Externalize deoptimization reasons.

src/assembler.cc

Index: src/assembler.cc
diff --git a/src/assembler.cc b/src/assembler.cc
index deabe3b776a9377e10f0f4d3346946ab036c10af..0c7e58f6f0edeed38959df69c18751c13156c3d4 100644
--- a/src/assembler.cc
+++ b/src/assembler.cc
@@ -328,6 +328,9 @@ const int kNonstatementPositionTag = 1;
 const int kStatementPositionTag = 2;
 const int kCommentTag = 3;
 
+// Reuse the same value for deopt reason tag in short record format.

[Michael Starzinger, 2015/02/04 11:30:51]

IIUC, this assumes that comments are always encoded in "long format" and deopt
reasons are always encoded in "short format". Correct? Can we make this explicit
in this comment?

[loislo, 2015/02/04 14:38:49]

done

+const int kDeoptReasonTag = 3;
+
 const int kPoolExtraTag = kPCJumpExtraTag - 2;
 const int kConstPoolTag = 0;
 const int kVeneerPoolTag = 1;
@@ -423,7 +426,10 @@ void RelocInfoWriter::Write(const RelocInfo* rinfo) {
   RelocInfo::Mode rmode = rinfo->rmode();
 
   // The two most common modes are given small tags, and usually fit in a byte.
-  if (rmode == RelocInfo::EMBEDDED_OBJECT) {
+  if (rmode == RelocInfo::DEOPT_REASON) {

[Michael Starzinger, 2015/02/04 11:30:51]

nit: Can we move this to after EMBEDDED_OBJECT, CODE_TARGET, and
CODE_TARGET_WITH_ID, just so that the comment talking about the "two most common
modes" is still accurate and the two most common modes really are handled first.

[loislo, 2015/02/04 14:38:50]

done

+    WriteTaggedPC(pc_delta, kLocatableTag);
+    WriteTaggedData(rinfo->data(), kDeoptReasonTag);

[Michael Starzinger, 2015/02/04 11:30:51]

Can we have a DCHECK here that the deopt reason really fits into kSmallDataBits?

[loislo, 2015/02/04 14:38:49]

done

+  } else if (rmode == RelocInfo::EMBEDDED_OBJECT) {
     WriteTaggedPC(pc_delta, kEmbeddedObjectTag);
   } else if (rmode == RelocInfo::CODE_TARGET) {
     WriteTaggedPC(pc_delta, kCodeTargetTag);
@@ -583,6 +589,12 @@ inline void RelocIterator::ReadTaggedPosition() {
 }
 
 
+inline void RelocIterator::ReadTaggedData() {
+  uint8_t unsigned_b = *pos_;
+  rinfo_.data_ = unsigned_b >> kTagBits;
+}
+
+
 static inline RelocInfo::Mode GetPositionModeFromTag(int tag) {
   DCHECK(tag == kNonstatementPositionTag ||
          tag == kStatementPositionTag);
@@ -616,9 +628,10 @@ void RelocIterator::next() {
           ReadTaggedId();
           return;
         }
+      } else if (locatable_tag == kDeoptReasonTag) {
+        ReadTaggedData();
+        if (SetMode(RelocInfo::DEOPT_REASON)) return;
       } else {
-        // Compact encoding is never used for comments,
-        // so it must be a position.
         DCHECK(locatable_tag == kNonstatementPositionTag ||
                locatable_tag == kStatementPositionTag);
         if (mode_mask_ & RelocInfo::kPositionMask) {
@@ -783,6 +796,8 @@ const char* RelocInfo::RelocModeName(RelocInfo::Mode rmode) {
       return "external reference";
     case RelocInfo::INTERNAL_REFERENCE:
       return "internal reference";
+    case RelocInfo::DEOPT_REASON:
+      return "deopt reason";
     case RelocInfo::CONST_POOL:
       return "constant pool";
     case RelocInfo::VENEER_POOL:
@@ -803,6 +818,9 @@ void RelocInfo::Print(Isolate* isolate, std::ostream& os) {  // NOLINT
   os << static_cast<const void*>(pc_) << "  " << RelocModeName(rmode_);
   if (IsComment(rmode_)) {
     os << "  (" << reinterpret_cast<char*>(data_) << ")";
+  } else if (rmode_ == DEOPT_REASON) {
+    os << "  (" << Deoptimizer::GetDeoptReason(
+                       static_cast<Deoptimizer::DeoptReason>(data_)) << ")";
   } else if (rmode_ == EMBEDDED_OBJECT) {
     os << "  (" << Brief(target_object()) << ")";
   } else if (rmode_ == EXTERNAL_REFERENCE) {
@@ -863,6 +881,7 @@ void RelocInfo::Verify(Isolate* isolate) {
     case STATEMENT_POSITION:
     case EXTERNAL_REFERENCE:
     case INTERNAL_REFERENCE:
+    case DEOPT_REASON:
     case CONST_POOL:
     case VENEER_POOL:
     case DEBUG_BREAK_SLOT: