Remove default monomorphic check code from functions and stubs that do not need it.

runtime/vm/object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/become.h"
@@ skipping 11561 matching lines @@
 
 #undef CHECK_FACTORY_FINGERPRINTS
 
   if (has_errors) {
     FATAL("Fingerprint mismatch.");
   }
 }
 #endif  // defined(DART_NO_SNAPSHOT) && !defined(PRODUCT).
 
 
-RawInstructions* Instructions::New(intptr_t size) {
+RawInstructions* Instructions::New(intptr_t size, bool has_single_entry_point) {
+  ASSERT(size >= 0);
   ASSERT(Object::instructions_class() != Class::null());
   if (size < 0 || size > kMaxElements) {
     // This should be caught before we reach here.
     FATAL1("Fatal error in Instructions::New: invalid size %" Pd "\n", size);
   }
   Instructions& result = Instructions::Handle();
   {
     uword aligned_size = Instructions::InstanceSize(size);
     RawObject* raw = Object::Allocate(Instructions::kClassId,
                                       aligned_size,
                                       Heap::kCode);
     NoSafepointScope no_safepoint;
     result ^= raw;
-    result.set_size(size);
+    result.set_size(has_single_entry_point ? size : -size);
   }
   return result.raw();
 }
 
 
 const char* Instructions::ToCString() const {
   return "Instructions";
 }
 
 
@@ skipping 2650 matching lines @@
       ObjectPool::Handle(assembler->object_pool_wrapper().MakeObjectPool());
 
   // Allocate the Code and Instructions objects.  Code is allocated first
   // because a GC during allocation of the code will leave the instruction
   // pages read-only.
   intptr_t pointer_offset_count = assembler->CountPointerOffsets();
   Code& code = Code::ZoneHandle(Code::New(pointer_offset_count));
 #ifdef TARGET_ARCH_IA32
   assembler->set_code_object(code);
 #endif
-  Instructions& instrs =
-      Instructions::ZoneHandle(Instructions::New(assembler->CodeSize()));
+  Instructions& instrs = Instructions::ZoneHandle(
+      Instructions::New(assembler->CodeSize(),
+                        assembler->has_single_entry_point()));
   INC_STAT(Thread::Current(), total_instr_size, assembler->CodeSize());
   INC_STAT(Thread::Current(), total_code_size, assembler->CodeSize());
 
   // Copy the instructions into the instruction area and apply all fixups.
   // Embedded pointers are still in handles at this point.
   MemoryRegion region(reinterpret_cast<void*>(instrs.PayloadStart()),
                       instrs.size());
   assembler->FinalizeInstructions(region);
   CPU::FlushICache(instrs.PayloadStart(), instrs.size());
 
@@ skipping 286 matching lines @@
   // frame slots which are marked as having objects.
   *maps = stackmaps();
   *map = Stackmap::null();
   for (intptr_t i = 0; i < maps->Length(); i++) {
     *map ^= maps->At(i);
     ASSERT(!map->IsNull());
     if (map->PcOffset() == pc_offset) {
       return map->raw();  // We found a stack map for this frame.
     }
   }
+  // TODO(regis): What is the purpose of this ASSERT? Is it correct?
   ASSERT(!is_optimized() || (pc_offset == Instructions::kUncheckedEntryOffset));

[rmacnak, 2016/11/01 00:50:17]

If we are missing a stack map, this must either be unoptimized code, or the
entry to an osr function. (In which case all stack slots are considered to have
tagged pointers.) So pc_offset == Instructions::kUncheckedEntryOffset
corresponds to  Instructions::UncheckedEntryPoint(...) in DRT_StackOverflow.

Given the entry isn't an fixed offset now, this should be pc_offset ==
unchecked_entry()) now.

Running with --verify-on-transition should hit this.

[regis, 2016/11/02 15:45:35]

Thanks!

The flag indeed revealed the issue. I added your explanation as a comment and
fixed the assert.
Generation of a handle in Code::UncheckedEntryPoint() does not seem to cause an
issue, but I could revert the use of a handle, or simply check 3 different
possible offsets (not as strict):
  ASSERT(!is_optimized() ||
         (pc_offset == Instructions::kPayloadOffset) ||
         (pc_offset == Instructions::kUncheckedEntryOffset) ||
         (pc_offset == Instructions::kCheckedEntryOffset));

   return Stackmap::null();
 }
 
 
 intptr_t Code::GetCallerId(intptr_t inlined_id) const {
   if (inlined_id < 0) {
     return -1;
   }
   const Array& map = Array::Handle(GetInlinedCallerIdMap());
   if (map.IsNull() || (map.Length() == 0)) {
@@ skipping 8449 matching lines @@
   return UserTag::null();
 }
 
 
 const char* UserTag::ToCString() const {
   const String& tag_label = String::Handle(label());
   return tag_label.ToCString();
 }
 
 }  // namespace dart