Turn redundant phi elimination into proper HPhase.

src/hydrogen-redundant-phi.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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+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "hydrogen-redundant-phi.h"
+
+namespace v8 {
+namespace internal {
+
+void HRedundantPhiEliminationPhase::Run() {
+  // We do a simple fixed point iteration without any work list, because
+  // machine-generated JavaScript can lead to a very dense Hydrogen graph with
+  // an enormous work list and will consequently result in OOM. Experiments
+  // showed that this simple algorithm is good enough, and even e.g. tracking
+  // the set or range of blocks to consider is not a real improvement.
+  bool need_another_iteration;
+  const ZoneList<HBasicBlock*>* blocks(graph()->blocks());
+  ZoneList<HPhi*> redundant_phis(blocks->length(), zone());
+  do {
+    need_another_iteration = false;
+    for (int i = 0; i < blocks->length(); ++i) {
+      HBasicBlock* block = blocks->at(i);
+      for (int j = 0; j < block->phis()->length(); j++) {
+        HPhi* phi = block->phis()->at(j);
+        HValue* replacement = phi->GetRedundantReplacement();
+        if (replacement != NULL) {
+          // Remember phi to avoid concurrent modification of the block's phis.
+          redundant_phis.Add(phi, zone());
+          for (HUseIterator it(phi->uses()); !it.Done(); it.Advance()) {
+            HValue* value = it.value();
+            value->SetOperandAt(it.index(), replacement);
+            need_another_iteration |= value->IsPhi();
+          }
+        }
+      }
+      for (int i = 0; i < redundant_phis.length(); i++) {
+        block->RemovePhi(redundant_phis[i]);
+      }
+      redundant_phis.Clear();
+    }
+  } while (need_another_iteration);
+
+#if DEBUG
+  // Make sure that we *really* removed all redundant phis.
+  for (int i = 0; i < blocks->length(); ++i) {
+    for (int j = 0; j < blocks->at(i)->phis()->length(); j++) {
+      ASSERT(blocks->at(i)->phis()->at(j)->GetRedundantReplacement() == NULL);
+    }
+  }
+#endif
+}
+
+} }  // namespace v8::internal