Blocks that contain soft deopts have no side effects.

src/hydrogen.cc

 // Copyright 2012 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
@@ skipping 1396 matching lines @@
 
 void HGlobalValueNumberer::ComputeBlockSideEffects() {
   for (int i = graph_->blocks()->length() - 1; i >= 0; --i) {
     // Compute side effects for the block.
     HBasicBlock* block = graph_->blocks()->at(i);
     HInstruction* instr = block->first();
     int id = block->block_id();
     int side_effects = 0;
     while (instr != NULL) {
       side_effects |= instr->ChangesFlags();
+      if (instr->IsSoftDeoptimize()) {
+        block_side_effects_[id] = 0;
+        side_effects = 0;
+        break;
+      }
       instr = instr->next();
     }
     block_side_effects_[id] |= side_effects;
 
     // Loop headers are part of their loop.
     if (block->IsLoopHeader()) {
       loop_side_effects_[id] |= side_effects;
     }
 
     // Propagate loop side effects upwards.
@@ skipping 5957 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify(false);  // No full verify.
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal