src/sksl/SkSLConstantFolder.cpp - platform/external/skia - Gitiles

 /*
  * Copyright 2020 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/SkSLConstantFolder.h"

 #include <limits>

 #include "src/sksl/SkSLContext.h"
 #include "src/sksl/SkSLErrorReporter.h"
 #include "src/sksl/ir/SkSLBinaryExpression.h"
 #include "src/sksl/ir/SkSLBoolLiteral.h"
 #include "src/sksl/ir/SkSLConstructor.h"
 #include "src/sksl/ir/SkSLConstructorCompound.h"
 #include "src/sksl/ir/SkSLConstructorSplat.h"
 #include "src/sksl/ir/SkSLExpression.h"
 #include "src/sksl/ir/SkSLFloatLiteral.h"
 #include "src/sksl/ir/SkSLIntLiteral.h"
 #include "src/sksl/ir/SkSLPrefixExpression.h"
 #include "src/sksl/ir/SkSLType.h"
 #include "src/sksl/ir/SkSLVariable.h"
 #include "src/sksl/ir/SkSLVariableReference.h"

 namespace SkSL {

 static std::unique_ptr<Expression> eliminate_no_op_boolean(const Expression& left,
                                                            Operator op,
                                                            const Expression& right) {
     SkASSERT(right.is<BoolLiteral>());
     bool rightVal = right.as<BoolLiteral>().value();

     // Detect no-op Boolean expressions and optimize them away.
     if ((op.kind() == Token::Kind::TK_LOGICALAND && rightVal)  ||  // (expr && true)  -> (expr)
         (op.kind() == Token::Kind::TK_LOGICALOR  && !rightVal) ||  // (expr || false) -> (expr)
         (op.kind() == Token::Kind::TK_LOGICALXOR && !rightVal) ||  // (expr ^^ false) -> (expr)
         (op.kind() == Token::Kind::TK_EQEQ       && rightVal)  ||  // (expr == true)  -> (expr)
         (op.kind() == Token::Kind::TK_NEQ        && !rightVal)) {  // (expr != false) -> (expr)

         return left.clone();
     }

     return nullptr;
 }

 static std::unique_ptr<Expression> short_circuit_boolean(const Expression& left,
                                                          Operator op,
                                                          const Expression& right) {
     SkASSERT(left.is<BoolLiteral>());
     bool leftVal = left.as<BoolLiteral>().value();

     // When the literal is on the left, we can sometimes eliminate the other expression entirely.
     if ((op.kind() == Token::Kind::TK_LOGICALAND && !leftVal) ||  // (false && expr) -> (false)
         (op.kind() == Token::Kind::TK_LOGICALOR  && leftVal)) {   // (true  || expr) -> (true)

         return left.clone();
     }

     // We can't eliminate the right-side expression via short-circuit, but we might still be able to
     // simplify away a no-op expression.
     return eliminate_no_op_boolean(right, op, left);
 }

 // 'T' is the actual stored type of the literal data (SKSL_FLOAT or SKSL_INT).
 // 'U' is an unsigned version of that, used to perform addition, subtraction, and multiplication,
 // to avoid signed-integer overflow errors. This mimics the use of URESULT vs. RESULT when doing
 // scalar folding in Simplify, later in this file.
 template <typename T, typename U = T>
 static std::unique_ptr<Expression> simplify_vector(const Context& context,
                                                    const Expression& left,
                                                    Operator op,
                                                    const Expression& right) {
     SkASSERT(left.type().isVector());
     SkASSERT(left.type() == right.type());
     const Type& type = left.type();

     // Handle boolean operations: == !=
     if (op.kind() == Token::Kind::TK_EQEQ || op.kind() == Token::Kind::TK_NEQ) {
         bool equality = (op.kind() == Token::Kind::TK_EQEQ);

         switch (left.compareConstant(right)) {
             case Expression::ComparisonResult::kNotEqual:
                 equality = !equality;
                 [[fallthrough]];

             case Expression::ComparisonResult::kEqual:
                 return BoolLiteral::Make(context, left.fOffset, equality);

             case Expression::ComparisonResult::kUnknown:
                 return nullptr;
         }
     }

     // Handle floating-point arithmetic: + - * /
     const auto vectorComponentwiseFold = [&](auto foldFn) -> std::unique_ptr<Expression> {
         const Type& componentType = type.componentType();
         ExpressionArray args;
         args.reserve_back(type.columns());
         for (int i = 0; i < type.columns(); i++) {
             U value = foldFn(left.getConstantSubexpression(i)->as<Literal<T>>().value(),
                              right.getConstantSubexpression(i)->as<Literal<T>>().value());
             args.push_back(Literal<T>::Make(left.fOffset, value, &componentType));
         }
         return ConstructorCompound::Make(context, left.fOffset, type, std::move(args));
     };

     switch (op.kind()) {
         case Token::Kind::TK_PLUS:  return vectorComponentwiseFold([](U a, U b) { return a + b; });
         case Token::Kind::TK_MINUS: return vectorComponentwiseFold([](U a, U b) { return a - b; });
         case Token::Kind::TK_STAR:  return vectorComponentwiseFold([](U a, U b) { return a * b; });
         case Token::Kind::TK_SLASH: return vectorComponentwiseFold([](T a, T b) { return a / b; });
         default:
             return nullptr;
     }
 }

 static std::unique_ptr<Expression> cast_expression(const Context& context,
                                                    const Expression& expr,
                                                    const Type& type) {
     ExpressionArray ctorArgs;
     ctorArgs.push_back(expr.clone());
     std::unique_ptr<Expression> ctor = Constructor::Convert(context, expr.fOffset, type,
                                                             std::move(ctorArgs));
     SkASSERT(ctor);
     return ctor;
 }

 static ConstructorSplat splat_scalar(const Expression& scalar, const Type& type) {
     SkASSERT(type.isVector());
     SkASSERT(type.componentType() == scalar.type());

