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https://issues.apache.org/jira/browse/CALCITE-3224?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17040647#comment-17040647
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Danny Chen commented on CALCITE-3224:
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Is this issue going to be resolved in release 1.22 ?
> 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
> Fix For: 1.22.0
>
> Attachments: RexNode-CodeGen.pdf, codegen.png
>
> Time Spent: 6.5h
> Remaining Estimate: 0h
>
> 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 “optimizings”. 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_*).
> *Other changes:*
> (1) ReImplement different RexCall implementations (e.g., CastImplementor,
> BinaryImplementor and etc.) as seperated files and remove them into the newly
> created package _org.apache.calcite.adapter.enumerable.rex,_ and organize
> them in RexCallImpTable.
> (2) move some util functions into EnumUtils.
> 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*_)
> [^RexNode-CodeGen.pdf]
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