Revert^2 "ART: Removes SuspendCheck for plain
loops with a low trip count."
This change removes SuspendCheck for plain loops with a low trip count.
The SuspendCheck in the codegen makes sure that the thread can be
interrupted during execution for GC. Not being able to do so might
decrease the responsiveness of GC in the case when a very long loop
or a long recursion is being executed.
However, for plain loops with a small trip count, the removal of
SuspendCheck should not affect the GC's responsiveness by a large
margin. Consequently, since the thread won't be interrupted for
plain loops, it is assumed that the performance might increase
by removing SuspendCheck.
Also add explicit checks to existing code to ensure that SuspendCheck
is never null when it is used.
This reverts commit 8f6b99fba2d043265a84d599a967d52f66738ad6
Reason for revert: Included fix for CHAGuardVisitor::HoistGuard crash
by disabling codegen for optimized SuspendCheck nodes instead of
removing the SuspendCheck node itself.
Test: art/test.py -v -j12 --host --64 -t 2233-checker\
-remove-loop-suspend-check --run-test --optimizing
Change-Id: Id6296aded91e1cf49b8f3f339dc83613cbedf876
diff --git a/compiler/optimizing/bounds_check_elimination.cc b/compiler/optimizing/bounds_check_elimination.cc
index dad3c81..0b11a6f 100644
--- a/compiler/optimizing/bounds_check_elimination.cc
+++ b/compiler/optimizing/bounds_check_elimination.cc
@@ -1818,6 +1818,7 @@
HInstruction* condition,
bool is_null_check = false) {
HInstruction* suspend = loop->GetSuspendCheck();
+ DCHECK(suspend != nullptr);
block->InsertInstructionBefore(condition, block->GetLastInstruction());
DeoptimizationKind kind =
is_null_check ? DeoptimizationKind::kLoopNullBCE : DeoptimizationKind::kLoopBoundsBCE;
diff --git a/compiler/optimizing/cha_guard_optimization.cc b/compiler/optimizing/cha_guard_optimization.cc
index c6232ef..d231593 100644
--- a/compiler/optimizing/cha_guard_optimization.cc
+++ b/compiler/optimizing/cha_guard_optimization.cc
@@ -200,6 +200,7 @@
block->RemoveInstruction(deopt);
HInstruction* suspend = loop_info->GetSuspendCheck();
+ DCHECK(suspend != nullptr);
// Need a new deoptimize instruction that copies the environment
// of the suspend instruction for the loop.
HDeoptimize* deoptimize = new (GetGraph()->GetAllocator()) HDeoptimize(
diff --git a/compiler/optimizing/code_generator.cc b/compiler/optimizing/code_generator.cc
index 27eabaf..8bd4406 100644
--- a/compiler/optimizing/code_generator.cc
+++ b/compiler/optimizing/code_generator.cc
@@ -1123,7 +1123,7 @@
for (HBasicBlock* block : graph.GetReversePostOrder()) {
if (block->IsLoopHeader()) {
HSuspendCheck* suspend_check = block->GetLoopInformation()->GetSuspendCheck();
- if (!suspend_check->GetEnvironment()->IsFromInlinedInvoke()) {
+ if (suspend_check != nullptr && !suspend_check->GetEnvironment()->IsFromInlinedInvoke()) {
loop_headers.push_back(suspend_check);
}
}
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index 2a0b481..2f8c0b2 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -1974,6 +1974,13 @@
void InstructionCodeGeneratorARM64::GenerateSuspendCheck(HSuspendCheck* instruction,