     // Use a constructor to splat the scalar expression across a vector.
     return ConstructorSplat{scalar.fOffset, type, scalar.clone()};
 }

 bool ConstantFolder::GetConstantInt(const Expression& value, SKSL_INT* out) {
     const Expression* expr = GetConstantValueForVariable(value);
     if (!expr->is<IntLiteral>()) {
         return false;
     }
     *out = expr->as<IntLiteral>().value();
     return true;
 }

 bool ConstantFolder::GetConstantFloat(const Expression& value, SKSL_FLOAT* out) {
     const Expression* expr = GetConstantValueForVariable(value);
     if (!expr->is<FloatLiteral>()) {
         return false;
     }
     *out = expr->as<FloatLiteral>().value();
     return true;
 }

 static bool is_constant_scalar_value(const Expression& inExpr, float match) {
     const Expression* expr = ConstantFolder::GetConstantValueForVariable(inExpr);
     return (expr->is<IntLiteral>()   && expr->as<IntLiteral>().value()   == match) ||
            (expr->is<FloatLiteral>() && expr->as<FloatLiteral>().value() == match);
 }

 static bool contains_constant_zero(const Expression& expr) {
     if (expr.isAnyConstructor()) {
         for (const auto& arg : expr.asAnyConstructor().argumentSpan()) {
             if (contains_constant_zero(*arg)) {
                 return true;
             }
         }
         return false;
     }
     return is_constant_scalar_value(expr, 0.0);
 }

 static bool is_constant_value(const Expression& expr, float value) {
     // This check only supports scalars and vectors (and in particular, not matrices).
     SkASSERT(expr.type().isScalar() || expr.type().isVector());

     if (expr.isAnyConstructor()) {
         for (const auto& arg : expr.asAnyConstructor().argumentSpan()) {
             if (!is_constant_value(*arg, value)) {
                 return false;
             }
         }
         return true;
     }
     return is_constant_scalar_value(expr, value);
 }

 bool ConstantFolder::ErrorOnDivideByZero(const Context& context, int offset, Operator op,
                                          const Expression& right) {
     switch (op.kind()) {
         case Token::Kind::TK_SLASH:
         case Token::Kind::TK_SLASHEQ:
         case Token::Kind::TK_PERCENT:
         case Token::Kind::TK_PERCENTEQ:
             if (contains_constant_zero(right)) {
                 context.fErrors.error(offset, "division by zero");
                 return true;
             }
             return false;
         default:
             return false;
     }
 }

 const Expression* ConstantFolder::GetConstantValueForVariable(const Expression& inExpr) {
     for (const Expression* expr = &inExpr;;) {
         if (!expr->is<VariableReference>()) {
             break;
         }
         const VariableReference& varRef = expr->as<VariableReference>();
         if (varRef.refKind() != VariableRefKind::kRead) {
             break;
         }
         const Variable& var = *varRef.variable();
         if (!(var.modifiers().fFlags & Modifiers::kConst_Flag)) {
             break;
         }
         expr = var.initialValue();
         if (!expr) {
             SkDEBUGFAILF("found a const variable without an initial value (%s)",
                          var.description().c_str());
             break;
         }
         if (expr->isCompileTimeConstant()) {
             return expr;
         }
         if (!expr->is<VariableReference>()) {
             break;
         }
     }
     // We didn't find a compile-time constant at the end. Return the expression as-is.
     return &inExpr;
 }

 std::unique_ptr<Expression> ConstantFolder::MakeConstantValueForVariable(
         std::unique_ptr<Expression> expr) {
     const Expression* constantExpr = GetConstantValueForVariable(*expr);
     if (constantExpr != expr.get()) {
         expr = constantExpr->clone();
     }
     return expr;
 }

 static std::unique_ptr<Expression> simplify_no_op_arithmetic(const Context& context,
                                                              const Expression& left,
                                                              Operator op,
                                                              const Expression& right,
                                                              const Type& resultType) {
     switch (op.kind()) {
         case Token::Kind::TK_PLUS:
             if (is_constant_value(right, 0.0)) {  // x + 0
                 return cast_expression(context, left, resultType);
             }
             if (is_constant_value(left, 0.0)) {   // 0 + x
                 return cast_expression(context, right, resultType);
             }
             break;

         case Token::Kind::TK_STAR:
             if (is_constant_value(right, 1.0)) {  // x * 1
                 return cast_expression(context, left, resultType);
             }
             if (is_constant_value(left, 1.0)) {   // 1 * x
                 return cast_expression(context, right, resultType);
             }
             if (is_constant_value(right, 0.0) && !left.hasSideEffects()) {  // x * 0
                 return cast_expression(context, right, resultType);
             }
             if (is_constant_value(left, 0.0) && !right.hasSideEffects()) {  // 0 * x
                 return cast_expression(context, left, resultType);
             }
             break;

         case Token::Kind::TK_MINUS:
             if (is_constant_value(right, 0.0)) {  // x - 0
                 return cast_expression(context, left, resultType);
             }
             if (is_constant_value(left, 0.0)) {   // 0 - x (to `-x`)
                 return PrefixExpression::Make(context, Token::Kind::TK_MINUS,
                                               cast_expression(context, right, resultType));
             }
             break;

         case Token::Kind::TK_SLASH:
             if (is_constant_value(right, 1.0)) {  // x / 1
                 return cast_expression(context, left, resultType);
             }
             if (is_constant_value(left, 0.0) &&
                 !is_constant_value(right, 0.0) &&
                 !right.hasSideEffects()) {        // 0 / x (where x is not 0)
                 return cast_expression(context, left, resultType);
             }
             break;

