#issuecomment-3858562112
