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

src/x64/codegen-x64.cc

Index: src/x64/codegen-x64.cc
diff --git a/src/x64/codegen-x64.cc b/src/x64/codegen-x64.cc
index ce69d15814139045e9f42e84f7259c48f347f843..a6f1659cd9e2c041dc3dbd34200ae1b46d27a334 100644
--- a/src/x64/codegen-x64.cc
+++ b/src/x64/codegen-x64.cc
@@ -686,19 +686,20 @@ void MathExpGenerator::EmitMathExp(MacroAssembler* masm,
 #undef __
 
 
-static const int kNoCodeAgeSequenceLength = 6;
+static const int kCodeAgeSequenceLength = 7;
 
 static byte* GetNoCodeAgeSequence(uint32_t* length) {
   static bool initialized = false;
-  static byte sequence[kNoCodeAgeSequenceLength];
-  *length = kNoCodeAgeSequenceLength;
+  static byte sequence[kCodeAgeSequenceLength];
+  *length = kCodeAgeSequenceLength;
   if (!initialized) {
     // The sequence of instructions that is patched out for aging code is the
     // following boilerplate stack-building prologue that is found both in
     // FUNCTION and OPTIMIZED_FUNCTION code:
-    CodePatcher patcher(sequence, kNoCodeAgeSequenceLength);
+    CodePatcher patcher(sequence, kCodeAgeSequenceLength);
     patcher.masm()->push(rbp);
     patcher.masm()->movq(rbp, rsp);
+    patcher.masm()->nop();
     patcher.masm()->push(rsi);
     patcher.masm()->push(rdi);
     initialized = true;
@@ -707,11 +708,40 @@ static byte* GetNoCodeAgeSequence(uint32_t* length) {
 }
 
 
+static byte* GetPreAgedCodeAgeSequence(uint32_t* length) {
+  static bool initialized = false;
+  static byte sequence[kCodeAgeSequenceLength];
+  *length = kCodeAgeSequenceLength;
+  if (!initialized) {
+    // If code is "pre-aged" then this sequence of instructions is found in the
+    // boilerplate stack-building prologue that is found in FUNCTIONS and
+    // OPTIMIZED_FUNCTION code, and is patched out for code aging.
+    CodePatcher patcher(sequence, kCodeAgeSequenceLength);
+    patcher.masm()->push(rbp);
+    patcher.masm()->movq(rbp, rsp);
+    patcher.masm()->push(rsi);
+    patcher.masm()->nop();
+    patcher.masm()->push(rdi);
+    initialized = true;
+  }
+  return sequence;
+}
+
+
 bool Code::IsYoungSequence(byte* sequence) {
   uint32_t young_length;
   byte* young_sequence = GetNoCodeAgeSequence(&young_length);
   bool result = (!memcmp(sequence, young_sequence, young_length));
-  ASSERT(result || *sequence == kCallOpcode);
+  ASSERT(result || *sequence == kCallOpcode || 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 || *sequence == kCallOpcode || IsYoungSequence(sequence));
   return result;
 }
 
@@ -721,6 +751,9 @@ 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 {
     sequence++;  // Skip the kCallOpcode byte
     Address target_address = sequence + *reinterpret_cast<int*>(sequence) +
@@ -744,7 +777,7 @@ void Code::PatchPlatformCodeAge(byte* sequence,
     CodePatcher patcher(sequence, young_length);
     patcher.masm()->call(stub->instruction_start());
     for (int i = 0;
-         i < kNoCodeAgeSequenceLength - Assembler::kShortCallInstructionLength;
+         i < kCodeAgeSequenceLength - Assembler::kShortCallInstructionLength;
          i++) {
       patcher.masm()->nop();
     }