         case Token::Kind::TK_PLUSEQ:
         case Token::Kind::TK_MINUSEQ:
             if (is_constant_value(right, 0.0)) {  // x += 0, x -= 0
                 std::unique_ptr<Expression> result = cast_expression(context, left, resultType);
                 Analysis::UpdateRefKind(result.get(), VariableRefKind::kRead);
                 return result;
             }
             break;

         case Token::Kind::TK_STAREQ:
         case Token::Kind::TK_SLASHEQ:
             if (is_constant_value(right, 1.0)) {  // x *= 1, x /= 1
                 std::unique_ptr<Expression> result = cast_expression(context, left, resultType);
                 Analysis::UpdateRefKind(result.get(), VariableRefKind::kRead);
                 return result;
             }
             break;

         default:
             break;
     }

     return nullptr;
 }

 std::unique_ptr<Expression> ConstantFolder::Simplify(const Context& context,
                                                      int offset,
                                                      const Expression& leftExpr,
                                                      Operator op,
                                                      const Expression& rightExpr,
                                                      const Type& resultType) {
     // When optimization is enabled, replace constant variables with trivial initial-values.
     const Expression* left;
     const Expression* right;
     if (context.fConfig->fSettings.fOptimize) {
         left = GetConstantValueForVariable(leftExpr);
         right = GetConstantValueForVariable(rightExpr);
     } else {
         left = &leftExpr;
         right = &rightExpr;
     }

     // If this is the comma operator, the left side is evaluated but not otherwise used in any way.
     // So if the left side has no side effects, it can just be eliminated entirely.
     if (op.kind() == Token::Kind::TK_COMMA && !left->hasSideEffects()) {
         return right->clone();
     }

     // If this is the assignment operator, and both sides are the same trivial expression, this is
     // self-assignment (i.e., `var = var`) and can be reduced to just a variable reference (`var`).
     // This can happen when other parts of the assignment are optimized away.
     if (op.kind() == Token::Kind::TK_EQ && Analysis::IsSameExpressionTree(*left, *right)) {
         return right->clone();
     }

     // Simplify the expression when both sides are constant Boolean literals.
     if (left->is<BoolLiteral>() && right->is<BoolLiteral>()) {
         bool leftVal  = left->as<BoolLiteral>().value();
         bool rightVal = right->as<BoolLiteral>().value();
         bool result;
         switch (op.kind()) {
             case Token::Kind::TK_LOGICALAND: result = leftVal && rightVal; break;
             case Token::Kind::TK_LOGICALOR:  result = leftVal || rightVal; break;
             case Token::Kind::TK_LOGICALXOR: result = leftVal ^  rightVal; break;
             case Token::Kind::TK_EQEQ:       result = leftVal == rightVal; break;
             case Token::Kind::TK_NEQ:        result = leftVal != rightVal; break;
             default: return nullptr;
         }
         return BoolLiteral::Make(context, offset, result);
     }

     // If the left side is a Boolean literal, apply short-circuit optimizations.
     if (left->is<BoolLiteral>()) {
         return short_circuit_boolean(*left, op, *right);
     }

     // If the right side is a Boolean literal...
     if (right->is<BoolLiteral>()) {
         // ... and the left side has no side effects...
         if (!left->hasSideEffects()) {
             // We can reverse the expressions and short-circuit optimizations are still valid.
             return short_circuit_boolean(*right, op, *left);
         }

         // We can't use short-circuiting, but we can still optimize away no-op Boolean expressions.
         return eliminate_no_op_boolean(*left, op, *right);
     }

     if (op.kind() == Token::Kind::TK_EQEQ && Analysis::IsSameExpressionTree(*left, *right)) {
         // With == comparison, if both sides are the same trivial expression, this is self-
         // comparison and is always true. (We are not concerned with NaN.)
         return BoolLiteral::Make(context, leftExpr.fOffset, /*value=*/true);
     }

     if (op.kind() == Token::Kind::TK_NEQ && Analysis::IsSameExpressionTree(*left, *right)) {
         // With != comparison, if both sides are the same trivial expression, this is self-
         // comparison and is always false. (We are not concerned with NaN.)
         return BoolLiteral::Make(context, leftExpr.fOffset, /*value=*/false);
     }

     if (ErrorOnDivideByZero(context, offset, op, *right)) {
         return nullptr;
     }

     // Optimize away no-op arithmetic like `x * 1`, `x *= 1`, `x + 0`, `x * 0`, `0 / x`, etc.
     const Type& leftType = left->type();
     const Type& rightType = right->type();
     if ((leftType.isScalar() || leftType.isVector()) &&
         (rightType.isScalar() || rightType.isVector())) {
         std::unique_ptr<Expression> expr = simplify_no_op_arithmetic(context, *left, op, *right,
                                                                      resultType);
         if (expr) {
             return expr;
         }
     }

     // Other than the cases above, constant folding requires both sides to be constant.
     if (!left->isCompileTimeConstant() || !right->isCompileTimeConstant()) {
         return nullptr;
     }

