Improve and simplify removal of unreachable code

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index 97c20e724f0fc28226926b330b0546457dc93d6f..568fe9ee7ce69ffc1d5ec8dbc83a6ef1ae5c40e1 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -346,22 +346,33 @@ bool LCodeGen::GenerateBody() {
     }
     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());
+      }
 
-    if (!CpuFeatures::IsSupported(SSE2)) FlushX87StackIfNecessary(instr);
+      if (!CpuFeatures::IsSupported(SSE2)) FlushX87StackIfNecessary(instr);
 
-    RecordAndUpdatePosition(instr->position());
+      RecordAndUpdatePosition(instr->position());
 
-    instr->CompileToNative(this);
+      instr->CompileToNative(this);
 
-    if (!CpuFeatures::IsSupported(SSE2)) {
-      if (FLAG_debug_code && FLAG_enable_slow_asserts) {
-        __ VerifyX87StackDepth(x87_stack_depth_);
+      if (!CpuFeatures::IsSupported(SSE2)) {
+        if (FLAG_debug_code && FLAG_enable_slow_asserts) {
+          __ VerifyX87StackDepth(x87_stack_depth_);
+        }
+      }
+    } 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());
       }
     }
   }
@@ -2207,6 +2218,7 @@ void LCodeGen::DoArithmeticT(LArithmeticT* instr) {
 
 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;