Turn UInt32 analysis into a proper HPhase.

src/hydrogen-uint32-analysis.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:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// 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
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "hydrogen-uint32-analysis.h"
+
+namespace v8 {
+namespace internal {
+
+
+bool HUint32AnalysisPhase::IsSafeUint32Use(HValue* val, HValue* use) {
+  // Operations that operate on bits are safe.
+  if (use->IsBitwise() ||
+      use->IsShl() ||
+      use->IsSar() ||
+      use->IsShr() ||
+      use->IsBitNot()) {
+    return true;
+  } else if (use->IsChange() || use->IsSimulate()) {
+    // Conversions and deoptimization have special support for unt32.
+    return true;
+  } else if (use->IsStoreKeyed()) {
+    HStoreKeyed* store = HStoreKeyed::cast(use);
+    if (store->is_external()) {
+      // Storing a value into an external integer array is a bit level
+      // operation.
+      if (store->value() == val) {
+        // Clamping or a conversion to double should have beed inserted.
+        ASSERT(store->elements_kind() != EXTERNAL_PIXEL_ELEMENTS);
+        ASSERT(store->elements_kind() != EXTERNAL_FLOAT_ELEMENTS);
+        ASSERT(store->elements_kind() != EXTERNAL_DOUBLE_ELEMENTS);
+        return true;
+      }
+    }
+  }
+
+  return false;
+}
+
+
+// Iterate over all uses and verify that they are uint32 safe: either don't
+// distinguish between int32 and uint32 due to their bitwise nature or
+// have special support for uint32 values.
+// Encountered phis are optimistically treated as safe uint32 uses,
+// marked with kUint32 flag and collected in the phis_ list. A separate
+// pass will be performed later by UnmarkUnsafePhis to clear kUint32 from
+// phis that are not actually uint32-safe (it requires fix point iteration).
+bool HUint32AnalysisPhase::Uint32UsesAreSafe(HValue* uint32val) {
+  bool collect_phi_uses = false;
+  for (HUseIterator it(uint32val->uses()); !it.Done(); it.Advance()) {
+    HValue* use = it.value();
+
+    if (use->IsPhi()) {
+      if (!use->CheckFlag(HInstruction::kUint32)) {
+        // There is a phi use of this value from a phi that is not yet
+        // collected in phis_ array. Separate pass is required.
+        collect_phi_uses = true;
+      }
+
+      // Optimistically treat phis as uint32 safe.
+      continue;
+    }
+
+    if (!IsSafeUint32Use(uint32val, use)) {
+      return false;
+    }
+  }
+
+  if (collect_phi_uses) {
+    for (HUseIterator it(uint32val->uses()); !it.Done(); it.Advance()) {
+      HValue* use = it.value();
+
+      // There is a phi use of this value from a phi that is not yet
+      // collected in phis_ array. Separate pass is required.
+      if (use->IsPhi() && !use->CheckFlag(HInstruction::kUint32)) {
+        use->SetFlag(HInstruction::kUint32);
+        phis_.Add(HPhi::cast(use), zone());
+      }
+    }
+  }
+
+  return true;
+}
+
+
+// Check if all operands to the given phi are marked with kUint32 flag.
+bool HUint32AnalysisPhase::CheckPhiOperands(HPhi* phi) {
+  if (!phi->CheckFlag(HInstruction::kUint32)) {
+    // This phi is not uint32 safe. No need to check operands.
+    return false;
+  }
+
+  for (int j = 0; j < phi->OperandCount(); j++) {
+    HValue* operand = phi->OperandAt(j);
+    if (!operand->CheckFlag(HInstruction::kUint32)) {
+      // Lazily mark constants that fit into uint32 range with kUint32 flag.
+      if (operand->IsInteger32Constant() &&
+          operand->GetInteger32Constant() >= 0) {
+        operand->SetFlag(HInstruction::kUint32);
+        continue;
+      }
+
+      // This phi is not safe, some operands are not uint32 values.
+      return false;
+    }
+  }
+
+  return true;
+}
+
+
+// Remove kUint32 flag from the phi itself and its operands. If any operand
+// was a phi marked with kUint32 place it into a worklist for
+// transitive clearing of kUint32 flag.
+void HUint32AnalysisPhase::UnmarkPhi(HPhi* phi, ZoneList<HPhi*>* worklist) {
+  phi->ClearFlag(HInstruction::kUint32);
+  for (int j = 0; j < phi->OperandCount(); j++) {
+    HValue* operand = phi->OperandAt(j);
+    if (operand->CheckFlag(HInstruction::kUint32)) {
+      operand->ClearFlag(HInstruction::kUint32);
+      if (operand->IsPhi()) {
+        worklist->Add(HPhi::cast(operand), zone());
+      }
+    }
+  }
+}
+
+
+void HUint32AnalysisPhase::UnmarkUnsafePhis() {
+  // No phis were collected. Nothing to do.
+  if (phis_.length() == 0) return;
+
+  // Worklist used to transitively clear kUint32 from phis that
+  // are used as arguments to other phis.
+  ZoneList<HPhi*> worklist(phis_.length(), zone());
+
+  // Phi can be used as a uint32 value if and only if
+  // all its operands are uint32 values and all its
+  // uses are uint32 safe.
+
+  // Iterate over collected phis and unmark those that
+  // are unsafe. When unmarking phi unmark its operands
+  // and add it to the worklist if it is a phi as well.
+  // Phis that are still marked as safe are shifted down
+  // so that all safe phis form a prefix of the phis_ array.
+  int phi_count = 0;
+  for (int i = 0; i < phis_.length(); i++) {
+    HPhi* phi = phis_[i];
+
+    if (CheckPhiOperands(phi) && Uint32UsesAreSafe(phi)) {
+      phis_[phi_count++] = phi;
+    } else {
+      UnmarkPhi(phi, &worklist);
+    }
+  }
+
+  // Now phis array contains only those phis that have safe
+  // non-phi uses. Start transitively clearing kUint32 flag
+  // from phi operands of discovered non-safe phis until
+  // only safe phis are left.
+  while (!worklist.is_empty())  {
+    while (!worklist.is_empty()) {
+      HPhi* phi = worklist.RemoveLast();
+      UnmarkPhi(phi, &worklist);
+    }
+
+    // Check if any operands to safe phis were unmarked
+    // turning a safe phi into unsafe. The same value
+    // can flow into several phis.
+    int new_phi_count = 0;
+    for (int i = 0; i < phi_count; i++) {
+      HPhi* phi = phis_[i];
+
+      if (CheckPhiOperands(phi)) {
+        phis_[new_phi_count++] = phi;
+      } else {
+        UnmarkPhi(phi, &worklist);
+      }
+    }
+    phi_count = new_phi_count;
+  }
+}
+
+
+void HUint32AnalysisPhase::Run() {
+  if (!graph()->has_uint32_instructions()) return;
+
+  ZoneList<HInstruction*>* uint32_instructions = graph()->uint32_instructions();
+  for (int i = 0; i < uint32_instructions->length(); ++i) {
+    // Analyze instruction and mark it with kUint32 if all
+    // its uses are uint32 safe.
+    HInstruction* current = uint32_instructions->at(i);
+    if (Uint32UsesAreSafe(current)) current->SetFlag(HInstruction::kUint32);
+  }
+
+  // Some phis might have been optimistically marked with kUint32 flag.
+  // Remove this flag from those phis that are unsafe and propagate
+  // this information transitively potentially clearing kUint32 flag
+  // from some non-phi operations that are used as operands to unsafe phis.
+  UnmarkUnsafePhis();
+}
+
+
+} }  // namespace v8::internal