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[skjson] Remove the scope index stack

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We already allocate a placeholder on the values stack -- we can use that
space to save the previous scope index instead of a dedicated stack.

Yields some minor perf improvements: ~3.5% arm32, ~0.5% x86_64.

Change-Id: I1be30aeb01b1c9661abfe06763a820673e3883f4
Reviewed-on: https://skia-review.googlesource.com/136178
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
This commit is contained in:
Florin Malita 2018-06-20 14:23:23 -04:00 committed by Skia Commit-Bot
parent f9ae670d05
commit 2e5c1aef58
1 changed files with 54 additions and 31 deletions
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85
src/utils/SkJSON.cpp
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@ -272,9 +272,7 @@ class DOMParser {
public:
explicit DOMParser(SkArenaAlloc& alloc)
: fAlloc(alloc) {
fValueStack.reserve(kValueStackReserve);
fScopeStack.reserve(kScopeStackReserve);
}
const Value parse(const char* p, size_t size) {
@ -361,15 +359,16 @@ public:
// goto match_post_value;
match_post_value:
SkASSERT(!fScopeStack.empty());
SkASSERT(!this->inTopLevelScope());
p = skip_ws(p);
switch (*p) {
case ',':
++p;
if (fScopeStack.back() >= 0) {
if (this->inObjectScope()) {
goto match_object_key;
} else {
SkASSERT(this->inArrayScope());
goto match_value;
}
case ']':
@ -386,7 +385,7 @@ public:
pop_object:
SkASSERT(*p == '}');
if (fScopeStack.back() < 0) {
if (this->inArrayScope()) {
return this->error(NullValue(), p, "unexpected object terminator");
}
@ -396,7 +395,7 @@ public:
pop_common:
SkASSERT(is_eoscope(*p));
if (fScopeStack.empty()) {
if (this->inTopLevelScope()) {
SkASSERT(fValueStack.size() == 1);
// Success condition: parsed the top level element and reached the stop token.
@ -425,7 +424,7 @@ public:
pop_array:
SkASSERT(*p == ']');
if (fScopeStack.back() >= 0) {
if (this->inObjectScope()) {
return this->error(NullValue(), p, "unexpected array terminator");
}
@ -444,14 +443,38 @@ public:
private:
SkArenaAlloc& fAlloc;
// Pending values stack.
static constexpr size_t kValueStackReserve = 256;
static constexpr size_t kScopeStackReserve = 128;
std::vector<Value > fValueStack;
std::vector<intptr_t> fScopeStack;
std::vector<Value> fValueStack;
// Tracks the current object/array scope, as an index into fStack:
//
// - for objects: fScopeIndex = (index of first value in scope)
// - for arrays : fScopeIndex = -(index of first value in scope)
//
// fScopeIndex == 0 IFF we are at the top level (no current/active scope).
intptr_t fScopeIndex = 0;
// Error reporting.
const char* fErrorToken = nullptr;
SkString fErrorMessage;
bool inTopLevelScope() const { return fScopeIndex == 0; }
bool inObjectScope() const { return fScopeIndex > 0; }
bool inArrayScope() const { return fScopeIndex < 0; }
// Helper for masquerading raw primitive types as Values (bypassing tagging, etc).
template <typename T>
class RawValue final : public Value {
public:
explicit RawValue(T v) {
static_assert(sizeof(T) <= sizeof(Value), "");
*this->cast<T>() = v;
}
T operator *() const { return *this->cast<T>(); }
};
template <typename VectorT>
void popScopeAsVec(size_t scope_start) {
SkASSERT(scope_start > 0);
@ -468,26 +491,27 @@ private:
const auto* begin = reinterpret_cast<const T*>(fValueStack.data() + scope_start);
// Instantiate the placeholder value added in onPush{Object/Array}.
fValueStack[scope_start - 1] = VectorT(begin, count, fAlloc);
// Restore the previous scope index from saved placeholder value,
// and instantiate as a vector of values in scope.
auto& placeholder = fValueStack[scope_start - 1];
fScopeIndex = *static_cast<RawValue<intptr_t>&>(placeholder);
placeholder = VectorT(begin, count, fAlloc);
// Drop the current scope.
fScopeStack.pop_back();
// Drop the (consumed) values in scope.
fValueStack.resize(scope_start);
}
void pushObjectScope() {
// Object placeholder.
fValueStack.emplace_back();
// Save a scope index now, and then later we'll overwrite this value as the Object itself.
fValueStack.push_back(RawValue<intptr_t>(fScopeIndex));
// Object scope marker (size).
fScopeStack.push_back(SkTo<intptr_t>(fValueStack.size()));
// New object scope.
fScopeIndex = SkTo<intptr_t>(fValueStack.size());
}
void popObjectScope() {
const auto scope_start = fScopeStack.back();
SkASSERT(scope_start > 0);
this->popScopeAsVec<ObjectValue>(SkTo<size_t>(scope_start));
SkASSERT(this->inObjectScope());
this->popScopeAsVec<ObjectValue>(SkTo<size_t>(fScopeIndex));
SkDEBUGCODE(
const auto& obj = fValueStack.back().as<ObjectValue>();
@ -499,17 +523,16 @@ private:
}
void pushArrayScope() {
// Array placeholder.
fValueStack.emplace_back();
// Save a scope index now, and then later we'll overwrite this value as the Array itself.
fValueStack.push_back(RawValue<intptr_t>(fScopeIndex));
// Array scope marker (-size).
fScopeStack.push_back(-SkTo<intptr_t>(fValueStack.size()));
// New array scope.
fScopeIndex = -SkTo<intptr_t>(fValueStack.size());
}
void popArrayScope() {
const auto scope_start = -fScopeStack.back();
SkASSERT(scope_start > 0);
this->popScopeAsVec<ArrayValue>(SkTo<size_t>(scope_start));
SkASSERT(this->inArrayScope());
this->popScopeAsVec<ArrayValue>(SkTo<size_t>(-fScopeIndex));
SkDEBUGCODE(
const auto& arr = fValueStack.back().as<ArrayValue>();
@ -518,9 +541,9 @@ private:
}
void pushObjectKey(const char* key, size_t size, const char* eos) {
SkASSERT(fScopeStack.back() >= 0);
SkASSERT(fValueStack.size() >= SkTo<size_t>(fScopeStack.back()));
SkASSERT(!((fValueStack.size() - SkTo<size_t>(fScopeStack.back())) & 1));
SkASSERT(this->inObjectScope());
SkASSERT(fValueStack.size() >= SkTo<size_t>(fScopeIndex));
SkASSERT(!((fValueStack.size() - SkTo<size_t>(fScopeIndex)) & 1));
this->pushString(key, size, eos);
}