GNU Compiler Collection (GCC) Internals: Dump files and streams

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#### 9.7.3 Dump files and streams

There are two separate output streams available for outputting optimization information from passes. Note that both these streams accept `stderr` and `stdout` as valid streams and thus it is possible to dump output to standard output or error. This is specially handy for outputting all available information in a single file by redirecting `stderr`.

``pstream``

  This stream is for pass-specific dump output. For example, `-fdump-tree-vect=foo.v` dumps tree vectorization pass output into the given file name `foo.v`. If the file name is not provided, the default file name is based on the source file and pass number. Note that one could also use special file names `stdout` and `stderr` for dumping to standard output and standard error respectively.

``alt_stream``

  This steam is used for printing optimization specific output in response to the `-fopt-info`. Again a file name can be given. If the file name is not given, it defaults to `stderr`.