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v8/test/unittests/compiler/bytecode-analysis-unittest.cc
Leszek Swirski 1a3027303b [turbofan] Never generate loop exit phis for the accumulator 
The accumulator should never be alive when jumping back to a loop
header, or jumping out of a loop. This means that as far as far as
TurboFan is concerned, we never need to create Phis or LoopExitValues
for the accumulator, as its value should not escape the loop.

For safety, this also augments the IsLivenessValid DCHECK in the
liveness analysis to check that the accumulator is not live in these
cases, and amends the bytecode analysis tests to kill the accumulator
where necessary to ensure this.

As a drive-by, added some comments to the more complex bytecode analysis
tests, since figuring out what they were for and how to fix them took a
non-trivial amount of time.

Change-Id: Idecf76a36681d724134c59768650c23cc6b0e9ef
Reviewed-on: https://chromium-review.googlesource.com/615168
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47388}
2017-08-17 05:09:31 +00:00

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// Copyright 2015 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "src/v8.h"
#include "src/compiler/bytecode-analysis.h"
#include "src/interpreter/bytecode-array-builder.h"
#include "src/interpreter/bytecode-array-iterator.h"
#include "src/interpreter/bytecode-decoder.h"
#include "src/interpreter/bytecode-label.h"
#include "src/interpreter/control-flow-builders.h"
#include "src/objects-inl.h"
#include "test/unittests/test-utils.h"
namespace v8 {
namespace internal {
namespace compiler {
using ToBooleanMode = interpreter::BytecodeArrayBuilder::ToBooleanMode;
class BytecodeAnalysisTest : public TestWithIsolateAndZone {
public:
BytecodeAnalysisTest() {}
~BytecodeAnalysisTest() override {}
static void SetUpTestCase() {
CHECK_NULL(save_flags_);
save_flags_ = new SaveFlags();
i::FLAG_ignition_elide_noneffectful_bytecodes = false;
i::FLAG_ignition_reo = false;
TestWithIsolateAndZone::SetUpTestCase();
}
static void TearDownTestCase() {
TestWithIsolateAndZone::TearDownTestCase();
delete save_flags_;
save_flags_ = nullptr;
}
std::string ToLivenessString(const BytecodeLivenessState* liveness) const {
const BitVector& bit_vector = liveness->bit_vector();
std::string out;
out.resize(bit_vector.length());
for (int i = 0; i < bit_vector.length(); ++i) {
if (bit_vector.Contains(i)) {
out[i] = 'L';
} else {
out[i] = '.';
}
}
return out;
}
void EnsureLivenessMatches(
Handle<BytecodeArray> bytecode,
const std::vector<std::pair<std::string, std::string>>&
expected_liveness) {
BytecodeAnalysis analysis(bytecode, zone(), true);
analysis.Analyze(BailoutId::None());
interpreter::BytecodeArrayIterator iterator(bytecode);
for (auto liveness : expected_liveness) {
std::stringstream ss;
ss << std::setw(4) << iterator.current_offset() << " : ";
iterator.PrintTo(ss);
EXPECT_EQ(liveness.first, ToLivenessString(analysis.GetInLivenessFor(
iterator.current_offset())))
<< " at bytecode " << ss.str();
EXPECT_EQ(liveness.second, ToLivenessString(analysis.GetOutLivenessFor(
iterator.current_offset())))
<< " at bytecode " << ss.str();
iterator.Advance();
}
EXPECT_TRUE(iterator.done());
}
private:
static SaveFlags* save_flags_;
DISALLOW_COPY_AND_ASSIGN(BytecodeAnalysisTest);
};
SaveFlags* BytecodeAnalysisTest::save_flags_ = nullptr;
TEST_F(BytecodeAnalysisTest, EmptyBlock) {
interpreter::BytecodeArrayBuilder builder(isolate(), zone(), 3, 3);
std::vector<std::pair<std::string, std::string>> expected_liveness;
interpreter::Register reg_0(0);
builder.Return();
expected_liveness.emplace_back("...L", "....");
Handle<BytecodeArray> bytecode = builder.ToBytecodeArray(isolate());
