This is only an estimate since it counts objects that could be shared,
for example strings, cow arrays, heap numbers, etc.
It however ignores objects that could be shared, but may only be used
by the context to be measured, for example shared function infos,
script objects, scope infos, etc.
R=jochen@chromium.org
Review URL: https://codereview.chromium.org/1268333004
Cr-Commit-Position: refs/heads/master@{#30029}
To avoid tanking context startup performance, only the actual installation of the
JS-exposed API is flag-guarded. The remainder of the implementation still
resides in the snapshot.
Review URL: https://codereview.chromium.org/1257063003
Cr-Commit-Position: refs/heads/master@{#30017}
Added a separate flag for this, since we intend to enable it for the linear allocator as well. Currently, the option is "on" for greedy, as a point in time to enable its testing (through the greedy allocator bots).
BUG=
Review URL: https://codereview.chromium.org/1256313003
Cr-Commit-Position: refs/heads/master@{#30005}
The BytecodeArrayBuilder has responsibility for emitting the BytecodeArray. It will be used by the AST walker.
Bytecode now uses an accumulator plus registers rather being pure register based.
Update BytecodeArray::Disassemble to print operand information.
BUG=v8:4280
LOG=N
Review URL: https://codereview.chromium.org/1266713004
Cr-Commit-Position: refs/heads/master@{#29970}
This is the first step in cutting the Gordian linkage/linkage-impl knot.
This basically changes the axis along which we organize call descriptor
building logic from having platform-specific files dedicated to all call
descriptor types to having call-descriptor-type-specific files that have
The next step is to factor the JS, code stub, and runtime call descriptors
similarly, dumping them into:
compiler/js-linkage.cc
compiler/runtime-linkage.cc
compiler/code-stub-linkage.cc
or, alternatively, all of them just into compiler/js-linkage.cc.
This also anticipates a wasm-linkage.cc file in the future.
R=bmeurer@chromium.org,danno@chromium.org
BUG=
Review URL: https://codereview.chromium.org/1266603002
Cr-Commit-Position: refs/heads/master@{#29931}
Adds basic support for generation of interpreter bytecode handler code
snippets. The InterpreterAssembler class exposes a set of low level,
interpreter specific operations which can be used to build a Turbofan
graph. The Interpreter class generates a bytecode handler snippet for
each bytecode by assembling operations using an InterpreterAssembler.
Currently only two simple bytecodes are supported: LoadLiteral0 and Return.
BUG=v8:4280
LOG=N
Review URL: https://codereview.chromium.org/1239793002
Cr-Commit-Position: refs/heads/master@{#29814}
Using the GraphBuilder base class forces each node creation to go
through a virtual function dispatch just for the sake of saving the
duplication of the NewNode helper methods. In total that added up to
saving minus (sic!) six lines of code.
R=titzer@chromium.org
Review URL: https://codereview.chromium.org/1252093002
Cr-Commit-Position: refs/heads/master@{#29799}
In many cases, the context that TurboFan's ASTGraphBuilder or subsequent
reduction operations attaches to nodes does not need to be that exact
context, but rather only needs to be one with the same native context,
because it is used internally only to fetch the native context, e.g. for
creating and throwing exceptions.
This reducer recognizes common cases where the context that is specified
for a node can be relaxed to a canonical, less specific one. This
relaxed context can either be the enclosing function's context or a specific
Module or Script context that is explicitly created within the function.
This optimization is especially important for TurboFan-generated code stubs
which use context specialization and inlining to generate optimal code.
Without context relaxation, many extraneous moves are generated to pass
exactly the right context to internal functions like ToNumber and
AllocateHeapNumber, which only need the native context. By turning context
relaxation on, these moves disappear because all these common internal
context uses are unified to the context passed into the stub function, which
is typically already in the correct context register and remains there for
short stubs. It also eliminates the explicit use of a specialized context
constant in the code stub in these cases, which could cause memory leaks.
Review URL: https://codereview.chromium.org/1244583003
Cr-Commit-Position: refs/heads/master@{#29763}
This CL exposes the constructor function, defines type related
information, and implements value type semantics.
It also refactors test/mjsunit/samevalue.js to test SameValue and SameValueZero.
