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* Copyright 2020 Google LLC
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#ifndef SkSLAnalysis_DEFINED
#define SkSLAnalysis_DEFINED
#include "include/private/SkSLDefines.h"
#include "include/private/SkSLSampleUsage.h"
#include <memory>
namespace SkSL {
class ErrorReporter;
class Expression;
class ForStatement;
class FunctionDeclaration;
class FunctionDefinition;
struct LoadedModule;
struct Program;
class ProgramElement;
class ProgramUsage;
class Statement;
class Variable;
class VariableReference;
enum class VariableRefKind : int8_t;
* Provides utilities for analyzing SkSL statically before it's composed into a full program.
struct Analysis {
* Determines how `program` samples `fp`. By default, assumes that the sample coords
* (SK_MAIN_COORDS_BUILTIN) might be modified, so `sample(fp, sampleCoords)` is treated as
* Explicit. If writesToSampleCoords is false, treats that as PassThrough, instead.
static SampleUsage GetSampleUsage(const Program& program,
const Variable& fp,
bool writesToSampleCoords = true);
static bool ReferencesBuiltin(const Program& program, int builtin);
static bool ReferencesSampleCoords(const Program& program);
static bool ReferencesFragCoords(const Program& program);
static int NodeCountUpToLimit(const FunctionDefinition& function, int limit);
* Finds unconditional exits from a switch-case. Returns true if this statement unconditionally
* causes an exit from this switch (via continue, break or return).
static bool SwitchCaseContainsUnconditionalExit(Statement& stmt);
* A switch-case "falls through" when it doesn't have an unconditional exit.
static bool SwitchCaseFallsThrough(Statement& stmt) {
return !SwitchCaseContainsUnconditionalExit(stmt);
* Finds conditional exits from a switch-case. Returns true if this statement contains a
* conditional that wraps a potential exit from the switch (via continue, break or return).
static bool SwitchCaseContainsConditionalExit(Statement& stmt);
static std::unique_ptr<ProgramUsage> GetUsage(const Program& program);
static std::unique_ptr<ProgramUsage> GetUsage(const LoadedModule& module);
static bool StatementWritesToVariable(const Statement& stmt, const Variable& var);
struct AssignmentInfo {
VariableReference* fAssignedVar = nullptr;
static bool IsAssignable(Expression& expr, AssignmentInfo* info = nullptr,
ErrorReporter* errors = nullptr);
// Updates the `refKind` field of exactly one VariableReference inside `expr`.
// `expr` must be `IsAssignable`; returns an error otherwise.
static bool MakeAssignmentExpr(Expression* expr, VariableRefKind kind, ErrorReporter* errors);
// Updates the `refKind` field of every VariableReference found within `expr`.
// `expr` is allowed to have zero, one, or multiple VariableReferences.
static void UpdateRefKind(Expression* expr, VariableRefKind refKind);
// A "trivial" expression is one where we'd feel comfortable cloning it multiple times in
// the code, without worrying about incurring a performance penalty. Examples:
// - true
// - 3.14159265
// - myIntVariable
// - myColor.rgb
// - myArray[123]
// - myStruct.myField
// - half4(0)
// Trivial-ness is stackable. Somewhat large expressions can occasionally make the cut:
// - half4(myColor.a)
// - myStruct.myArrayField[7].xyz
static bool IsTrivialExpression(const Expression& expr);
// Returns true if both expression trees are the same. Used by the optimizer to look for self-
// assignment or self-comparison; won't necessarily catch complex cases. Rejects expressions
// that may cause side effects.
static bool IsSameExpressionTree(const Expression& left, const Expression& right);
// Is 'expr' a constant-expression, as defined by GLSL 1.0, section 5.10? A constant expression
// is one of:
// - A literal value
// - A global or local variable qualified as 'const', excluding function parameters
// - An expression formed by an operator on operands that are constant expressions, including
// getting an element of a constant vector or a constant matrix, or a field of a constant
// structure
// - A constructor whose arguments are all constant expressions
// GLSL (but not SkSL, yet - also provides:
// - A built-in function call whose arguments are all constant expressions, with the exception
// of the texture lookup functions
static bool IsConstantExpression(const Expression& expr);
struct UnrollableLoopInfo {
const Variable* fIndex;
double fStart;
double fDelta;
int fCount;
// Ensures that a for-loop meets the strict requirements of The OpenGL ES Shading Language 1.00,
// Appendix A, Section 4.
