HP UX SoftBench Software Chapter, Debugging Optimized Code, In effect, optimization transforms a program into a different program

Using SoftBench Debugger

Debugging Optimized Code

Debugging Optimized Code

Source-level debugging of unoptimized code is relatively easy because you have a simple correspondence between source code statements and the assembly code instructions into which they are translated. Also, program variables are stored in memory and are therefore easy to access.

Optimization performs a series of transformations on the object code in order to make the program run faster. In effect, optimization transforms a program into a different program. The executable program you debug is actually not the same program as the source program. In addition, program variables may be stored in registers instead of memory and are therefore more difficult to access.

Ordinarily, you first compile and debug your program without optimization. All or nearly all of the bugs in your program show up in the unoptimized version. After eliminating all the bugs that you can find, turn on optimization (compile with -O). If the program behaves incorrectly, scan the source code for the most common kinds of bugs that appear for the first time in optimized code:

•Uninitialized variables

•Out-of-bounds array references

•Variable references based on the assumption that two variables are adjacent in memory

SoftBench CodeAdvisor may assist you with some of these categories of problems. Others require more extensive code examination.

These kinds of problems, however, are often very difficult to find by examining the source code. If you cannot determine the reason for the program's misbehavior, you need to debug the optimized code. For tutorial and task-oriented information on how to debug optimized code using the debugger, see SoftBench Online Help.

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