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8341696: C2: Non-fluid StringBuilder pattern bails out in OptoStringConcat

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Reviewed-by: epeter
This commit is contained in:
Theo Weidmann 2025-01-23 08:41:02 +00:00 committed by Emanuel Peter
parent caa3c78f78
commit 6032f6ea04
4 changed files with 315 additions and 67 deletions
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161
src/hotspot/share/opto/stringopts.cpp
View File

@ -173,6 +173,9 @@ class StringConcat : public ResourceObj {
assert(!_control.contains(ctrl), "only push once");
_control.push(ctrl);
}
bool has_control(Node* ctrl) {
return _control.contains(ctrl);
}
void add_constructor(Node* init) {
assert(!_constructors.contains(init), "only push once");
_constructors.push(init);
@ -407,7 +410,66 @@ Node_List PhaseStringOpts::collect_toString_calls() {
return string_calls;
}
// Recognize a fluent-chain of StringBuilder/Buffer. They are either explicit usages
PhaseStringOpts::ProcessAppendResult PhaseStringOpts::process_append_candidate(CallStaticJavaNode* cnode,
StringConcat* sc,
ciMethod* m,
ciSymbol* string_sig,
ciSymbol* int_sig,
ciSymbol* char_sig) {
if (cnode->method() != nullptr && !cnode->method()->is_static() &&
cnode->method()->holder() == m->holder() &&
cnode->method()->name() == ciSymbols::append_name() &&
(cnode->method()->signature()->as_symbol() == string_sig ||
cnode->method()->signature()->as_symbol() == char_sig ||
cnode->method()->signature()->as_symbol() == int_sig)) {
if (sc->has_control(cnode)) {
return ProcessAppendResult::AppendWasAdded;
}
sc->add_control(cnode);
Node* arg = cnode->in(TypeFunc::Parms + 1);
if (arg == nullptr || arg->is_top()) {
#ifndef PRODUCT
if (PrintOptimizeStringConcat) {
tty->print("giving up because the call is effectively dead");
cnode->jvms()->dump_spec(tty);
tty->cr();
}
#endif
return ProcessAppendResult::AbortOptimization;
}
if (cnode->method()->signature()->as_symbol() == int_sig) {
sc->push_int(arg);
} else if (cnode->method()->signature()->as_symbol() == char_sig) {
sc->push_char(arg);
} else if (arg->is_Proj() && arg->in(0)->is_CallStaticJava()) {
CallStaticJavaNode* csj = arg->in(0)->as_CallStaticJava();
if (csj->method() != nullptr &&
csj->method()->intrinsic_id() == vmIntrinsics::_Integer_toString &&
arg->outcnt() == 1) {
// _control is the list of StringBuilder calls nodes which
// will be replaced by new String code after this optimization.
// Integer::toString() call is not part of StringBuilder calls
// chain. It could be eliminated only if its result is used
// only by this SB calls chain.
// Another limitation: it should be used only once because
// it is unknown that it is used only by this SB calls chain
// until all related SB calls nodes are collected.
assert(arg->unique_out() == cnode, "sanity");
sc->add_control(csj);
sc->push_int(csj->in(TypeFunc::Parms));
} else {
sc->push_string(arg);
}
} else {
sc->push_string(arg);
}
return ProcessAppendResult::AppendWasAdded;
}
return ProcessAppendResult::CandidateIsNotAppend;
}
// Recognize fluent-chain and non-fluent uses of StringBuilder/Buffer. They are either explicit usages
// of them or the legacy bytecodes of string concatenation prior to JEP-280. eg.
//
// String result = new StringBuilder()
@ -416,18 +478,17 @@ Node_List PhaseStringOpts::collect_toString_calls() {
// .append(123)
// .toString(); // "foobar123"
//
// PS: Only a certain subset of constructor and append methods are acceptable.
// The criterion is that the length of argument is easy to work out in this phrase.
// It will drop complex cases such as Object.
// Fluent-chains are recognized by walking upwards along the receivers, starting from toString().
// Once the allocation of the StringBuilder has been reached, DU pairs are examined to find the
// constructor and non-fluent uses of the StringBuilder such as in this example:
//
// Since it walks along the receivers of fluent-chain, it will give up if the codeshape is
// not "fluent" enough. eg.
// StringBuilder sb = new StringBuilder();
// sb.append("foo");
// sb.toString();
//
// The receiver of toString method is the result of Allocation Node(CheckCastPP).
// The append method is overlooked. It will fail at validate_control_flow() test.
// PS: Only a certain subset of constructor and append methods are acceptable.
// The criterion is that the length of argument is easy to work out in this phrase.
// It will drop complex cases such as Object.
//
StringConcat* PhaseStringOpts::build_candidate(CallStaticJavaNode* call) {
