And thus massively speed up ascii-case-insensitive atom comparisons when both
atoms are lowercase (which is the common case by far).
This removes almost all the slow selector-matching in this page, and it seems
an easier fix than storing the lowercased version of all class-names in quirks
mode in elements and selectors...
Differential Revision: https://phabricator.services.mozilla.com/D10945
--HG--
extra : moz-landing-system : lando
This saves one word per static atom, per process.
The `nsGkAtoms` change is only a small part of this commit.
In regen_atoms.py:
- There is now only one link name per platform: nsGkAtoms::sAtoms[].
- But there is a new constant per atom, giving the index into
nsGkAtoms::sAtoms[].
- And the `atom!` macro for each atom indexes into nsGkAtoms::sAtoms[] using
the index constant.
- A couple of `*mut` pointers are now `*const`.
Elsewhere, the `(nsStaticAtom*)` casts within the `AppendElement()` calls are
necessary to avoid link errors, presumably due to some template instantiation
wrinkle.
--HG--
extra : rebase_source : 629642e708c8bc6e27d6057beae5f35955fdd837
Presumably the commit that introduced `aStringOffset` could have removed this,
but overlooked it.
--HG--
extra : rebase_source : 176f14ce01c18ed4c83892d2b7a9e7a54fb5c836
Static atom registration is a bit of a mess. NS_InitAtomTable() calls
nsGkAtoms::RegisterStaticAtoms(), which calls NS_RegisterStaticAtoms(); i.e. we
go from nsAtomTable.cpp to nsGkAtoms.cpp and back.
(And NS_RegisterStaticAtoms() is declared in a .cpp file, not a .h file!)
This commit makes NS_InitAtomTable() a friend of nsGkAtoms, so NS_InitAtomTable
can see nsGkAtoms's atoms array directly, thus removing the need for
NS_RegisterAtomTable() and nsGkAtoms::RegisterStaticAtoms().
This commit also removes an out-of-date part of a comment from XPCOMInit.cpp.
--HG--
extra : rebase_source : 7e1f9aa0a9f7cb5088159fe4c953948b931f6d68
nsGkAtoms.h has a big comment explaining how static atom definitions get
expanded by macros. This comment was very useful when there were multiple
sources of static atoms and their definitions used macros a lot. But bug
1482782 combined all the static atom sources into nsGkAtoms and removed a lot
of macro use. So now the comment is now something of a hindrance, duplicating
quite a bit of the code (and not entirely accurately).
This commit removes the big comment, and moves the still-useful parts inline
with the code. This makes things much easier to follow.
This commit also reformats some of the remaining macros so they are easier to
read.
--HG--
extra : rebase_source : 4377be2fa0edc4ea1f592985ded89acbb76fb104
Each nsStaticAtomSetup contains a pointer to a static atom, and also a pointer
to the canonical pointer to that static atom. Which is pretty weird! The
notable thing thing about it is that these structs are in an array, and that
gives us the only way to iterate over all static atoms in a single class, for
registration and lookups.
But thanks to various other recent changes to the implementation of static
atoms, we can now put the static atoms themselves into an array, which can be
iterated over. So this patch does that. With that done, nsStaticAtomSetup is no
longer necessary.
According to the `size` utility, on Linux64 this reduces the size of libxul.so
by the following amounts:
> text: 62008 bytes
> data: 20992 bytes
> bss: 21040 bytes
> total: 104040 bytes
- The bss reduction is one word per atom, because the canonical static atom
pointers (e.g. nsGkAtoms::foo) have moved from .bss to .data, because they're
now initialized at compile time instead of runtime.
- The data reduction is one word per atom, because we remove two words per atom
for the nsStaticAtomSetup removal, but gain one word per atom from the
previous bullet point.
- I'm not sure about the text reduction. It's three words per atom. Maybe
because there is one less relocation per atom?
Other notable things in the patch:
- nsICSSAnonBoxPseudo and nsICSSPseudoElement now inherit from nsStaticAtom,
not nsAtom, because that's more precise.
