Improve and simplify removal of unreachable code

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
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       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
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// 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
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "v8.h"
+
+#include "lithium-codegen.h"
+
+#if V8_TARGET_ARCH_IA32
+#include "ia32/lithium-ia32.h"
+#include "ia32/lithium-codegen-ia32.h"
+#elif V8_TARGET_ARCH_X64
+#include "x64/lithium-x64.h"
+#include "x64/lithium-codegen-x64.h"
+#elif V8_TARGET_ARCH_ARM
+#include "arm/lithium-arm.h"
+#include "arm/lithium-codegen-arm.h"
+#elif V8_TARGET_ARCH_MIPS
+#include "mips/lithium-codegeng.h"
+#include "mips/lithium-codegen-mips.h"
+#else
+#error Unsupported target architecture.
+#endif
+
+namespace v8 {
+namespace internal {
+
+
+HGraph* LCodeGenBase::graph() const {
+  return chunk()->graph();
+}
+
+
+LCodeGenBase::LCodeGenBase(LChunk* chunk,
+                           MacroAssembler* assembler,
+                           CompilationInfo* info)
+    : chunk_(static_cast<LPlatformChunk*>(chunk)),
+      masm_(assembler),
+      info_(info),
+      zone_(info->zone()),
+      status_(UNUSED),
+      current_block_(-1),
+      current_instruction_(-1),
+      instructions_(chunk->instructions()),
+      last_lazy_deopt_pc_(0) {
+}
+
+
+bool LCodeGenBase::GenerateBody() {
+  ASSERT(is_generating());
+  bool emit_instructions = true;
+  LCodeGen* codegen = static_cast<LCodeGen*>(this);
+  for (current_instruction_ = 0;
+       !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() &&
+          (!FLAG_unreachable_code_elimination ||
+           instr->hydrogen_value()->block()->IsReachable());
+      if (FLAG_code_comments && !emit_instructions) {
+        Comment(
+            ";;; <@%d,#%d> -------------------- B%d (unreachable/replaced) "
+            "--------------------",
+            current_instruction_,
+            instr->hydrogen_value()->id(),
+            instr->hydrogen_value()->block()->block_id());
+      }
+    }
+    if (!emit_instructions) continue;
+
+    if (FLAG_code_comments && instr->HasInterestingComment(codegen)) {
+      Comment(";;; <@%d,#%d> %s",
+              current_instruction_,
+              instr->hydrogen_value()->id(),
+              instr->Mnemonic());
+    }
+
+    GenerateBodyInstructionPre(instr);
+
+    RecordAndUpdatePosition(instr->position());
+
+    instr->CompileToNative(codegen);
+
+    GenerateBodyInstructionPost(instr);
+  }
+  EnsureSpaceForLazyDeopt(Deoptimizer::patch_size());
+  last_lazy_deopt_pc_ = masm()->pc_offset();
+  return !is_aborted();
+}
+
+
+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
+  // issues when the stack allocated buffer goes out of scope.
+  size_t length = builder.position();
+  Vector<char> copy = Vector<char>::New(length + 1);
+  OS::MemCopy(copy.start(), builder.Finalize(), copy.length());
+  masm()->RecordComment(copy.start());
+}
+
+
+int LCodeGenBase::GetNextEmittedBlock() const {
+  for (int i = current_block_ + 1; i < graph()->blocks()->length(); ++i) {
+    if (!chunk_->GetLabel(i)->HasReplacement()) return i;
+  }
+  return -1;
+}
+
+
+} }  // namespace v8::internal