On Mon, 12 Jan 2026 10:29:39 GMT, Damon Fenacci <[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 Overall, the fix idea with `Opaque` nodes looks good to me! src/hotspot/share/opto/library_call.hpp line 161: > 159: Node* generate_negative_guard(Node* index, RegionNode* region, > 160: // resulting CastII of index: > 161: Node* *pos_index = nullptr, Suggestion: Node** pos_index = nullptr, ------------- PR Review: https://git.openjdk.org/jdk/pull/29164#pullrequestreview-3710064929 PR Review Comment: https://git.openjdk.org/jdk/pull/29164#discussion_r2731064422