TEST=test/mjsunit/harmony/simd.js, test/cctest/test-simd.cc
LOG=Y
BUG=v8:4124
Committed: https://crrev.com/e5ed3bee99807c502fa7d7a367ec401e16d3f773
Cr-Commit-Position: refs/heads/master@{#29689}
Review URL: https://codereview.chromium.org/1219943002
Cr-Commit-Position: refs/heads/master@{#29712}
This CL exposes the constructor function, defines type related
information, and implements value type semantics.
It also refactors test/mjsunit/samevalue.js to test SameValue and SameValueZero.
TEST=test/mjsunit/harmony/simd.js, test/cctest/test-simd.cc
LOG=Y
BUG=v8:4124
Review URL: https://codereview.chromium.org/1219943002
Cr-Commit-Position: refs/heads/master@{#29689}
Until now, TF-generated code stubs piggy-backed off of the builtin
context. Since generation of code stubs is lazy, stubs generated at
different times in different native contexts would contain embedded
pointers different builtin contexts, leading to cross-context references
and memory leaks.
After this CL, all TF-generated code stubs are generated inside a
internal thinned-out, native context that lives solely for the
purpose of hosting generated code stubs.
Review URL: https://codereview.chromium.org/1213203007
Cr-Commit-Position: refs/heads/master@{#29593}
The breakage to Chrome seems to be based on @@isConcatSpreadable
and turning that part off with this patch fixes the Maps Tips & Tricks
test case.
BUG=chromium:507553
LOG=Y
R=adamk
Review URL: https://codereview.chromium.org/1226063002
Cr-Commit-Position: refs/heads/master@{#29545}
Optimize string "length" property access based on static type
information if possible, but also optimistically optimize the access
based on type feedback from the LoadIC.
R=jarin@chromium.org
Review URL: https://codereview.chromium.org/1216593003
Cr-Commit-Position: refs/heads/master@{#29543}
The RawMachineAssembler will be used to build the interpreter, so it needs
to move back to src/compiler.
This reverts commit b5b00cc031.
BUG=v8:4280
LOG=N
Review URL: https://codereview.chromium.org/1221303014
Cr-Commit-Position: refs/heads/master@{#29519}
We have to reland these two commits at once, because the first breaks
some asm.js benchmarks without the second. The change was reverted
because of bogus checks in the verifier, which will not work in the
presence of OSR (and where hidden because of the type back propagation
hack in OSR so far). Original messages are below:
[turbofan] Add new JSFrameSpecialization reducer.
The JSFrameSpecialization specializes an OSR graph to the current
unoptimized frame on which we will perform the on-stack replacement.
This is used for asm.js functions, where we cannot reuse the OSR
code object anyway because of context specialization, and so we could as
well specialize to the max instead.
It works by replacing all OsrValues in the graph with their values
in the JavaScriptFrame.
The idea is that using this trick we get better performance without
doing the unsound backpropagation of types to OsrValues later. This
is the first step towards fixing OSR for TurboFan.
[turbofan] Perform OSR deconstruction early and remove type propagation.
This way we don't have to deal with dead pre-OSR code in the graph
and risk optimizing the wrong code, especially we don't make
optimistic assumptions in the dead code that leaks into the OSR code
(i.e. deopt guards are in dead code, but the types propagate to OSR
code via the OsrValue type back propagation).
BUG=v8:4273
LOG=n
R=jarin@chromium.org
Review URL: https://codereview.chromium.org/1226673005
Cr-Commit-Position: refs/heads/master@{#29486}
The JSFrameSpecialization specializes an OSR graph to the current
unoptimized frame on which we will perform the on-stack replacement.
This is used for asm.js functions, where we cannot reuse the OSR code
object anyway because of context specialization, and so we could as well
specialize to the max instead.
It works by replacing all OsrValues in the graph with their values in
the JavaScriptFrame.
The idea is that using this trick we get better performance without
doing the unsound backpropagation of types to OsrValues later. This is
the first step towards fixing OSR for TurboFan.
R=jarin@chromium.org
BUG=v8:4273
LOG=n
Review URL: https://codereview.chromium.org/1225683004
Cr-Commit-Position: refs/heads/master@{#29476}
Conditionally including Array and TypedArray methods seems to cause
a slowdown in V8 context creation, possibly due to the new code added.
