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8254317: C2: Resource consumption of ConvI2LNode::Ideal() grows exponentially

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Prevent exponential number of calls to ConvI2LNode::Ideal() when AddIs are used
multiple times by other AddIs in the optimization ConvI2L(AddI(x, y)) ->
AddL(ConvI2L(x), ConvI2L(y)). This is achieved by (1) reusing existing ConvI2Ls
if possible rather than eagerly creating new ones and (2) postponing the
optimization of newly created ConvI2Ls. Remove hook node solution introduced in
8217359, since this is subsumed by (2). Use phase->is_IterGVN() rather than
can_reshape to check if ConvI2LNode::Ideal() is called within iterative GVN, for
clarity. Add regression tests that cover different shapes and sizes of AddI
subgraphs, implicitly checking (by not timing out) that there is no
combinatorial explosion.

Co-authored-by: Vladimir Ivanov <vlivanov@openjdk.org>
Reviewed-by: vlivanov, kvn
This commit is contained in:
Roberto Castañeda Lozano 2020-11-11 10:18:36 +00:00 committed by Tobias Hartmann
parent 79ac041844
commit 432c387e21
2 changed files with 186 additions and 10 deletions
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32
src/hotspot/share/opto/convertnode.cpp
View File

@ -258,14 +258,30 @@ static inline bool long_ranges_overlap(jlong lo1, jlong hi1,
// Two ranges overlap iff one range's low point falls in the other range.
return (lo2 <= lo1 && lo1 <= hi2) || (lo1 <= lo2 && lo2 <= hi1);
}
// If there is an existing ConvI2L node with the given parent and type, return
// it. Otherwise, create and return a new one. Both reusing existing ConvI2L
// nodes and postponing the idealization of new ones are needed to avoid an
// explosion of recursive Ideal() calls when compiling long AddI chains.
static Node* find_or_make_convI2L(PhaseIterGVN* igvn, Node* parent,
const TypeLong* type) {
Node* n = new ConvI2LNode(parent, type);
Node* existing = igvn->hash_find_insert(n);
if (existing != NULL) {
n->destruct(igvn);
return existing;
}
return igvn->register_new_node_with_optimizer(n);
}
#endif
//------------------------------Ideal------------------------------------------
Node *ConvI2LNode::Ideal(PhaseGVN *phase, bool can_reshape) {
PhaseIterGVN *igvn = phase->is_IterGVN();
const TypeLong* this_type = this->type()->is_long();
Node* this_changed = NULL;
if (can_reshape) {
if (igvn != NULL) {
// Do NOT remove this node's type assertion until no more loop ops can happen.
if (phase->C->post_loop_opts_phase()) {
const TypeInt* in_type = phase->type(in(1))->isa_int();
@ -334,10 +350,9 @@ Node *ConvI2LNode::Ideal(PhaseGVN *phase, bool can_reshape) {
Node* z = in(1);
int op = z->Opcode();
if (op == Op_AddI || op == Op_SubI) {
if (!can_reshape) {
// Postpone this optimization to after parsing because with deep AddNode
// chains a large amount of dead ConvI2L nodes might be created that are
// not removed during parsing. As a result, we might hit the node limit.
if (igvn == NULL) {
// Postpone this optimization to iterative GVN, where we can handle deep
// AddI chains without an exponential number of recursive Ideal() calls.
phase->record_for_igvn(this);
return this_changed;
}
@ -399,11 +414,8 @@ Node *ConvI2LNode::Ideal(PhaseGVN *phase, bool can_reshape) {
}
assert(rxlo == (int)rxlo && rxhi == (int)rxhi, "x should not overflow");
assert(rylo == (int)rylo && ryhi == (int)ryhi, "y should not overflow");
Node* cx = phase->C->constrained_convI2L(phase, x, TypeInt::make(rxlo, rxhi, widen), NULL);
Node *hook = new Node(1);
hook->init_req(0, cx); // Add a use to cx to prevent him from dying
Node* cy = phase->C->constrained_convI2L(phase, y, TypeInt::make(rylo, ryhi, widen), NULL);
hook->destruct(phase);
Node* cx = find_or_make_convI2L(igvn, x, TypeLong::make(rxlo, rxhi, widen));
Node* cy = find_or_make_convI2L(igvn, y, TypeLong::make(rylo, ryhi, widen));
switch (op) {
case Op_AddI: return new AddLNode(cx, cy);
case Op_SubI: return new SubLNode(cx, cy);

