SkSLSwitchCaseContainsExit.cpp

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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 "src/sksl/SkSLAnalysis.h"
 
#include "src/sksl/analysis/SkSLProgramVisitor.h"
#include "src/sksl/ir/SkSLIRNode.h"
#include "src/sksl/ir/SkSLStatement.h"
 
namespace SkSL {
 
class Expression;
 
namespace {
 
class SwitchCaseContainsExit : public ProgramVisitor {
public:
    SwitchCaseContainsExit(bool conditionalExits) : fConditionalExits(conditionalExits) {}
 
    bool visitExpression(const Expression& expr) override {
        // We can avoid processing expressions entirely.
        return false;
    }
 
    bool visitStatement(const Statement& stmt) override {
        switch (stmt.kind()) {
            case Statement::Kind::kBlock:
            case Statement::Kind::kSwitchCase:
                return INHERITED::visitStatement(stmt);
 
            case Statement::Kind::kReturn:
                // Returns are an early exit regardless of the surrounding control structures.
                return fConditionalExits ? fInConditional : !fInConditional;
 
            case Statement::Kind::kContinue:
                // Continues are an early exit from switches, but not loops.
                return !fInLoop &&
                       (fConditionalExits ? fInConditional : !fInConditional);
 
            case Statement::Kind::kBreak:
                // Breaks cannot escape from switches or loops.
                return !fInLoop && !fInSwitch &&
                       (fConditionalExits ? fInConditional : !fInConditional);
 
            case Statement::Kind::kIf: {
                ++fInConditional;
                bool result = INHERITED::visitStatement(stmt);
                --fInConditional;
                return result;
            }
 
            case Statement::Kind::kFor:
            case Statement::Kind::kDo: {
                // Loops are treated as conditionals because a loop could potentially execute zero
                // times. We don't have a straightforward way to determine that a loop definitely
                // executes at least once.
                ++fInConditional;
                ++fInLoop;
                bool result = INHERITED::visitStatement(stmt);
                --fInLoop;
                --fInConditional;
                return result;
            }
 
            case Statement::Kind::kSwitch: {
                ++fInSwitch;
                bool result = INHERITED::visitStatement(stmt);
                --fInSwitch;
                return result;
            }
 
            default:
                return false;
        }
    }
 
    bool fConditionalExits = false;
    int fInConditional = 0;
    int fInLoop = 0;
    int fInSwitch = 0;
    using INHERITED = ProgramVisitor;
};
 
}  // namespace
 
bool Analysis::SwitchCaseContainsUnconditionalExit(const Statement& stmt) {
    return SwitchCaseContainsExit{/*conditionalExits=*/false}.visitStatement(stmt);
}
 
bool Analysis::SwitchCaseContainsConditionalExit(const Statement& stmt) {
    return SwitchCaseContainsExit{/*conditionalExits=*/true}.visitStatement(stmt);
}
 
}  // namespace SkSL