BUG=chromium:504629
R=adamk@chromium.org
LOG=Y
Review URL: https://codereview.chromium.org/1215863003
Cr-Commit-Position: refs/heads/master@{#29430}
Separated core greedy allocator concepts, exposing the APIs we would want to continue working with. In particular, this change completely reworks CoalescedLiveRanges to reflect the fact that we expect more than one possible conflict, scrapping the initial design of the structure. Since this is a critical part of the design, this change may be thought of as a full rewrite of the algorithm.
Reduced all heuristics to just 2 essential ones: split "somewhere", which we'll still need when all other heuristics fail; and spill.
Introduced a simple primitive for splitting - at GapPosition::START. The goal is to use such primitives to quickly and reliably author heuristics.
I expected this primitive to "just work" for any arbitrary instruction index within a live range - e.g. its middle. That's not the case, it seems to upset execution in certain scenarios. Restricting to either before/after use positions seems to work. I'm still investigating what the source of failures is in the case of "arbitrary instruction in the range" case.
I intended to document the rationale and prove the soundness of always using START for splits, but I will postpone to after this last remaining issue is resolved.
Review URL: https://codereview.chromium.org/1205173002
Cr-Commit-Position: refs/heads/master@{#29352}
The three different concerns that the ControlReducer used to deal with
are now properly separated into
a.) DeadCodeElimination, which is a regular AdvancedReducer, that
propagates Dead via control edges,
b.) CommonOperatorReducer, which does strength reduction on common
operators (i.e. Branch, Phi, and friends), and
c.) GraphTrimming, which removes dead->live edges from the graph.
This will make it possible to run the DeadCodeElimination together with
other passes that actually introduce Dead nodes, i.e. typed lowering;
and it opens the door for general inlining without two stage fix point
iteration.
To make the DeadCodeElimination easier and more uniform, we basically
reverted the introduction of DeadValue and DeadEffect, and changed the
Dead operator to produce control, value and effect. Note however that
this is not a requirement, but merely a way to make dead propagation
easier and more uniform. We could always go back and decide to have
different Dead operators if some other change requires that.
Note that there are several additional opportunities for cleanup now,
i.e. OSR deconstruction could be a regular reducer now, and we don't
need to use TheHole as dead value marker in the GraphReducer. And we can
actually run the dead code elimination together with the other passes
instead of using separate passes over the graph. We will do this in
follow up CLs.
R=jarin@chromium.org, mstarzinger@chromium.org
Review URL: https://codereview.chromium.org/1193833002
Cr-Commit-Position: refs/heads/master@{#29146}
Up until now that was still mixed with control reduction in the
ControlReducer. This separation allows us to remove the horrible
Reducer::Finish hack and also do graph trimming at more appropriate
places in the pipeline (i.e. trim dead nodes after generic lowering,
which can also make nodes dead).
R=jarin@chromium.org,mstarzinger@chromium.org
Review URL: https://codereview.chromium.org/1188433010
Cr-Commit-Position: refs/heads/master@{#29077}
Opportunistically removed GreedyAllocator::TryReuseSpillForPhi because it is actually unsuitable for Greedy. It was copied from Linear and it relies on hints, however, the current implementation of hints assumes linear scan.
This change doesn't aim to address performance nor correctness for Greedy.
BUG=
Review URL: https://codereview.chromium.org/1184183002
Cr-Commit-Position: refs/heads/master@{#29054}
This patch includes the following changes.
1, Enable the turbofan backend support for X87 platform. It depends on previous CL: 3fdfebd26.
2, Enable the test cases which are disabled because turbofan for X87 was not enabled.
BUG=v8:4135
LOG=N
Review URL: https://codereview.chromium.org/1179763004
Cr-Commit-Position: refs/heads/master@{#29049}
Pushed the detection logic down to ParseAndClassifyIdentifier in
preparation to having patterns in parameter positions.
R=arv@chromium.org,rossberg@chromium.org,wingo@igalia.com
BUG=v8:811
LOG=N
Review URL: https://codereview.chromium.org/1170153003
Cr-Commit-Position: refs/heads/master@{#28876}
In a nutshell: The FILTER_KEY builtin is gone, and was replaced by a
simple runtime call to ForInFilter, which does everything and is even
cheaper (because FILTER_KEY used to call into the runtime anyway).
And ForInFilter returns either the name or undefined, which makes it
possible to remove the control flow construction from the AstGraphBuilder,
and thereby make both the initialization and the per-loop code of for-in
optimizable later (in typed lowering).