EnsureLivenessMatches(bytecode, expected_liveness);
}
TEST_F(BytecodeAnalysisTest, SimpleLoad) {
interpreter::BytecodeArrayBuilder builder(isolate(), zone(), 3, 3);
std::vector<std::pair<std::string, std::string>> expected_liveness;
interpreter::Register reg_0(0);
builder.LoadAccumulatorWithRegister(reg_0);
expected_liveness.emplace_back("L...", "...L");
builder.Return();
expected_liveness.emplace_back("...L", "....");
Handle<BytecodeArray> bytecode = builder.ToBytecodeArray(isolate());
EnsureLivenessMatches(bytecode, expected_liveness);
}
TEST_F(BytecodeAnalysisTest, StoreThenLoad) {
interpreter::BytecodeArrayBuilder builder(isolate(), zone(), 3, 3);
std::vector<std::pair<std::string, std::string>> expected_liveness;
interpreter::Register reg_0(0);
builder.StoreAccumulatorInRegister(reg_0);
expected_liveness.emplace_back("...L", "L...");
builder.LoadAccumulatorWithRegister(reg_0);
expected_liveness.emplace_back("L...", "...L");
builder.Return();
expected_liveness.emplace_back("...L", "....");
Handle<BytecodeArray> bytecode = builder.ToBytecodeArray(isolate());
EnsureLivenessMatches(bytecode, expected_liveness);
}
TEST_F(BytecodeAnalysisTest, DiamondLoad) {
interpreter::BytecodeArrayBuilder builder(isolate(), zone(), 3, 3);
std::vector<std::pair<std::string, std::string>> expected_liveness;
interpreter::Register reg_0(0);
interpreter::Register reg_1(1);
interpreter::Register reg_2(2);
interpreter::BytecodeLabel ld1_label;
interpreter::BytecodeLabel end_label;
builder.JumpIfTrue(ToBooleanMode::kConvertToBoolean, &ld1_label);
expected_liveness.emplace_back("LLLL", "LLL.");
builder.LoadAccumulatorWithRegister(reg_0);
expected_liveness.emplace_back("L.L.", "..L.");
builder.Jump(&end_label);
expected_liveness.emplace_back("..L.", "..L.");
builder.Bind(&ld1_label);
builder.LoadAccumulatorWithRegister(reg_1);
expected_liveness.emplace_back(".LL.", "..L.");
builder.Bind(&end_label);
builder.LoadAccumulatorWithRegister(reg_2);
expected_liveness.emplace_back("..L.", "...L");
builder.Return();
expected_liveness.emplace_back("...L", "....");
Handle<BytecodeArray> bytecode = builder.ToBytecodeArray(isolate());
EnsureLivenessMatches(bytecode, expected_liveness);
}
TEST_F(BytecodeAnalysisTest, DiamondLookupsAndBinds) {
interpreter::BytecodeArrayBuilder builder(isolate(), zone(), 3, 3);
std::vector<std::pair<std::string, std::string>> expected_liveness;
interpreter::Register reg_0(0);
interpreter::Register reg_1(1);
interpreter::Register reg_2(2);
interpreter::BytecodeLabel ld1_label;
interpreter::BytecodeLabel end_label;
builder.StoreAccumulatorInRegister(reg_0);
expected_liveness.emplace_back(".LLL", "LLLL");
builder.JumpIfTrue(ToBooleanMode::kConvertToBoolean, &ld1_label);
expected_liveness.emplace_back("LLLL", "LLL.");
{
builder.LoadAccumulatorWithRegister(reg_0);
expected_liveness.emplace_back("L...", "...L");
builder.StoreAccumulatorInRegister(reg_2);
expected_liveness.emplace_back("...L", "..L.");
builder.Jump(&end_label);
expected_liveness.emplace_back("..L.", "..L.");
}
builder.Bind(&ld1_label);
{
builder.LoadAccumulatorWithRegister(reg_1);
expected_liveness.emplace_back(".LL.", "..L.");
}
builder.Bind(&end_label);
builder.LoadAccumulatorWithRegister(reg_2);
expected_liveness.emplace_back("..L.", "...L");
builder.Return();
expected_liveness.emplace_back("...L", "....");
Handle<BytecodeArray> bytecode = builder.ToBytecodeArray(isolate());
EnsureLivenessMatches(bytecode, expected_liveness);
}
TEST_F(BytecodeAnalysisTest, SimpleLoop) {
interpreter::BytecodeArrayBuilder builder(isolate(), zone(), 3, 3);
std::vector<std::pair<std::string, std::string>> expected_liveness;
interpreter::Register reg_0(0);
interpreter::Register reg_1(1);
interpreter::Register reg_2(2);
// Kill r0.