     // Note that we expressly do not worry about precision and overflow here -- we use the maximum
     // precision to calculate the results and hope the result makes sense.
     // TODO(skia:10932): detect and handle integer overflow properly.
     using SKSL_UINT = uint64_t;
     #define RESULT(t, op)   t ## Literal::Make(offset, leftVal op rightVal, &resultType)
     #define URESULT(t, op)  t ## Literal::Make(offset, (SKSL_UINT)(leftVal) op \
                                                        (SKSL_UINT)(rightVal), &resultType)
     if (left->is<IntLiteral>() && right->is<IntLiteral>()) {
         SKSL_INT leftVal  = left->as<IntLiteral>().value();
         SKSL_INT rightVal = right->as<IntLiteral>().value();
         switch (op.kind()) {
             case Token::Kind::TK_PLUS:       return URESULT(Int, +);
             case Token::Kind::TK_MINUS:      return URESULT(Int, -);
             case Token::Kind::TK_STAR:       return URESULT(Int, *);
             case Token::Kind::TK_SLASH:
                 if (leftVal == std::numeric_limits<SKSL_INT>::min() && rightVal == -1) {
                     context.fErrors.error(offset, "arithmetic overflow");
                     return nullptr;
                 }
                 return RESULT(Int, /);
             case Token::Kind::TK_PERCENT:
                 if (leftVal == std::numeric_limits<SKSL_INT>::min() && rightVal == -1) {
                     context.fErrors.error(offset, "arithmetic overflow");
                     return nullptr;
                 }
                 return RESULT(Int, %);
             case Token::Kind::TK_BITWISEAND: return RESULT(Int,  &);
             case Token::Kind::TK_BITWISEOR:  return RESULT(Int,  |);
             case Token::Kind::TK_BITWISEXOR: return RESULT(Int,  ^);
             case Token::Kind::TK_EQEQ:       return RESULT(Bool, ==);
             case Token::Kind::TK_NEQ:        return RESULT(Bool, !=);
             case Token::Kind::TK_GT:         return RESULT(Bool, >);
             case Token::Kind::TK_GTEQ:       return RESULT(Bool, >=);
             case Token::Kind::TK_LT:         return RESULT(Bool, <);
             case Token::Kind::TK_LTEQ:       return RESULT(Bool, <=);
             case Token::Kind::TK_SHL:
                 if (rightVal >= 0 && rightVal <= 31) {
                     // Left-shifting a negative (or really, any signed) value is undefined behavior
                     // in C++, but not GLSL. Do the shift on unsigned values, to avoid UBSAN.
                     return URESULT(Int,  <<);
                 }
                 context.fErrors.error(offset, "shift value out of range");
                 return nullptr;
             case Token::Kind::TK_SHR:
                 if (rightVal >= 0 && rightVal <= 31) {
                     return RESULT(Int,  >>);
                 }
                 context.fErrors.error(offset, "shift value out of range");
                 return nullptr;

             default:
                 return nullptr;
         }
     }

     // Perform constant folding on pairs of floating-point literals.
     if (left->is<FloatLiteral>() && right->is<FloatLiteral>()) {
         SKSL_FLOAT leftVal  = left->as<FloatLiteral>().value();
         SKSL_FLOAT rightVal = right->as<FloatLiteral>().value();
         switch (op.kind()) {
             case Token::Kind::TK_PLUS:  return RESULT(Float, +);
             case Token::Kind::TK_MINUS: return RESULT(Float, -);
             case Token::Kind::TK_STAR:  return RESULT(Float, *);
             case Token::Kind::TK_SLASH: return RESULT(Float, /);
             case Token::Kind::TK_EQEQ: return RESULT(Bool, ==);
             case Token::Kind::TK_NEQ:  return RESULT(Bool, !=);
             case Token::Kind::TK_GT:   return RESULT(Bool, >);
             case Token::Kind::TK_GTEQ: return RESULT(Bool, >=);
             case Token::Kind::TK_LT:   return RESULT(Bool, <);
             case Token::Kind::TK_LTEQ: return RESULT(Bool, <=);
             default:                   return nullptr;
         }
     }

     // Perform constant folding on pairs of vectors.
     if (leftType.isVector() && leftType == rightType) {
         if (leftType.componentType().isFloat()) {
             return simplify_vector<SKSL_FLOAT>(context, *left, op, *right);
         }
         if (leftType.componentType().isInteger()) {
             return simplify_vector<SKSL_INT, SKSL_UINT>(context, *left, op, *right);
         }
         return nullptr;
     }

     // Perform constant folding on vectors against scalars, e.g.: half4(2) + 2
     if (leftType.isVector() && leftType.componentType() == rightType) {
         if (rightType.isFloat()) {
             return simplify_vector<SKSL_FLOAT>(context, *left, op,
                                                splat_scalar(*right, left->type()));
         }
         if (rightType.isInteger()) {
             return simplify_vector<SKSL_INT, SKSL_UINT>(context, *left, op,
                                                         splat_scalar(*right, left->type()));
         }
         return nullptr;
     }

     // Perform constant folding on scalars against vectors, e.g.: 2 + half4(2)
     if (rightType.isVector() && rightType.componentType() == leftType) {
         if (leftType.isFloat()) {
             return simplify_vector<SKSL_FLOAT>(context, splat_scalar(*left, right->type()), op,
                                                *right);
         }
         if (leftType.isInteger()) {
             return simplify_vector<SKSL_INT, SKSL_UINT>(context, splat_scalar(*left, right->type()),
                                                         op, *right);
         }
         return nullptr;
     }

     // Perform constant folding on pairs of matrices or arrays.
     if ((leftType.isMatrix() && rightType.isMatrix()) ||
         (leftType.isArray() && rightType.isArray())) {
         bool equality;
         switch (op.kind()) {
             case Token::Kind::TK_EQEQ:
                 equality = true;
                 break;
             case Token::Kind::TK_NEQ:
                 equality = false;
                 break;
             default:
                 return nullptr;
         }

         switch (left->compareConstant(*right)) {
             case Expression::ComparisonResult::kNotEqual:
                 equality = !equality;
                 [[fallthrough]];

             case Expression::ComparisonResult::kEqual:
                 return BoolLiteral::Make(context, offset, equality);

             case Expression::ComparisonResult::kUnknown:
                 return nullptr;
         }
     }