R=jarin@chromium.org
Review URL: https://codereview.chromium.org/1160983004
Cr-Commit-Position: refs/heads/master@{#28711}
The SimplifiedOperatorReducer is (mostly) unused, except for the very
rough store elimination, and just eats compilation time.
R=jarin@chromium.org
Review URL: https://codereview.chromium.org/1162563002
Cr-Commit-Position: refs/heads/master@{#28673}
This adds a new external type (v8::SharedArrayBuffer) that uses a JSArrayBuffer
under the hood. It can be distinguished from an ArrayBuffer by the newly-added
is_shared() bit.
Currently there is no difference in functionality between a SharedArrayBuffer
and an ArrayBuffer. However, a future CL will add the Atomics API, which is
only available on an SharedArrayBuffer. All non-atomic accesses are identical
to ArrayBuffer accesses.
LOG=N
BUG=
Review URL: https://codereview.chromium.org/1136553006
Cr-Commit-Position: refs/heads/master@{#28594}
Reason for revert:
breaks build
Original issue's description:
> Implement SharedArrayBuffer.
>
> This adds a new external type (v8::SharedArrayBuffer) that uses a JSArrayBuffer under the hood. It can be distinguished from an ArrayBuffer by the newly-added is_shared() bit.
>
> Currently there is no difference in functionality between a SharedArrayBuffer and an ArrayBuffer. However, a future CL will add the Atomics API, which is only available on an SharedArrayBuffer. All non-atomic accesses are identical to ArrayBuffer accesses.
>
> BUG=
>
> Committed: https://crrev.com/57170bff7baf341c666252a7f6a49e9c08d51263
> Cr-Commit-Position: refs/heads/master@{#28588}
TBR=jarin@chromium.org,jochen@chromium.org,binji@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=
Review URL: https://codereview.chromium.org/1149203003
Cr-Commit-Position: refs/heads/master@{#28589}
This adds a new external type (v8::SharedArrayBuffer) that uses a JSArrayBuffer under the hood. It can be distinguished from an ArrayBuffer by the newly-added is_shared() bit.
Currently there is no difference in functionality between a SharedArrayBuffer and an ArrayBuffer. However, a future CL will add the Atomics API, which is only available on an SharedArrayBuffer. All non-atomic accesses are identical to ArrayBuffer accesses.
BUG=
Review URL: https://codereview.chromium.org/1136553006
Cr-Commit-Position: refs/heads/master@{#28588}
All the builtin iterators as well as the generator objects have an
object called %IteratorPrototype% in the spec between them and
%ObjectPrototype%.
BUG=v8:3568
LOG=N
Review URL: https://codereview.chromium.org/1128233008
Cr-Commit-Position: refs/heads/master@{#28426}
This patch:
- Refactors Parser::ParseVariableDeclarations
- Introduces Parser::PatternMatcher class
- Implements matching a single variable pattern
- Implements rudimentary matching against object literal pattern
as a proof of concept
R=arv@chromium.org,rossberg@chromium.org
BUG=v8:811
LOG=N
Review URL: https://codereview.chromium.org/1130623004
Cr-Commit-Position: refs/heads/master@{#28345}
Instead of making them an extra option that gets passed in and compiled
at the end of the natives file for a given run of js2c, we now make them a
separate run of js2c with a separate natives file output.
This natives file output is then compiled in the bootstrapper. It is not part
of the snapshot (yet), but instead is treated similar to the experimental
natives, just without any of the complexity that comes from tieing the
behavior to flags. We also don't need counterparts to
InitializeExperimentalGlobal and InstallExperimentalNativeFunctions (yet?).
This fixes the issue with https://codereview.chromium.org/1129743003 by making
the dummy file that is generated for snapshots with no extras (or no experimental
features) nonempty.
R=yangguo@chromium.org, jochen@chromium.org
BUG=
Review URL: https://codereview.chromium.org/1130993003
Cr-Commit-Position: refs/heads/master@{#28311}
Reason for revert:
https://build.chromium.org/p/client.v8/builders/V8-Blink%20Linux%2064%20%28dbg%29/builds/2745
Original issue's description:
> Make V8 extras a separate type of native
>
> Instead of making them an extra option that gets passed in and compiled
> at the end of the natives file for a given run of js2c, we now make them a
> separate run of js2c with a separate natives file output.
