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/GL (Whole program optimization)

  • Article

Enables whole program optimization.

Syntax

/GL[-]

Remarks

Whole program optimization allows the compiler to perform optimizations with information on all modules in the program. Without whole program optimization, optimizations are performed on a per-module (compiland) basis.

Whole program optimization is off by default and must be explicitly enabled. However, it's also possible to explicitly disable it with /GL-.

With information on all modules, the compiler can:

  • Optimize the use of registers across function boundaries.

  • Do a better job of tracking modifications to global data, allowing a reduction in the number of loads and stores.

  • Track the possible set of items modified by a pointer dereference, reducing the required loads and stores.

  • Inline a function in a module even when the function is defined in another module.

.obj files produced with /GL aren't usable by linker utilities such as EDITBIN and DUMPBIN.

If you compile your program with /GL and /c, you should use the /LTCG linker option to create the output file.

/ZI can't be used with /GL

The format of files produced with /GL in the current version often isn't readable by later versions of Visual Studio and the MSVC toolset. Unless you're willing to ship copies of the .lib file for all versions of Visual Studio you expect your users to use, now and in the future, don't ship a .lib file made up of .obj files produced by /GL . For more information, see Restrictions on binary compatibility.

.obj files produced by /GL and precompiled header files shouldn't be used to build a .lib file unless the .lib file is linked on the same machine that produced the /GL .obj file. Information from the .obj file's precompiled header file is needed at link time.

For more information on the optimizations available with and the limitations of whole program optimization, see /LTCG. /GL also makes profile guided optimization available. When compiling for profile guided optimizations and if you want function ordering from your profile guided optimizations, you must compile with /Gy or a compiler option that implies /Gy.

To set this linker option in the Visual Studio development environment

For more information on how to specify /GL in the development environment, see /LTCG (Link-time code generation) .

To set this linker option programmatically

See also

MSVC compiler options
MSVC compiler command-line syntax