RemoveSwitchFallThrough.cpp

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Author : Stuart Morgan
Date : 2019-08-14 12:25:12
Hash : 9d737966
Message : Standardize copyright notices to project style For all "ANGLE Project" copyrights, standardize to the format specified by the style guide. Changes: - "Copyright (c)" and "Copyright(c)" changed to just "Copyright". - Removed the second half of date ranges ("Y1Y1-Y2Y2"->"Y1Y1"). - Fixed a small number of files that had no copyright date using the initial commit year from the version control history. - Fixed one instance of copyright being "The ANGLE Project" rather than "The ANGLE Project Authors" These changes are applied both to the copyright of source file, and where applicable to copyright statements that are generated by templates. BUG=angleproject:3811 Change-Id: I973dd65e4ef9deeba232d5be74c768256a0eb2e5 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1754397 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>

src/compiler/translator/tree_ops/RemoveSwitchFallThrough.cpp

//
// 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.
//
// RemoveSwitchFallThrough.cpp: Remove fall-through from switch statements.
// Note that it is unsafe to do further AST transformations on the AST generated
// by this function. It leaves duplicate nodes in the AST making replacements
// unreliable.

#include "compiler/translator/tree_ops/RemoveSwitchFallThrough.h"

#include "compiler/translator/Diagnostics.h"
#include "compiler/translator/tree_util/IntermTraverse.h"

namespace sh
{

namespace
{

class RemoveSwitchFallThroughTraverser : public TIntermTraverser
{
  public:
    static TIntermBlock *removeFallThrough(TIntermBlock *statementList,
                                           PerformanceDiagnostics *perfDiagnostics);

  private:
    RemoveSwitchFallThroughTraverser(TIntermBlock *statementList,
                                     PerformanceDiagnostics *perfDiagnostics);

    void visitSymbol(TIntermSymbol *node) override;
    void visitConstantUnion(TIntermConstantUnion *node) override;
    bool visitDeclaration(Visit, TIntermDeclaration *node) override;
    bool visitBinary(Visit, TIntermBinary *node) override;
    bool visitUnary(Visit, TIntermUnary *node) override;
    bool visitTernary(Visit visit, TIntermTernary *node) override;
    bool visitSwizzle(Visit, TIntermSwizzle *node) override;
    bool visitIfElse(Visit visit, TIntermIfElse *node) override;
    bool visitSwitch(Visit, TIntermSwitch *node) override;
    bool visitCase(Visit, TIntermCase *node) override;
    bool visitAggregate(Visit, TIntermAggregate *node) override;
    bool visitBlock(Visit, TIntermBlock *node) override;
    bool visitLoop(Visit, TIntermLoop *node) override;
    bool visitBranch(Visit, TIntermBranch *node) override;

    void outputSequence(TIntermSequence *sequence, size_t startIndex);
    void handlePreviousCase();

    TIntermBlock *mStatementList;
    TIntermBlock *mStatementListOut;
    bool mLastStatementWasBreak;
    TIntermBlock *mPreviousCase;
    std::vector<TIntermBlock *> mCasesSharingBreak;
    PerformanceDiagnostics *mPerfDiagnostics;
};

TIntermBlock *RemoveSwitchFallThroughTraverser::removeFallThrough(
    TIntermBlock *statementList,
    PerformanceDiagnostics *perfDiagnostics)
{
    RemoveSwitchFallThroughTraverser rm(statementList, perfDiagnostics);
    ASSERT(statementList);
    statementList->traverse(&rm);
    ASSERT(rm.mPreviousCase || statementList->getSequence()->empty());
    if (!rm.mLastStatementWasBreak && rm.mPreviousCase)
    {
        // Make sure that there's a branch at the end of the final case inside the switch statement.
        // This also ensures that any cases that fall through to the final case will get the break.
        TIntermBranch *finalBreak = new TIntermBranch(EOpBreak, nullptr);
        rm.mPreviousCase->getSequence()->push_back(finalBreak);
        rm.mLastStatementWasBreak = true;
    }
    rm.handlePreviousCase();
    return rm.mStatementListOut;
}

RemoveSwitchFallThroughTraverser::RemoveSwitchFallThroughTraverser(
    TIntermBlock *statementList,
    PerformanceDiagnostics *perfDiagnostics)
    : TIntermTraverser(true, false, false),
      mStatementList(statementList),
      mLastStatementWasBreak(false),
      mPreviousCase(nullptr),
      mPerfDiagnostics(perfDiagnostics)
{
    mStatementListOut = new TIntermBlock();
}

void RemoveSwitchFallThroughTraverser::visitSymbol(TIntermSymbol *node)
{
    // Note that this assumes that switch statements which don't begin by a case statement
    // have already been weeded out in validation.
    mPreviousCase->getSequence()->push_back(node);
    mLastStatementWasBreak = false;
}

void RemoveSwitchFallThroughTraverser::visitConstantUnion(TIntermConstantUnion *node)
{
    // Conditions of case labels are not traversed, so this is a constant statement like "0;".
    // These are no-ops so there's no need to add them back to the statement list. Should have
    // already been pruned out of the AST, in fact.
    UNREACHABLE();
}

bool RemoveSwitchFallThroughTraverser::visitDeclaration(Visit, TIntermDeclaration *node)
{
    mPreviousCase->getSequence()->push_back(node);
    mLastStatementWasBreak = false;
    return false;
}