     // We aren't able to constant-fold.
     #undef RESULT
     #undef URESULT
     return nullptr;
 }

 }  // namespace SkSL
	/*
	* Copyright 2020 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/SkSLConstantFolder.h"

	#include <limits>

	#include "src/sksl/SkSLContext.h"
	#include "src/sksl/SkSLErrorReporter.h"
	#include "src/sksl/ir/SkSLBinaryExpression.h"
	#include "src/sksl/ir/SkSLBoolLiteral.h"
	#include "src/sksl/ir/SkSLConstructor.h"
	#include "src/sksl/ir/SkSLConstructorCompound.h"
	#include "src/sksl/ir/SkSLConstructorSplat.h"
	#include "src/sksl/ir/SkSLExpression.h"
	#include "src/sksl/ir/SkSLFloatLiteral.h"
	#include "src/sksl/ir/SkSLIntLiteral.h"
	#include "src/sksl/ir/SkSLPrefixExpression.h"
	#include "src/sksl/ir/SkSLType.h"
	#include "src/sksl/ir/SkSLVariable.h"
	#include "src/sksl/ir/SkSLVariableReference.h"

	namespace SkSL {

	static std::unique_ptr<Expression> eliminate_no_op_boolean(const Expression& left,
	Operator op,
	const Expression& right) {
	SkASSERT(right.is<BoolLiteral>());
	bool rightVal = right.as<BoolLiteral>().value();

	// Detect no-op Boolean expressions and optimize them away.
	if ((op.kind() == Token::Kind::TK_LOGICALAND && rightVal) \|\| // (expr && true) -> (expr)
	(op.kind() == Token::Kind::TK_LOGICALOR && !rightVal) \|\| // (expr \|\| false) -> (expr)
	(op.kind() == Token::Kind::TK_LOGICALXOR && !rightVal) \|\| // (expr ^^ false) -> (expr)
	(op.kind() == Token::Kind::TK_EQEQ && rightVal) \|\| // (expr == true) -> (expr)
	(op.kind() == Token::Kind::TK_NEQ && !rightVal)) { // (expr != false) -> (expr)

	return left.clone();
	}

	return nullptr;
	}

	static std::unique_ptr<Expression> short_circuit_boolean(const Expression& left,
	Operator op,
	const Expression& right) {
	SkASSERT(left.is<BoolLiteral>());
	bool leftVal = left.as<BoolLiteral>().value();

	// When the literal is on the left, we can sometimes eliminate the other expression entirely.
	if ((op.kind() == Token::Kind::TK_LOGICALAND && !leftVal) \|\| // (false && expr) -> (false)
	(op.kind() == Token::Kind::TK_LOGICALOR && leftVal)) { // (true \|\| expr) -> (true)

	return left.clone();
	}

	// We can't eliminate the right-side expression via short-circuit, but we might still be able to
	// simplify away a no-op expression.
	return eliminate_no_op_boolean(right, op, left);
	}

	// 'T' is the actual stored type of the literal data (SKSL_FLOAT or SKSL_INT).
	// 'U' is an unsigned version of that, used to perform addition, subtraction, and multiplication,
	// to avoid signed-integer overflow errors. This mimics the use of URESULT vs. RESULT when doing
	// scalar folding in Simplify, later in this file.
	template <typename T, typename U = T>
	static std::unique_ptr<Expression> simplify_vector(const Context& context,
	const Expression& left,
	Operator op,
	const Expression& right) {
	SkASSERT(left.type().isVector());
	SkASSERT(left.type() == right.type());
	const Type& type = left.type();

	// Handle boolean operations: == !=
	if (op.kind() == Token::Kind::TK_EQEQ \|\| op.kind() == Token::Kind::TK_NEQ) {
	bool equality = (op.kind() == Token::Kind::TK_EQEQ);

	switch (left.compareConstant(right)) {
	case Expression::ComparisonResult::kNotEqual:
	equality = !equality;
	[[fallthrough]];

	case Expression::ComparisonResult::kEqual:
	return BoolLiteral::Make(context, left.fOffset, equality);

	case Expression::ComparisonResult::kUnknown:
	return nullptr;
	}
	}

	// Handle floating-point arithmetic: + - * /
	const auto vectorComponentwiseFold = [&](auto foldFn) -> std::unique_ptr<Expression> {
	const Type& componentType = type.componentType();
	ExpressionArray args;
	args.reserve_back(type.columns());
	for (int i = 0; i < type.columns(); i++) {
	U value = foldFn(left.getConstantSubexpression(i)->as<Literal<T>>().value(),
	right.getConstantSubexpression(i)->as<Literal<T>>().value());
	args.push_back(Literal<T>::Make(left.fOffset, value, &componentType));
	}
	return ConstructorCompound::Make(context, left.fOffset, type, std::move(args));
	};

	switch (op.kind()) {
	case Token::Kind::TK_PLUS: return vectorComponentwiseFold([](U a, U b) { return a + b; });
	case Token::Kind::TK_MINUS: return vectorComponentwiseFold([](U a, U b) { return a - b; });
	case Token::Kind::TK_STAR: return vectorComponentwiseFold([](U a, U b) { return a * b; });
	case Token::Kind::TK_SLASH: return vectorComponentwiseFold([](T a, T b) { return a / b; });
	default:
	return nullptr;
	}
	}

	static std::unique_ptr<Expression> cast_expression(const Context& context,
	const Expression& expr,
	const Type& type) {
	ExpressionArray ctorArgs;
	ctorArgs.push_back(expr.clone());
	std::unique_ptr<Expression> ctor = Constructor::Convert(context, expr.fOffset, type,
	std::move(ctorArgs));
	SkASSERT(ctor);
	return ctor;
	}

	static ConstructorSplat splat_scalar(const Expression& scalar, const Type& type) {
	SkASSERT(type.isVector());
	SkASSERT(type.componentType() == scalar.type());

