Externalize deoptimization reasons.

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index ac158f44eae32173f57c7b803f2d0edc5a3774a2..11cdbe237d610ba973c1c9972f6c412009b57b29 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -365,7 +365,7 @@ class RelocInfo {
     CODE_TARGET,  // Code target which is not any of the above.
     CODE_TARGET_WITH_ID,
     CONSTRUCT_CALL,  // code target that is a call to a JavaScript constructor.
-    DEBUG_BREAK,  // Code target for the debugger statement.
+    DEBUG_BREAK,     // Code target for the debugger statement.
     EMBEDDED_OBJECT,
     CELL,
 
@@ -373,9 +373,10 @@ class RelocInfo {
     RUNTIME_ENTRY,
     JS_RETURN,  // Marks start of the ExitJSFrame code.
     COMMENT,
-    POSITION,  // See comment for kNoPosition above.
+    DEOPT_REASON,        // Deoptimization reason index.

[Sven Panne, 2015/01/30 11:50:08]

Ooops, I just noticed that this might not work: We are probably running out of
bits for the reason. You should have a closer look at that, perhaps I'm wrong...

Another thing to watch out for is performance: The encoding of the RelocInfo is
very sensitive to minor changes, and mvstanton@ had problems with this in the
past. Perhaps that's a non-issue here (if we only emit the new kind of infos
with --trace-deopt), but nevertheless something to watch out for (and measure).

[loislo, 2015/01/30 13:17:47]

I did an investigation and found that we have about 60 different reasons for
deopt at the moment across all the platforms. So we fit into 6 bit of short
version (2 bytes) of RelocInfo. The overall encoding schema for 1 byte and 2
bytes RelocInfo looks reasonable but the layout for the long version looks a bit
strange and could not be extended. So I'm thinking how it could be redesigned.
Fortunately it could be done as a separate patch with proper performance
regression testing.

[Sven Panne, 2015/01/30 13:25:47]

I was more concerned about encoding the Mode. Adding Michael...

[loislo, 2015/02/04 07:54:56]

I used short encoding and reused b11 as the short mode id. It looks safe because
we don't use kComment for the short encoding but might be I missed something.

+    POSITION,            // See comment for kNoPosition above.
     STATEMENT_POSITION,  // See comment for kNoPosition above.
-    DEBUG_BREAK_SLOT,  // Additional code inserted for debug break slot.
+    DEBUG_BREAK_SLOT,    // Additional code inserted for debug break slot.
     EXTERNAL_REFERENCE,  // The address of an external C++ function.
     INTERNAL_REFERENCE,  // An address inside the same function.
 
@@ -386,9 +387,9 @@ class RelocInfo {
 
     // add more as needed
     // Pseudo-types
-    NUMBER_OF_MODES,  // There are at most 15 modes with noncompact encoding.
-    NONE32,  // never recorded 32-bit value
-    NONE64,  // never recorded 64-bit value
+    NUMBER_OF_MODES,    // There are at most 15 modes with noncompact encoding.
+    NONE32,             // never recorded 32-bit value
+    NONE64,             // never recorded 64-bit value
     CODE_AGE_SEQUENCE,  // Not stored in RelocInfo array, used explictly by
                         // code aging.
     FIRST_REAL_RELOC_MODE = CODE_TARGET,
@@ -733,6 +734,7 @@ class RelocIterator: public Malloced {
   int GetLocatableTypeTag();
   void ReadTaggedId();
   void ReadTaggedPosition();
+  void ReadTaggedData();
 
   // If the given mode is wanted, set it in rinfo_ and return true.
   // Else return false. Used for efficiently skipping unwanted modes.