HBasicBlock* successor) {
+ if (instruction->IsNoOp()) {
+ if (successor != nullptr) {
+ __ B(codegen_->GetLabelOf(successor));
+ }
+ return;
+ }
+
if (codegen_->CanUseImplicitSuspendCheck()) {
__ Ldr(kImplicitSuspendCheckRegister, MemOperand(kImplicitSuspendCheckRegister));
codegen_->RecordPcInfo(instruction, instruction->GetDexPc());
diff --git a/compiler/optimizing/graph_checker.cc b/compiler/optimizing/graph_checker.cc
index d1769ce..eda6363 100644
--- a/compiler/optimizing/graph_checker.cc
+++ b/compiler/optimizing/graph_checker.cc
@@ -674,13 +674,14 @@
loop_information->GetPreHeader()->GetSuccessors().size()));
}
- if (loop_information->GetSuspendCheck() == nullptr) {
- AddError(StringPrintf(
- "Loop with header %d does not have a suspend check.",
- loop_header->GetBlockId()));
+ if (!GetGraph()->SuspendChecksAreAllowedToNoOp() &&
+ loop_information->GetSuspendCheck() == nullptr) {
+ AddError(StringPrintf("Loop with header %d does not have a suspend check.",
+ loop_header->GetBlockId()));
}
- if (loop_information->GetSuspendCheck() != loop_header->GetFirstInstructionDisregardMoves()) {
+ if (!GetGraph()->SuspendChecksAreAllowedToNoOp() &&
+ loop_information->GetSuspendCheck() != loop_header->GetFirstInstructionDisregardMoves()) {
AddError(StringPrintf(
"Loop header %d does not have the loop suspend check as the first instruction.",
loop_header->GetBlockId()));
diff --git a/compiler/optimizing/loop_optimization.cc b/compiler/optimizing/loop_optimization.cc
index 2d7c208..604d3d2 100644
--- a/compiler/optimizing/loop_optimization.cc
+++ b/compiler/optimizing/loop_optimization.cc
@@ -681,6 +681,50 @@
}
//
+// This optimization applies to loops with plain simple operations
+// (I.e. no calls to java code or runtime) with a known small trip_count * instr_count
+// value.
+//
+bool HLoopOptimization::TryToRemoveSuspendCheckFromLoopHeader(LoopAnalysisInfo* analysis_info,
+ bool generate_code) {
+ if (!graph_->SuspendChecksAreAllowedToNoOp()) {
+ return false;
+ }
+
+ int64_t trip_count = analysis_info->GetTripCount();
+
+ if (trip_count == LoopAnalysisInfo::kUnknownTripCount) {
+ return false;
+ }
+
+ int64_t instruction_count = analysis_info->GetNumberOfInstructions();
+ int64_t total_instruction_count = trip_count * instruction_count;
+
+ // The inclusion of the HasInstructionsPreventingScalarOpts() prevents this
+ // optimization from being applied to loops that have calls.
+ bool can_optimize =
+ total_instruction_count <= HLoopOptimization::kMaxTotalInstRemoveSuspendCheck &&
+ !analysis_info->HasInstructionsPreventingScalarOpts();
+
+ if (!can_optimize) {
+ return false;
+ }
+
+ // If we should do the optimization, disable codegen for the SuspendCheck.
+ if (generate_code) {
+ HLoopInformation* loop_info = analysis_info->GetLoopInfo();
+ HBasicBlock* header = loop_info->GetHeader();
+ HSuspendCheck* instruction = header->GetLoopInformation()->GetSuspendCheck();
+ // As other optimizations depend on SuspendCheck
+ // (e.g: CHAGuardVisitor::HoistGuard), disable its codegen instead of
+ // removing the SuspendCheck instruction.
+ instruction->SetIsNoOp(true);
+ }
+
+ return true;
+}
+
+//
// Optimization.