	// Use a constructor to splat the scalar expression across a vector.
	return ConstructorSplat{scalar.fOffset, type, scalar.clone()};
	}

	bool ConstantFolder::GetConstantInt(const Expression& value, SKSL_INT* out) {
	const Expression* expr = GetConstantValueForVariable(value);
	if (!expr->is<IntLiteral>()) {
	return false;
	}
	*out = expr->as<IntLiteral>().value();
	return true;
	}

	bool ConstantFolder::GetConstantFloat(const Expression& value, SKSL_FLOAT* out) {
	const Expression* expr = GetConstantValueForVariable(value);
	if (!expr->is<FloatLiteral>()) {
	return false;
	}
	*out = expr->as<FloatLiteral>().value();
	return true;
	}

	static bool is_constant_scalar_value(const Expression& inExpr, float match) {
	const Expression* expr = ConstantFolder::GetConstantValueForVariable(inExpr);
	return (expr->is<IntLiteral>() && expr->as<IntLiteral>().value() == match) \|\|
	(expr->is<FloatLiteral>() && expr->as<FloatLiteral>().value() == match);
	}

	static bool contains_constant_zero(const Expression& expr) {
	if (expr.isAnyConstructor()) {
	for (const auto& arg : expr.asAnyConstructor().argumentSpan()) {
	if (contains_constant_zero(*arg)) {
	return true;
	}
	}
	return false;
	}
	return is_constant_scalar_value(expr, 0.0);
	}

	static bool is_constant_value(const Expression& expr, float value) {
	// This check only supports scalars and vectors (and in particular, not matrices).
	SkASSERT(expr.type().isScalar() \|\| expr.type().isVector());

	if (expr.isAnyConstructor()) {
	for (const auto& arg : expr.asAnyConstructor().argumentSpan()) {
	if (!is_constant_value(*arg, value)) {
	return false;
	}
	}
	return true;
	}
	return is_constant_scalar_value(expr, value);
	}

	bool ConstantFolder::ErrorOnDivideByZero(const Context& context, int offset, Operator op,
	const Expression& right) {
	switch (op.kind()) {
	case Token::Kind::TK_SLASH:
	case Token::Kind::TK_SLASHEQ:
	case Token::Kind::TK_PERCENT:
	case Token::Kind::TK_PERCENTEQ:
	if (contains_constant_zero(right)) {
	context.fErrors.error(offset, "division by zero");
	return true;
	}
	return false;
	default:
	return false;
	}
	}

	const Expression* ConstantFolder::GetConstantValueForVariable(const Expression& inExpr) {
	for (const Expression* expr = &inExpr;;) {
	if (!expr->is<VariableReference>()) {
	break;
	}
	const VariableReference& varRef = expr->as<VariableReference>();
	if (varRef.refKind() != VariableRefKind::kRead) {
	break;
	}
	const Variable& var = *varRef.variable();
	if (!(var.modifiers().fFlags & Modifiers::kConst_Flag)) {
	break;
	}
	expr = var.initialValue();
	if (!expr) {
	SkDEBUGFAILF("found a const variable without an initial value (%s)",
	var.description().c_str());
	break;
	}
	if (expr->isCompileTimeConstant()) {
	return expr;
	}
	if (!expr->is<VariableReference>()) {
	break;
	}
	}
	// We didn't find a compile-time constant at the end. Return the expression as-is.
	return &inExpr;
	}

	std::unique_ptr<Expression> ConstantFolder::MakeConstantValueForVariable(
	std::unique_ptr<Expression> expr) {
	const Expression* constantExpr = GetConstantValueForVariable(*expr);
	if (constantExpr != expr.get()) {
	expr = constantExpr->clone();
	}
	return expr;
	}

	static std::unique_ptr<Expression> simplify_no_op_arithmetic(const Context& context,
	const Expression& left,
	Operator op,
	const Expression& right,
	const Type& resultType) {
	switch (op.kind()) {
	case Token::Kind::TK_PLUS:
	if (is_constant_value(right, 0.0)) { // x + 0
	return cast_expression(context, left, resultType);
	}
	if (is_constant_value(left, 0.0)) { // 0 + x
	return cast_expression(context, right, resultType);
	}
	break;

	case Token::Kind::TK_STAR:
	if (is_constant_value(right, 1.0)) { // x * 1
	return cast_expression(context, left, resultType);
	}
	if (is_constant_value(left, 1.0)) { // 1 * x
	return cast_expression(context, right, resultType);
	}
	if (is_constant_value(right, 0.0) && !left.hasSideEffects()) { // x * 0
	return cast_expression(context, right, resultType);
	}
	if (is_constant_value(left, 0.0) && !right.hasSideEffects()) { // 0 * x
	return cast_expression(context, left, resultType);
	}
	break;

	case Token::Kind::TK_MINUS:
	if (is_constant_value(right, 0.0)) { // x - 0
	return cast_expression(context, left, resultType);
	}
	if (is_constant_value(left, 0.0)) { // 0 - x (to `-x`)
	return PrefixExpression::Make(context, Token::Kind::TK_MINUS,
	cast_expression(context, right, resultType));
	}
	break;

	case Token::Kind::TK_SLASH:
	if (is_constant_value(right, 1.0)) { // x / 1
	return cast_expression(context, left, resultType);
	}
	if (is_constant_value(left, 0.0) &&
	!is_constant_value(right, 0.0) &&
	!right.hasSideEffects()) { // 0 / x (where x is not 0)
	return cast_expression(context, left, resultType);
	}
	break;

