This section provides some guidance on how to achieve smaller object and smaller executable size when using the optimizing features of Intel compilers.
To begin, there are two compiler options that are designed to prioritize code size over performance:
Favors size over speed |
Linux*: -Os Windows*: /Os |
This option enables optimizations that do not increase code size; it produces smaller code size than option O2. Option Os disables some optimizations that may increase code size for a small speed benefit. |
Minimizes code size |
Linux*: -O1 Windows*: /O1 |
Compared to option Os, option O1 disables even more optimizations that are generally known to increase code size. Specifying option O1 implies option Os. As an intermediate step in reducing code size, you can replace option O3 with option O2 before specifying option O1. Option O1 may improve performance for applications with very large code size, many branches, and execution time not dominated by code within loops. |
For more information about the above options, see their full descriptions in the Compiler Reference.
The rest of this section briefly discusses methods that may help you further improve code size even when compared to the default behaviors of options Os and O1.
The following table summarizes the topics in this section.
Most Common Methods to Reduce Code Size: |
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Disable or Decrease the Amount of Inlining |
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Strip Symbols from Your Binaries |
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Dynamically Link Intel-Provided Libraries |
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Exclude Unused Code and Data from the Executable |
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Disable Recognition and Expansion of Intrinsic Functions |
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Optimize Exception Handling Data on Linux Systems |
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Methods to Use Only When Code Size is Very Important: |
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Disable Loop Unrolling |
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Disable Automatic Vectorization |
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Methods to Use Under Special Circumstances: |
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Avoid References to Compiler-Specific Libraries |
The following are important considerations:
Some of these methods may already be applied by default when options Os and O1 are specified. All the methods mentioned in subsequent topics can be applied at higher optimization levels.
Some of the options referred to in these topics will not necessarily cause code size reduction, and they may provide varying results (good, bad, or neutral) based on the characteristics of the target code. Still, these are the recommended things to try to see if they cause your binaries to become smaller while maintaining acceptable performance.
Read the full description of compiler options that are mentioned in these topics to get complete information about their behavior, syntax, and target platforms.