[turbofan] Greedy: Unset hints at eviction.

BUG=

Review URL: https://codereview.chromium.org/1313023003

Cr-Commit-Position: refs/heads/master@{#30540}

src/compiler/greedy-allocator.cc

@@ -21,12 +21,19 @@ const float GreedyAllocator::kAllocatedRangeMultiplier = 10.0;
 
 namespace {
 
-
-void UpdateOperands(TopLevelLiveRange* range, RegisterAllocationData* data) {
+void UpdateOperands(LiveRange* range, RegisterAllocationData* data) {
   int reg_id = range->assigned_register();
   range->SetUseHints(reg_id);
-  if (range->is_phi()) {
-    data->GetPhiMapValueFor(range)->set_assigned_register(reg_id);
+  if (range->IsTopLevel() && range->TopLevel()->is_phi()) {
+    data->GetPhiMapValueFor(range->TopLevel())->set_assigned_register(reg_id);
+  }
+}
+
+
+void UnsetOperands(LiveRange* range, RegisterAllocationData* data) {
+  range->UnsetUseHints();
+  if (range->IsTopLevel() && range->TopLevel()->is_phi()) {
+    data->GetPhiMapValueFor(range->TopLevel())->UnsetAssignedRegister();
   }
 }
 
@@ -45,7 +52,6 @@ LiveRange* Split(LiveRange* range, RegisterAllocationData* data,
 
 // TODO(mtrofin): explain why splitting in gap START is always OK.
 LifetimePosition GetSplitPositionForInstruction(const LiveRange* range,
-                                                const InstructionSequence* code,
                                                 int instruction_index) {
   LifetimePosition ret = LifetimePosition::Invalid();
 
@@ -88,11 +94,11 @@ LifetimePosition GetLastResortSplitPosition(const LiveRange* range,
   for (UsePosition* pos = range->first_pos(); pos != nullptr;
        pos = pos->next()) {
     if (pos->type() != UsePositionType::kRequiresRegister) continue;
-    LifetimePosition before = GetSplitPositionForInstruction(
-        range, code, pos->pos().ToInstructionIndex());
+    LifetimePosition before =
+        GetSplitPositionForInstruction(range, pos->pos().ToInstructionIndex());
     if (before.IsValid()) return before;
     LifetimePosition after = GetSplitPositionForInstruction(
-        range, code, pos->pos().ToInstructionIndex() + 1);
+        range, pos->pos().ToInstructionIndex() + 1);
     if (after.IsValid()) return after;
   }
   return LifetimePosition::Invalid();
@@ -140,6 +146,7 @@ void GreedyAllocator::AssignRangeToRegister(int reg_id, LiveRange* range) {
   TRACE("Assigning %s to range %d%d.\n", RegisterName(reg_id),
         range->TopLevel()->vreg(), range->relative_id());
   range->set_assigned_register(reg_id);
+  UpdateOperands(range, data());
 }
 
 
@@ -189,24 +196,42 @@ void GreedyAllocator::TryAllocateLiveRange(LiveRange* range) {
         range->relative_id());
   int free_reg = -1;
   int evictable_reg = -1;
+  int hinted_reg = -1;
+
   EnsureValidRangeWeight(range);
   DCHECK(range->weight() != LiveRange::kInvalidWeight);
 
-  float smallest_weight = LiveRange::kMaxWeight;
-
-  // Seek either the first free register, or, from the set of registers
-  // where the maximum conflict is lower than the candidate's weight, the one
-  // with the smallest such weight.
-  for (int i = 0; i < num_registers(); i++) {
-    float max_conflict_weight = GetMaximumConflictingWeight(i, range);
+  // Can we allocate at the hinted register?
+  if (range->FirstHintPosition(&hinted_reg) != nullptr) {
+    DCHECK(hinted_reg >= 0);
+    float max_conflict_weight = GetMaximumConflictingWeight(hinted_reg, range);
     if (max_conflict_weight == LiveRange::kInvalidWeight) {
-      free_reg = i;
-      break;
+      free_reg = hinted_reg;
+    } else if (max_conflict_weight < range->weight()) {
+      evictable_reg = hinted_reg;
     }
-    if (max_conflict_weight < range->weight() &&
-        max_conflict_weight < smallest_weight) {
-      smallest_weight = max_conflict_weight;
-      evictable_reg = i;
+  }
+
+  if (free_reg < 0 && evictable_reg < 0) {
+    // There was no hinted reg, or we cannot allocate there.
+    float smallest_weight = LiveRange::kMaxWeight;
+
+    // Seek either the first free register, or, from the set of registers
+    // where the maximum conflict is lower than the candidate's weight, the one
+    // with the smallest such weight.
+    for (int i = 0; i < num_registers(); i++) {
+      // Skip unnecessarily re-visiting the hinted register, if any.
+      if (i == hinted_reg) continue;
+      float max_conflict_weight = GetMaximumConflictingWeight(i, range);
+      if (max_conflict_weight == LiveRange::kInvalidWeight) {
+        free_reg = i;
+        break;
+      }
+      if (max_conflict_weight < range->weight() &&
+          max_conflict_weight < smallest_weight) {
+        smallest_weight = max_conflict_weight;
+        evictable_reg = i;
+      }
     }
   }
 
@@ -243,6 +268,7 @@ void GreedyAllocator::EvictAndRescheduleConflicts(unsigned reg_id,
     DCHECK(conflict->HasRegisterAssigned());
     CHECK(!conflict->TopLevel()->IsFixed());
     conflict->UnsetAssignedRegister();
+    UnsetOperands(conflict, data());
     UpdateWeightAtEviction(conflict);
     scheduler().Schedule(conflict);
     TRACE("Evicted range %d%d.\n", conflict->TopLevel()->vreg(),
@@ -274,7 +300,7 @@ void GreedyAllocator::SplitAndSpillRangesDefinedByMemoryOperand() {
       // Do not spill live range eagerly if use position that can benefit from
       // the register is too close to the start of live range.
       auto split_pos = GetSplitPositionForInstruction(
-          range, data()->code(), pos->pos().ToInstructionIndex());
+          range, pos->pos().ToInstructionIndex());
       // There is no place to split, so we can't split and spill.
       if (!split_pos.IsValid()) continue;
 
@@ -304,15 +330,6 @@ void GreedyAllocator::AllocateRegisters() {
     TryAllocateCandidate(candidate);
   }
 
-
-  // We do not rely on the hint mechanism used by LinearScan, so no need to
-  // actively update/reset operands until the end.
-  for (auto range : data()->live_ranges()) {
-    if (CanProcessRange(range) && range->HasRegisterAssigned()) {
-      UpdateOperands(range, data());
-    }
-  }
-
   for (size_t i = 0; i < allocations_.size(); ++i) {
     if (!allocations_[i]->empty()) {
       data()->MarkAllocated(mode(), static_cast<int>(i));