[jira] [Updated] (CALCITE-3224) New RexNode-to-Expression CodeGen Implementation

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CALCITE-3224?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

ASF GitHub Bot updated CALCITE-3224:
------------------------------------
    Labels: pull-request-available  (was: )

> New RexNode-to-Expression CodeGen Implementation
> ------------------------------------------------
>
>                 Key: CALCITE-3224
>                 URL: https://issues.apache.org/jira/browse/CALCITE-3224
>             Project: Calcite
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 1.20.0
>            Reporter: Feng Zhu
>            Assignee: Feng Zhu
>            Priority: Critical
>              Labels: pull-request-available
>         Attachments: codegen.png
>
>
> h3. *Background*
>     Current RexNode-to-Expression implementation relies on BlockBuilder's incorrect “optimizations” to inline unsafe operations. As illustrated in CALCITE-3173, when this cooperation is broken in some special cases, it will cause exceptions like NPE, such as CALCITE-3142, CALCITE-3143, CALCITE-3150.
>     Though we can fix these problems under current implementation framework with some efforts like the PR in CALCITE-3142, the logic will become more and more complex. To pursue a thorough and elegant solution, we implement a new one. Moreover, it also ensures the correctness for non-optimized code.
> h3. *Major Features*
>  * *Visitor Pattern*: Each RexNode will be visited only once in a bottom-up way, rather than recursively visiting a RexNode many times with different NullAs settings.
>  * *Conditional Semantic*: It can naturally guarantee the correctness even without BlockBuilder’s “optimizing” operation. Each line of code generated for a RexNode is null safe.
>  * *Interface Compatibility*: The implementation only updates _RexToLixTranslator_ and _RexImpTable_. Interfaces such as CallImplementor keep unchanged.
> h3. *Implementation*
>     For each RexNode, the visitor will generally generate two declaration statements, one for value and one for nullable. The code snippet is like:
>  
> {code:java}
> {valueVariable} = {valueExpression}
> {isNullVariable} = {isNullExpression}
> {code}
>  
> The visitor’s result will be the variable pair (*_isNullVariable_*, *_valueVariable_*).
> h3. *Example Demonstration*
> Take a simple test case as example, in which the "commission" column is nullable.
> {code:java}
> @Test public void testNPE() {
>   CalciteAssert.hr()
>     .query("select \"commission\" + 10 as s\n"
>       + "from \"hr\".\"emps\"")
>     .returns("S=1010\nS=510\nS=null\nS=260\n");
> }
> {code}
> The codegen progress and non-optimized code are demonstrated in the figure below.
> !codegen.png!
>  # When visiting *RexInputRef (commission)*, the visitor generates three lines of code, the result is a pair of ParameterExpression (*_input_isNull_*, *_input_value_*).
>  # Then the visitor visits *RexLiteral (10)* and generates two lines of code. The result is (*_literal_isNull_*, *_literal_value_*).
>  # After that, when visiting *RexCall(Add)*, (_*input_isNull*_, _*input_value*_) and (_*literal_isNull*_, _*literal_value*_) can be used to implement the logic. The visitor also generates two lines of code and return the variable pair.
> In the end, the result Expression is constructed based on (_*binary_call_isNull*_, _*binary_call_value*_)



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