builder.StoreAccumulatorInRegister(reg_0);
expected_liveness.emplace_back("..LL", "L.L.");
{
interpreter::LoopBuilder loop_builder(&builder, nullptr, nullptr);
loop_builder.LoopHeader();
builder.LoadUndefined();
expected_liveness.emplace_back("L.L.", "L.LL");
builder.JumpIfTrue(ToBooleanMode::kConvertToBoolean,
loop_builder.break_labels()->New());
expected_liveness.emplace_back("L.LL", "L.L.");
// Gen r0.
builder.LoadAccumulatorWithRegister(reg_0);
expected_liveness.emplace_back("L...", "L..L");
// Kill r2.
builder.StoreAccumulatorInRegister(reg_2);
expected_liveness.emplace_back("L..L", "L.L.");
loop_builder.BindContinueTarget();
loop_builder.JumpToHeader(0);
expected_liveness.emplace_back("L.L.", "L.L.");
}
// Gen r2.
builder.LoadAccumulatorWithRegister(reg_2);
expected_liveness.emplace_back("..L.", "...L");
builder.Return();
expected_liveness.emplace_back("...L", "....");
Handle<BytecodeArray> bytecode = builder.ToBytecodeArray(isolate());
EnsureLivenessMatches(bytecode, expected_liveness);
}
TEST_F(BytecodeAnalysisTest, TryCatch) {
interpreter::BytecodeArrayBuilder builder(isolate(), zone(), 3, 3);
std::vector<std::pair<std::string, std::string>> expected_liveness;
interpreter::Register reg_0(0);
interpreter::Register reg_1(1);
interpreter::Register reg_context(2);
// Kill r0.
builder.StoreAccumulatorInRegister(reg_0);
expected_liveness.emplace_back(".LLL", "LLL.");
interpreter::TryCatchBuilder try_builder(&builder, HandlerTable::CAUGHT);
try_builder.BeginTry(reg_context);
{
// Gen r0.
builder.LoadAccumulatorWithRegister(reg_0);
expected_liveness.emplace_back("LLL.", ".LLL");
// Kill r0.
builder.StoreAccumulatorInRegister(reg_0);
expected_liveness.emplace_back(".LLL", ".LL.");
builder.CallRuntime(Runtime::kThrow);
expected_liveness.emplace_back(".LL.", ".LLL");
builder.StoreAccumulatorInRegister(reg_0);
// Star can't throw, so doesn't take handler liveness
expected_liveness.emplace_back("...L", "...L");
}
try_builder.EndTry();
expected_liveness.emplace_back("...L", "...L");
// Catch
{
builder.LoadAccumulatorWithRegister(reg_1);
expected_liveness.emplace_back(".L..", "...L");
}
try_builder.EndCatch();
builder.Return();
expected_liveness.emplace_back("...L", "....");
Handle<BytecodeArray> bytecode = builder.ToBytecodeArray(isolate());
EnsureLivenessMatches(bytecode, expected_liveness);
}
TEST_F(BytecodeAnalysisTest, DiamondInLoop) {
// For a logic diamond inside a loop, the liveness down one path of the
// diamond should eventually propagate up the other path when the loop is
// reprocessed.
