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![Indexed Assignment Indexed assignment of the form A:=B[I] and A[I]:=B. the first statement sets A to the value in the location I memory units beyond location B. In the later statement A [I]:=B, sets the location I units beyondA to the value of B. In Both instructions ,A, B, and I are assumed to refer data objects and will represented by pointers to the symbol table.](https://image.slidesharecdn.com/threeaddresscode-140514051636-phpapp01/75/Three-address-code-In-Compiler-Design-19-2048.jpg)
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Three address code In Compiler Design
The document provides an overview of three address code (TAC), an intermediate code used in compilers to optimize code generation. It explains the structure of TAC, detailing its various forms and the data structures used to represent it, such as quadruples and triples. Additionally, it discusses the advantages and disadvantages of using TAC in optimizing compilers and the types of assignment and control flow statements it encompasses.
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Introduction by Shineraj Arathil, covering address code generation in compilers during B.Tech presentation.
Intermediate code acts as an abstraction layer between source and target languages, optimizing cross-platform compiler creation.
Three Address Code (TAC) helps in code transformations with at most three operands per instruction, exemplifying simple assignments.
Data structures such as Quadruples, Triples, and Indirect Triples are utilized in Three Address Code, including examples for clarity.
Quadruples necessitate temporary variable management, while Triples face issues with statement movement affecting references.
Different forms of Three Address Code including assignment, jump, and procedure calls are discussed with examples.
Jump statements in Three Address Code manage control flow dynamics through conditional and unconditional jumps.
Procedure calls are represented as a series of statements in Three Address Code, facilitating parameter handling.
Illustrates indexed assignments in memory locations and how assignments for addresses and pointers are handled in Three Address Code.
Summary covering the key concepts of Intermediate Code, Three Address Code, and related data structures.
Conclusion of the presentation with thanks provided by the presenter.
Three address code In Compiler Design
- 1. 3 Address CodeGeneration ShinerajArathil B.Tech (CSE) 6th Sem Presented By:
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- 3. Intermediate Code ▪ Anlanguage b/w source and target language ▪ Provides an intermediate level of abstraction ▪ More details than the source ▪ Fewer details than the target PREPARED BY SHINE 3 SOURCE LANGUAGE TARGET LANGUAGE Intermediate Code
- 4. Benefits of intermediatecode generation ▪ A compiler for different machines can be created by attaching different backend to the existing front ends of each machine ▪ A compiler for different source languages (on the same machine) can be created by proving different front ends for corresponding source language to existing back end. ▪ A machine independent code optimizer can be applied to intermediate code in order to optimize the code generation PREPARED BY SHINE 4
- 5. Three Address Code ▪Is an intermediate code used by optimizing compilers to aid in the implementation of code-improving transformations. ▪ EachTAC instruction has at most three operands and is typically a combination of assignment and a binary operator ▪ InTAC, there is at most one operator on the right side of an instruction.That is no built- up arithmetic expressions are permitted Example : x + y * z t1 = y * z t2 = x + t1 t1 and t2 are compiler-generated temporary names PREPARED BY SHINE 5
- 6. ▪ Statements inthis language are of the form: x:=y op z ▪ where x, y and z are names, constants or compiler-generated temporary variables, and ‘op’ stands for any operator PREPARED BY SHINE 6
- 7. ▪ Three AddressCode is a linearized representation of a syntax trees or a DAG PREPARED BY SHINE 7 T1 = b – c T2 = a * t1 T3 = a + t2 T4 = t1 * d T5 = t3 + t4
- 8. Data structures forthree address codes Quadruples Has four fields: op, arg1, arg2 and result Triples Temporaries are not used and instead references to instructions are made Indirect triples In addition to triples we use a list of pointers to triples PREPARED BY SHINE 8
- 9. Example ▪ b *minus c + b * minus c t1 = minus c t2 = b * t1 t3 = minus c t4 = b * t3 t5 = t2 + t4 a = t5 Three address code minus * minus c t3 * + = c t1 b t2t1 b t4t3 t2 t5t4 t5 a arg1 resultarg2op Quadruples minus * minus c * + = c b (0) b (2) (1) (3) a arg1 arg2op Triples (4) 0 1 2 3 4 5 minus * minus c * + = c b (0) b (2) (1) (3) a arg1 arg2op Indirect Triples (4) 0 1 2 3 4 5 (0) (1) (2) (3) (4) (5) op 35 36 37 38 39 40
- 10. Disadvantage Of quadruples ▪Temporary names must be entered into the symbol table as they are created. ▪ This increases the time and size of the symbol table. PREPARED BY SHINE 10 Pro: easy to rearrange code for global optimization Cons: lots of temporaries
- 11. Disadvantage OfTRIPLES ▪ Movinga statement that define a temporary value requires us to change all references to that statement in arg1 and arg2 arrays.This problem makes triple difficult to use in an optimizing compiler. PREPARED BY SHINE 11
- 12. Types ofThree-Address Code ▪Assignment statement x := y op z ▪ Assignment statement x := op y ▪ Copy statement x := y ▪ Unconditional jump goto L ▪ Conditional jump if x relop y goto L ▪ Procedural call param x call p return y
- 13. Assignment Statement ▪ Assignmentstatements can be in the following two forms 1. x:=op y 2. x:=y op z First statement op is a unary operation. Essential unary operations are unary minus, logical negation, shift operators and conversion operators. Second statement op is a binary arithmetic or logical operator.
- 14. 5/14/2014 14 Three-Address Statements Apopular form of intermediate code used in optimizing compilers is three-address statements. Source statement: x = a + b c + d Three address statements with temporaries t1 and t2: t1 = b c t2 = a + t1 x = t2 + d
- 15. Jump Statements source statementlike if-then-else and while-do cause jump in the control flow through three address code so any statement in three address code can be given label to make it the target of a jump. The statement goto L Cause an unconditional jump to the statement with label L. the statement
- 16. if x relopy goto L Causes a jump to L condition if and only if Boolean condition is true. This instruction applies relational operator relop (>,=,<, etc.) to x and y, and executes statement L next of x statement x relop y. If not, the three address statement following if x relop y goto L is executed next, as in the usual sequence.
- 17. Procedure Call /Return A procedure call like P(A1,A2, A3,……….An) may have to many addresses for one statement in three-address code so it is shown as a sequence of n +1 statements’ Param A1 Param A2 M Param An Call p,n
- 18. Where P isthe name of the procedure and and n is a integer indicating the number of actual parameters in the call. This information is redundant, as n can be computed by counting the number of par am statements. It is a convenience to have n available with the call statement.
- 19. Indexed Assignment Indexed assignmentof the form A:=B[I] and A[I]:=B. the first statement sets A to the value in the location I memory units beyond location B. In the later statement A [I]:=B, sets the location I units beyondA to the value of B. In Both instructions ,A, B, and I are assumed to refer data objects and will represented by pointers to the symbol table.
- 20. Address and PointerAssignment Address and pointer assignment x := &y x := *y *x := y First statement, sets the value of x to be the location of y. In x := *y, here y is a pointer or temporary whose r-value is a location. The r-value of x is made equal to the contents of that location. *x := y sets the r-value of the object pointed to by a to the r-value of y.
- 21. Summary ▪ Intermediate Code ▪3 Address Code ▪ Data Structures Of 3Address Code ▪ Types ofThree-Address Code PREPARED BY SHINE 21
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