Turn propagate deoptimizing mark into a proper HPhase.

src/hydrogen-deoptimizing-mark.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
+//       copyright notice, this list of conditions and the following
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+//       with the distribution.
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+//       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
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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-deoptimizing-mark.h"
+
+namespace v8 {
+namespace internal {
+
+void HPropagateDeoptimizingMarkPhase::MarkAsDeoptimizing() {
+  HBasicBlock* block = graph()->entry_block();
+  ZoneList<HBasicBlock*> stack(graph()->blocks()->length(), zone());
+  for (;;) {

[Dmitry Lomov (no reviews), 2013/07/15 09:14:27]

Can we make the terminating condition for this loop more clear? block here is
"inlined" top of the stack, so how about having 'block != NULL' as a loop guard?

[Benedikt Meurer, 2013/07/15 09:22:53]

Done.

+    const ZoneList<HBasicBlock*>* dominated_blocks(block->dominated_blocks());
+    if (!dominated_blocks->is_empty()) {
+      if (block->IsDeoptimizing()) {
+        for (int i = 0; i < dominated_blocks->length(); ++i) {
+          dominated_blocks->at(i)->MarkAsDeoptimizing();
+        }
+      }
+      for (int i = dominated_blocks->length(); --i > 0; ) {
+        stack.Add(dominated_blocks->at(i), zone());
+      }
+      block = dominated_blocks->at(0);
+    } else if (stack.is_empty()) {
+      break;
+    } else {
+      block = stack.RemoveLast();
+    }
+  }
+}
+
+
+void HPropagateDeoptimizingMarkPhase::NullifyUnreachableInstructions() {
+  if (!FLAG_unreachable_code_elimination) return;
+  for (int i = 0; i < graph()->blocks()->length(); ++i) {
+    HBasicBlock* block = graph()->blocks()->at(i);
+    bool nullify = false;
+    const ZoneList<HBasicBlock*>* predecessors = block->predecessors();
+    int predecessors_length = predecessors->length();
+    bool all_predecessors_deoptimizing = (predecessors_length > 0);
+    for (int j = 0; j < predecessors_length; ++j) {
+      if (!predecessors->at(j)->IsDeoptimizing()) {
+        all_predecessors_deoptimizing = false;
+        break;
+      }
+    }
+    if (all_predecessors_deoptimizing) nullify = true;
+    for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
+      HInstruction* instr = it.Current();
+      // Leave the basic structure of the graph intact.
+      if (instr->IsBlockEntry()) continue;
+      if (instr->IsControlInstruction()) continue;
+      if (instr->IsSimulate()) continue;
+      if (instr->IsEnterInlined()) continue;
+      if (instr->IsLeaveInlined()) continue;
+      if (nullify) {
+        HInstruction* last_dummy = NULL;
+        for (int j = 0; j < instr->OperandCount(); ++j) {
+          HValue* operand = instr->OperandAt(j);
+          // Insert an HDummyUse for each operand, unless the operand
+          // is an HDummyUse itself. If it's even from the same block,
+          // remember it as a potential replacement for the instruction.
+          if (operand->IsDummyUse()) {
+            if (operand->block() == instr->block() &&
+                last_dummy == NULL) {
+              last_dummy = HInstruction::cast(operand);
+            }
+            continue;
+          }
+          if (operand->IsControlInstruction()) {
+            // Inserting a dummy use for a value that's not defined anywhere
+            // will fail. Some instructions define fake inputs on such
+            // values as control flow dependencies.
+            continue;
+          }
+          HDummyUse* dummy = new(graph()->zone()) HDummyUse(operand);
+          dummy->InsertBefore(instr);
+          last_dummy = dummy;
+        }
+        if (last_dummy == NULL) last_dummy = graph()->GetConstant1();
+        instr->DeleteAndReplaceWith(last_dummy);
+        continue;
+      }
+      if (instr->IsSoftDeoptimize()) {
+        ASSERT(block->IsDeoptimizing());
+        nullify = true;
+      }
+    }
+  }
+}
+
+
+void HPropagateDeoptimizingMarkPhase::Run() {
+  // Skip this phase if there is nothing to be done anyway.
+  if (!graph()->has_soft_deoptimize()) return;
+  MarkAsDeoptimizing();
+  NullifyUnreachableInstructions();
+}
+
+} }  // namespace v8::internal