// Information about the loop's structure are placed in outLoopInfo (if not nullptr).
// If the function returns false, specific reasons are reported via errors (if not nullptr).
static bool ForLoopIsValidForES2(int offset,
const Statement* loopInitializer,
const Expression* loopTest,
const Expression* loopNext,
const Statement* loopStatement,
UnrollableLoopInfo* outLoopInfo,
ErrorReporter* errors);
static void ValidateIndexingForES2(const ProgramElement& pe, ErrorReporter& errors);
// Detects functions that fail to return a value on at least one path.
static bool CanExitWithoutReturningValue(const FunctionDeclaration& funcDecl,
const Statement& body);
* Utility class to visit every element, statement, and expression in an SkSL program IR.
* This is intended for simple analysis and accumulation, where custom visitation behavior is only
* needed for a limited set of expression kinds.
* Subclasses should override visitExpression/visitStatement/visitProgramElement as needed and
* intercept elements of interest. They can then invoke the base class's function to visit all
* sub expressions. They can also choose not to call the base function to arrest recursion, or
* implement custom recursion.
* The visit functions return a bool that determines how the default implementation recurses. Once
* any visit call returns true, the default behavior stops recursing and propagates true up the
* stack.
template <typename T>
class TProgramVisitor {
virtual ~TProgramVisitor() = default;
virtual bool visitExpression(typename T::Expression& expression);
virtual bool visitStatement(typename T::Statement& statement);
virtual bool visitProgramElement(typename T::ProgramElement& programElement);
virtual bool visitExpressionPtr(typename T::UniquePtrExpression& expr) = 0;
virtual bool visitStatementPtr(typename T::UniquePtrStatement& stmt) = 0;
// ProgramVisitors take const types; ProgramWriters do not.
struct ProgramVisitorTypes {
using Program = const SkSL::Program;
using Expression = const SkSL::Expression;
using Statement = const SkSL::Statement;
using ProgramElement = const SkSL::ProgramElement;
using UniquePtrExpression = const std::unique_ptr<SkSL::Expression>;
using UniquePtrStatement = const std::unique_ptr<SkSL::Statement>;
struct ProgramWriterTypes {
using Program = SkSL::Program;
using Expression = SkSL::Expression;
using Statement = SkSL::Statement;
using ProgramElement = SkSL::ProgramElement;
using UniquePtrExpression = std::unique_ptr<SkSL::Expression>;
using UniquePtrStatement = std::unique_ptr<SkSL::Statement>;
// Squelch bogus Clang warning about template vtables:
#if defined(__clang__)
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wweak-template-vtables"
extern template class TProgramVisitor<ProgramVisitorTypes>;
extern template class TProgramVisitor<ProgramWriterTypes>;
#if defined(__clang__)
#pragma clang diagnostic pop
class ProgramVisitor : public TProgramVisitor<ProgramVisitorTypes> {
bool visit(const Program& program);
// ProgramVisitors shouldn't need access to unique_ptrs, and marking these as final should help
// these accessors inline away. Use ProgramWriter if you need the unique_ptrs.
bool visitExpressionPtr(const std::unique_ptr<Expression>& e) final {
return this->visitExpression(*e);
bool visitStatementPtr(const std::unique_ptr<Statement>& s) final {
return this->visitStatement(*s);
class ProgramWriter : public TProgramVisitor<ProgramWriterTypes> {
// Subclass these methods if you want access to the unique_ptrs of IRNodes in a program.
// This will allow statements or expressions to be replaced during a visit.
bool visitExpressionPtr(std::unique_ptr<Expression>& e) override {
return this->visitExpression(*e);
bool visitStatementPtr(std::unique_ptr<Statement>& s) override {
return this->visitStatement(*s);
} // namespace SkSL