Add comment better explaining the calling-stubs-from-stubs issue.

src/code-stubs.h

 // Copyright 2011 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
@@ skipping 16 matching lines @@
 
 #ifndef V8_CODE_STUBS_H_
 #define V8_CODE_STUBS_H_
 
 #include "allocation.h"
 #include "globals.h"
 
 namespace v8 {
 namespace internal {
 
-// List of code stubs used on all platforms. The order in this list is important
-// as only the stubs up to and including Instanceof allows nested stub calls.
+// List of code stubs used on all platforms.
 #define CODE_STUB_LIST_ALL_PLATFORMS(V)  \
   V(CallFunction)                        \
   V(UnaryOp)                             \
   V(BinaryOp)                            \
   V(StringAdd)                           \
   V(SubString)                           \
   V(StringCompare)                       \
-  V(SmiOp)                               \
   V(Compare)                             \
-  V(CompareIC)                           \
   V(MathPow)                             \
   V(TranscendentalCache)                 \
   V(Instanceof)                          \
+  /* All stubs above this line only exist in a few versions, which are */  \
+  /* generated ahead of time.  Therefore inserting a call to one of    */  \

[Kevin Millikin (Chromium), 2011/05/25 12:22:29]

Maybe less ambiguous: "inserting" --> "compiling", and below.  Also below,
"generating" --> "compiling".

[Erik Corry, 2011/05/25 12:51:06]

Done.

+  /* them can't cause a new stub to be compiled, so inserting a call to*/  \
+  /* them is GC safe.  The ones below this line exist in many variants */  \
+  /* so code generating a call to one can cause a GC.  This means they */  \
+  /* can't be called from other stubs, since stub generation code is   */  \
+  /* not GC safe.                                                      */  \
   V(ConvertToDouble)                     \
   V(WriteInt32ToHeapNumber)              \
   V(StackCheck)                          \
   V(FastNewClosure)                      \
   V(FastNewContext)                      \
   V(FastCloneShallowArray)               \
   V(RevertToNumber)                      \
   V(ToBoolean)                           \
   V(ToNumber)                            \
   V(CounterOp)                           \
@@ skipping 126 matching lines @@
   virtual void Print() { PrintF("%s\n", GetName()); }
 #endif
 
   // Computes the key based on major and minor.
   uint32_t GetKey() {
     ASSERT(static_cast<int>(MajorKey()) < NUMBER_OF_IDS);
     return MinorKeyBits::encode(MinorKey()) |
            MajorKeyBits::encode(MajorKey());
   }
 
+  // See comment above, where Instanceof is defined.
   bool AllowsStubCalls() { return MajorKey() <= Instanceof; }
 
   class MajorKeyBits: public BitField<uint32_t, 0, kMajorBits> {};
   class MinorKeyBits: public BitField<uint32_t, kMajorBits, kMinorBits> {};
 
   friend class BreakPointIterator;
 };
 
 
 // Helper interface to prepare to/restore after making runtime calls.
@@ skipping 794 matching lines @@
   DECLARE_ARRAY_STUB_PRINT(KeyedStoreExternalArrayStub)
 
  protected:
   ExternalArrayType array_type_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_CODE_STUBS_H_