The constant pool is now an ordinary package, created with the netlist
and instantiated under $root like any other package, and most special
handling has been removed, including AstConstPool. Lookups go through
V3ConstPool, which has a singleton instance owned by V3Global. Static
methods on V3Common form the public interfce to add/find constant pool
entries.
With that, the constant pool is usable at any stage during compilation,
so enum and dimension tables created by V3Width, and enum value tables
created by V3Randomize now also live in the constant pool instead of
$unit, so identical tables are shared.
Associative array constants are handled separately from unpacked
tables, which used to be broken but unused.
Emitted constant pool variables use direct initialization, and
`constinit` with C++20 where the type allows it. This ensures we don't
change a run-time in a way that would result in unintended code size
increase.
-fno-merge-const-pool, which was introduced years ago but never prompted
a bug report is deprecated and has no effect.
This is also prep for future work.
This patch introduces V3HashTable.h, which defines an open addressing,
linear probing hash table. The table implement the public V3HashSet and
V3HashMap templates, which are generic containers. The benefit of this
over std::unordered_map and std::unordered_set is far better memory
locality during lookup. (The STL containers use chaining and require a
new heap allocation for every insertion, similarly probing involves
pointer chasing on collisions).
The new data structure is use in V3DfgCache, and V3DfgCse and yields a
significant speed improvement of those passes on large designs.
Geza Lore