Refactor HInferRepresentation into an HPhase and use the phase zone.

src/hydrogen-phases.cc

+// Copyright 2013 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
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+//     * Redistributions in binary form must reproduce the above
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+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "hydrogen-phases.h"
+
+namespace v8 {
+namespace internal {
+
+void HInferRepresentationPhase::AddToWorklist(HValue* current) {
+  if (current->representation().IsTagged()) return;
+  if (!current->CheckFlag(HValue::kFlexibleRepresentation)) return;
+  if (in_worklist_.Contains(current->id())) return;
+  worklist_.Add(current, zone());
+  in_worklist_.Add(current->id());
+}
+
+
+void HInferRepresentationPhase::Run() {
+  // (1) Initialize bit vectors and count real uses. Each phi gets a
+  // bit-vector of length <number of phis>.
+  const ZoneList<HPhi*>* phi_list = graph()->phi_list();
+  int phi_count = phi_list->length();
+  ZoneList<BitVector*> connected_phis(phi_count, zone());
+  for (int i = 0; i < phi_count; ++i) {
+    phi_list->at(i)->InitRealUses(i);
+    BitVector* connected_set = new(zone()) BitVector(phi_count, zone());
+    connected_set->Add(i);
+    connected_phis.Add(connected_set, zone());
+  }
+
+  // (2) Do a fixed point iteration to find the set of connected phis.  A
+  // phi is connected to another phi if its value is used either directly or
+  // indirectly through a transitive closure of the def-use relation.
+  bool change = true;
+  while (change) {
+    change = false;
+    // We normally have far more "forward edges" than "backward edges",
+    // so we terminate faster when we walk backwards.
+    for (int i = phi_count - 1; i >= 0; --i) {
+      HPhi* phi = phi_list->at(i);
+      for (HUseIterator it(phi->uses()); !it.Done(); it.Advance()) {
+        HValue* use = it.value();
+        if (use->IsPhi()) {
+          int id = HPhi::cast(use)->phi_id();
+          if (connected_phis[i]->UnionIsChanged(*connected_phis[id]))
+            change = true;
+        }
+      }
+    }
+  }
+
+  // Set truncation flags for groups of connected phis. This is a conservative
+  // approximation; the flag will be properly re-computed after representations
+  // have been determined.
+  if (phi_count > 0) {
+    BitVector done(phi_count, zone());
+    for (int i = 0; i < phi_count; ++i) {
+      if (done.Contains(i)) continue;
+
+      // Check if all uses of all connected phis in this group are truncating.
+      bool all_uses_everywhere_truncating = true;
+      for (BitVector::Iterator it(connected_phis[i]);
+           !it.Done();
+           it.Advance()) {
+        int index = it.Current();
+        all_uses_everywhere_truncating &=
+            phi_list->at(index)->CheckFlag(HInstruction::kTruncatingToInt32);
+        done.Add(index);
+      }
+      if (all_uses_everywhere_truncating) {
+        continue;  // Great, nothing to do.
+      }
+      // Clear truncation flag of this group of connected phis.
+      for (BitVector::Iterator it(connected_phis[i]);
+           !it.Done();
+           it.Advance()) {
+        int index = it.Current();
+        phi_list->at(index)->ClearFlag(HInstruction::kTruncatingToInt32);
+      }
+    }
+  }
+
+  // Simplify constant phi inputs where possible.
+  // This step uses kTruncatingToInt32 flags of phis.
+  for (int i = 0; i < phi_count; ++i) {
+    phi_list->at(i)->SimplifyConstantInputs();
+  }
+
+  // Use the phi reachability information from step 2 to
+  // sum up the non-phi use counts of all connected phis.
+  for (int i = 0; i < phi_count; ++i) {
+    HPhi* phi = phi_list->at(i);
+    for (BitVector::Iterator it(connected_phis[i]);
+         !it.Done();
+         it.Advance()) {
+      int index = it.Current();
+      HPhi* it_use = phi_list->at(index);
+      if (index != i) phi->AddNonPhiUsesFrom(it_use);  // Don't count twice.
+    }
+  }
+
+  // Initialize work list
+  for (int i = 0; i < graph()->blocks()->length(); ++i) {
+    HBasicBlock* block = graph()->blocks()->at(i);
+    const ZoneList<HPhi*>* phis = block->phis();
+    for (int j = 0; j < phis->length(); ++j) {
+      AddToWorklist(phis->at(j));
+    }
+
+    HInstruction* current = block->first();
+    while (current != NULL) {
+      AddToWorklist(current);
+      current = current->next();
+    }
+  }
+
+  // Do a fixed point iteration, trying to improve representations
+  while (!worklist_.is_empty()) {
+    HValue* current = worklist_.RemoveLast();
+    in_worklist_.Remove(current->id());
+    current->InferRepresentation(this);
+  }
+
+  // Lastly: any instruction that we don't have representation information
+  // for defaults to Tagged.
+  for (int i = 0; i < graph()->blocks()->length(); ++i) {
+    HBasicBlock* block = graph()->blocks()->at(i);
+    const ZoneList<HPhi*>* phis = block->phis();
+    for (int j = 0; j < phis->length(); ++j) {
+      HPhi* phi = phis->at(j);
+      if (phi->representation().IsNone()) {
+        phi->ChangeRepresentation(Representation::Tagged());
+      }
+    }
+    for (HInstruction* current = block->first();
+         current != NULL; current = current->next()) {
+      if (current->representation().IsNone() &&
+          current->CheckFlag(HInstruction::kFlexibleRepresentation)) {
+        if (current->CheckFlag(HInstruction::kCannotBeTagged)) {
+          current->ChangeRepresentation(Representation::Double());
+        } else {
+          current->ChangeRepresentation(Representation::Tagged());
+        }
+      }
+    }
+  }
+}
+
+} }  // namespace v8::internal