vhdl-speedbar-scan-limit

vhdl-speedbar-scan-limit is a variable defined in `vhdl-mode.el'.
Its value is

(10000000 (1000000 50))

Documentation:
Limits scanning of large files and netlists.
Design units: maximum file size to scan for design units
Hierarchy (instances of subcomponents):
File size: maximum file size to scan for instances (in bytes)
Instances per arch: maximum number of instances to scan per architecture

"None" always means that there is no limit.
In case of files not or incompletely scanned, a warning message and the file
names are printed out.
Background: scanning for instances is considerably slower than scanning for
design units, especially when there are many instances. These limits should
prevent the scanning of large netlists.

You can customize this variable.