Debug information and high optimization
Technical Note 62015
11/6/2015 2:27 PM
This Technical Note discusses which information in C-SPY that is reliable (and which is unreliable) at optimization level 'high'.
The optimization system in IAR C /C++ Compiler consists of different parts that aim to make as small and/or fast output as possible. When these parts are enabled, the debug information that the compiler generates become less and less reliable.
...comes from C-SPY windows that shows information collected from the target system. For example the following windows:
- Disassembly window
- Memory window
- Register window
- Stack window
- Call Stack window
Reliable (most of the time) information
These windows are reliable most of the time, but any write might have been moved due to optimzations. That is, a write of a value might not have been done yet. This applies to for example the following windows:
- Statics window
- Symbolic Memory window
- Symbols window
C-SPY windows that shows information based on debug information becomes unreliable. For example the follwoing windows:
- Watch window
- Locals window
- Auto window
- Live Watch windows
- Quick Watch window
More information can be found in Help > C-SPY Debugging Guide, chapter "Effects of optimizations" and also Help > C/C++ Development Guide, chapter "Optimization Levels".
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