RFR: 8323682: C2: guard check is not generated in Arrays.copyOfRange intrinsic when allocation is eliminated by EA

[Daniel Lundén]

On Mon, 25 Mar 2024 13:28:32 GMT, Daniel Lundén <dlunden at openjdk.org> wrote:

> The library intrinsic `_copyOfRange` does not add a guard for start indices that are larger than the length of the source arrays. Macro expansion of `ArrayCopy` nodes later adds such a guard, but in certain situations escape analysis may result in removing the `ArrayCopy` node before it is expanded. The result is incorrect behavior of the compiled program (as the missing guard may have relevant side effects, such as throwing an exception).
> 
> ### Changeset
> 
> - Add the missing guard (start index <= source array length).
> - Remove an unnecessary guard (end index >= 0) that holds as a result of the other guards. The updated set of guards then more closely follows the `copyOfRange` [Java API documentation](https://docs.oracle.com/en/java/javase/22/docs/api/java.base/java/util/Arrays.html#copyOfRange(U[],int,int,java.lang.Class)).
> - Add a regression test.
> 
> ### Testing
> 
> - [GitHub Actions](https://github.com/dlunde/jdk/actions/runs/8388044152)
> - tier1 to tier5 on windows-x64, linux-x64, linux-aarch64, macosx-x64, and macosx-aarch64.

src/hotspot/share/opto/library_call.cpp line 4396:

> 4394:         newcopy = new_array(klass_node, length, 0);  // no arguments to push
> 4395: 
> 4396:         ArrayCopyNode* ac = ArrayCopyNode::make(this, true, original, start, newcopy, intcon(0), moved, true, true,

Note: we can now specify `true` for the argument `has_negative_length_guard`.

src/hotspot/share/opto/macroArrayCopy.cpp line 1269:

> 1267:                        adr_type, T_OBJECT,
> 1268:                        src, src_offset, dest, dest_offset, length,
> 1269:                        true, !ac->is_copyofrange());

We cannot use this anymore, since we then ignore the `has_negative_length_guard` for `copyOfRange` (and generate the negative length guard twice).

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

PR Review Comment: https://git.openjdk.org/jdk/pull/18472#discussion_r1537712946
PR Review Comment: https://git.openjdk.org/jdk/pull/18472#discussion_r1537716349