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8369646: Detection of redundant conversion patterns in add_users_of_use_to_worklist is too restrictive #27900

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8369646: Detection of redundant conversion patterns in add_users_of_use_to_worklist is too restrictive #27900

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c63e308
8369646: Add second test run with -XX:+StressIGVN and stress seed
benoitmaillard Oct 20, 2025
402def2
8369646: Fix excissively restrictive pattern in add_users_of_use_to_w…
benoitmaillard Oct 20, 2025
86ed466
Add new issue name to jtreg headers
benoitmaillard Oct 20, 2025
1270663
Missing -XX:+UnlockDiagnosticVMOptions
benoitmaillard Oct 20, 2025
16842d0
Add -XX:+StressIGVN to run without fixed seed
benoitmaillard Oct 27, 2025
103cc58
Add comments to clarify how add_users_to_worklist and add_users_of_us…
benoitmaillard Nov 6, 2025
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13 changes: 8 additions & 5 deletions src/hotspot/share/opto/phaseX.cpp
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Expand Up @@ -2566,13 +2566,16 @@ void PhaseIterGVN::add_users_of_use_to_worklist(Node* n, Node* use, Unique_Node_
// ConvI2F->ConvF2I->ConvI2F
// Note: there may be other 3-nodes conversion chains that would require to be added here, but these
// are the only ones that are known to trigger missed optimizations otherwise
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@eme64 eme64 Oct 30, 2025

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You may want to update the description, and give a bit of extra information. Because you are saying n does not have to be a conversion, but it may be that n is about to be replaced with a conversion, right?

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@benoitmaillard benoitmaillard Nov 4, 2025

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Yes, in some cases add_users_of_use_to_worklist is called with the node about to be replaced as argument n. The point is that we might replace n with a node that already has other uses, and we only want to notify the uses for which there is a potential change.
But this is in no way specific to this one optimization, so I think adding something here would cause more confusion than anything else. Perhaps we should update the description of add_users_of_use_to_worklist then?

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@eme64 eme64 Nov 4, 2025

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Right, this is not specific to this optimization here. Why not add something at the level of add_users_of_use_to_worklist.

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@benoitmaillard benoitmaillard Nov 6, 2025

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Sorry for the delay, I ended up adding comments to the definition of both add_users_to_worklist and add_users_of_use_to_worklist. I think this might help avoid some confusion in the future.

if ((n->Opcode() == Op_ConvD2L && use_op == Op_ConvL2D) ||
(n->Opcode() == Op_ConvF2I && use_op == Op_ConvI2F) ||
(n->Opcode() == Op_ConvF2L && use_op == Op_ConvL2F) ||
(n->Opcode() == Op_ConvI2F && use_op == Op_ConvF2I)) {
if (use_op == Op_ConvL2D ||
use_op == Op_ConvI2F ||
use_op == Op_ConvL2F ||
use_op == Op_ConvF2I) {
for (DUIterator_Fast i2max, i2 = use->fast_outs(i2max); i2 < i2max; i2++) {
Node* u = use->fast_out(i2);
if (u->Opcode() == n->Opcode()) {
if ((use_op == Op_ConvL2D && u->Opcode() == Op_ConvD2L) ||
(use_op == Op_ConvI2F && u->Opcode() == Op_ConvF2I) ||
(use_op == Op_ConvL2F && u->Opcode() == Op_ConvF2L) ||
(use_op == Op_ConvF2I && u->Opcode() == Op_ConvI2F)) {
worklist.push(u);
}
}
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10 changes: 8 additions & 2 deletions test/hotspot/jtreg/compiler/c2/TestEliminateRedundantConversionSequences.java
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Expand Up @@ -23,13 +23,19 @@

/*
* @test
* @bug 8359603
* @bug 8359603 8369646
* @summary Redundant ConvX2Y->ConvY2X->ConvX2Y sequences should be
* simplified to a single ConvX2Y operation when applicable
* VerifyIterativeGVN checks that this optimization was applied
* @run main/othervm -XX:+IgnoreUnrecognizedVMOptions
* -XX:CompileCommand=compileonly,compiler.c2.TestEliminateRedundantConversionSequences::test*
* -XX:-TieredCompilation -Xbatch -XX:VerifyIterativeGVN=1110 compiler.c2.TestEliminateRedundantConversionSequences
* -XX:-TieredCompilation -Xbatch -XX:VerifyIterativeGVN=1110
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@chhagedorn chhagedorn Oct 27, 2025

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You could either add a separate run with -XX:+StressIGVN without a fixed seed or just add -XX:+StressIGVN here. I guess the latter is good enough.

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@benoitmaillard benoitmaillard Oct 27, 2025

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I agree, and I just added -XX:+StressIGVN to the existing run.

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@chhagedorn chhagedorn Oct 27, 2025

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Looks good, thanks!

* compiler.c2.TestEliminateRedundantConversionSequences
* @run main/othervm -XX:+IgnoreUnrecognizedVMOptions
* -XX:CompileCommand=compileonly,compiler.c2.TestEliminateRedundantConversionSequences::test*
* -XX:-TieredCompilation -Xbatch -XX:VerifyIterativeGVN=1110
* -XX:+UnlockDiagnosticVMOptions -XX:+StressIGVN -XX:StressSeed=115074401
* compiler.c2.TestEliminateRedundantConversionSequences
* @run main compiler.c2.TestEliminateRedundantConversionSequences
*
*/
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