Compiler Development (CMPSC 401) Three Address Code Janyl - - PowerPoint PPT Presentation

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Compiler Development (CMPSC 401) Three Address Code Janyl - - PowerPoint PPT Presentation

Nov 20, 2022 384 likes •789 views

Compiler Development (CMPSC 401) Three Address Code Janyl Jumadinova April 2, 2019 Janyl Jumadinova Compiler Development (CMPSC 401) April 2, 2019 1 / 30 Three Address Code (TAC) High-level assembly where each operation has at most three

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Compiler Development (CMPSC 401)

Three Address Code Janyl Jumadinova April 2, 2019

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Three Address Code (TAC)

High-level assembly where each operation has at most three operands (e.g., an add instruction has three operands: two for each argument and one for the result).

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Three Address Code (TAC)

High-level assembly where each operation has at most three operands (e.g., an add instruction has three operands: two for each argument and one for the result). The operands are called addresses and can be held in a virtual register. The compiler back-end will convert TAC instructions and registers into specific machine instructions and hardware registers.

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Temporary Variables

The “three” in “three-address code” refers to the number of operands in any instruction. Evaluating an expression with more than three subexpressions requires the introduction of temporary variables.

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TAC Sample

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TAC Sample

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TAC Sample

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TAC Sample

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TAC Sample

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TAC Sample

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Simple TAC Instructions

Variable assignment allows assignments of the form : var = constant;

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Simple TAC Instructions

Variable assignment allows assignments of the form : var = constant; var1 = var2;

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Simple TAC Instructions

Variable assignment allows assignments of the form : var = constant; var1 = var2; var1 = var2 op var3;

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Simple TAC Instructions

Variable assignment allows assignments of the form : var = constant; var1 = var2; var1 = var2 op var3; var1 = constant op var2;

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Simple TAC Instructions

Variable assignment allows assignments of the form : var = constant; var1 = var2; var1 = var2 op var3; var1 = constant op var2; var1 = var2 op constant;

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Simple TAC Instructions

Variable assignment allows assignments of the form : var = constant; var1 = var2; var1 = var2 op var3; var1 = constant op var2; var1 = var2 op constant; var = constant1 op constant2; Permitted operators are + , - , * , / , % .

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Simple TAC Instructions

Variable assignment allows assignments of the form : var = constant; var1 = var2; var1 = var2 op var3; var1 = constant op var2; var1 = var2 op constant; var = constant1 op constant2; Permitted operators are + , - , * , / , % . How would you compile y = -x; ?

Janyl Jumadinova Compiler Development (CMPSC 401) April 2, 2019 10 / 30

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Simple TAC Instructions

Variable assignment allows assignments of the form : var = constant; var1 = var2; var1 = var2 op var3; var1 = constant op var2; var1 = var2 op constant; var = constant1 op constant2; Permitted operators are + , - , * , / , % . How would you compile y = -x; ? y = 0 - x; y = -1 * x;

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TAC with bools

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TAC with bools

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TAC with bools

Boolean variables are represented as integers that have zero or nonzero values. In addition to the arithmetic operator, TAC supports: <, ==, ||, and &&.

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TAC with bools

Boolean variables are represented as integers that have zero or nonzero values. In addition to the arithmetic operator, TAC supports: <, ==, ||, and &&. How might you compile b = (x ≤ y)?

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Control Flow Statements

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Control Flow Statements

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Labels

TAC allows for named labels indicating particular points in the code that can be jumped to. There are two control flow instructions:

1

Goto label;

2

IfZ value Goto label;

Note that IfZ is always paired with Goto.

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Control Flow Statements

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Control Flow Statements

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Compiling Functions

Decaf functions consist of four pieces:

1 A label identifying the start of the function. 2 A BeginFunc N; instruction reserving N bytes of space for locals and

temporaries.

3 The body of the function. 4 An EndFunc; instruction marking the end of the function.

– When reached, cleans up stack frame and returns.

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A Complete Decaf Program

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A Logical Decaf Stack Frame

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A Logical Decaf Stack Frame

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Compiling Function Calls

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Compiling Function Calls

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Stack Management in TAC

The BeginFunc N; instruction only needs to reserve room for local variables and temporaries. The EndFunc; instruction reclaims the room allocated with BeginFunc N; A single parameter is pushed onto the stack by the caller using the PushParam var instruction. Space for parameters is reclaimed by the caller using the PopParams N; instruction. N is measured in bytes, not number of arguments.

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Compiling Function Calls

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Compiling Function Calls

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Compiling Function Calls

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Compiling Function Calls

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Instruction Formats

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