8262739: String inflation C2 intrinsic prevents insertion of anti-dependencies

[TobiHartmann]

The string inflation intrinsic StrInflatedCopyNode which converts the String internal byte[] to char[] has bottom_type Type::MEMORY:

jdk/src/hotspot/share/opto/intrinsicnode.hpp

Lines 143 to 145 in f71e8a6

	StrIntrinsicNode(control, arymem, s1, s2, c, none) {};
	virtual int Opcode() const;
	virtual const Type* bottom_type() const { return Type::MEMORY; }

Memory users (i.e. loads) should therefore be checked for nearby anti-dependent stores:

jdk/src/hotspot/share/opto/node.cpp

Lines 1482 to 1486 in f71e8a6

	bool Node::needs_anti_dependence_check() const {
	if (req() < 2 || (_flags & Flag_needs_anti_dependence_check) == 0) {
	return false;
	}
	return in(1)->bottom_type()->has_memory();

However, since InstructForm::captures_bottom_type returns false for StrInflatedCopyNode, after matching, the corresponding MachNode version will have bottom_type Type::BOTTOM and no anti-dependency analysis will be performed for its users. Scheduling then incorrectly orders loads from the char array with anti-dependent stores to the same array, leading to incorrect results.

StrCompressedCopyNode does not need this because it has TypeInt::INT as bottom_type (the memory output is handled via a SCMemProjNode):

jdk/src/hotspot/share/opto/intrinsicnode.hpp

Lines 131 to 133 in f71e8a6

	StrIntrinsicNode(control, arymem, s1, s2, c, none) {};
	virtual int Opcode() const;
	virtual const Type* bottom_type() const { return TypeInt::INT; }

Thanks,
Tobias

---

Progress

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Issue

• JDK-8262739: String inflation C2 intrinsic prevents insertion of anti-dependencies

Reviewers

• Nils Eliasson (@neliasso - Reviewer) ⚠️ Review applies to c132b1e
• Christian Hagedorn (@chhagedorn - Reviewer)

Download

$ git fetch https://git.openjdk.java.net/jdk pull/3025/head:pull/3025
$ git checkout pull/3025

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[mlbridge]

Webrevs

• 01: Full - Incremental (7660c4c)
• 00: Full (c132b1e)

[neliasso]

Looks good.

[openjdk]

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

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

8262739: String inflation C2 intrinsic prevents insertion of anti-dependencies

Reviewed-by: neliasso, chagedorn

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At the time when this comment was updated there had been 4 new commits pushed to the master branch:

• 4517d72: 8263612: Unused variables in C1 runtime
• 83a9a02: 8263509: LdapSchemaParser.readNextTag checks array length incorrectly
• 9c50b8e: 8263587: C2: JVMS not cloned when needs_clone_jvms() is true
• 68deb24: 8080272: Refactor I/O stream copying to use InputStream.transferTo/readAllBytes and Files.copy

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

Thanks for the review, Nils!

[chhagedorn]

Otherwise, the fix looks good!

[chhagedorn]

Should not be inside #if INCLUDE_SHENANDOAHGC.

[TobiHartmann]

Yes, good catch, thank you! (That happens when doing last-minute re-ordering ...). Fixed.

[TobiHartmann]

Thanks for the review, Christian!

[TobiHartmann]

/integrate

[openjdk]

@TobiHartmann Since your change was applied there have been 216 commits pushed to the master branch:

• 19a6ac4: 8264142: Remove TRAPS/THREAD parameters for verifier related functions
• aefc156: 8264179: [TESTBUG] Some compiler tests fail when running without C2
• 30b4b17: 8264334: Use the blessed modifier order in jdk.jpackage
• 8ee9a05: 8259623: JfrTypeSet::_subsystem_callback is left dangling after use
• 1f54ed0: 8264096: slowdebug jvm crashes when StrInflatedCopy match rule is not supported
• 447e0df: 8263769: simplify PhaseMacroExpand::extract_call_projections()
• 99b4bab: 8263188: JSSE should fail fast if there isn't supported signature algorithm
• 6678b01: 8264328: Broken license in javax/swing/JComboBox/8072767/bug8072767.java
• 2fa6a3c: 8264006: Fix AOT library loading on CPUs with 256-byte dcache line
• c986457: 8264329: Z cannot be 1 for Diffie-Hellman key agreement
• ... and 206 more: https://git.openjdk.java.net/jdk/compare/a31a23d5e72c4618b5b67e854ef4909110a1b5b4...master

Your commit was automatically rebased without conflicts.

Pushed as commit 3caea47.

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