ciMethod* m = call->method();
@ -466,7 +527,7 @@ StringConcat* PhaseStringOpts::build_candidate(CallStaticJavaNode* call) {
if (cnode == nullptr) {
alloc = recv->isa_Allocate();
if (alloc == nullptr) {
break;
return nullptr;
}
// Find the constructor call
Node* result = alloc->result_cast();
@ -478,7 +539,7 @@ StringConcat* PhaseStringOpts::build_candidate(CallStaticJavaNode* call) {
alloc->jvms()->dump_spec(tty); tty->cr();
}
#endif
break;
return nullptr;
}
Node* constructor = nullptr;
for (SimpleDUIterator i(result); i.has_next(); i.next()) {
@ -489,6 +550,10 @@ StringConcat* PhaseStringOpts::build_candidate(CallStaticJavaNode* call) {
use->method()->name() == ciSymbols::object_initializer_name() &&
use->method()->holder() == m->holder()) {
// Matched the constructor.
if (constructor != nullptr) {
// The constructor again. We must only process it once.
continue;
}
ciSymbol* sig = use->method()->signature()->as_symbol();
if (sig == ciSymbols::void_method_signature() ||
sig == ciSymbols::int_void_signature() ||
@ -542,7 +607,16 @@ StringConcat* PhaseStringOpts::build_candidate(CallStaticJavaNode* call) {
}
#endif
}
break;
} else if (use != nullptr) {
if (process_append_candidate(use, sc, m, string_sig, int_sig, char_sig) == ProcessAppendResult::AbortOptimization) {
// We must abort if process_append_candidate tells us to...
return nullptr;
}
// ...but we do not care if we really found an append or not:
// - If we found an append, that's perfect. Nothing further to do.
// - If this is a call to an unrelated method, validate_mem_flow() (and validate_control_flow())
// will later check if this call prevents the optimization. So nothing to do here.
// We will continue to look for the constructor (if not found already) and appends.
}
}
if (constructor == nullptr) {
@ -553,7 +627,7 @@ StringConcat* PhaseStringOpts::build_candidate(CallStaticJavaNode* call) {
alloc->jvms()->dump_spec(tty); tty->cr();
}
#endif
break;
return nullptr;
}
// Walked all the way back and found the constructor call so see
@ -568,62 +642,23 @@ StringConcat* PhaseStringOpts::build_candidate(CallStaticJavaNode* call) {
} else {
return nullptr;
}
} else if (cnode->method() == nullptr) {
break;
} else if (!cnode->method()->is_static() &&
cnode->method()->holder() == m->holder() &&
cnode->method()->name() == ciSymbols::append_name() &&
(cnode->method()->signature()->as_symbol() == string_sig ||
cnode->method()->signature()->as_symbol() == char_sig ||
cnode->method()->signature()->as_symbol() == int_sig)) {
sc->add_control(cnode);
Node* arg = cnode->in(TypeFunc::Parms + 1);
if (arg == nullptr || arg->is_top()) {
} else {
ProcessAppendResult result = process_append_candidate(cnode, sc, m, string_sig, int_sig, char_sig);
if (result == ProcessAppendResult::AbortOptimization) {
return nullptr;
} else if (result == ProcessAppendResult::CandidateIsNotAppend) {
// some unhandled signature
#ifndef PRODUCT
if (PrintOptimizeStringConcat) {
tty->print("giving up because the call is effectively dead");
cnode->jvms()->dump_spec(tty); tty->cr();
tty->print("giving up because encountered unexpected signature ");
cnode->tf()->dump();
tty->cr();
cnode->in(TypeFunc::Parms + 1)->dump();
}
#endif
break;
return nullptr;
}
if (cnode->method()->signature()->as_symbol() == int_sig) {
sc->push_int(arg);
} else if (cnode->method()->signature()->as_symbol() == char_sig) {
sc->push_char(arg);
} else {
if (arg->is_Proj() && arg->in(0)->is_CallStaticJava()) {
CallStaticJavaNode* csj = arg->in(0)->as_CallStaticJava();
if (csj->method() != nullptr &&
csj->method()->intrinsic_id() == vmIntrinsics::_Integer_toString &&
arg->outcnt() == 1) {
// _control is the list of StringBuilder calls nodes which
// will be replaced by new String code after this optimization.
// Integer::toString() call is not part of StringBuilder calls
// chain. It could be eliminated only if its result is used
// only by this SB calls chain.
// Another limitation: it should be used only once because
// it is unknown that it is used only by this SB calls chain
// until all related SB calls nodes are collected.
assert(arg->unique_out() == cnode, "sanity");
sc->add_control(csj);
sc->push_int(csj->in(TypeFunc::Parms));
continue;
}
}
sc->push_string(arg);
}
continue;
} else {
// some unhandled signature
#ifndef PRODUCT
if (PrintOptimizeStringConcat) {
tty->print("giving up because encountered unexpected signature ");
cnode->tf()->dump(); tty->cr();
cnode->in(TypeFunc::Parms + 1)->dump();
}
#endif
break;
}
}
return nullptr;