>
> This natives file output is then compiled in the bootstrapper. It is not part
> of the snapshot (yet), but instead is treated similar to the experimental
> natives, just without any of the complexity that comes from tieing the
> behavior to flags. We also don't add counterparts to
> InitializeExperimentalGlobal and InstallExperimentalNativeFunctions, yet.
>
> R=yangguo@chromium.org, jochen@chromium.org
> BUG=
>
> Committed: https://crrev.com/c93aff4ac63ad9ffb6318e750335208de32b7902
> Cr-Commit-Position: refs/heads/master@{#28296}
TBR=jochen@chromium.org,yangguo@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=
Review URL: https://codereview.chromium.org/1131903002
Cr-Commit-Position: refs/heads/master@{#28299}
Instead of making them an extra option that gets passed in and compiled
at the end of the natives file for a given run of js2c, we now make them a
separate run of js2c with a separate natives file output.
This natives file output is then compiled in the bootstrapper. It is not part
of the snapshot (yet), but instead is treated similar to the experimental
natives, just without any of the complexity that comes from tieing the
behavior to flags. We also don't add counterparts to
InitializeExperimentalGlobal and InstallExperimentalNativeFunctions, yet.
R=yangguo@chromium.org, jochen@chromium.org
BUG=
Review URL: https://codereview.chromium.org/1129743003
Cr-Commit-Position: refs/heads/master@{#28296}
Tail calls are matched on the graph, with a dedicated tail call
optimization that is actually testable. The instruction selection can
still fall back to a regular if the platform constraints don't allow to
emit a tail call (i.e. the return locations of caller and callee differ
or the callee takes non-register parameters, which is a restriction that
will be removed in the future).
Also explicitly limit tail call optimization to stubs for now and drop
the global flag.
BUG=v8:4076
LOG=n
Review URL: https://codereview.chromium.org/1114163005
Cr-Commit-Position: refs/heads/master@{#28219}
Split interface and implementation of ControlEquivalence and add a
dedicated trace flag --trace-turbo-ceq to make it reusable outside the
scheduler.
R=jarin@chromium.org
Review URL: https://codereview.chromium.org/1056093005
Cr-Commit-Position: refs/heads/master@{#27862}
The libdl library is already included on target builds of Android and needs
to be added to the build command line with a particular order to avoid
undefined references in other libraries. Fix this by only explicitly including
it in host builds and relying on the implicit inclusion on target builds.
Also remove the librt hack which is not longer necessary due to the AOSP build
bot having been removed.
BUG=chromium:469973
LOG=Y
Review URL: https://codereview.chromium.org/1036133005
Cr-Commit-Position: refs/heads/master@{#27535}
This prepares for re-landing crrev.com/956373002
This pulls all decision about the snapshot [no|internal|external] into one rule. Previously, this logic was in separate places and not /quite/ the same, which causes build problems.
BUG=
Review URL: https://codereview.chromium.org/1016603004
Cr-Commit-Position: refs/heads/master@{#27523}
This change introduces a liveness analyzer for local variables in frame states.
The main idea is to use the AstGraphBuilder::Environment class to build the control flow graph, and record local variable loads, stores and checkpoints in the CFG basic blocks (LivenessAnalyzerBlock class).
After the graph building finishes, we run a simple data flow analysis over the CFG to figure out liveness of each local variable at each checkpoint. Finally, we run a pass over all the checkpoints and replace dead local variables in the frame states with the 'undefined' value.
Performance numbers for Embenchen are below.
----------- box2d.js
Current --turbo-deoptimization: EmbenchenBox2d(RunTime): 11265 ms.
d8-master --turbo-deoptimization: EmbenchenBox2d(RunTime): 11768 ms.
d8-master: EmbenchenBox2d(RunTime): 10996 ms.
----------- bullet.js
Current --turbo-deoptimization: EmbenchenBullet(RunTime): 17049 ms.
d8-master --turbo-deoptimization: EmbenchenBullet(RunTime): 17384 ms.
d8-master: EmbenchenBullet(RunTime): 16153 ms.
----------- copy.js
Current --turbo-deoptimization: EmbenchenCopy(RunTime): 4877 ms.
d8-master --turbo-deoptimization: EmbenchenCopy(RunTime): 4938 ms.
d8-master: EmbenchenCopy(RunTime): 4940 ms.
