Enable preaging of code objects when --optimize-for-size.

src/arm/codegen-arm.cc

Index: src/arm/codegen-arm.cc
diff --git a/src/arm/codegen-arm.cc b/src/arm/codegen-arm.cc
index faf7b54d43a139139d37789afca4ce46eb639c24..fd82f80bb0619df1a942f8119cd7f527fbef80ef 100644
--- a/src/arm/codegen-arm.cc
+++ b/src/arm/codegen-arm.cc
@@ -847,7 +847,27 @@ static byte* GetNoCodeAgeSequence(uint32_t* length) {
     CodePatcher patcher(byte_sequence, kNoCodeAgeSequenceLength);
     PredictableCodeSizeScope scope(patcher.masm(), *length);
     patcher.masm()->stm(db_w, sp, r1.bit() | cp.bit() | fp.bit() | lr.bit());
-    patcher.masm()->nop(ip.code());
+    patcher.masm()->nop(kNoAgeCodeNopType);
+    patcher.masm()->add(fp, sp, Operand(2 * kPointerSize));
+    initialized = true;
+  }
+  return byte_sequence;
+}
+
+
+static byte* GetPreAgedCodeAgeSequence(uint32_t* length) {
+  // If code is "pre-aged" then this sequence of instructions is found in the
+  // boilerplate stack-building prologue that is found in FUNCTIONS, and is
+  // patched out for code aging.
+  static bool initialized = false;
+  static uint32_t sequence[kNoCodeAgeSequenceLength];
+  byte* byte_sequence = reinterpret_cast<byte*>(sequence);
+  *length = kNoCodeAgeSequenceLength * Assembler::kInstrSize;
+  if (!initialized) {
+    CodePatcher patcher(byte_sequence, kNoCodeAgeSequenceLength);
+    PredictableCodeSizeScope scope(patcher.masm(), *length);
+    patcher.masm()->stm(db_w, sp, r1.bit() | cp.bit() | fp.bit() | lr.bit());
+    patcher.masm()->nop(kPreAgeCodeNopType);
     patcher.masm()->add(fp, sp, Operand(2 * kPointerSize));
     initialized = true;
   }
@@ -860,7 +880,19 @@ bool Code::IsYoungSequence(byte* sequence) {
   byte* young_sequence = GetNoCodeAgeSequence(&young_length);
   bool result = !memcmp(sequence, young_sequence, young_length);
   ASSERT(result ||
-         Memory::uint32_at(sequence) == kCodeAgePatchFirstInstruction);
+         Memory::uint32_at(sequence) == kCodeAgePatchFirstInstruction ||
+         IsPreAgedSequence(sequence));
+  return result;
+}
+
+
+bool Code::IsPreAgedSequence(byte* sequence) {
+  uint32_t pre_aged_length;
+  byte* pre_aged_sequence = GetPreAgedCodeAgeSequence(&pre_aged_length);
+  bool result = !memcmp(sequence, pre_aged_sequence, pre_aged_length);
+  ASSERT(result ||
+         Memory::uint32_at(sequence) == kCodeAgePatchFirstInstruction ||
+         IsYoungSequence(sequence));
   return result;
 }
 
@@ -870,6 +902,9 @@ void Code::GetCodeAgeAndParity(byte* sequence, Age* age,
   if (IsYoungSequence(sequence)) {
     *age = kNoAge;
     *parity = NO_MARKING_PARITY;
+  } else if (IsPreAgedSequence(sequence)) {
+    *age = kPreAgedCodeAge;
+    *parity = NO_MARKING_PARITY;
   } else {
     Address target_address = Memory::Address_at(
         sequence + Assembler::kInstrSize * (kNoCodeAgeSequenceLength - 1));