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### 16.17 Including Patterns in Machine Descriptions.

The `include` pattern tells the compiler tools where to look for patterns that are in files other than in the file `.md`. This is used only at build time and there is no preprocessing allowed.

It looks like:

    (include
      pathname)

For example:

    (include "filestuff")

Where pathname is a string that specifies the location of the file, specifies the include file to be in `gcc/config/target/filestuff`. The directory `gcc/config/target` is regarded as the default directory.

Machine descriptions may be split up into smaller more manageable subsections and placed into subdirectories.

By specifying:

    (include "BOGUS/filestuff")

the include file is specified to be in `gcc/config/target/BOGUS/filestuff`.

Specifying an absolute path for the include file such as;

    (include "/u2/BOGUS/filestuff")

is permitted but is not encouraged.

#### 16.17.1 RTL Generation Tool Options for Directory Search

The `-Idir` option specifies directories to search for machine descriptions. For example:

    genrecog -I/p1/abc/proc1 -I/p2/abcd/pro2 target.md

Add the directory dir to the head of the list of directories to be searched for header files. This can be used to override a system machine definition file, substituting your own version, since these directories are searched before the default machine description file directories. If you use more than one `-I` option, the directories are scanned in left-to-right order; the standard default directory come after.

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