8371178: Preserve fast version of getfield and putfield in AOTCache #28121

ashu-mehra · 2025-11-04T02:10:13Z

Preserve the "fast" version of getfield and putfield bytecodes in the AOTCache during the assembly phase if the constant pool entry referred by the bytecodes is stored in resolved state in the AOTCache.

Testing:
Testing with JTREG="AOT_JDK=true" TEST=hotspot_runtime_no_cds passed on x86-64

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JDK-8371178: Preserve fast version of getfield and putfield in AOTCache (Enhancement - P4)

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Andrew Dinn (@adinn - Reviewer)
Ioi Lam (@iklam - Reviewer)

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Signed-off-by: Ashutosh Mehra <asmehra@redhat.com>

bridgekeeper · 2025-11-04T02:11:52Z

👋 Welcome back asmehra! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2025-11-04T02:13:50Z

@ashu-mehra This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8371178: Preserve fast version of getfield and putfield in AOTCache

Reviewed-by: adinn, iklam

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At the time when this comment was updated there had been 219 new commits pushed to the master branch:

acc8a76: 8357034: GifImageDecoder can produce wrong transparent pixels
5a37374: 8368576: PrintJob.getGraphics() does not specify behavior after PrintJob.end()
2872f81: 8360120: Bundled macOS applications not receiving OpenURL events when launched as subprocess
... and 216 more: https://git.openjdk.org/jdk/compare/d8ebe387595af43e2cdbbce396547d6daaf8c7dc...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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openjdk · 2025-11-04T02:14:36Z

@ashu-mehra The following label will be automatically applied to this pull request:

hotspot-runtime

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

mlbridge · 2025-11-04T02:18:41Z

Webrevs

01: Full - Incremental (40430e3c)
00: Full (a5fd053b)

ashu-mehra · 2025-11-04T03:55:19Z

For the record, I tried to preserve _fast_Xaccess_0 bytecodes (these are the fast versions for the pair (aload_0, getfield)) but then these bytecodes breaks serviceability/jvmti/FieldAccessWatch/FieldAccessWatch.java test because the JVMTI event notifications for field access are skipped. Morevoer, I believe setting JVMTI breakpoint on the original location of the getfield bytecode won't work either.
While the notifications to field access can be fixed, enabling breakpoint is more challenging and probably not worth the effort.
So in this patch I only preserve the fast versions of getfield and putfield bytecodes.

ashu-mehra · 2025-11-04T03:55:40Z

@iklam @adinn can you please review this patch.

iklam · 2025-11-04T16:32:54Z

src/hotspot/share/cds/aotMetaspace.cpp

+        switch(rfe->tos_state()) {
+        case btos:
+          // fallthrough
+        case ztos:
+          new_code = Bytecodes::_fast_bgetfield;
+          break;


Why is this switch block necessary? Is it possible for new_code to be different than *bcs.bcp()? If not, it might be easier to initialize new_code to Bytecodes::_illegal and then do the rewriting only if new_code has been updated.

Why is this switch block necessary? Is it possible for new_code to be different than *bcs.bcp()?

During preimage dumping all the fast bytecodes will be converted to nofast version because the CP entries are not resolved. So in the assembly phase *bcs.bcp() would be nofast version. If the CP entry is resolved, we can convert it to fast version. And we determine the type of the fast version using tos_state of the resolved field entry. So the new_code will be different than the *bcs.bcp() in the assembly phase.
They may be same when dumping dynamic archives, but not when dumping static archive or the final AOTCache.
Does that help?

I see. Could you add a comment? Maybe the code should be reformatted like this to make it easier to navigate?

case ftos: new_code = Bytecodes::_fast_fgetfield; break; case dtos: new_code = Bytecodes::_fast_dgetfield; break; default: ShouldNotReachHere();

iklam · 2025-11-04T16:36:54Z

src/hotspot/share/cds/aotMetaspace.cpp

+    case Bytecodes::_aload_0:
+      new_code = Bytecodes::_nofast_aload_0;


Maybe add a comment here that _fast_Xaccess_0 bytecodes will be reverted?

iklam · 2025-11-04T17:28:09Z

src/hotspot/share/cds/aotMetaspace.cpp

+        switch(rfe->tos_state()) {
+        case btos:
+          // fallthrough
+        case ztos:
+          new_code = Bytecodes::_fast_bgetfield;
+          break;


I see. Could you add a comment? Maybe the code should be reformatted like this to make it easier to navigate?

case ftos: new_code = Bytecodes::_fast_fgetfield; break; case dtos: new_code = Bytecodes::_fast_dgetfield; break; default: ShouldNotReachHere();

iklam · 2025-11-04T17:30:50Z

src/hotspot/share/cds/aotMetaspace.cpp

+#ifdef ASSERT
+      if (CDSConfig::is_dumping_preimage_static_archive()) {
+        assert(!is_resolved, "preimage should not have resolved field references");
+      }
+#endif // ASSERT
+      if (is_resolved) {


I think the above can be simplified:

if (is_resolved) { assert(!CDSConfig::is_dumping_preimage_static_archive(), "preimage should not have resolved field references");

Signed-off-by: Ashutosh Mehra <asmehra@redhat.com>

ashu-mehra · 2025-11-05T01:30:18Z

@iklam addressed the review comments in the new commit. I also updated function names to remove "nofast" to better reflect the updates to their functionality.

ashu-mehra · 2025-11-05T14:06:01Z

@adinn thanks for the review.

iklam

LGTM

ashu-mehra · 2025-11-05T21:38:11Z

@iklam thanks for the review.

ashu-mehra · 2025-11-05T21:38:17Z

/integrate

openjdk · 2025-11-05T21:38:42Z

Going to push as commit 1357be9.
Since your change was applied there have been 219 commits pushed to the master branch:

acc8a76: 8357034: GifImageDecoder can produce wrong transparent pixels
5a37374: 8368576: PrintJob.getGraphics() does not specify behavior after PrintJob.end()
2872f81: 8360120: Bundled macOS applications not receiving OpenURL events when launched as subprocess
... and 216 more: https://git.openjdk.org/jdk/compare/d8ebe387595af43e2cdbbce396547d6daaf8c7dc...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-11-05T21:38:54Z

@ashu-mehra Pushed as commit 1357be9.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

8371178: Preserve fast version of getfield and putfield in AOTCache

a5fd053

Signed-off-by: Ashutosh Mehra <asmehra@redhat.com>

openjdk bot added the hotspot-runtime hotspot-runtime-dev@openjdk.org label Nov 4, 2025

openjdk bot added the rfr Pull request is ready for review label Nov 4, 2025

iklam reviewed Nov 4, 2025

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Address review comments

40430e3

Signed-off-by: Ashutosh Mehra <asmehra@redhat.com>

adinn approved these changes Nov 5, 2025

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iklam approved these changes Nov 5, 2025

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openjdk bot closed this Nov 5, 2025

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Nov 5, 2025

		case Bytecodes::_aload_0:
		new_code = Bytecodes::_nofast_aload_0;

8371178: Preserve fast version of getfield and putfield in AOTCache #28121

8371178: Preserve fast version of getfield and putfield in AOTCache #28121

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