Debug information and high optimization

Introduction

This Technical Note discusses which information in C-SPY that is reliable (and which is unreliable) at optimization level 'high'.

Background

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.

Reliable information...

...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

Unreliable information

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

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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