Developer Guide and Reference

Contents

Methods to Optimize Code Size

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*
and
macOS*
:
-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*
and
macOS*
:
-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:
Disable or Decrease the Amount of Inlining
Strip Symbols from Your Binaries
Dynamically Link Intel-Provided Libraries
Exclude Unused Code and Data from the Executable
Disable Recognition and Expansion of Intrinsic Functions
Optimize Exception Handling Data on Linux
and
macOS*
Systems
Methods to Use Only When Code Size is Very Important:
Disable Passing Arguments in Registers Instead of On the Stack
Disable Loop Unrolling
Disable Automatic Vectorization
Methods
to Use Under Special Circumstances:
Avoid References to Compiler-Specific Libraries
Avoid Unnecessary 16-Byte Alignment
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.
  • You should read the full description of compiler options that are mentioned in these topics to get complete information about their behavior, syntax, and target platforms.