Reviewers: jarin,
Message:
PTAL
Description:
[turbofan] Don't introduce additional computation when hoisting out of
loops.
Please review this at https://codereview.chromium.org/958533002/
Base URL: https://chromium.googlesource.com/v8/v8.git@master
Affected files (+30, -14 lines):
M src/compiler/scheduler.cc
M test/unittests/compiler/scheduler-unittest.cc
Index: src/compiler/scheduler.cc
diff --git a/src/compiler/scheduler.cc b/src/compiler/scheduler.cc
index
674b89ef66762d0b5ffa5c5b052e094d3ac0d290..3e7d353cb7bf8e675b177b10f79079a71d09d536
100644
--- a/src/compiler/scheduler.cc
+++ b/src/compiler/scheduler.cc
@@ -587,7 +587,8 @@ class SpecialRPONumberer : public ZoneObject {
loops_(zone),
backedges_(zone),
stack_(zone),
- previous_block_count_(0) {}
+ previous_block_count_(0),
+ empty_(0, zone) {}
// Computes the special reverse-post-order for the main control flow
graph,
// that is for the graph spanned between the schedule's start and end
blocks.
@@ -624,6 +625,14 @@ class SpecialRPONumberer : public ZoneObject {
#endif
}
+ const ZoneList<BasicBlock*>& GetOutgoingBlocks(BasicBlock* block) {
+ if (HasLoopNumber(block)) {
+ LoopInfo const& loop = loops_[GetLoopNumber(block)];
+ if (loop.outgoing) return *loop.outgoing;
+ }
+ return empty_;
+ }
+
private:
typedef std::pair<BasicBlock*, size_t> Backedge;
@@ -1046,6 +1055,7 @@ class SpecialRPONumberer : public ZoneObject {
ZoneVector<Backedge> backedges_;
ZoneVector<SpecialRPOStackFrame> stack_;
size_t previous_block_count_;
+ ZoneList<BasicBlock*> const empty_;
};
@@ -1346,7 +1356,7 @@ class ScheduleLateNodeVisitor {
// Hoist nodes out of loops if possible. Nodes can be hoisted
iteratively
// into enclosing loop pre-headers until they would preceed their
schedule
// early position.
- BasicBlock* hoist_block = GetPreHeader(block);
+ BasicBlock* hoist_block = GetHoistBlock(block);
if (hoist_block &&
hoist_block->dominator_depth() >= min_block->dominator_depth()) {
do {
@@ -1354,7 +1364,7 @@ class ScheduleLateNodeVisitor {
node->op()->mnemonic(), hoist_block->id().ToInt());
DCHECK_LT(hoist_block->loop_depth(), block->loop_depth());
block = hoist_block;
- hoist_block = GetPreHeader(hoist_block);
+ hoist_block = GetHoistBlock(hoist_block);
} while (hoist_block &&
hoist_block->dominator_depth() >=
min_block->dominator_depth());
} else if (scheduler_->flags_ & Scheduler::kSplitNodes) {
@@ -1465,14 +1475,23 @@ class ScheduleLateNodeVisitor {
return block;
}
- BasicBlock* GetPreHeader(BasicBlock* block) {
- if (block->IsLoopHeader()) {
- return block->dominator();
- } else if (block->loop_header() != NULL) {
- return block->loop_header()->dominator();
- } else {
- return NULL;
+ BasicBlock* GetHoistBlock(BasicBlock* block) {
+ if (block->IsLoopHeader()) return block->dominator();
+ // We have to check to make sure that the {block} dominates all
+ // of the outgoing blocks. If it doesn't, then there is a path
+ // out of the loop which does not execute this {block}, so we
+ // can't hoist operations from this {block} out of the loop, as
+ // that would introduce additional computations.
+ if (BasicBlock* header_block = block->loop_header()) {
+ for (BasicBlock* outgoing_block :
+ scheduler_->special_rpo_->GetOutgoingBlocks(header_block)) {
+ if (BasicBlock::GetCommonDominator(block, outgoing_block) !=
block) {
+ return nullptr;
+ }
+ }
+ return header_block->dominator();
}
+ return nullptr;
}
BasicBlock* GetCommonDominatorOfUses(Node* node) {
Index: test/unittests/compiler/scheduler-unittest.cc
diff --git a/test/unittests/compiler/scheduler-unittest.cc
b/test/unittests/compiler/scheduler-unittest.cc
index
afca98ca9b1fb109d0502886eeefea5dad168838..9ff6a63998b8eaa423cfe75c4879376b21baf757
100644
--- a/test/unittests/compiler/scheduler-unittest.cc
+++ b/test/unittests/compiler/scheduler-unittest.cc
@@ -1579,10 +1579,7 @@ TEST_F(SchedulerTest,
BuildScheduleSimpleLoopWithCodeMotion) {
graph()->SetStart(n0);
graph()->SetEnd(n22);
- Schedule* schedule = ComputeAndVerifySchedule(19);
- // Make sure the integer-only add gets hoisted to a different block that
the
- // JSAdd.
- EXPECT_NE(schedule->block(n19), schedule->block(n20));
+ ComputeAndVerifySchedule(19);
}
--
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