issuesindesignofcodegenerator-150227091230-conversion-gate01
- 1. Presented by, M.Selva Vinitha B.E/CSE M.Kumarasamy college of engineering Karur.
- 2. Code generator Final phase of compiler design Optimized intermediate code is provided as input It generates target code 9/15/2015 2Issues in design of code generator
- 3. Code generation and Instruction Selection 4 Symbol table input output Front end Intermediate Code generator Code generator 9/15/2015 Issues in design of code generator
- 4. Contd… output code must be correct output code must be of high quality code generator should run efficiently 9/15/2015 4Issues in design of code generator
- 5. Pre-requisites Instruction set of target machine. Instruction addressing modes. No. of registers. Configuration of ALU 9/15/2015 5Issues in design of code generator
- 6. Issues in the design of a code generator Input to the code generator Memory management Target programs Instruction selection Register allocation Evaluation order Approaches to code generation 9/15/2015 6Issues in design of code generator
- 7. Input to the code generator The intermediate representation of the source program produced by the front end Several choices for the intermediate language Linear - postfix nottion 3 address - quadruples Virtual machie - stack machine code Graphical - syntax tree &dags 9/15/2015 7Issues in design of code generator
- 8. Memory management Mapping names in the source program to addresses of data objects in run-time memory Done by the front end and the code generator. A name in a three- address statement refers to a symbol- table entry for the name. A relative address can be determined 9/15/2015 8Issues in design of code generator
- 9. Target programs Absolute machine language Relocatable machine language Assembly language 9/15/2015 9Issues in design of code generator
- 10. Contd.. Absolute machine language: Produce an absolute machine language program can be placed in a fixed location in memory and immediately executed. 9/15/2015 10Issues in design of code generator
- 11. Contd.. Relocatable machine language: Producing a relocatable machine language program subprograms to be compiled separately. relocatable object modules can be linked together and loaded for execution by a linking loader. must provide explicit relocation information to the loader, to link the separately compiled program segments. 9/15/2015 11Issues in design of code generator
- 12. Contd… Assembly language: Producing an assembly language program makes the process of code generation easier 9/15/2015 12Issues in design of code generator
- 13. Instruction selection The factors to be considered during instruction selection are: The uniformity and completeness of the instruction set. Instruction speed and machine idioms. Size of the instruction set. 9/15/2015 13Issues in design of code generator
- 14. Contd… Eg., for the following address code is: a := b + c d := a + e inefficient assembly code is: MOV b, R0 R0 ← b ADD c, R0 R0 ← c + R0 MOV R0, a a ← R0 MOV a, R0 R0 ← a ADD e, R0 R0 ← e + R0 MOV R0 , d d ← R0 Here the fourth statement is redundant, and so is the third statement if , 'a' is not subsequently used. 9/15/2015 14Issues in design of code generator
- 15. Register allocation • Instructions with register operands are usually shorter and faster • Efficient utilization of registers is important in generating good code. 9/15/2015 15Issues in design of code generator
- 16. Contd.. Register allocation phase: • Select the set of variables that will reside in registers Register assignment phase: • Pick the specific register that a variable will reside in. 9/15/2015 16Issues in design of code generator
- 17. Evaluation order The order in which computations are performed Affect the efficiency of the target code. Some computation orders require fewer registers to hold intermediate results 9/15/2015 17Issues in design of code generator
- 18. Approaches to code generation Most important criteria for code generator is that it produces correct code Correctness takes on special signification It contains a straightforward code generation algorithm The output of such code generator can be improved by peephole optimization technique 9/15/2015 18Issues in design of code generator
- 19. Conclusion Output of code generator phase is dependent on: Target language Operating system Memory management system Instruction selection Register allocation Evaluation order 9/15/2015 19Issues in design of code generator