26
src/hotspot/share/opto/stringopts.hpp
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2009, 2023, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2009, 2025, 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
@ -34,7 +34,7 @@ class IdealVariable;
class PhaseStringOpts : public Phase {
friend class StringConcat;
private:
private:
PhaseGVN* _gvn;
// List of dead nodes to clean up aggressively at the end
@ -53,6 +53,23 @@ class PhaseStringOpts : public Phase {
// a single string construction.
StringConcat* build_candidate(CallStaticJavaNode* call);
enum class ProcessAppendResult {
// Indicates that the candidate was indeed an append and process_append_candidate processed it
// accordingly (added it to the StringConcat etc.)
AppendWasAdded,
// The candidate turned out not to be an append call. process_append_candidate did not do anything.
CandidateIsNotAppend,
// The candidate is an append call, but circumstances completely preventing string concat
// optimization were detected and the optimization must abort.
AbortOptimization
};
// Called from build_candidate. Looks at an "append candidate", a call that might be a call
// to StringBuilder::append. If so, adds it to the StringConcat.
ProcessAppendResult process_append_candidate(CallStaticJavaNode* cnode, StringConcat* sc,
ciMethod* m, ciSymbol* string_sig, ciSymbol* int_sig,
ciSymbol* char_sig);
// Replace all the SB calls in concat with an optimization String allocation
void replace_string_concat(StringConcat* concat);
@ -105,12 +122,13 @@ class PhaseStringOpts : public Phase {
unroll_string_copy_length = 6
};
public:
public:
PhaseStringOpts(PhaseGVN* gvn);
#ifndef PRODUCT
static void print_statistics();
private:
private:
static uint _stropts_replaced;
static uint _stropts_merged;
static uint _stropts_total;

134
test/hotspot/jtreg/compiler/stringopts/TestFluidAndNonFluid.java Normal file
View File