//
@@ -824,7 +868,7 @@
}
bool HLoopOptimization::OptimizeInnerLoop(LoopNode* node) {
- return TryOptimizeInnerLoopFinite(node) || TryPeelingAndUnrolling(node);
+ return TryOptimizeInnerLoopFinite(node) || TryLoopScalarOpts(node);
}
//
@@ -928,7 +972,7 @@
return true;
}
-bool HLoopOptimization::TryPeelingAndUnrolling(LoopNode* node) {
+bool HLoopOptimization::TryLoopScalarOpts(LoopNode* node) {
HLoopInformation* loop_info = node->loop_info;
int64_t trip_count = LoopAnalysis::GetLoopTripCount(loop_info, &induction_range_);
LoopAnalysisInfo analysis_info(loop_info);
@@ -941,10 +985,16 @@
if (!TryFullUnrolling(&analysis_info, /*generate_code*/ false) &&
!TryPeelingForLoopInvariantExitsElimination(&analysis_info, /*generate_code*/ false) &&
- !TryUnrollingForBranchPenaltyReduction(&analysis_info, /*generate_code*/ false)) {
+ !TryUnrollingForBranchPenaltyReduction(&analysis_info, /*generate_code*/ false) &&
+ !TryToRemoveSuspendCheckFromLoopHeader(&analysis_info, /*generate_code*/ false)) {
return false;
}
+ // Try the suspend check removal even for non-clonable loops. Also this
+ // optimization doesn't interfere with other scalar loop optimizations so it can
+ // be done prior to them.
+ bool removed_suspend_check = TryToRemoveSuspendCheckFromLoopHeader(&analysis_info);
+
// Run 'IsLoopClonable' the last as it might be time-consuming.
if (!LoopClonerHelper::IsLoopClonable(loop_info)) {
return false;
@@ -952,7 +1002,7 @@
return TryFullUnrolling(&analysis_info) ||
TryPeelingForLoopInvariantExitsElimination(&analysis_info) ||
- TryUnrollingForBranchPenaltyReduction(&analysis_info);
+ TryUnrollingForBranchPenaltyReduction(&analysis_info) || removed_suspend_check;
}
//
diff --git a/compiler/optimizing/loop_optimization.h b/compiler/optimizing/loop_optimization.h
index b178616..0535c74 100644
--- a/compiler/optimizing/loop_optimization.h
+++ b/compiler/optimizing/loop_optimization.h
@@ -47,6 +47,11 @@
static constexpr const char* kLoopOptimizationPassName = "loop_optimization";
+ // The maximum number of total instructions (trip_count * instruction_count),
+ // where the optimization of removing SuspendChecks from the loop header could
+ // be performed.
+ static constexpr int64_t kMaxTotalInstRemoveSuspendCheck = 128;
+
private:
/**
* A single loop inside the loop hierarchy representation.
@@ -179,8 +184,19 @@
// should be actually applied.
bool TryFullUnrolling(LoopAnalysisInfo* analysis_info, bool generate_code = true);
- // Tries to apply scalar loop peeling and unrolling.
- bool TryPeelingAndUnrolling(LoopNode* node);
+ // Tries to remove SuspendCheck for plain loops with a low trip count. The
+ // SuspendCheck in the codegen makes sure that the thread can be interrupted
+ // during execution for GC. Not being able to do so might decrease the
+ // responsiveness of GC when a very long loop or a long recursion is being
+ // executed. However, for plain loops with a small trip count, the removal of
+ // SuspendCheck should not affect the GC's responsiveness by a large margin.
+ // Consequently, since the thread won't be interrupted for plain loops, it is
+ // assumed that the performance might increase by removing SuspendCheck.
+ bool TryToRemoveSuspendCheckFromLoopHeader(LoopAnalysisInfo* analysis_info,
+ bool generate_code = true);
+
+ // Tries to apply scalar loop optimizations.
