Check that environments assigned via AssignEnvironment are actually used.

src/lithium-codegen.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
@@ skipping 104 matching lines @@
     instr->CompileToNative(codegen);
 
     GenerateBodyInstructionPost(instr);
   }
   EnsureSpaceForLazyDeopt(Deoptimizer::patch_size());
   last_lazy_deopt_pc_ = masm()->pc_offset();
   return !is_aborted();
 }
 
 
+void LCodeGenBase::CheckEnvironmentUsage() {
+#ifdef DEBUG
+  bool live_block = true;
+  for (int i = 0; i < instructions_->length(); i++) {
+    LInstruction* instr = instructions_->at(i);
+    if (instr->IsLabel()) live_block = !LLabel::cast(instr)->HasReplacement();
+    if (live_block &&
+        instr->hydrogen_value()->block()->IsReachable() &&
+        instr->HasEnvironment() &&
+        !instr->environment()->has_been_used()) {
+      FunctionLiteral* lit = info_->function();
+      V8_Fatal(__FILE__, __LINE__, "unused environment in %s <@%d,#%d> %s\n",
+               lit == NULL ? "<UNKNOWN>" : lit->name()->ToCString().get(),
+               i, instr->hydrogen_value()->id(), instr->Mnemonic());
+    }
+  }
+#endif
+}
+
+
 void LCodeGenBase::Comment(const char* format, ...) {
   if (!FLAG_code_comments) return;
   char buffer[4 * KB];
   StringBuilder builder(buffer, ARRAY_SIZE(buffer));
   va_list arguments;
   va_start(arguments, format);
   builder.AddFormattedList(format, arguments);
   va_end(arguments);
 
   // Copy the string before recording it in the assembler to avoid
@@ skipping 53 matching lines @@
   for (int i = 0; i < objects.length(); i++) {
     AddWeakObjectToCodeDependency(isolate()->heap(), objects.at(i), code);
   }
   for (int i = 0; i < cells.length(); i++) {
     AddWeakObjectToCodeDependency(isolate()->heap(), cells.at(i), code);
   }
 }
 
 
 } }  // namespace v8::internal