@ -0,0 +1,134 @@
/*
* Copyright (c) 2025 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.
*/
/*
* @test
* @bug 8341696
* @summary Allow C2 to also optimize non-fluid string builder calls.
* @library /test/lib /
* @run driver compiler.c2.irTests.stringopts.TestFluidAndNonFluid
*/
package compiler.c2.irTests.stringopts;
import compiler.lib.ir_framework.*;
import jdk.test.lib.Asserts;
public class TestFluidAndNonFluid {
public static int unknown = 1;
public static void main(String[] args) {
// Dont inline any StringBuilder methods for this IR test to check if string opts are applied or not.
TestFramework.runWithFlags("-XX:CompileCommand=dontinline,java.lang.StringBuilder::*");
}
@DontInline
public static void opaque(StringBuilder builder) {
builder.append("Z");
}
@Run(test = {"fluid", "nonFluid", "nonFinal", "nonFluidExtraneousVariable", "nonFluidConditional",
"nonFluidOpaqueCall"})
public void runMethod() {
Asserts.assertEQ("0ac", fluidNoParam());
Asserts.assertEQ("ac", nonFluidNoParam());
Asserts.assertEQ("ac", fluid("c"));
Asserts.assertEQ("ac", nonFluid("c"));
Asserts.assertEQ("ac", nonFinal("c"));
Asserts.assertEQ("ac", nonFluidExtraneousVariable("c"));
Asserts.assertEQ("ac", nonFluidConditional("c"));
Asserts.assertEQ("aZ", nonFluidOpaqueCall());
}
@Test
@IR(failOn = {IRNode.ALLOC_OF, "StringBuilder", IRNode.CALL_OF_METHOD, "toString", IRNode.INTRINSIC_TRAP})
public static String fluidNoParam() {
return new StringBuilder("0").append("a").append("c").toString();
}
@Test
@IR(failOn = {IRNode.ALLOC_OF, "StringBuilder", IRNode.CALL_OF_METHOD, "toString", IRNode.INTRINSIC_TRAP})
public static String nonFluidNoParam() {
final StringBuilder sb = new StringBuilder();
sb.append("a");
sb.append("c");
return sb.toString();
}
@Test
@IR(failOn = {IRNode.ALLOC_OF, "StringBuilder", IRNode.CALL_OF_METHOD, "toString"})
public static String fluid(String a) {
return new StringBuilder().append("a").append(a).toString();
}
@Test
@IR(failOn = {IRNode.ALLOC_OF, "StringBuilder", IRNode.CALL_OF_METHOD, "toString"})
public static String nonFluid(String a) {
final StringBuilder sb = new StringBuilder();
sb.append("a");
sb.append(a);
return sb.toString();
}
@Test
@IR(failOn = {IRNode.ALLOC_OF, "StringBuilder", IRNode.CALL_OF_METHOD, "toString"})
public static String nonFinal(String a) {
StringBuilder sb = new StringBuilder();
sb.append("a");
sb.append(a);
return sb.toString();
}
@Test
@IR(failOn = {IRNode.ALLOC_OF, "StringBuilder", IRNode.CALL_OF_METHOD, "toString"})
public static String nonFluidExtraneousVariable(String a) {
final StringBuilder sb = new StringBuilder();
final StringBuilder x = sb;
sb.append("a");
x.append(a);
return sb.toString();
}
@Test
@IR(counts = {IRNode.ALLOC_OF, "StringBuilder", "1", IRNode.CALL_OF_METHOD, "toString", "1"})
@IR(failOn = IRNode.INTRINSIC_TRAP)
static String nonFluidConditional(String a) {
final StringBuilder sb = new StringBuilder();
sb.append("a");
if (unknown == 1) {
sb.append(a);
}
return sb.toString();
}
@Test
@IR(counts = {IRNode.ALLOC_OF, "StringBuilder", "1", IRNode.CALL_OF_METHOD, "toString", "1"})
@IR(failOn = IRNode.INTRINSIC_TRAP)
static String nonFluidOpaqueCall() {
final StringBuilder sb = new StringBuilder();
sb.append("a");
opaque(sb);
return sb.toString();
}
}

61
test/micro/org/openjdk/bench/vm/compiler/FluidSBBench.java Normal file
View File

@ -0,0 +1,61 @@
/*
* Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
* Copyright (c) 2025, 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 org.openjdk.bench.vm.compiler;
import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Fork;
import org.openjdk.jmh.annotations.Measurement;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Warmup;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.Scope;
import java.util.concurrent.TimeUnit;
@Warmup(iterations = 3, time = 300, timeUnit = TimeUnit.MILLISECONDS)
@Measurement(iterations = 3, time = 300, timeUnit = TimeUnit.MILLISECONDS)
@Fork(value = 1, jvmArgsAppend = {"-XX:+UseParallelGC", "-Xmx1g", "-Xms1g"})
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@State(Scope.Thread)
public class FluidSBBench {
static final String PREFIX = "a";
String foo = "aaaaa aaaaa aaaaa aaaaa aaaaa";
@Benchmark
public String fluid() {
return new StringBuilder().append(PREFIX).append(foo).toString();
}
@Benchmark
public String nonFluid() {
final StringBuilder sb = new StringBuilder();
sb.append(PREFIX);
sb.append(foo);
return sb.toString();
}
}