8316533: C2 compilation fails with assert(verify(phase)) failed: missing Value() optimization #16361

eme64 · 2023-10-25T14:29:07Z

Problem
We have a abstract class A with no subtype. Hence, a reference of type A must always be null (unless a subclass were to be loaded, which we guard against with a compile dependency).

But there are at least these two ways a A:NotNull can be created:

Null-Check: CastPP after null-check improves type from A to A:NotNull.
Forced compilation (eg CTW) of a member method of A. Then Parm0 has type A, which is improved to A:NotNull because the this/self pointer cannot be null.

This means we are now left with an impossible type A:NotNull, a path that uses this type will never be executed.

The question is now what should happen at a SubTypeCheck if we do:
SubTypeCheck( oop #A:NotNull , constant-classptr-A-exact )

The verification happens because we do these two different things:

SubTypeCheck: we first detect that we have a constant classptr of a class A, which is abstract and has no subtype. Hence, we conclude that any oop compared to it cannot be a subtype (there are no subtypes), and it cannot be of the same type (class is abstract). Hence, any oop must be a supertype (TypeInt::CC_GT).
The verification code computes the subtype check by computing the klass of the oop via LoadKlass (this constant folds to constant-classptr-A-exact, because the type of the oop is A:NotNull). The CmpP node compares the two klasses, and sees that they are identical, and returns an TypeInt::CC_EQ.

Alternatives

Both results are reasonable, but they are in fact both supersets of the true result. We should take the intersection of the two and get Type:TOP, since the input type is already impossible. In fact, it would be best if the impossible type was never created. We could do that by improving CmpP to detect the impossible type and constant fold towards the null path, removing the A:NotNull path. It is harder to deal with the forced-compilation of non-static methods of an abstract class with no subclasses - here we would basically have to forbid compilation or replace the compilation with a Halt.

Solution

Instead, I have now decided to change the logic in SubTypeCheckNode to return EQ in case the oop has the same klass and is NotNull.

Testing

Tier1-6 and stress testing. Running...

Progress

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Commit message must refer to an issue

Issue

JDK-8316533: C2 compilation fails with assert(verify(phase)) failed: missing Value() optimization (Bug - P4)

Reviewers

Roberto Castañeda Lozano (@robcasloz - Reviewer)
Tobias Hartmann (@TobiHartmann - Reviewer)
Roland Westrelin (@rwestrel - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/16361/head:pull/16361
$ git checkout pull/16361

Update a local copy of the PR:
$ git checkout pull/16361
$ git pull https://git.openjdk.org/jdk.git pull/16361/head

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Checkout this PR locally:
$ git pr checkout 16361

View PR using the GUI difftool:
$ git pr show -t 16361

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Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/16361.diff

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bridgekeeper · 2023-10-25T14:30:37Z

👋 Welcome back epeter! 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 · 2023-10-25T14:32:41Z

@eme64 The following label will be automatically applied to this pull request:

hotspot-compiler

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 · 2023-11-02T09:20:21Z

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robcasloz · 2023-11-02T12:56:32Z

test/hotspot/jtreg/compiler/types/TestSubTypeOfAsbtractClass.java

+
+package compiler.types;
+
+public class TestSubTypeOfAsbtractClass {


Typo:

Suggested change

public class TestSubTypeOfAsbtractClass {

public class TestSubTypeOfAbstractClass {

I had copied the mistake from the other test: TestSubTypeOfAsbtractClassWrongResult.java

robcasloz · 2023-11-02T12:57:22Z

test/hotspot/jtreg/compiler/types/TestSubTypeOfAsbtractClass.java

+ * @bug 8316533
+ * @summary Oop of abstract class A is subtype checked after null-check
+ * @requires vm.compiler2.enabled
+ * @run main/othervm -XX:CompileCommand=printcompilation,*A::test


-XX:CompileCommand=printcompilation,*A::test is unnecessary.

robcasloz · 2023-11-02T13:00:36Z

test/hotspot/jtreg/compiler/types/TestSubTypeOfAsbtractClass.java

+
+

Please remove these extra line breaks.

robcasloz

Looks good, I just have a few minor comments and style suggestions.

src/hotspot/share/opto/subtypenode.cpp

openjdk · 2023-11-02T15:23:40Z

@eme64 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:

8316533: C2 compilation fails with assert(verify(phase)) failed: missing Value() optimization

Reviewed-by: rcastanedalo, thartmann, roland

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 8 new commits pushed to the master branch:

c146685: 8319165: hsdis binutils: warns on empty string as option string
01c0d5d: 8319412: RISC-V: Simple fix of indent in c2_MacroAssembler_riscv.hpp
df599db: 8295159: DSO created with -ffast-math breaks Java floating-point arithmetic
c099cf5: 8318422: Allow poller threads be virtual threads
29cf2c4: 8319053: Segment dump files remain after parallel heap dump on Windows
ea6a88a: 8318466: Improve spec of NumberFormat's methods with unsupported operations
de6667c: 8225377: type annotations are not visible to javac plugins across compilation boundaries
008ca2a: 8317620: Build JDK tools with ModuleMainClass attribute

