Improve and simplify removal of unreachable code

src/x64/lithium-codegen-x64.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 253 matching lines @@
        !is_aborted() && current_instruction_ < instructions_->length();
        current_instruction_++) {
     LInstruction* instr = instructions_->at(current_instruction_);
 
     // Don't emit code for basic blocks with a replacement.
     if (instr->IsLabel()) {
       emit_instructions = !LLabel::cast(instr)->HasReplacement();
     }
     if (!emit_instructions) continue;
 
-    if (FLAG_code_comments && instr->HasInterestingComment(this)) {
-      Comment(";;; <@%d,#%d> %s",
-              current_instruction_,
-              instr->hydrogen_value()->id(),
-              instr->Mnemonic());
+    if (instr->hydrogen_value()->block()->IsReachable()) {
+      if (FLAG_code_comments && instr->HasInterestingComment(this)) {
+        Comment(";;; <@%d,#%d> %s",
+                current_instruction_,
+                instr->hydrogen_value()->id(),
+                instr->Mnemonic());
+      }
+
+      RecordAndUpdatePosition(instr->position());
+
+      instr->CompileToNative(this);
+    } else {
+      if (FLAG_code_comments && instr->IsLabel()) {
+        Comment(
+            ";;; <@%d,#%d> -------------------- B%d (unreachable/elided) "
+            "--------------------",
+            current_instruction_,
+            instr->hydrogen_value()->id(),
+            instr->hydrogen_value()->block()->block_id());
+      }
     }
-
-    RecordAndUpdatePosition(instr->position());
-
-    instr->CompileToNative(this);
   }
   EnsureSpaceForLazyDeopt(Deoptimizer::patch_size());
   return !is_aborted();
 }
 
 
 bool LCodeGen::GenerateJumpTable() {
   Label needs_frame;
   if (jump_table_.length() > 0) {
     Comment(";;; -------------------- Jump table --------------------");
@@ skipping 1571 matching lines @@
   ASSERT(ToRegister(instr->result()).is(rax));
 
   BinaryOpStub stub(instr->op(), NO_OVERWRITE);
   CallCode(stub.GetCode(isolate()), RelocInfo::CODE_TARGET, instr);
   __ nop();  // Signals no inlined code.
 }
 
 
 int LCodeGen::GetNextEmittedBlock() const {
   for (int i = current_block_ + 1; i < graph()->blocks()->length(); ++i) {
+    if (!graph()->blocks()->at(i)->IsReachable()) continue;
     if (!chunk_->GetLabel(i)->HasReplacement()) return i;
   }
   return -1;
 }
 
 
 template<class InstrType>
 void LCodeGen::EmitBranch(InstrType instr, Condition cc) {
   int left_block = instr->TrueDestination(chunk_);
   int right_block = instr->FalseDestination(chunk_);
@@ skipping 3625 matching lines @@
                                FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64