JDK-8273914: Indy string concat changes order of operations #5844

cushon · 2021-10-06T21:00:04Z

This change makes string concatenation call toString on the arguments eagerly, to preserve the correct evaluation order of the arguments and the calls to toString.

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Issues

JDK-8273914: Indy string concat changes order of operations
JDK-8274863: Indy string concat changes order of operations (CSR)

Reviewers

Vicente Romero (@vicente-romero-oracle - Reviewer)
Jan Lahoda (@lahodaj - Reviewer)

Reviewing

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$ git checkout pull/5844

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$ git pull https://git.openjdk.java.net/jdk pull/5844/head

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https://git.openjdk.java.net/jdk/pull/5844.diff

bridgekeeper · 2021-10-06T21:00:53Z

👋 Welcome back cushon! 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 · 2021-10-06T21:04:11Z

@cushon The following labels will be automatically applied to this pull request:

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mlbridge · 2021-10-06T21:08:36Z

Webrevs

forax · 2021-10-06T21:36:30Z

src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/StringConcat.java

+         * Returns true if the argument should be converted to a string eagerly, to preserve
+         * possible side-effects.
+         */
+        protected boolean shouldConvertToStringEagerly(Type argType) {


For me the implementation should be neither a primitive type nor a final class of java.lang. I think that at least the wrappers should not be converted eagerly

@forax can you expand on the suggestion here?

The current implementation is not eagerly converting boxes for primitives types, which wrappers should not be converted eagerly?

Also note that one of the motivating examples was StringBuilder, which is a final class in java.lang. It's not just about toString() not having side-effects, it's also about insulting the operands from each others's side effects (e.g. myStringBuilder.append("foo") + myStringBuilder.append("bar"))

The current implementation is not eagerly converting boxes for primitives types, which wrappers should not be converted eagerly?

I was just thinking that not calling Boolean or Double.toString() explicitly was Ok

myStringBuilder.append("foo") + myStringBuilder.append("bar")

Aaaah, so only primitives + their boxes should not be evaluated eagerly.

jddarcy · 2021-10-06T21:38:11Z

/csr needed

jddarcy · 2021-10-06T21:38:41Z

Please file a CSR for this issues to discuss the behavioral changes, even if to fix a bug.

openjdk · 2021-10-06T21:38:46Z

@jddarcy has indicated that a compatibility and specification (CSR) request is needed for this pull request.
@cushon please create a CSR request for issue JDK-8273914. This pull request cannot be integrated until the CSR request is approved.

cushon · 2021-10-06T22:31:03Z

@jddarcy thanks, I have opened a CSR: https://bugs.openjdk.java.net/browse/JDK-8274863

dholmes-ora

Can you explain the changes made in relation to the runtime test:

test/hotspot/jtreg/runtime/modules/AccessCheck/MethodAccessReadTwice.java

please. The connection to this fix is not at all apparent, nor what the conversion to jasm is achieving.

Thanks,
David

shipilev

Thank you for fixing this. It looks nominally fine, but I would defer to javac experts to approve this. Minor testing suggestions below.

shipilev · 2021-10-07T10:00:36Z

test/langtools/tools/javac/StringConcat/StringAppendEvaluatesInOrder.java

+ * @test
+ * @bug     8273914
+ * @summary Indy string concat changes order of operations
+ *


Here and later: please add the test block with -XDstringConcat=inline here as well, so that test would verify that every javac strategy produces the same result?

Done, thanks

(The WellKnownTypes test still only exercises the indy strategies, because it's testing logic that only exists in those strategies.)

But still, we probably want to confirm that inline strategy yields the same answer in WellKnownTypes? That's my thinking why to test inline: that is a baseline.

I agree in general about using inline as a baseline, but WellKnownTypes doesn't currently check the output of string concatenation, it checks the signature of the invokedynamic it find in the test case.

What do you have in mind for inline here? Should I update the test to assert on the output of string concatenation (and tolerate not being able to find an invokedynamic, which could make the coverage for the indy strategies more fragile)? Or add a different test with similar inputs, and check the output of string concatenation on primitives and boxes?

I think it might make sense to rely on other tests to ensure inline and the indy strategies produce the same results, and use WellKnownTypes as a test just for shouldConvertToStringEagerly, which is only used by the indy strategies.

Ah, I missed that WellKnownTypes does not verify concat output. Yes, that resolves my concern, we don't need to handle inline there. Maybe rename WellKnownTypes to WellKnownTypeSignatures or something?

But yes, I think adding another test that verifies the "special" input types produce consistent results across all strategies would be useful.

Sure, thanks--I renamed WellKnownTypes to WellKnownTypeSignatures, and added a new WellKnownTypes that tests the actual concat behaviour on primitives for all of the strategies.

Thank you, the last change resolves my comments.

cushon · 2021-10-07T19:59:05Z

@dholmes-ora

Can you explain the changes made in relation to the runtime test:

test/hotspot/jtreg/runtime/modules/AccessCheck/MethodAccessReadTwice.java

please. The connection to this fix is not at all apparent, nor what the conversion to jasm is achieving.