	case Token::Kind::TK_PLUSEQ:
	case Token::Kind::TK_MINUSEQ:
	if (is_constant_value(right, 0.0)) { // x += 0, x -= 0
	std::unique_ptr<Expression> result = cast_expression(context, left, resultType);
	Analysis::UpdateRefKind(result.get(), VariableRefKind::kRead);
	return result;
	}
	break;

	case Token::Kind::TK_STAREQ:
	case Token::Kind::TK_SLASHEQ:
	if (is_constant_value(right, 1.0)) { // x *= 1, x /= 1
	std::unique_ptr<Expression> result = cast_expression(context, left, resultType);
	Analysis::UpdateRefKind(result.get(), VariableRefKind::kRead);
	return result;
	}
	break;

	default:
	break;
	}

	return nullptr;
	}

	std::unique_ptr<Expression> ConstantFolder::Simplify(const Context& context,
	int offset,
	const Expression& leftExpr,
	Operator op,
	const Expression& rightExpr,
	const Type& resultType) {
	// When optimization is enabled, replace constant variables with trivial initial-values.
	const Expression* left;
	const Expression* right;
	if (context.fConfig->fSettings.fOptimize) {
	left = GetConstantValueForVariable(leftExpr);
	right = GetConstantValueForVariable(rightExpr);
	} else {
	left = &leftExpr;
	right = &rightExpr;
	}

	// If this is the comma operator, the left side is evaluated but not otherwise used in any way.
	// So if the left side has no side effects, it can just be eliminated entirely.
	if (op.kind() == Token::Kind::TK_COMMA && !left->hasSideEffects()) {
	return right->clone();
	}

	// If this is the assignment operator, and both sides are the same trivial expression, this is
	// self-assignment (i.e., `var = var`) and can be reduced to just a variable reference (`var`).
	// This can happen when other parts of the assignment are optimized away.
	if (op.kind() == Token::Kind::TK_EQ && Analysis::IsSameExpressionTree(left, right)) {
	return right->clone();
	}

	// Simplify the expression when both sides are constant Boolean literals.
	if (left->is<BoolLiteral>() && right->is<BoolLiteral>()) {
	bool leftVal = left->as<BoolLiteral>().value();
	bool rightVal = right->as<BoolLiteral>().value();
	bool result;
	switch (op.kind()) {
	case Token::Kind::TK_LOGICALAND: result = leftVal && rightVal; break;
	case Token::Kind::TK_LOGICALOR: result = leftVal \|\| rightVal; break;
	case Token::Kind::TK_LOGICALXOR: result = leftVal ^ rightVal; break;
	case Token::Kind::TK_EQEQ: result = leftVal == rightVal; break;
	case Token::Kind::TK_NEQ: result = leftVal != rightVal; break;
	default: return nullptr;
	}
	return BoolLiteral::Make(context, offset, result);
	}

	// If the left side is a Boolean literal, apply short-circuit optimizations.
	if (left->is<BoolLiteral>()) {
	return short_circuit_boolean(left, op, right);
	}

	// If the right side is a Boolean literal...
	if (right->is<BoolLiteral>()) {
	// ... and the left side has no side effects...
	if (!left->hasSideEffects()) {
	// We can reverse the expressions and short-circuit optimizations are still valid.
	return short_circuit_boolean(right, op, left);
	}

	// We can't use short-circuiting, but we can still optimize away no-op Boolean expressions.
	return eliminate_no_op_boolean(left, op, right);
	}

	if (op.kind() == Token::Kind::TK_EQEQ && Analysis::IsSameExpressionTree(left, right)) {
	// With == comparison, if both sides are the same trivial expression, this is self-
	// comparison and is always true. (We are not concerned with NaN.)
	return BoolLiteral::Make(context, leftExpr.fOffset, /value=/true);
	}

	if (op.kind() == Token::Kind::TK_NEQ && Analysis::IsSameExpressionTree(left, right)) {
	// With != comparison, if both sides are the same trivial expression, this is self-
	// comparison and is always false. (We are not concerned with NaN.)
	return BoolLiteral::Make(context, leftExpr.fOffset, /value=/false);
	}

	if (ErrorOnDivideByZero(context, offset, op, *right)) {
	return nullptr;
	}

	// Optimize away no-op arithmetic like `x * 1`, `x = 1`, `x + 0`, `x 0`, `0 / x`, etc.
	const Type& leftType = left->type();
	const Type& rightType = right->type();
	if ((leftType.isScalar() \|\| leftType.isVector()) &&
	(rightType.isScalar() \|\| rightType.isVector())) {
	std::unique_ptr<Expression> expr = simplify_no_op_arithmetic(context, left, op, right,
	resultType);
	if (expr) {
	return expr;
	}
	}

	// Other than the cases above, constant folding requires both sides to be constant.
	if (!left->isCompileTimeConstant() \|\| !right->isCompileTimeConstant()) {
	return nullptr;
	}

