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//
// Copyright 2002 The ANGLE Project Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// During parsing, all constant expressions are folded to constant union nodes. The expressions that
// have been folded may have had precision qualifiers, which should affect the precision of the
// consuming operation. If the folded constant union nodes are written to output as such they won't
// have any precision qualifiers, and their effect on the precision of the consuming operation is
// lost.
//
// RecordConstantPrecision is an AST traverser that inspects the precision qualifiers of constants
// and hoists the constants outside the containing expression as precision qualified named variables
// in case that is required for correct precision propagation.
//
#include "compiler/translator/tree_ops/RecordConstantPrecision.h"
#include "compiler/translator/InfoSink.h"
#include "compiler/translator/tree_util/IntermNode_util.h"
#include "compiler/translator/tree_util/IntermTraverse.h"
namespace sh
{
namespace
{
class RecordConstantPrecisionTraverser : public TIntermTraverser
{
public:
RecordConstantPrecisionTraverser(TSymbolTable *symbolTable);
void visitConstantUnion(TIntermConstantUnion *node) override;
protected:
bool operandAffectsParentOperationPrecision(TIntermTyped *operand);
};
RecordConstantPrecisionTraverser::RecordConstantPrecisionTraverser(TSymbolTable *symbolTable)
: TIntermTraverser(true, false, true, symbolTable)
{}
bool RecordConstantPrecisionTraverser::operandAffectsParentOperationPrecision(TIntermTyped *operand)
{
if (getParentNode()->getAsCaseNode() || getParentNode()->getAsBlock())
{
return false;
}
if (operand->getBasicType() == EbtBool || operand->getBasicType() == EbtStruct)
{
return false;
}
const TIntermBinary *parentAsBinary = getParentNode()->getAsBinaryNode();
if (parentAsBinary != nullptr)
{
// If the constant is assigned or is used to initialize a variable, or if it's an index,
// its precision has no effect.
switch (parentAsBinary->getOp())
{
case EOpInitialize:
case EOpAssign:
case EOpIndexDirect:
case EOpIndexDirectStruct:
case EOpIndexDirectInterfaceBlock:
case EOpIndexIndirect:
return false;
default:
return true;
}
}
TIntermAggregate *parentAsAggregate = getParentNode()->getAsAggregate();
if (parentAsAggregate != nullptr)
{
// The precision of an aggregate is derived from children only in the following conditions:
//
// - Built-in math operations
// - Constructors
//
return parentAsAggregate->isConstructor() ||
BuiltInGroup::IsMath(parentAsAggregate->getOp());
}
return true;
}
void RecordConstantPrecisionTraverser::visitConstantUnion(TIntermConstantUnion *node)
{
// If the constant has lowp or undefined precision, it can't increase the precision of consuming
// operations.
if (node->getPrecision() < EbpMedium)
return;
// It's possible the node has no effect on the precision of the consuming expression, depending
// on the consuming expression, and the precision of the other parameters of the expression.
if (!operandAffectsParentOperationPrecision(node))
return;
// Make the constant a precision-qualified named variable to make sure it affects the precision
// of the consuming expression.
TIntermDeclaration *variableDeclaration = nullptr;
TVariable *variable = DeclareTempVariable(mSymbolTable, node, EvqConst, &variableDeclaration);
insertStatementInParentBlock(variableDeclaration);
queueReplacement(CreateTempSymbolNode(variable), OriginalNode::IS_DROPPED);
}
} // namespace
bool RecordConstantPrecision(TCompiler *compiler, TIntermNode *root, TSymbolTable *symbolTable)
{
RecordConstantPrecisionTraverser traverser(symbolTable);
root->traverse(&traverser);
return traverser.updateTree(compiler, root);
}
} // namespace sh
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