Method createMatrixConstructor

SPIRV/SpvBuilder.cpp:4308–4435

Comments in header

// Comments in header
Id Builder::createMatrixConstructor(Decoration precision, const std::vector<Id>& sources, Id resultTypeId)
{
    Id componentTypeId = getScalarTypeId(resultTypeId);
    unsigned int numCols = getTypeNumColumns(resultTypeId);
    unsigned int numRows = getTypeNumRows(resultTypeId);

    Instruction* instr = module.getInstruction(componentTypeId);
    const unsigned bitCount = instr->getImmediateOperand(0);

    // Optimize matrix constructed from a bigger matrix
    if (isMatrix(sources[0]) && getNumColumns(sources[0]) >= numCols && getNumRows(sources[0]) >= numRows) {
        // To truncate the matrix to a smaller number of rows/columns, we need to:
        // 1. For each column, extract the column and truncate it to the required size using shuffle
        // 2. Assemble the resulting matrix from all columns
        Id matrix = sources[0];
        Id columnTypeId = getContainedTypeId(resultTypeId);
        Id sourceColumnTypeId = getContainedTypeId(getTypeId(matrix));

        std::vector<unsigned> channels;
        for (unsigned int row = 0; row < numRows; ++row)
            channels.push_back(row);

        std::vector<Id> matrixColumns;
        for (unsigned int col = 0; col < numCols; ++col) {
            std::vector<unsigned> indexes;
            indexes.push_back(col);
            Id colv = createCompositeExtract(matrix, sourceColumnTypeId, indexes);
            setPrecision(colv, precision);

            if (numRows != getNumRows(matrix)) {
                matrixColumns.push_back(createRvalueSwizzle(precision, columnTypeId, colv, channels));
            } else {
                matrixColumns.push_back(colv);
            }
        }

        return setPrecision(createCompositeConstruct(resultTypeId, matrixColumns), precision);
    }

    // Detect a matrix being constructed from a repeated vector of the correct size.
    // Create the composite directly from it.
    if (sources.size() == numCols && isVector(sources[0]) && getNumComponents(sources[0]) == numRows &&
        std::equal(sources.begin() + 1, sources.end(), sources.begin())) {
        return setPrecision(createCompositeConstruct(resultTypeId, sources), precision);
    }

    // Otherwise, will use a two step process
    // 1. make a compile-time 2D array of values
    // 2. construct a matrix from that array

    // Step 1.

    // initialize the array to the identity matrix
    Id ids[maxMatrixSize][maxMatrixSize];
    Id  one = (bitCount == 64 ? makeDoubleConstant(1.0) : makeFloatConstant(1.0));
    Id zero = (bitCount == 64 ? makeDoubleConstant(0.0) : makeFloatConstant(0.0));
    for (int col = 0; col < 4; ++col) {
        for (int row = 0; row < 4; ++row) {