	// Note that we expressly do not worry about precision and overflow here -- we use the maximum
	// precision to calculate the results and hope the result makes sense.
	// TODO(skia:10932): detect and handle integer overflow properly.
	using SKSL_UINT = uint64_t;
	#define RESULT(t, op) t ## Literal::Make(offset, leftVal op rightVal, &resultType)
	#define URESULT(t, op) t ## Literal::Make(offset, (SKSL_UINT)(leftVal) op \
	(SKSL_UINT)(rightVal), &resultType)
	if (left->is<IntLiteral>() && right->is<IntLiteral>()) {
	SKSL_INT leftVal = left->as<IntLiteral>().value();
	SKSL_INT rightVal = right->as<IntLiteral>().value();
	switch (op.kind()) {
	case Token::Kind::TK_PLUS: return URESULT(Int, +);
	case Token::Kind::TK_MINUS: return URESULT(Int, -);
	case Token::Kind::TK_STAR: return URESULT(Int, *);
	case Token::Kind::TK_SLASH:
	if (leftVal == std::numeric_limits<SKSL_INT>::min() && rightVal == -1) {
	context.fErrors.error(offset, "arithmetic overflow");
	return nullptr;
	}
	return RESULT(Int, /);
	case Token::Kind::TK_PERCENT:
	if (leftVal == std::numeric_limits<SKSL_INT>::min() && rightVal == -1) {
	context.fErrors.error(offset, "arithmetic overflow");
	return nullptr;
	}
	return RESULT(Int, %);
	case Token::Kind::TK_BITWISEAND: return RESULT(Int, &);
	case Token::Kind::TK_BITWISEOR: return RESULT(Int, \|);
	case Token::Kind::TK_BITWISEXOR: return RESULT(Int, ^);
	case Token::Kind::TK_EQEQ: return RESULT(Bool, ==);
	case Token::Kind::TK_NEQ: return RESULT(Bool, !=);
	case Token::Kind::TK_GT: return RESULT(Bool, >);
	case Token::Kind::TK_GTEQ: return RESULT(Bool, >=);
	case Token::Kind::TK_LT: return RESULT(Bool, <);
	case Token::Kind::TK_LTEQ: return RESULT(Bool, <=);
	case Token::Kind::TK_SHL:
	if (rightVal >= 0 && rightVal <= 31) {
	// Left-shifting a negative (or really, any signed) value is undefined behavior
	// in C++, but not GLSL. Do the shift on unsigned values, to avoid UBSAN.
	return URESULT(Int, <<);
	}
	context.fErrors.error(offset, "shift value out of range");
	return nullptr;
	case Token::Kind::TK_SHR:
	if (rightVal >= 0 && rightVal <= 31) {
	return RESULT(Int, >>);
	}
	context.fErrors.error(offset, "shift value out of range");
	return nullptr;

	default:
	return nullptr;
	}
	}

	// Perform constant folding on pairs of floating-point literals.
	if (left->is<FloatLiteral>() && right->is<FloatLiteral>()) {
	SKSL_FLOAT leftVal = left->as<FloatLiteral>().value();
	SKSL_FLOAT rightVal = right->as<FloatLiteral>().value();
	switch (op.kind()) {
	case Token::Kind::TK_PLUS: return RESULT(Float, +);
	case Token::Kind::TK_MINUS: return RESULT(Float, -);
	case Token::Kind::TK_STAR: return RESULT(Float, *);
	case Token::Kind::TK_SLASH: return RESULT(Float, /);
	case Token::Kind::TK_EQEQ: return RESULT(Bool, ==);
	case Token::Kind::TK_NEQ: return RESULT(Bool, !=);
	case Token::Kind::TK_GT: return RESULT(Bool, >);
	case Token::Kind::TK_GTEQ: return RESULT(Bool, >=);
	case Token::Kind::TK_LT: return RESULT(Bool, <);
	case Token::Kind::TK_LTEQ: return RESULT(Bool, <=);
	default: return nullptr;
	}
	}

	// Perform constant folding on pairs of vectors.
	if (leftType.isVector() && leftType == rightType) {
	if (leftType.componentType().isFloat()) {
	return simplify_vector<SKSL_FLOAT>(context, left, op, right);
	}
	if (leftType.componentType().isInteger()) {
	return simplify_vector<SKSL_INT, SKSL_UINT>(context, left, op, right);
	}
	return nullptr;
	}

	// Perform constant folding on vectors against scalars, e.g.: half4(2) + 2
	if (leftType.isVector() && leftType.componentType() == rightType) {
	if (rightType.isFloat()) {
	return simplify_vector<SKSL_FLOAT>(context, *left, op,
	splat_scalar(*right, left->type()));
	}
	if (rightType.isInteger()) {
	return simplify_vector<SKSL_INT, SKSL_UINT>(context, *left, op,
	splat_scalar(*right, left->type()));
	}
	return nullptr;
	}

	// Perform constant folding on scalars against vectors, e.g.: 2 + half4(2)
	if (rightType.isVector() && rightType.componentType() == leftType) {
	if (leftType.isFloat()) {
	return simplify_vector<SKSL_FLOAT>(context, splat_scalar(*left, right->type()), op,
	*right);
	}
	if (leftType.isInteger()) {
	return simplify_vector<SKSL_INT, SKSL_UINT>(context, splat_scalar(*left, right->type()),
	op, *right);
	}
	return nullptr;
	}

	// Perform constant folding on pairs of matrices or arrays.
	if ((leftType.isMatrix() && rightType.isMatrix()) \|\|
	(leftType.isArray() && rightType.isArray())) {
	bool equality;
	switch (op.kind()) {
	case Token::Kind::TK_EQEQ:
	equality = true;
	break;
	case Token::Kind::TK_NEQ:
	equality = false;
	break;
	default:
	return nullptr;
	}

	switch (left->compareConstant(*right)) {
	case Expression::ComparisonResult::kNotEqual:
	equality = !equality;
	[[fallthrough]];

	case Expression::ComparisonResult::kEqual:
	return BoolLiteral::Make(context, offset, equality);

	case Expression::ComparisonResult::kUnknown:
	return nullptr;
	}
	}

	// We aren't able to constant-fold.
	#undef RESULT
	#undef URESULT
	return nullptr;
	}

	} // namespace SkSL