The following warning occurs during XST low-level synthesis:
"WARNING:Xst:637 - Naming conflict during MERGE on SEQUENTIAL: renaming <name> to <name>1."
When low-level synthesis is performed, XST checks to ensure that there are no naming conflicts within the design. This warning occurs when these conflicts are resolved by XST.
One situation that would produce this warning is if an expanded bus bit matched an existing signal name. When buses are expanded, XST names them using an underscore ("_") and the bit number; therefore, any signal with the same base and naming convention would conflict.
For example, foo[3:0] would expand to "foo_3", "foo_2", "foo_1", and "foo_0", which would conflict with any individual signals that already have those names.
Another situation of this type might occur when signals of identical names are used in separate modules within the design. If the hierarchy is flattened and these identically named signals do not connect, this renaming might be necessary to prevent contention.
To avoid this situation, either create unique names for these signals, or use the "keep_hierarchy" attribute to maintain hierarchical boundaries (forcing XST to keep the long, unique hierarchical names).