7.1 Performance Considerations

The GNAT system provides a number of options that allow a trade-off between

• performance of the generated code
• speed of compilation
• minimization of dependences and recompilation
• the degree of run-time checking.

The defaults (if no options are selected) aim at improving the speed of compilation and minimizing dependences, at the expense of performance of the generated code:

• no optimization
• no inlining of subprogram calls
• all run-time checks enabled except overflow and elaboration checks

These options are suitable for most program development purposes. This chapter describes how you can modify these choices, and also provides some guidelines on debugging optimized code.

• Controlling Run-Time Checks
• Use of Restrictions
• Optimization Levels
• Debugging Optimized Code
• Inlining of Subprograms
• Vectorization of loops
• Other Optimization Switches
• Optimization and Strict Aliasing
• Aliased Variables and Optimization
• Atomic Variables and Optimization
• Passive Task Optimization