On Tue, 13 Jan 2026 20:01:31 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 > > src/hotspot/share/opto/library_call.hpp line 170: > >> 168: Node* length, bool char_count, >> 169: bool halt_on_oob = false, >> 170: bool is_opaque = false); > > Do we really need to introduce two new toggles: `halt_on_oob` and > `is_opaque`? At all call-sites either one of the following is used: > > 1. `halt_on_oob=true, is_opaque=!VerifyIntrinsicChecks` > 2. defaults (i.e., `halt_on_oob=is_opaque=false`) > > Can we instead only settle one, e.g., `halt_on_oob=VerifyIntrinsicChecks`? Giving this a second thought, do we need these two flags anyway? That is, 1. We can remove `if (is_opaque)` add the `OpaqueGuard` anyway, since it is ineffective for `!ASSERT`. (This is what `must_be_not_null` does too.) 2. We can replace `if (halt_on_oob) { ... } else { ... }` with `#ifdef ASSERT ...`. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/29164#discussion_r2689690430