Please see this link for an up-to-date comparison between the source branch of this pull request and the master branch.
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.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

From Roberto Co-authored-by: Roberto Castañeda Lozano <robcasloz@users.noreply.github.com>

…316533

openjdk · 2023-11-02T16:13:54Z

⚠️ @eme64 This pull request contains merges that bring in commits not present in the target repository. Since this is not a "merge style" pull request, these changes will be squashed when this pull request in integrated. If this is your intention, then please ignore this message. If you want to preserve the commit structure, you must change the title of this pull request to Merge <project>:<branch> where <project> is the name of another project in the OpenJDK organization (for example Merge jdk:master).

TobiHartmann

Looks good to me. @rwestrel should take a look as well.

rwestrel

Looks reasonable to me.

eme64 · 2023-11-06T10:40:16Z

Thanks @TobiHartmann @robcasloz @rwestrel for the reviews!
/integrate

openjdk · 2023-11-06T10:41:11Z

Going to push as commit b5c863b.
Since your change was applied there have been 9 commits pushed to the master branch:

377138c: 8318959: C2: define MachNode::fill_new_machnode() statically
c146685: 8319165: hsdis binutils: warns on empty string as option string
01c0d5d: 8319412: RISC-V: Simple fix of indent in c2_MacroAssembler_riscv.hpp
df599db: 8295159: DSO created with -ffast-math breaks Java floating-point arithmetic
c099cf5: 8318422: Allow poller threads be virtual threads
29cf2c4: 8319053: Segment dump files remain after parallel heap dump on Windows
ea6a88a: 8318466: Improve spec of NumberFormat's methods with unsupported operations
de6667c: 8225377: type annotations are not visible to javac plugins across compilation boundaries
008ca2a: 8317620: Build JDK tools with ModuleMainClass attribute

Your commit was automatically rebased without conflicts.

openjdk · 2023-11-06T10:41:19Z

@eme64 Pushed as commit b5c863b.

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

8316533

4a8f679

openjdk bot changed the title ~~8316533~~ 8316533: C2 compilation fails with assert(verify(phase)) failed: missing Value() optimization Oct 25, 2023

openjdk bot added the hotspot-compiler hotspot-compiler-dev@openjdk.org label Oct 25, 2023

eme64 added 8 commits October 26, 2023 16:31

first fix

d16501f

add comment

01967ea

more comment

dc9287c

add ignore flag to test

f0c08cc

CmpP null-check solution

146da88

return EQ instead of TOP

2f32dfd

remove CmpP and more comments

70b527e

Merge branch 'master' into JDK-8316533

446e00e

eme64 marked this pull request as ready for review November 2, 2023 09:14

openjdk bot added the rfr Pull request is ready for review label Nov 2, 2023

robcasloz reviewed Nov 2, 2023

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robcasloz approved these changes Nov 2, 2023

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src/hotspot/share/opto/subtypenode.cpp Outdated Show resolved Hide resolved

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openjdk bot added the ready Pull request is ready to be integrated label Nov 2, 2023

eme64 and others added 4 commits November 2, 2023 17:02

Apply suggestions from code review

53f5e74

From Roberto Co-authored-by: Roberto Castañeda Lozano <robcasloz@users.noreply.github.com>

fix type on class name, spotted by Roberto

8a23af2

Merge branch 'JDK-8316533' of https://github.com/eme64/jdk into JDK-8…

366090e

…316533

Merge branch 'master' into JDK-8316533

0ac7d02

robcasloz approved these changes Nov 3, 2023

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TobiHartmann approved these changes Nov 3, 2023

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Merge branch 'master' into JDK-8316533

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rwestrel approved these changes Nov 6, 2023

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openjdk bot added the integrated Pull request has been integrated label Nov 6, 2023

openjdk bot closed this Nov 6, 2023

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Nov 6, 2023

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8316533: C2 compilation fails with assert(verify(phase)) failed: missing Value() optimization #16361

8316533: C2 compilation fails with assert(verify(phase)) failed: missing Value() optimization #16361

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		package compiler.types;

		public class TestSubTypeOfAsbtractClass {

	public class TestSubTypeOfAsbtractClass {
	public class TestSubTypeOfAbstractClass {

8316533: C2 compilation fails with assert(verify(phase)) failed: missing Value() optimization #16361

8316533: C2 compilation fails with assert(verify(phase)) failed: missing Value() optimization #16361

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