bool RemoveSwitchFallThroughTraverser::visitBinary(Visit, TIntermBinary *node)
{
    mPreviousCase->getSequence()->push_back(node);
    mLastStatementWasBreak = false;
    return false;
}

bool RemoveSwitchFallThroughTraverser::visitUnary(Visit, TIntermUnary *node)
{
    mPreviousCase->getSequence()->push_back(node);
    mLastStatementWasBreak = false;
    return false;
}

bool RemoveSwitchFallThroughTraverser::visitTernary(Visit, TIntermTernary *node)
{
    mPreviousCase->getSequence()->push_back(node);
    mLastStatementWasBreak = false;
    return false;
}

bool RemoveSwitchFallThroughTraverser::visitSwizzle(Visit, TIntermSwizzle *node)
{
    mPreviousCase->getSequence()->push_back(node);
    mLastStatementWasBreak = false;
    return false;
}

bool RemoveSwitchFallThroughTraverser::visitIfElse(Visit, TIntermIfElse *node)
{
    mPreviousCase->getSequence()->push_back(node);
    mLastStatementWasBreak = false;
    return false;
}

bool RemoveSwitchFallThroughTraverser::visitSwitch(Visit, TIntermSwitch *node)
{
    mPreviousCase->getSequence()->push_back(node);
    mLastStatementWasBreak = false;
    // Don't go into nested switch statements
    return false;
}

void RemoveSwitchFallThroughTraverser::outputSequence(TIntermSequence *sequence, size_t startIndex)
{
    for (size_t i = startIndex; i < sequence->size(); ++i)
    {
        mStatementListOut->getSequence()->push_back(sequence->at(i));
    }
}

void RemoveSwitchFallThroughTraverser::handlePreviousCase()
{
    if (mPreviousCase)
        mCasesSharingBreak.push_back(mPreviousCase);
    if (mLastStatementWasBreak)
    {
        for (size_t i = 0; i < mCasesSharingBreak.size(); ++i)
        {
            ASSERT(!mCasesSharingBreak.at(i)->getSequence()->empty());
            if (mCasesSharingBreak.at(i)->getSequence()->size() == 1)
            {
                // Fall-through is allowed in case the label has no statements.
                outputSequence(mCasesSharingBreak.at(i)->getSequence(), 0);
            }
            else
            {
                // Include all the statements that this case can fall through under the same label.
                if (mCasesSharingBreak.size() > i + 1u)
                {
                    mPerfDiagnostics->warning(mCasesSharingBreak.at(i)->getLine(),
                                              "Performance: non-empty fall-through cases in "
                                              "switch statements generate extra code.",
                                              "switch");
                }
                for (size_t j = i; j < mCasesSharingBreak.size(); ++j)
                {
                    size_t startIndex =
                        j > i ? 1 : 0;  // Add the label only from the first sequence.
                    outputSequence(mCasesSharingBreak.at(j)->getSequence(), startIndex);
                }
            }
        }
        mCasesSharingBreak.clear();
    }
    mLastStatementWasBreak = false;
    mPreviousCase          = nullptr;
}

bool RemoveSwitchFallThroughTraverser::visitCase(Visit, TIntermCase *node)
{
    handlePreviousCase();
    mPreviousCase = new TIntermBlock();
    mPreviousCase->getSequence()->push_back(node);
    mPreviousCase->setLine(node->getLine());
    // Don't traverse the condition of the case statement
    return false;
}

bool RemoveSwitchFallThroughTraverser::visitAggregate(Visit, TIntermAggregate *node)
{
    mPreviousCase->getSequence()->push_back(node);
    mLastStatementWasBreak = false;
    return false;
}

bool DoesBlockAlwaysBreak(TIntermBlock *node)
{
    if (node->getSequence()->empty())
    {
        return false;
    }

    TIntermBlock *lastStatementAsBlock = node->getSequence()->back()->getAsBlock();
    if (lastStatementAsBlock)
    {
        return DoesBlockAlwaysBreak(lastStatementAsBlock);
    }

    TIntermBranch *lastStatementAsBranch = node->getSequence()->back()->getAsBranchNode();
    return lastStatementAsBranch != nullptr;
}

bool RemoveSwitchFallThroughTraverser::visitBlock(Visit, TIntermBlock *node)
{
    if (node != mStatementList)
    {
        mPreviousCase->getSequence()->push_back(node);
        mLastStatementWasBreak = DoesBlockAlwaysBreak(node);
        return false;
    }
    return true;
}

bool RemoveSwitchFallThroughTraverser::visitLoop(Visit, TIntermLoop *node)
{
    mPreviousCase->getSequence()->push_back(node);
    mLastStatementWasBreak = false;
    return false;
}

bool RemoveSwitchFallThroughTraverser::visitBranch(Visit, TIntermBranch *node)
{
    mPreviousCase->getSequence()->push_back(node);
    // TODO: Verify that accepting return or continue statements here doesn't cause problems.
    mLastStatementWasBreak = true;
    return false;
}

}  // anonymous namespace

TIntermBlock *RemoveSwitchFallThrough(TIntermBlock *statementList,
                                      PerformanceDiagnostics *perfDiagnostics)
{
    return RemoveSwitchFallThroughTraverser::removeFallThrough(statementList, perfDiagnostics);
}

}  // namespace sh

kc3-lang/angle/src/compiler/translator/tree_ops/RemoveSwitchFallThrough.cpp

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kc3-lang/angle /src/compiler/translator/tree_ops/RemoveSwitchFallThrough.cpp