The -xe switch drives the placer and router to use extensive algorithms to achieve a placed and routed design.
This is very runtime sensitive and can cause long run times.
The Tool will try to achieve a proper placement and routing when there are timing violations or unroutable nets.
The -xe option is available when running timing-driven packing and placement with the -timing option, and sets the extra effort level.
Syntax : -xe effort_level
effort_level can be set to n (normal) or c (continue).
When -xe is set to c, MAP continues to attempt to improve packing until little or no improvement can be made.
Use this option to set the extra effort level.
Syntax: -xe n|c
Note Use of extra effort c can result in extremely long runtimes.
To use the -xe option, you must also set the -ol (Overall Effort Level) option to high or have the -pl (Placer Effort Level) option and -rl (Router Effort Level) option set to high.
For information on similar switches and optimizations refer to the command line user guide: http://www.xilinx.com/support/documentation/sw_manuals/xilinx13_2/devref.pdf