Thanks, good question:

That test is for JDK-8174954, which checks for an expected IllegalAccessError when the parameter type of an invokedynamic is inaccessible. It's assuming that given "" + param, javac generates an invokedynamic that uses the specific type of param. This change make javac eagerly convert param to a String before passing it to the invokedynamic call, which avoids the accessibility issue the test is trying to exercise.

Using jasm preserves the existing bytecode (including the signature of the invokedynamic) that the test is expecting.

mlbridge · 2021-10-08T01:02:39Z

Mailing list message from David Holmes on hotspot-runtime-dev:

On 8/10/2021 6:02 am, Liam Miller-Cushon wrote:

On Thu, 7 Oct 2021 01:20:04 GMT, David Holmes <dholmes at openjdk.org> wrote:

Liam Miller-Cushon has updated the pull request incrementally with two additional commits since the last revision:

- Also test evaluation order for 'inline'
- Remove sharpestAccessible logic, since types are now passed as strings

Can you explain the changes made in relation to the runtime test:

test/hotspot/jtreg/runtime/modules/AccessCheck/MethodAccessReadTwice.java

please. The connection to this fix is not at all apparent, nor what the conversion to jasm is achieving.

Thanks,
David

@dholmes-ora

Can you explain the changes made in relation to the runtime test:

test/hotspot/jtreg/runtime/modules/AccessCheck/MethodAccessReadTwice.java

please. The connection to this fix is not at all apparent, nor what the conversion to jasm is achieving.

Thanks, good question:

That test is for [JDK-8174954](https://bugs.openjdk.java.net/browse/JDK-8174954), which checks for an expected `IllegalAccessError` when the parameter type of an invokedynamic is inaccessible. It's assuming that given `"" + param`, javac generates an invokedynamic that uses the specific type of `param`. This change make javac eagerly convert `param` to a `String` before passing it to the `invokedynamic` call, which avoids the accessibility issue the test is trying to exercise.

Using `jasm` preserves the existing bytecode (including the signature of the `invokedynamic`) that the test is expecting.

Okay, can you please add a comment to the jasm file that explains that.
It is useful to know what Java code a jasm file represents and where/why
it differs from how that Java code would compile.

Thanks,
David
-----

cushon · 2021-10-08T18:19:00Z

Okay, can you please add a comment to the jasm file that explains that.

Done

shipilev · 2021-10-12T06:19:50Z

@lahodaj, want to review the compiler change?

lahodaj · 2021-10-12T07:23:32Z

How about code like:

        StringBuilder builder2 = new StringBuilder("foo");
        Object oo = builder2;
        oo += "" + builder2.append("bar");

Should that be covered as well? From looking at the patch (not really trying it), it does not seem to be covered?

shipilev · 2021-10-12T07:53:42Z

        StringBuilder builder2 = new StringBuilder("foo");
        Object oo = builder2;
        oo += "" + builder2.append("bar"); 
Should that be covered as well? From looking at the patch (not really trying it), it does not seem to be covered?

Tried it, still not correct:

$ cat Concat.java 
public class Concat {
	public static void main(String... args) {
	        StringBuilder builder2 = new StringBuilder("foo");
	        Object oo = builder2;
        	oo += "" + builder2.append("bar");
		System.out.println(oo);
	}
}

$ build/linux-x86_64-server-fastdebug/images/jdk/bin/javac Concat.java
$ build/linux-x86_64-server-fastdebug/images/jdk/bin/java Concat
foobarfoobar

I believe if (shouldConvertToStringEagerly(argType)) branch should be handled for first argument as well, i.e. code should be shaped as:

if (!first || generateFirstArg) {
    genExpr(arg, arg.type).load();
}
if (shouldConvertToStringEagerly(argType)) {
    gen.callMethod(pos, syms.stringType, names.valueOf, List.of(syms.objectType), true);
    argType = syms.stringType;
}
dynamicArgs.add(argType);

This produces the correct result:

$ build/linux-x86_64-server-fastdebug/images/jdk/bin/java Concat
foofoobar

@cushon, could you do this change and add a relevant test case?

cushon · 2021-10-12T16:22:20Z

        StringBuilder builder2 = new StringBuilder("foo");
        Object oo = builder2;
        oo += "" + builder2.append("bar"); 
Should that be covered as well? From looking at the patch (not really trying it), it does not seem to be covered?
Tried it, still not correct:

I believe if (shouldConvertToStringEagerly(argType)) branch should be handled for first argument as well, i.e. code should be shaped as:

@cushon, could you do this change and add a relevant test case?

