8273409: Receiver type narrowed by CCP does not always trigger post-parse call devirtualization

[TobiHartmann]

While working on JDK-8273323, I noticed that even if CCP is able to narrow the receiver type of a virtual call to an exact type, post-parse call devirtualization is not always triggered. The problem is that CCP only adds nodes to the IGVN worklist if their types have been improved:

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

Lines 1961 to 1965 in 4023646

	// If x is a TypeNode, capture any more-precise type permanently into Node
	if (t != n->bottom_type()) {
	hash_delete(n); // changing bottom type may force a rehash
	n->raise_bottom_type(t);
	_worklist.push(n); // n re-enters the hash table via the worklist

And in turn, IGVN only adds user nodes to the worklist if the type of the parent node could be further improved. As a result, a CallNode is not always added to the worklist if the type of its receiver node has been improved. Often, we are lucky and macro expansion or another optimization phase after CCP adds the CallNode to the worklist. However, as testDynamicCallWithCCP shows, that's not always the case.

The fix is to explicitly add CallStaticJavaNode and CallDynamicJava to the worklist after CCP to give call devirtualization a chance to run:

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

Lines 1054 to 1057 in 4023646

	Node* CallStaticJavaNode::Ideal(PhaseGVN* phase, bool can_reshape) {
	CallGenerator* cg = generator();
	if (can_reshape && cg != NULL) {
	assert(IncrementalInlineMH, "required");

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

Lines 1137 to 1140 in 4023646

	Node* CallDynamicJavaNode::Ideal(PhaseGVN* phase, bool can_reshape) {
	CallGenerator* cg = generator();
	if (can_reshape && cg != NULL) {
	assert(IncrementalInlineVirtual, "required");

I also considered moving the optimization from Ideal to Value (which in contrast to Ideal is already executed during CCP) but we can't trust receiver types during CCP (because CCP goes from optimistic types to pessimistic ones). Also, the current implementation relies on setting the _generator field which is not possible from Value which is declared const:

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

Lines 1169 to 1172 in 4023646

	// Register for late inlining.
	cg->set_callee_method(callee);
	phase->C->prepend_late_inline(cg); // MH late inlining prepends to the list, so do the same
	set_generator(NULL);

All the newly added tests fail IR verification if post-parse call devirtualization is disabled (-XX:-IncrementalInlineVirtual -XX:-IncrementalInlineMH). Without the fix, testDynamicCallWithCCP always fails.

I filed JDK-8273496 to improve how CCP handles this.

Thanks,
Tobias

---

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Issue

• JDK-8273409: Receiver type narrowed by CCP does not always trigger post-parse call devirtualization

Reviewers

• Vladimir Ivanov (@iwanowww - Reviewer)
• Nils Eliasson (@neliasso - Reviewer)

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[mlbridge]

Webrevs

• 01: Full - Incremental (b3709171)
• 00: Full (577d7bee)

[iwanowww]

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:

8273409: Receiver type narrowed by CCP does not always trigger post-parse call devirtualization

Reviewed-by: vlivanov, neliasso

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At the time when this comment was updated there had been 3 new commits pushed to the master branch:

• 7e662e7: 8272413: Incorrect num of element count calculation for vector cast
• f2f8136: 8265443: IGV: disambiguate groups by emiting additional properties
• 59c9f75: 8273375: Remove redundant 'new String' calls after concatenation in java.desktop

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[TobiHartmann]

Thanks, Vladimir!

[neliasso]

Looks good!

[TobiHartmann]

Thanks, Nils!

[TobiHartmann]

/integrate

[openjdk]

Going to push as commit 4866eaa.
Since your change was applied there have been 25 commits pushed to the master branch:

• 5ca26cb: 8273433: Enable parallelism in vmTestbase_nsk_sysdict tests
• f6cc173: 8273539: [PPC64] gtest build error after JDK-8264207
• 9690df7: 8273476: G1: refine G1CollectedHeap::par_iterate_regions_array_part_from
• 00e059d: 8133686: HttpURLConnection.getHeaderFields and URLConnection.getRequestProperties methods return field values in reverse order
• aa93111: 8273483: Zero: Clear pending JNI exception check in native method handler
• 8c16f48: 8273487: Zero: Handle "zero" variant in runtime tests
• dc33bd8: 8273315: Parallelize and increase timeouts for java/foreign/TestMatrix.java test
• 5b1dfe4: 8273439: Fix G1CollectedHeap includes and forward declarations
• 6eba443: 8273387: remove some unreferenced gtk-related functions
• 5df2648: 8273218: G1: Rename g1EvacuationInfo to g1EvacInfo
• ... and 15 more: https://git.openjdk.java.net/jdk/compare/faa942c8ba8ad778b6be20ff6d98a5040a9079e9...master

Your commit was automatically rebased without conflicts.

[openjdk]

@TobiHartmann Pushed as commit 4866eaa.

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