+ bool TryLoopScalarOpts(LoopNode* node);
//
// Vectorization analysis and synthesis.
diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index d35ed1c..90c8f74 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -3047,6 +3047,7 @@
HSuspendCheck* suspend_check = new (allocator_) HSuspendCheck(header->GetDexPc());
new_header->AddInstruction(suspend_check);
new_body->AddInstruction(new (allocator_) HGoto());
+ DCHECK(loop->GetSuspendCheck() != nullptr);
suspend_check->CopyEnvironmentFromWithLoopPhiAdjustment(
loop->GetSuspendCheck()->GetEnvironment(), header);
diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index 7a0059f..0767bf5 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -678,6 +678,13 @@
return cha_single_implementation_list_;
}
+ // In case of OSR we intend to use SuspendChecks as an entry point to the
+ // function; for debuggable graphs we might deoptimize to interpreter from
+ // SuspendChecks. In these cases we should always generate code for them.
+ bool SuspendChecksAreAllowedToNoOp() const {
+ return !IsDebuggable() && !IsCompilingOsr();
+ }
+
void AddCHASingleImplementationDependency(ArtMethod* method) {
cha_single_implementation_list_.insert(method);
}
@@ -719,7 +726,7 @@
return ReferenceTypeInfo::Create(handle_cache_.GetObjectClassHandle(), /* is_exact= */ false);
}
- uint32_t GetNumberOfCHAGuards() { return number_of_cha_guards_; }
+ uint32_t GetNumberOfCHAGuards() const { return number_of_cha_guards_; }
void SetNumberOfCHAGuards(uint32_t num) { number_of_cha_guards_ = num; }
void IncrementNumberOfCHAGuards() { number_of_cha_guards_++; }
@@ -6714,9 +6721,10 @@
class HSuspendCheck final : public HExpression<0> {
public:
- explicit HSuspendCheck(uint32_t dex_pc = kNoDexPc)
+ explicit HSuspendCheck(uint32_t dex_pc = kNoDexPc, bool is_no_op = false)
: HExpression(kSuspendCheck, SideEffects::CanTriggerGC(), dex_pc),
slow_path_(nullptr) {
+ SetPackedFlag<kFlagIsNoOp>(is_no_op);
}
bool IsClonable() const override { return true; }
@@ -6725,6 +6733,10 @@
return true;
}
+ void SetIsNoOp(bool is_no_op) { SetPackedFlag<kFlagIsNoOp>(is_no_op); }
+ bool IsNoOp() const { return GetPackedFlag<kFlagIsNoOp>(); }
+
+
void SetSlowPath(SlowPathCode* slow_path) { slow_path_ = slow_path; }
SlowPathCode* GetSlowPath() const { return slow_path_; }
@@ -6733,6 +6745,15 @@
protected:
DEFAULT_COPY_CONSTRUCTOR(SuspendCheck);
+ // True if the HSuspendCheck should not emit any code during codegen. It is
+ // not possible to simply remove this instruction to disable codegen, as
+ // other optimizations (e.g: CHAGuardVisitor::HoistGuard) depend on
+ // HSuspendCheck being present in every loop.
+ static constexpr size_t kFlagIsNoOp = kNumberOfGenericPackedBits;
+ static constexpr size_t kNumberOfSuspendCheckPackedBits = kFlagIsNoOp + 1;
+ static_assert(kNumberOfSuspendCheckPackedBits <= HInstruction::kMaxNumberOfPackedBits,
+ "Too many packed fields.");
+
private:
// Only used for code generation, in order to share the same slow path between back edges
// of a same loop.
diff --git a/test/2233-checker-remove-loop-suspend-check/expected-stderr.txt b/test/2233-checker-remove-loop-suspend-check/expected-stderr.txt
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/test/2233-checker-remove-loop-suspend-check/expected-stderr.txt
diff --git a/test/2233-checker-remove-loop-suspend-check/expected-stdout.txt b/test/2233-checker-remove-loop-suspend-check/expected-stdout.txt
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/test/2233-checker-remove-loop-suspend-check/expected-stdout.txt
diff --git a/test/2233-checker-remove-loop-suspend-check/info.txt b/test/2233-checker-remove-loop-suspend-check/info.txt
new file mode 100644
index 0000000..fe8d8eb
--- /dev/null
+++ b/test/2233-checker-remove-loop-suspend-check/info.txt
@@ -0,0 +1 @@
+Test to check the removal of SuspendCheck for finite simple plain loops.