Fixed, thanks!

and add more functional test coverage for string concat of well-known types, covering all strategies.

shipilev

Current change passes tier{1,2,3,4} for me. Still, I think compiler folks have to approve the javac change. @lahodaj, could you do it, or ask somebody else?

cushon · 2021-10-18T16:42:53Z

@shipilev this is also blocked on the CSR, I think the next step is for it to be 'reviewed by at least one engineer familiar with that technology area', is that something you'd be able to help with? https://bugs.openjdk.java.net/browse/JDK-8274863

bridgekeeper · 2021-11-15T20:44:16Z

@cushon This pull request has been inactive for more than 4 weeks and will be automatically closed if another 4 weeks passes without any activity. To avoid this, simply add a new comment to the pull request. Feel free to ask for assistance if you need help with progressing this pull request towards integration!

cushon · 2021-11-15T20:45:44Z

This pull request has been inactive for more than 4 weeks

The CSR is still in progress

cushon · 2021-12-07T23:52:27Z

The CSR has been approved for 19, this is ready for review pending integration after the JDK 18 branch is cut.

bridgekeeper · 2022-01-05T01:51:34Z

@cushon This pull request has been inactive for more than 4 weeks and will be automatically closed if another 4 weeks passes without any activity. To avoid this, simply add a new comment to the pull request. Feel free to ask for assistance if you need help with progressing this pull request towards integration!

cushon · 2022-01-07T11:28:55Z

@lahodaj would you be willing to review for the compiler group?

vicente-romero-oracle

the compiler changes look good to me

openjdk · 2022-01-07T17:21:28Z

@cushon 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:

8273914: Indy string concat changes order of operations

Reviewed-by: vromero, jlahoda

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 1099 new commits pushed to the master branch:

4243f4c: 8279540: Shenandoah: Should only clear CLD::_claim_strong mark for strong CLD iterations
62d03c2: 8279547: [vectorapi] Enable vector cast tests after JDK-8278948
6a42fba: 8279258: Auto-vectorization enhancement for two-dimensional array operations
8d0f385: 8279520: SPNEGO has not passed channel binding info into the underlying mechanism
b3dbfc6: 4884570: StreamPrintService.isAttributeValueSupported does not work properly for SheetCollate
8703f14: 8273322: Enhance macro logic optimization for masked logic operations.
bc12381: 8279505: Update documentation for RETRY_COUNT and REPEAT_COUNT
2dbb936: 8279339: (ch) Input/Output streams returned by Channels factory methods don't support concurrent read/write ops
456bd1e: 8211004: javac is complaining about non-denotable types and refusing to generate the class file
844dfb3: Merge
... and 1089 more: https://git.openjdk.java.net/jdk/compare/c10de3538b47c182d7bfeb02f348fac9b2ad0641...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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lahodaj

Looks reasonable.

cushon · 2022-01-11T15:43:55Z

/integrate

openjdk · 2022-01-11T15:45:25Z

Going to push as commit cfee451.
Since your change was applied there have been 1143 commits pushed to the master branch:

c3d0a94: 8279833: Loop optimization issue in String.encodeUTF8_UTF16
9e02447: 8279834: Alpine Linux fails to build when --with-source-date enabled
08e14c6: 8278207: G1: Tighten verification in G1ResetSkipCompactingClosure
c08b2ac: 8225093: Special property jdk.boot.class.path.append should not default to empty string
4c52eb3: 8279669: test/jdk/com/sun/jdi/TestScaffold.java uses wrong condition
d46410c: 8279785: JFR: 'jfr configure' should show default values
2bbeae3: 8279668: x86: AVX2 versions of vpxor should be asserted
3121898: 8279703: G1: Remove unused force_not_compacted local in G1CalculatePointersClosure::do_heap_region
bf7bcaa: 8277748: Obsolete the MinInliningThreshold flag in JDK 19
126328c: 8279560: AArch64: generate_compare_long_string_same_encoding and LARGE_LOOP_PREFETCH alignment
... and 1133 more: https://git.openjdk.java.net/jdk/compare/c10de3538b47c182d7bfeb02f348fac9b2ad0641...master

Your commit was automatically rebased without conflicts.

openjdk · 2022-01-11T15:45:42Z

@cushon Pushed as commit cfee451.

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

JDK-8273914: Indy string concat changes order of operations.

dd3abbe

openjdk bot added the rfr Pull request is ready for review label Oct 6, 2021

openjdk bot added hotspot-runtime hotspot-runtime-dev@openjdk.org compiler compiler-dev@openjdk.org labels Oct 6, 2021

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cushon changed the title ~~JDK-8273914: Indy string concat changes order of operations.~~ JDK-8273914: Indy string concat changes order of operations Oct 6, 2021

dholmes-ora reviewed Oct 7, 2021

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shipilev reviewed Oct 7, 2021

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cushon added 2 commits October 7, 2021 12:42

Remove sharpestAccessible logic, since types are now passed as strings

5ec29ad

Also test evaluation order for 'inline'

fabecf5

Document the rationale for the jasm changes

bd4cb71

Fix eager toString conversion for compound assignment

53dddf6

Rename WellKnownTypes to WellKnownTypeSignatures

d23a324

and add more functional test coverage for string concat of well-known types, covering all strategies.

shipilev reviewed Oct 18, 2021

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openjdk bot removed the csr Pull request needs approved CSR before integration label Dec 7, 2021

vicente-romero-oracle approved these changes Jan 7, 2022

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openjdk bot closed this Jan 11, 2022

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Jan 11, 2022

JDK-8273914: Indy string concat changes order of operations #5844

JDK-8273914: Indy string concat changes order of operations #5844

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