164
test/hotspot/jtreg/compiler/conversions/TestMoveConvI2LThroughAddIs.java Normal file
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@ -0,0 +1,164 @@
/*
* Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* 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
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package compiler.conversions;
import java.util.Random;
import jdk.test.lib.Asserts;
/*
* @test
* @bug 8254317
* @requires vm.compiler2.enabled
* @summary Exercises the optimization that moves integer-to-long conversions
* upwards through different shapes of integer addition
* subgraphs. Contains three small functional tests and two stress
* tests that resulted in a compilation time and memory explosion
* before fixing bug 8254317. The stress tests run with -Xbatch to wait
* for C2, so that a timeout or an out-of-memory error is triggered if
* there was an explosion. These tests use a timeout of 30s to catch
* the explosion earlier.
* @library /test/lib /
* @run main/othervm
* compiler.conversions.TestMoveConvI2LThroughAddIs functional
* @run main/othervm/timeout=30 -Xbatch
* compiler.conversions.TestMoveConvI2LThroughAddIs stress1
* @run main/othervm/timeout=30 -Xbatch
* compiler.conversions.TestMoveConvI2LThroughAddIs stress2
*/
public class TestMoveConvI2LThroughAddIs {
// Number of repetitions of each test. Should be sufficiently large for the
// method under test to be compiled with C2.
static final int N = 100_000;
// Chain-shaped functional test.
static long testChain(boolean cnd) {
int a = cnd ? 1 : 2;
int b = a + a;
int c = b + b;
int d = c + c;
return d;
}
// Tree-shaped functional test.
static long testTree(boolean cnd) {
int a0 = cnd ? 1 : 2;
int a1 = cnd ? 1 : 2;
int a2 = cnd ? 1 : 2;
int a3 = cnd ? 1 : 2;
int a4 = cnd ? 1 : 2;
int a5 = cnd ? 1 : 2;
int a6 = cnd ? 1 : 2;
int a7 = cnd ? 1 : 2;
int b0 = a0 + a1;
int b1 = a2 + a3;
int b2 = a4 + a5;
int b3 = a6 + a7;
int c0 = b0 + b1;
int c1 = b2 + b3;
int d = c0 + c1;
return d;
}
// DAG-shaped functional test.
static long testDAG(boolean cnd) {
int a0 = cnd ? 1 : 2;
int a1 = cnd ? 1 : 2;
int a2 = cnd ? 1 : 2;
int a3 = cnd ? 1 : 2;
int b0 = a0 + a1;
int b1 = a1 + a2;
int b2 = a2 + a3;
int c0 = b0 + b1;
int c1 = b1 + b2;
int d = c0 + c1;
return d;
}
// Chain-shaped stress test. Before fixing bug 8254317, this test would
// result in an out-of-memory error after minutes running.
static long testStress1(boolean cnd) {
// C2 infers a finite, small value range for a. Note that there are
// different ways to achieve this, for example a might take the value of
// the induction variable in an outer counted loop.
int a = cnd ? 1 : 2;
// C2 fully unrolls this loop, creating a long chain of AddIs.
for (int i = 0; i < 28; i++) {
a = a + a;
}
// C2 places a ConvI2L at the end of the AddI chain.
return a;
}
// DAG-shaped stress test. Before fixing bug 8254317, this test would result
// in an out-of-memory error after minutes running.
static long testStress2(boolean cnd) {
int a = cnd ? 1 : 2;
int b = a;
int c = a + a;
for (int i = 0; i < 20; i++) {
b = b + c;
c = b + c;
}
int d = b + c;
return d;
}
public static void main(String[] args) {
// We use a random number generator to avoid constant propagation in C2
// and produce a variable ("a" in the different tests) with a finite,
// small value range.
Random rnd = new Random();
switch(args[0]) {
case "functional":
// Small, functional tests.
for (int i = 0; i < N; i++) {
boolean cnd = rnd.nextBoolean();
Asserts.assertEQ(testChain(cnd), cnd ? 8L : 16L);
Asserts.assertEQ(testTree(cnd), cnd ? 8L : 16L);
Asserts.assertEQ(testDAG(cnd), cnd ? 8L : 16L);
}
break;
case "stress1":
// Chain-shaped stress test.
for (int i = 0; i < N; i++) {
boolean cnd = rnd.nextBoolean();
Asserts.assertEQ(testStress1(cnd),
cnd ? 268435456L : 536870912L);
}
break;
case "stress2":
// DAG-shaped stress test.
for (int i = 0; i < N; i++) {
boolean cnd = rnd.nextBoolean();
Asserts.assertEQ(testStress2(cnd),
cnd ? 701408733L : 1402817466L);
}
break;
default:
System.out.println("invalid mode");
}
}
}