----------- corrections.js
Current --turbo-deoptimization: EmbenchenCorrections(RunTime): 7068 ms.
d8-master --turbo-deoptimization: EmbenchenCorrections(RunTime): 6718 ms.
d8-master: EmbenchenCorrections(RunTime): 6858 ms.
----------- fannkuch.js
Current --turbo-deoptimization: EmbenchenFannkuch(RunTime): 4167 ms.
d8-master --turbo-deoptimization: EmbenchenFannkuch(RunTime): 4608 ms.
d8-master: EmbenchenFannkuch(RunTime): 4149 ms.
----------- fasta.js
Current --turbo-deoptimization: EmbenchenFasta(RunTime): 9981 ms.
d8-master --turbo-deoptimization: EmbenchenFasta(RunTime): 9848 ms.
d8-master: EmbenchenFasta(RunTime): 9640 ms.
----------- lua_binarytrees.js
Current --turbo-deoptimization: EmbenchenLuaBinaryTrees(RunTime): 11571 ms.
d8-master --turbo-deoptimization: EmbenchenLuaBinaryTrees(RunTime): 13089 ms.
d8-master: EmbenchenLuaBinaryTrees(RunTime): 10957 ms.
----------- memops.js
Current --turbo-deoptimization: EmbenchenMemOps(RunTime): 7766 ms.
d8-master --turbo-deoptimization: EmbenchenMemOps(RunTime): 7346 ms.
d8-master: EmbenchenMemOps(RunTime): 7738 ms.
----------- primes.js
Current --turbo-deoptimization: EmbenchenPrimes(RunTime): 7459 ms.
d8-master --turbo-deoptimization: EmbenchenPrimes(RunTime): 7453 ms.
d8-master: EmbenchenPrimes(RunTime): 7451 ms.
----------- skinning.js
Current --turbo-deoptimization: EmbenchenSkinning(RunTime): 15564 ms.
d8-master --turbo-deoptimization: EmbenchenSkinning(RunTime): 15611 ms.
d8-master: EmbenchenSkinning(RunTime): 15583 ms.
----------- zlib.js
Current --turbo-deoptimization: EmbenchenZLib(RunTime): 10825 ms.
d8-master --turbo-deoptimization: EmbenchenZLib(RunTime): 11180 ms.
d8-master: EmbenchenZLib(RunTime): 10823 ms.
BUG=
Review URL: https://codereview.chromium.org/949743002
Cr-Commit-Position: refs/heads/master@{#27232}
Instead of the current approach of storing flat vectors in frame states (and possibly reusing the last vector in AST graph builder), this change list builds a tree for the values and tries to reuse the nodes for different frame states. At the moment, we only use this for the local variable part of frame state, but nothing prevents us from using this for all parts.
This change provides two new classes: one for creating the tree (StateValuesCache) and one for iterating the trees (StateValuesAccess).
BUG=
Review URL: https://codereview.chromium.org/1008213002
Cr-Commit-Position: refs/heads/master@{#27222}
Mechanical change.
This will break dependency between profiler-generator and heap-profiler-generator.
Later this will help us to reuse SourcePosition in cpu-profiler.
BUG=452067
LOG=n
Review URL: https://codereview.chromium.org/945873002
Cr-Commit-Position: refs/heads/master@{#26780}
ModuleDescriptor will end up holding the set of data described in the
spec as a "Module record". This introduces a little bit of confusion
with ModuleInfo, but I hope that'll become clearer over time.
Also removed the interface-printing flags. We probably want
Module-printing flags, but that can wait until we have more
Module-related structures.
BUG=v8:1569
LOG=n
Review URL: https://codereview.chromium.org/935723004
Cr-Commit-Position: refs/heads/master@{#26728}
This adds a new ControlFlowOptimizer that - for now - recognizes chains
of Branches generated by the SwitchBuilder for a subset of javascript
switches into Switch nodes. Those Switch nodes are then lowered to
either table or lookup switches.
Also rename Case to IfValue (and introduce IfDefault) for consistency.
BUG=v8:3872
LOG=n
Review URL: https://codereview.chromium.org/931623002
Cr-Commit-Position: refs/heads/master@{#26691}
