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8279837: C2: assert(is_Loop()) failed: invalid node class: Region
Reviewed-by: kvn, thartmann
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chhagedorn committed Jan 13, 2022
1 parent 5aecb37 commit 65eb066b630b892f22492457e0f86165e5ef4765
Showing 2 changed files with 87 additions and 0 deletions.
@@ -3425,6 +3425,11 @@ bool IdealLoopTree::do_one_iteration_loop(PhaseIdealLoop *phase) {
//=============================================================================
//------------------------------iteration_split_impl---------------------------
bool IdealLoopTree::iteration_split_impl(PhaseIdealLoop *phase, Node_List &old_new) {
if (!_head->is_Loop()) {
// Head could be a region with a NeverBranch that was added in beautify loops but the region was not
// yet transformed into a LoopNode. Bail out and wait until beautify loops turns it into a Loop node.
return false;
}
// Compute loop trip count if possible.
compute_trip_count(phase);

@@ -0,0 +1,82 @@
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
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* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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*
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/*
* @test
* @requires vm.compiler2.enabled
* @bug 8279837
* @summary Tests infinite loop with region head in iteration split.
* @run main/othervm -Xcomp -XX:-TieredCompilation
* -XX:CompileCommand=compileonly,compiler.loopopts.TestIterationSplitWithRegionHead::test
* -XX:CompileCommand=dontinline,compiler.loopopts.TestIterationSplitWithRegionHead::*
* compiler.loopopts.TestIterationSplitWithRegionHead
*/

package compiler.loopopts;

public class TestIterationSplitWithRegionHead {

static boolean flagFalse = false;

public static void main(String[] args) {
test();
}

public static void test() {
// 1) The loop tree is built. We find that nested loop N2 is an infinite loop and add a NeverBranch
// to the inner loop to make it reachable. But the current loop tree does not have N2, yet. The
// resulting loop tree is:
//
// Loop: N0/N0 has_call has_sfpt
// Loop: N77/N121 has_call // N1 outer
// Loop: N77/N111 has_call sfpts={ 111 97 } // N1 inner
//
// 2) beautify_loops() finds that the outer loop head of N1 is shared and thus adds a new region
// in merge_many_backedges(). As a result, the loop tree is built again. This time, the NeverBranch
// in the inner loop of N2 allows that a loop tree can be built for it:
//
// Loop: N0/N0 has_call has_sfpt
// Loop: N216/N213 limit_check profile_predicated predicated has_call sfpts={ 111 97 } // N1 shared loop head
// Loop: N196/N201 sfpts={ 201 } // N2 inner loop now discovered with the new NeverBranch
//
// However, a LoopNode is only added by beautify_loops() which won't be called until the next iteration of loop opts.
// This means that we have a Region node (N196) as head in the loop tree which cannot be handled by iteration_split_impl()
// resulting in an assertion failure.

// Nested loop N1
while (flagFalse) {
while (dontInlineFalse()) {
}
}
dontInlineFalse();

// Nested loop N2
while (flagFalse) {
while (true) ; // Detected as infinite inner loop by C2 -> NeverBranch added
}
}

public static boolean dontInlineFalse() {
return false;
}
}

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