I made this change in my arrays working branch and liked it
enough to split it out and test/submit it early. treating
the range of valid Elm slots as a vanilla open-ended range
[0..m_used) simplifies a bunch of code.
They aren't used anymore, except to implement isVectorData(),
which we can make pure-virtual and implement more efficiently
in each subclass of ArrayData.
nvSet() only casts the value from TypedValue* to const Variant&; do it
at callsites. Inlined array_setm_ik1_v0() and array_setm_s0k1_v0() into
their only remaining callsites in translator-runtime.cpp.
The in-situ allocation case can be easily detected by checking m_data == m_inline_data.slots. Therefore there's no need for two distinct flags to track current and future allocation strategy.
ArrayData gets on a diet, down to 32 bytes
devirtualized destructor call in HphpArray::release()
aggressively inlined constructors for ArrayData (do away with defaulted arguments)
eliminate a dead memset() for the hashtable in HphpArray(uint size, const TypedValue* values)
I've done this refactoring without efficiency in mind - it's one of the steps toward more aggressive in-situ allocation. Yet to my surprise perflab rewarded this simple refactoring with a whopping decrease in I-TLB misses. I myself am wondering what has caused this. Anyhow let's run perflab once more and get this baby on the road.
I've run a bunch of experiments on HphpArray speed and am still yet to have a major breakthrough. However, there are a few clear small winners that I'm submitting with this diff. CPU instructions, CPU loads, and CPU stores are all as green as the Eternal Hunting Grounds. Speed is drowned in noise but I sususpect will be measurable on these changes combined.
I'm committing my work on HphpArray in bite-sized pieces for easier review. This piece replaces calls to NEW with a factory method. There are many problems with operator new, starting with the fact that the allocator cannot communicate properly with the constructor.
The newly introduced factory method should return ArrayData but that causes many issues right now, so I left that step to a future diff.
I was learning from @jdelong and he said that you should use
double quotes for local includes and angle brackets for library
includes. I asked why our code was the way it was, and he said he wanted
to clean it up. I beat him to it :)
Conflicts:
hphp/runtime/base/server/admin_request_handler.cpp
hphp/runtime/vm/named_entity.h
Make the targetcache the one true home for constants,
so we dont need to (also) insert them all into
VMExecutionContext::m_constants (which is now gone).
By also making "non-volatile" constants persistent, we save
initializing most of them at all in RepoAuthoritative mode.
Streamline the array access methods by always returning an array
pointer instead of a new pointer or null. Callsites compare
(new != old) to detect escalation, rather than (new != null).
Replaces the awkward getFullPos() and setFullPos() methods with a more
intuitive advanceFullPos() method. This refactoring also reduces the number
of virtual calls made when doing mutable iteration on an array.
Fixing various bugs all over the VM that make assumptions about RefData
and TypedValue layout. Here are the assumptions fixed by this diff:
offsetof(RefData, m_tv) == 0. Both JIT's assumed this in many subtle
ways, by punning RefData* as TypedValue* without adding an offset.
This assumption also causes RefData._count to overlap TypedValue.m_aux,
which constraints TypedValue layout.
offsetof(TypedValue, m_data) == 0. gen_ext_hhvm.php assumes you
can cast TypedValue* to Value*; the JITs often weren't using
offsetof(TypedValue, m_data) in their addressing calculations. HHIR
assumed return-by-value TV's have m_data/m_type in rax/rdx, which
can change when TV layout changes.
offsetof(TypedValue, m_type) > 8 is an assumption baked into the
pass-by-value register assignment logic in HHIR's codegen.cpp; if
the type is in the low word, register assignment is swapped.
sizeof(TypedValue::m_type) == 4. We used dword-sized operations
in both JIT's when accessing m_type. Now, we use helper functions
that are sensitive to sizeof(DataType)
Configuration:
DEBUG=: (opt) same layouts as trunk for RefData & TypedValue
DEBUG=1: (dbg) new RefData layout (m_tv doesn't overlap RefData::_count)
PACKED_TV=1, DEBUG=*: new RefData and TypedValue layout.
Of the four horsemen of the SmartAllocator, ArrayData was the only virtual
call. This meant an extra layer of indirection when coming from the TC
to allow the c++ compiler to emit its virtual call, and slightly larger
callsites when using non-generic paths.
While we're moving in this direction, consolidate ArrayData introspection
on its type enum. isSharedMap() was previously implemented with a vtable
slot, and we had no way of asking if an ArrayData was a NameValueTable.
Access to TypedValue.m_aux must now be via TypedValueAux. For now,
TypedValueAux is an empty subclass with accessors to m_aux, which is
now private. Once RefData.m_tv is moved out from under RefData._count,
we can move TypedValue.m_aux to TypedValueAux.
Removed unnecessary initialization of m_aux.u_hash from c_Vector.
This diff removes initializing stores to TypedValue._count, renames
_count to m_aux, and makes m_aux a union with members typed
and named according to their specialized uses. The few remaining
uses of that field for random tweaks are more obvious and easy to
grep for.
TypedValue no longer extends Value, (allowing m_data to move to a
different offset in the future), and Variant now extends TypedValue,
so we only have to maintain one definition.
HphpArray now explicitly uses TypedValue.m_pad instead of overlapping
TypedValue with an anonymous struct, again so we don't have to maintain
another structure to match TypedValue's layout.
The JIT's were using offsetof(TypedValue, _count) all over the place
for access to String/Array/Object/RefData::_count. Instead, use
FAST_REFCOUNT_OFFSET.
This diff refactors some of the VM's logic for iterators (with a focus on
mutable iteration), delivering several improvements:
1) MIterCtx was renamed to MArrayIter, and the m_key and m_val fields
were eliminated.
2) Eliminated the need for MArrayIter to dynamically allocate a
MutableArrayIter object, and removed other layers of indirection as
well.
3) Reduced the size of HPHP::VM::Iter from 64 bytes down to 32 bytes.
4) Removed the "if (siPastEnd())" check when adding a new element to an
HphpArray or a ZendArray.
5) Moved all of the iterator logic into a single .cpp file.
This diff reworks FullPos's to point to current element instead of pointing
to the next element. It also splits up the IterFree instruction into two
instructions (IterFree and MIterFree). These changes allowed various logic
to be simplified and data structures to be reduced in size. There is
definitely more opportunity for refactoring, but I know the JIT helpers for
iteration have been carefully tuned and so I'll leave further refactoring
for future diffs.
Finally, I spent a little time cleaning up the bytecode spec a bit, mostly
with respect to iteration.
This change is mostly for FB internal organizational reasons.
Building is not effected beyond the fact that the target now
lands in hphp/hhvm/hhvm rather than src/hhvm/hhvm.
Edwin Smith