### 25.5 Internal flags controlling `lto1`

The following flags are passed into `lto1` and are not meant to be used directly from the command line.

- -fwpa This option runs the serial part of the link-time optimizer performing the inter-procedural propagation (WPA mode). The compiler reads in summary information from all inputs and performs an analysis based on summary information only. It generates object files for subsequent runs of the link-time optimizer where individual object files are optimized using both summary information from the WPA mode and the actual function bodies. It then drives the LTRANS phase.
- -fltrans This option runs the link-time optimizer in the local-transformation (LTRANS) mode, which reads in output from a previous run of the LTO in WPA mode. In the LTRANS mode, LTO optimizes an object and produces the final assembly.
- -fltrans-output-list=file This option specifies a file to which the names of LTRANS output files are written. This option is only meaningful in conjunction with `-fwpa`.
- -fresolution=file This option specifies the linker resolution file. This option is only meaningful in conjunction with `-fwpa` and as option to pass through to the LTO linker plugin.