This document discusses code generation for control flow statements and boolean expressions in programming languages. It introduces type conversions, abstract syntax trees, control flow, and generating three-address code for booleans. A key technique discussed is backpatching, which allows saving instruction labels as indices and later inserting target addresses to avoid an extra pass for setting jump targets. An example shows applying backpatching to an annotated parse tree for a boolean expression.

1. CSE 420
Intermediate Code Generation
Lecture 13

2. Conversions between primitive typesConversions between primitive types
in Javain Java

3. Introducing type conversions intoIntroducing type conversions into
expression evaluationexpression evaluation

4. Abstract syntax tree for theAbstract syntax tree for the
function definitionfunction definition
fun length(x) =
if null(x) then 0 else length(tl(x)+1)
This is a polymorphic function in ML language

5. Control FlowControl Flow
Boolean expressions are often used to:
• Alter the flow of control.
• Compute logical values.

6. Short-Circuit Code
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7. Flow-of-Control StatementsFlow-of-Control Statements

8. Syntax-directed definitionSyntax-directed definition

9. Generating three-address code forGenerating three-address code for
booleansbooleans

10. translation of a simple if-statementtranslation of a simple if-statement
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11. BackpatchingBackpatching
• Previous codes for Boolean expressions insert symbolic
labels for jumps
• It therefore needs a separate pass to set them to
appropriate addresses
• We can use a technique named backpatching to avoid
this
• We assume we save instructions into an array and labels
will be indices in the array
• For non-terminal B we use two attributes B.truelist and
B.falselist together with following functions:
▫ makelist(i): create a new list containing only I, an index into the
array of instructions
▫ Merge(p1,p2): concatenates the lists pointed by p1 and p2 and
returns a pointer to the concatenated list
▫ Backpatch(p,i): inserts i as the target label for each of the
instruction on the list pointed to by p

12. Backpatching for Boolean ExpressionsBackpatching for Boolean Expressions
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13. Backpatching for Boolean ExpressionsBackpatching for Boolean Expressions
• Annotated parse tree for x < 100 || x > 200 && x ! = y

14. Flow-of-Control StatementsFlow-of-Control Statements

15. Translation of a switch-statementTranslation of a switch-statement

16. Any Question?