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/*
* Copyright 2021 Google LLC
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "include/core/SkTypes.h"
#include "include/private/SkSLModifiers.h"
#include "include/private/SkSLProgramElement.h"
#include "src/core/SkTHash.h"
#include "src/sksl/SkSLCompiler.h"
#include "src/sksl/SkSLConstantFolder.h"
#include "src/sksl/analysis/SkSLProgramUsage.h"
#include "src/sksl/ir/SkSLExpression.h"
#include "src/sksl/ir/SkSLFunctionDefinition.h"
#include "src/sksl/ir/SkSLVariable.h"
#include "src/sksl/ir/SkSLVariableReference.h"
#include "src/sksl/transform/SkSLProgramWriter.h"
#include "src/sksl/transform/SkSLTransform.h"
#include <cstddef>
#include <memory>
#include <string>
#include <string_view>
#include <vector>
namespace SkSL {
void Transform::ReplaceConstVarsWithLiterals(Module& module, ProgramUsage* usage) {
class ConstVarReplacer : public ProgramWriter {
public:
ConstVarReplacer(ProgramUsage* usage) : fUsage(usage) {}
using ProgramWriter::visitProgramElement;
bool visitExpressionPtr(std::unique_ptr<Expression>& expr) override {
// If this is a variable...
if (expr->is<VariableReference>()) {
VariableReference& var = expr->as<VariableReference>();
// ... and it's a candidate for size reduction...
if (fCandidates.contains(var.variable())) {
// ... get its constant value...
if (const Expression* value =
ConstantFolder::GetConstantValueOrNullForVariable(var)) {
// ... and replace it with that value.
fUsage->remove(expr.get());
expr = value->clone();
fUsage->add(expr.get());
return false;
}
}
}
return INHERITED::visitExpressionPtr(expr);
}
ProgramUsage* fUsage;
SkTHashSet<const Variable*> fCandidates;
using INHERITED = ProgramWriter;
};
ConstVarReplacer visitor{usage};
for (const auto& [var, count] : usage->fVariableCounts) {
// We can only replace const variables that still exist, and that have initial values.
if (!count.fVarExists || count.fWrite != 1) {
continue;
}
if (!(var->modifiers().fFlags & Modifiers::kConst_Flag)) {
continue;
}
if (!var->initialValue()) {
continue;
}
// The current size is:
// strlen("const type varname=initialvalue;`") + count*strlen("varname").
size_t initialvalueSize = ConstantFolder::GetConstantValueForVariable(*var->initialValue())
->description()
.size();
size_t totalOldSize = var->description().size() + // const type varname
1 + // =
initialvalueSize + // initialvalue
1 + // ;
count.fRead * var->name().size(); // count * varname
// If we replace varname with initialvalue everywhere, the new size would be:
// count*strlen("initialvalue")
size_t totalNewSize = count.fRead * initialvalueSize; // count * initialvalue
if (totalNewSize <= totalOldSize) {
visitor.fCandidates.add(var);
}
}
if (!visitor.fCandidates.empty()) {
for (std::unique_ptr<ProgramElement>& pe : module.fElements) {
if (pe->is<FunctionDefinition>()) {
visitor.visitProgramElement(*pe);
}
}
}
}
} // namespace SkSL
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