 Cx51 User's Guide | |
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Cx51 User's Guide
Cx51 Introduction Compiling Programs Language Extensions Preprocessor Advanced Programming Customization Files
Startup Code Variable Initialization Code XBANKING.A51 Basic I/O Memory Allocation Optimizer Optimizer Options General Optimizations 8051-Specific Optimizations Global Register Coloring Segment Naming Conventions Data Objects Program Objects Parameters and Local Variables Interfacing C to Assembler Global Variables Function Parameters Passing in Memory Passing in Registers Function Return Values Using the SRC Directive Register Usage Overlaying Segments Small Model Example Compact Model Example Large Model Example Interfacing C programs to PL/M-51 Data Storage Formats Bit Variables 1-Byte Scalars 2-Byte Scalars 4-Byte Scalars Generic and Far Pointers Floating-point Numbers Floating-point Errors Absolute Memory Locations Absolute Access Macros Linker Location Controls The _at_ Keyword Debugging 8051 Derivatives Error Messages Library Reference Appendix8051-Specific Optimizations
- AJMP/ACALL Maximizing (Linker Optimization) (Level 0-7)
The linker rearranges code segments to maximize AJMP and ACALL instructions which are shorter than LJMP and LCALL instructions. - Case/Switch Optimizing (Level 4)
Code involving switch and case statements is optimized using jump tables or jump strings. - Data Overlaying (Level 2)
Data and bit segments suitable for static overlay are identified and internally marked. The linker has the capability, through global data flow analysis, of selecting segments which can then be overlaid. - Extended Access Optimizing (Level 4)
Variables from the IDATA, XDATA, PDATA and CODE areas are directly included in operations. Intermediate registers are frequently unnecessary. - Peephole Optimizing (Level 3)
Redundant MOV instructions are removed. This includes unnecessary loading of objects from the memory as well as load operations with constants. Complex operations are replaced by simple operations when memory space or execution time can be saved.
Note
- Linker optimizations are performed by the LX51 Linker only. The BL51 Linker does not perform any optimizations.
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