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//
// Copyright 2018 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.
//
// PruneEmptyCases.cpp: The PruneEmptyCases function prunes cases that are followed by nothing from
// the AST.
#include "compiler/translator/tree_ops/PruneEmptyCases.h"
#include "compiler/translator/Symbol.h"
#include "compiler/translator/tree_util/IntermTraverse.h"
namespace sh
{
namespace
{
bool AreEmptyBlocks(const TIntermSequence *statements);
bool IsEmptyBlock(TIntermNode *node)
{
TIntermBlock *asBlock = node->getAsBlock();
if (asBlock)
{
return AreEmptyBlocks(asBlock->getSequence());
}
// Empty declarations should have already been pruned, otherwise they would need to be handled
// here. Note that declarations for struct types do contain a nameless child node.
ASSERT(node->getAsDeclarationNode() == nullptr ||
!node->getAsDeclarationNode()->getSequence()->empty());
// Pure literal statements should also already be pruned.
ASSERT(node->getAsConstantUnion() == nullptr);
return false;
}
// Return true if all statements in "statements" consist only of empty blocks and no-op statements.
// Returns true also if there are no statements.
bool AreEmptyBlocks(const TIntermSequence *statements)
{
for (size_t i = 0u; i < statements->size(); ++i)
{
if (!IsEmptyBlock(statements->at(i)))
{
return false;
}
}
return true;
}
class PruneEmptyCasesTraverser : private TIntermTraverser
{
public:
[[nodiscard]] static bool apply(TCompiler *compiler, TIntermBlock *root);
private:
PruneEmptyCasesTraverser();
bool visitSwitch(Visit visit, TIntermSwitch *node) override;
};
bool PruneEmptyCasesTraverser::apply(TCompiler *compiler, TIntermBlock *root)
{
PruneEmptyCasesTraverser prune;
root->traverse(&prune);
return prune.updateTree(compiler, root);
}
PruneEmptyCasesTraverser::PruneEmptyCasesTraverser() : TIntermTraverser(true, false, false) {}
bool PruneEmptyCasesTraverser::visitSwitch(Visit visit, TIntermSwitch *node)
{
// This may mutate the statementList, but that's okay, since traversal has not yet reached
// there.
TIntermBlock *statementList = node->getStatementList();
TIntermSequence *statements = statementList->getSequence();
// Iterate block children in reverse order. Cases that are only followed by other cases or empty
// blocks are marked for pruning.
size_t i = statements->size();
size_t lastNoOpInStatementList = i;
while (i > 0)
{
--i;
TIntermNode *statement = statements->at(i);
if (statement->getAsCaseNode() || IsEmptyBlock(statement))
{
lastNoOpInStatementList = i;
}
else
{
break;
}
}
if (lastNoOpInStatementList == 0)
{
// Remove the entire switch statement, extracting the init expression if needed.
TIntermTyped *init = node->getInit();
if (init->hasSideEffects())
{
queueReplacement(init, OriginalNode::IS_DROPPED);
}
else
{
TIntermSequence emptyReplacement;
ASSERT(getParentNode()->getAsBlock());
mMultiReplacements.emplace_back(getParentNode()->getAsBlock(), node,
std::move(emptyReplacement));
}
return false;
}
if (lastNoOpInStatementList < statements->size())
{
statements->erase(statements->begin() + lastNoOpInStatementList, statements->end());
}
return true;
}
} // namespace
bool PruneEmptyCases(TCompiler *compiler, TIntermBlock *root)
{
return PruneEmptyCasesTraverser::apply(compiler, root);
}
} // namespace sh
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