Refactor compute minus zero checks into a proper HPhase.

src/hydrogen-minus-zero.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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+//       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-minus-zero.h"
+
+namespace v8 {
+namespace internal {
+
+void HComputeMinusZeroChecksPhase::Run() {
+  const ZoneList<HBasicBlock*>* blocks(graph()->blocks());
+  for (int i = 0; i < blocks->length(); ++i) {
+    for (HInstructionIterator it(blocks->at(i)); !it.Done(); it.Advance()) {
+      HInstruction* current = it.Current();
+      if (current->IsChange()) {
+        HChange* change = HChange::cast(current);
+        // Propagate flags for negative zero checks upwards from conversions
+        // int32-to-tagged and int32-to-double.
+        Representation from = change->value()->representation();
+        ASSERT(from.Equals(change->from()));
+        if (from.IsInteger32()) {
+          ASSERT(change->to().IsTagged() ||
+                 change->to().IsDouble() ||
+                 change->to().IsSmi());
+          ASSERT(visited_.IsEmpty());
+          PropagateMinusZeroChecks(change->value());
+          visited_.Clear();
+        }
+      }
+    }
+  }
+}
+
+
+void HComputeMinusZeroChecksPhase::PropagateMinusZeroChecks(HValue* value) {
+  for (HValue* current = value;
+       current != NULL && !visited_.Contains(current->id());
+       current = current->EnsureAndPropagateNotMinusZero(&visited_)) {
+    // For phis, we must propagate the check to all of its inputs.
+    if (current->IsPhi()) {
+      visited_.Add(current->id());
+      HPhi* phi = HPhi::cast(current);
+      for (int i = 0; i < phi->OperandCount(); ++i) {
+        PropagateMinusZeroChecks(phi->OperandAt(i));
+      }
+      break;
+    }
+
+    // For multiplication, division, and Math.min/max(), we must propagate
+    // to the left and the right side.
+    if (current->IsMul() || current->IsDiv() || current->IsMathMinMax()) {
+      HBinaryOperation* operation = HBinaryOperation::cast(current);
+      operation->EnsureAndPropagateNotMinusZero(&visited_);
+      PropagateMinusZeroChecks(operation->left());
+      PropagateMinusZeroChecks(operation->right());
+    }
+  }
+}
+
+} }  // namespace v8::internal