Method CodegenSetNullIndicator

be/src/runtime/descriptors.cc:841–872

Example IR for setting the first null bit to a non-constant 'is_null' value: %14 = bitcast { i8, [7 x i8], %"class.impala::TimestampValue" }* %agg_tuple to i8 %null_byte_ptr3 = getelementptr i8, i8* %14, i32 0 %null_byte4 = load i8, i8* %null_byte_ptr3 %null_bit_cleared = and i8 %null_byte4, -2 %15 = sext i1 %result_is_null to i8 %null_bit = and i8 %15, 1 %null_bit_set = or i8 %null_bit_cleared, %

//  %null_bit_set = or i8 %null_bit_cleared, %null_bit
//  store i8 %null_bit_set, i8* %null_byte_ptr3
void SlotDescriptor::CodegenSetNullIndicator(
    LlvmCodeGen* codegen, LlvmBuilder* builder, llvm::Value* tuple, llvm::Value* is_null)
    const {
  DCHECK_EQ(is_null->getType(), codegen->bool_type());
  llvm::Value* null_byte_ptr;
  llvm::Value* null_byte =
      CodegenGetNullByte(codegen, builder, null_indicator_offset_, tuple, &null_byte_ptr);
  llvm::Constant* mask = codegen->GetI8Constant(null_indicator_offset_.bit_mask);
  llvm::Constant* not_mask = codegen->GetI8Constant(~null_indicator_offset_.bit_mask);

  llvm::ConstantInt* constant_is_null = llvm::dyn_cast<llvm::ConstantInt>(is_null);
  llvm::Value* result = nullptr;
  if (constant_is_null != nullptr) {
    if (constant_is_null->isOne()) {
      result = builder->CreateOr(null_byte, mask, "null_bit_set");
    } else {
      DCHECK(constant_is_null->isZero());
      result = builder->CreateAnd(null_byte, not_mask, "null_bit_cleared");
    }
  } else {
    // Avoid branching by computing the new byte as:
    // (null_byte & ~mask) | (-null & mask);
    llvm::Value* byte_with_cleared_bit =
        builder->CreateAnd(null_byte, not_mask, "null_bit_cleared");
    llvm::Value* sign_extended_null =
        builder->CreateSExt(is_null, codegen->i8_type());
    llvm::Value* bit_only = builder->CreateAnd(sign_extended_null, mask, "null_bit");
    result = builder->CreateOr(byte_with_cleared_bit, bit_only, "null_bit_set");
  }

  builder->CreateStore(result, null_byte_ptr);
}

// Example IR for materializing a string column with non-NULL 'pool'. Includes the part
// that is generated by CodegenAnyVal::ToReadWriteInfo().