diff --git a/test/2233-checker-remove-loop-suspend-check/src/Main.java b/test/2233-checker-remove-loop-suspend-check/src/Main.java
new file mode 100644
index 0000000..bea67e7
--- /dev/null
+++ b/test/2233-checker-remove-loop-suspend-check/src/Main.java
@@ -0,0 +1,91 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+public class Main {
+
+ static final int ITERATIONS = 16;
+
+ // Test 1: This test checks whether the SuspendCheck is removed from the
+ // header.
+
+ /// CHECK-START-ARM64: void Main.$noinline$testRemoveSuspendCheck(int[]) disassembly (after)
+ /// CHECK: SuspendCheck loop:<<LoopId:B\d+>>
+ /// CHECK-NEXT: dex_pc:{{.*}}
+ /// CHECK: Goto loop:<<LoopId>>
+ /// CHECK-NEXT: b
+ /// CHECK-NOT: SuspendCheckSlowPathARM64
+
+ public static void $noinline$testRemoveSuspendCheck(int[] a) {
+ for (int i = 0; i < ITERATIONS; i++) {
+ a[i++] = i;
+ }
+ }
+
+ // Test 2: This test checks that the SuspendCheck is not removed from the
+ // header because it contains a call to another function.
+
+ /// CHECK-START-ARM64: void Main.testRemoveSuspendCheckWithCall(int[]) disassembly (after)
+ /// CHECK: SuspendCheck loop:<<LoopId:B\d+>>
+ /// CHECK: Goto loop:<<LoopId>>
+ /// CHECK-NEXT: ldr
+ /// CHECK: SuspendCheckSlowPathARM64
+ /// CHECK: SuspendCheckSlowPathARM64
+
+ public static void testRemoveSuspendCheckWithCall(int[] a) {
+ for (int i = 0; i < ITERATIONS; i++) {
+ a[i++] = i;
+ $noinline$testRemoveSuspendCheck(a);
+ }
+ }
+
+ // Test 3: This test checks that the SuspendCheck is not removed from the
+ // header because INSTR_COUNT * TRIP_COUNT exceeds the defined heuristic.
+
+ /// CHECK-START-ARM64: void Main.testRemoveSuspendCheckAboveHeuristic(int[]) disassembly (after)
+ /// CHECK: SuspendCheck loop:<<LoopId:B\d+>>
+ /// CHECK: Goto loop:<<LoopId>>
+ /// CHECK-NEXT: ldr
+ /// CHECK: SuspendCheckSlowPathARM64
+
+ public static void testRemoveSuspendCheckAboveHeuristic(int[] a) {
+ for (int i = 0; i < ITERATIONS * 6; i++) {
+ a[i++] = i;
+ }
+ }
+
+ // Test 4: This test checks that the SuspendCheck is not removed from the
+ // header because the trip count is not known at compile time.
+
+ /// CHECK-START-ARM64: void Main.testRemoveSuspendCheckUnknownCount(int[], int) disassembly (after)
+ /// CHECK: SuspendCheck loop:<<LoopId:B\d+>>
+ /// CHECK: Goto loop:<<LoopId>>
+ /// CHECK-NEXT: ldr
+ /// CHECK: SuspendCheckSlowPathARM64
+
+ public static void testRemoveSuspendCheckUnknownCount(int[] a, int n) {
+ for (int i = 0; i < n; i++) {
+ a[i++] = i;
+ }
+ }
+
+ public static void main(String[] args) {
+ int[] a = new int[100];
+ $noinline$testRemoveSuspendCheck(a);
+ testRemoveSuspendCheckWithCall(a);
+ testRemoveSuspendCheckAboveHeuristic(a);
+ testRemoveSuspendCheckUnknownCount(a, 4);
+ }
+}