- Each static atoms array now has an enum associated with it, which is used in
various ways.
- In the big comment about the macros at the top of nsStaticAtom.h, the pre-
and post-expansion forms are now shown interleaved. The interleaving reduces
duplication and makes the comment much easier to read and maintain. The
comment also has an introduction that explains the constraints and goals of
the implementation.
- The SUBCLASS macro variations are gone. There are few enough users of these
macros now that always passing the atom type has become simpler.
MozReview-Commit-ID: 1GmfKidLjaU
--HG--
extra : rebase_source : 2352590101fc6693ba388f885ca4714a42963943
Currently static atoms are stored on the heap, but their char buffers are
stored in read-only static memory.
This patch changes the representation of nsStaticAtom (thus making it a
non-trivial subclass of nsAtom). Instead of a pointer to the string, it now has
an mStringOffset field which is a 32-bit offset to the string. (This requires
placement of the string and the atom within the same object so that the offset
is known to be small. The docs and macros in nsStaticAtom.h handle that.)
Static and dynamic atoms now store their chars in different ways: nsStaticAtom
stores them inline, nsDynamicAtom has a pointer to separate storage. So
`mString` and GetStringBuffer() move from nsAtom to nsDynamicAtom.
The change to static atoms means they can be made constexpr and stored in
read-only memory instead of on the heap. On 64-bit this reduces the per-process
overhead by 16 bytes; on 32-bit the saving is 12 bytes. (Further reductions
will be possible in follow-up patches.)
The increased use of constexpr required multiple workarounds for MSVC.
- Multiple uses of MOZ_{PUSH,POP}_DISABLE_INTEGRAL_CONSTANT_OVERFLOW_WARNING to
disable warnings about (well-defined!) overflow of unsigned integer
arithmetic.
- The use of -Zc:externConstexpr on all files defining static atoms, to make
MSVC follow the C++ standard(!) and let constexpr variables have external
linkage.
- The use of -constexpr:steps300000 to increase the number of operations
allowed in a constexpr value, in order to handle gGkAtoms, which requires
hashing ~2,500 atom strings.
The patch also changes how HTML5 atoms are handled. They are now treated as
dynamic atoms, i.e. we have "dynamic normal" atoms and "dynamic HTML5 atoms",
and "dynamic atoms" covers both cases, and both are represented via
nsDynamicAtom. The main difference between the two kinds is that dynamic HTML5
atoms still aren't allowed to be used in various operations, most notably
AddRef()/Release(). All this also required moving nsDynamicAtom into the header
file.
There is a slight performance cost to all these changes: now that nsStaticAtom
and nsDynamicAtom store their chars in different ways, a conditional branch is
required in the following functions: Equals(), GetUTF16String(),
WeakAtom::as_slice().
Finally, in about:memory the "explicit/atoms/static/atom-objects" value is no
longer needed, because that memory is static instead of heap-allocated.
MozReview-Commit-ID: 4AxPv05ngZy
These functions no longer perform any refcounting, so the existing names are
misleading.
MozReview-Commit-ID: LX55e0bUP8N
--HG--
extra : rebase_source : 89a3da577325286c1d31723acfd4153754f49703
This list of atoms isn't particularly DOM-ish, and having it in xpcom/ will
help with the next patch.
MozReview-Commit-ID: 1Y3Fhn9lNbh
--HG--
rename : dom/base/nsGkAtomList.h => xpcom/ds/nsGkAtomList.h
rename : dom/base/nsGkAtoms.cpp => xpcom/ds/nsGkAtoms.cpp
rename : dom/base/nsGkAtoms.h => xpcom/ds/nsGkAtoms.h
extra : rebase_source : 0a0f6ab4432e0d58ea4662299b750a8c52325ad5
Sylvestre Ledru
Cameron McCormack
Emilio Cobos Álvarez
Nicholas Nethercote
Narcis Beleuzu