interpreter::BytecodeArrayBuilder builder(isolate(), zone(), 3, 3);
std::vector<std::pair<std::string, std::string>> expected_liveness;
interpreter::Register reg_0(0);
{
interpreter::LoopBuilder loop_builder(&builder, nullptr, nullptr);
loop_builder.LoopHeader();
builder.LoadUndefined();
expected_liveness.emplace_back("L...", "L..L");
builder.JumpIfTrue(ToBooleanMode::kConvertToBoolean,
loop_builder.break_labels()->New());
expected_liveness.emplace_back("L..L", "L..L");
interpreter::BytecodeLabel ld1_label;
interpreter::BytecodeLabel end_label;
builder.JumpIfTrue(ToBooleanMode::kConvertToBoolean, &ld1_label);
expected_liveness.emplace_back("L..L", "L...");
{
builder.Jump(&end_label);
expected_liveness.emplace_back("L...", "L...");
}
builder.Bind(&ld1_label);
{
// Gen r0.
builder.LoadAccumulatorWithRegister(reg_0);
expected_liveness.emplace_back("L...", "L...");
}
builder.Bind(&end_label);
loop_builder.BindContinueTarget();
loop_builder.JumpToHeader(0);
expected_liveness.emplace_back("L...", "L...");
}
builder.LoadUndefined();
expected_liveness.emplace_back("....", "...L");
builder.Return();
expected_liveness.emplace_back("...L", "....");
Handle<BytecodeArray> bytecode = builder.ToBytecodeArray(isolate());
EnsureLivenessMatches(bytecode, expected_liveness);
}
TEST_F(BytecodeAnalysisTest, KillingLoopInsideLoop) {
// For a loop inside a loop, the inner loop has to be processed after the
// outer loop has been processed, to ensure that it can propagate the
// information in its header. Consider
//
// 0: do {
// 1: acc = r0;
// 2: acc = r1;
// 3: do {
// 4: r0 = acc;
// 5: break;
// 6: } while(true);
// 7: } while(true);
//
// r0 should should be dead at 3 and 6, while r1 is live throughout. On the
// initial pass, r1 is dead from 3-7. On the outer loop pass, it becomes live
// in 3 and 7 (but not 4-6 because 6 only reads liveness from 3). Only after
// the inner loop pass does it become live in 4-6. It's necessary, however, to
// still process the inner loop when processing the outer loop, to ensure that
// r1 becomes live in 3 (via 5), but r0 stays dead (because of 4).
interpreter::BytecodeArrayBuilder builder(isolate(), zone(), 3, 3);
std::vector<std::pair<std::string, std::string>> expected_liveness;
interpreter::Register reg_0(0);
interpreter::Register reg_1(1);
{
interpreter::LoopBuilder loop_builder(&builder, nullptr, nullptr);
loop_builder.LoopHeader();
// Gen r0.
builder.LoadAccumulatorWithRegister(reg_0);
expected_liveness.emplace_back("LL..", ".L..");
// Gen r1.
builder.LoadAccumulatorWithRegister(reg_1);
expected_liveness.emplace_back(".L..", ".L.L");
builder.JumpIfTrue(ToBooleanMode::kConvertToBoolean,
loop_builder.break_labels()->New());
expected_liveness.emplace_back(".L.L", ".L..");
{
interpreter::LoopBuilder inner_loop_builder(&builder, nullptr, nullptr);
inner_loop_builder.LoopHeader();
// Kill r0.
builder.LoadUndefined();
expected_liveness.emplace_back(".L..", ".L.L");
builder.StoreAccumulatorInRegister(reg_0);
expected_liveness.emplace_back(".L.L", "LL.L");
builder.JumpIfTrue(ToBooleanMode::kConvertToBoolean,
inner_loop_builder.break_labels()->New());
expected_liveness.emplace_back("LL.L", "LL..");
inner_loop_builder.BindContinueTarget();
inner_loop_builder.JumpToHeader(1);
expected_liveness.emplace_back(".L..", ".L..");
}
loop_builder.BindContinueTarget();
loop_builder.JumpToHeader(0);
expected_liveness.emplace_back("LL..", "LL..");
}
builder.LoadUndefined();
expected_liveness.emplace_back("....", "...L");
builder.Return();
expected_liveness.emplace_back("...L", "....");
Handle<BytecodeArray> bytecode = builder.ToBytecodeArray(isolate());
EnsureLivenessMatches(bytecode, expected_liveness);
}
} // namespace compiler
} // namespace internal
} // namespace v8
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