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.
Prep for fixing test added in #7913.
This is a large scale no functional change refactor, however, MT output
is perturbed as tied scores will be broken differently due to ordering
changes (still deterministic).
Split multi-threaded scheduling out of the monolithic
V3OrderParallel.cpp, into relatively independent parts, simplify the
data structures, and drop redundant or unused code.
New translation units:
- V3OrderMTaskGraph.h/.cpp: OrderMTaskGraph, the graph of LogicMTask
vertices and MTaskEdge edges. LogicMTask and MTaskEdge no longer
depend on the coarsening algorithm's merge candidate types;
per-algorithm auxiliary data is attached externally via the vertex and
edge user pointers.
- V3OrderMTaskFixHazards.cpp: data hazard fixup, was FixDataHazards.
- V3OrderMTaskContraction.cpp: graph coarsening, was Partitioner
together with PropagateCp and the merge candidate types.
- V3OrderParallel.cpp: now just the partitioning driver and ExecMTask
graph construction.
Data structure changes:
- Delete V3Scoreboard.h/.cpp. The generic template had a single user, now
a file-local MergeCandidateScoreboard in V3OrderMTaskContraction.cpp.
- Merge candidates are now MergeCandidate/SiblingMC/EdgeMC, distinguished
by a bit in the candidate id rather than by a vtable, and allocated by
the scoreboard, which owns their lifetime. This removes the multiple
inheritance previously used by MTaskEdge.
Move `hashGraphDebug` which prints the hash of a graph's shape for debugging
to generic `V3Graph::hashGraphDebug`.
Removed (can be added back later):
- Unnecesasry self tests that force special data stucture requirements.
- Per stage --stats output under --debug. (Final figures still reported.)
- Various debug dumps
Remove the expression combination counts from the default stats file,
and add a new `--dump-ast-patterns` option, which will dump new
`*_ast_patterns_*.txt` files. These contain the expression combinations
in a similar S-expression format as Dfg already produces with
`--dump-dfg-stats`. These dumps are not produced by just `--stats` as
they are fairly expensive to compute. Currently the new option will dump
at two points: just before we change to C types via widthMin usage, and
just before emit.
As per discussion. Remove the unsound V3SplitAs pass. The
isolate_assignments attribute/directive is now parsed and ignored in the
frontend for compatibility but otherwise have no effect.
Fixes#7144
Introduce new pass that converts impure expressions, or those with
function and method calls into simple assignment statements. Please see
the blurb at the top of the file why this is useful and how it works.
In particular currently it enables more Dfg optimization as functions
will be inlined without AstExprStmt.
Ideally we should enforce this lowering is applied to every procedural
statement (there are still a handful of exceptions). With that, long
term with this pass + #6820, there should be no need to ever use an
AstExprStmt past this new lowering pass, which should enable more easier
optimization down the line.
Also ideally this should be run earlier. Currently it's after V3Tristate
as that calls pinReconnectSimple so we don't have to touch Cell ports.
Currently disabled when code coverage is enabled due to #7119.
Add a new Dfg pass 'pushDownSel'. This will try to move selects through
a tree of concatenations in order to eliminate temporary nodes holding
intermediate concatenation results. This can get rid of a lot of
variables when packed arrays are assigned in parts (e.g. bit-wise).
Add V3SchedUtil.cpp that contains common small utility functions.
Add V3SchedTrigger.cpp that contains functionality building the trigger
mechanism code.
No functional change, just code movement. Prep for some further work.
All code is built as C++ via CXX, but we still have some references to
CC. Trying to make sure we don't add plain C later by hiding the C
compiler. (So it's always enough to override CXX=... in configure)
This patch implements #6480. All loop statements are represented using
AstLoop and AstLoopTest.
This necessitates rework of the loop unroller to handle loops of
arbitrary form. To enable this, I have split the old unroller used for
'generate for' statements and moved it into V3Param, and subsequently
rewrote V3Unroll to handle the new representation. V3Unroll can now
unroll more complex loops, including with loop conditions containing
multiple variable references or inlined functions.
Handling the more generic code also requires some restrictions. If a
loop contains any of the following, it cannot be unrolled:
- A timing control that might suspend the loop
- A non-inlined call to a non-pure function
These constructs can change the values of variables in the loop, so are
generally not safe to unroll if they are present. (We could still unroll
if all the variables needed for unrolling are automatic, however we
don't do that right now.)
These restrictions seem ok in the benchmark suite, where the new
unroller can generally unroll many more loops than before.
Added a mini type system for Dfg using DfgDataType to replace Dfg's use
of AstNodeDType. This is much more restricted and represents only the
types Dfg can handle in a canonical form. This will be needed when
adding more support for unpacked arrays and maybe unpacked structs one
day.
Also added an internal type checker for DfgGraphs which encodes all the
assumptions the code makes about type relationships in the graph. Run
this in a few places with --debug-check. Fix resulting fallout.
Parts of this algorithm were distributed over many files some
masquerading as re-usable APIs, they were not. Move everything into one
file and avoid unnecessary virtual functions.
This patch adds DfgLogic, which is a vertex that represents a whole,
arbitrarily complex combinational AstAlways or AstAssignW in the
DfgGraph.
Implementing this requires computing the variables live at entry to the
AstAlways (variables read by the block), so there is a new
ControlFlowGraph data structure and a classical data-flow analysis based
live variable analysis to do that at the variable level (as opposed to
bit/element level).
The actual CFG construction and live variable analysis is best effort,
and might fail for currently unhandled constructs or data types. This
can be extended later.
V3DfgAstToDfg is changed to convert the Ast into an initial DfgGraph
containing only DfgLogic, DfgVertexSplice and DfgVertexVar vertices.
The DfgLogic are then subsequently synthesized into primitive operations
by the new V3DfgSynthesize pass, which is a combination of the old
V3DfgAstToDfg conversion and new code to handle AstAlways blocks with
complex flow control.
V3DfgSynthesize by default will synthesize roughly the same constructs
as V3DfgAstToDfg used to handle before, plus any logic that is part of a
combinational cycle within the DfgGraph. This enables breaking up these
cycles, for which there are extensions to V3DfgBreakCycles in this patch
as well. V3DfgSynthesize will then delete all non synthesized or non
synthesizable DfgLogic vertices and the rest of the Dfg pipeline is
identical, with minor changes to adjust for the changed representation.
Because with this change we can now eliminate many more UNOPTFLAT, DFG
has been disabled in all the tests that specifically target testing the
scheduling and reporting of circular combinational logic.
Both V3DfgBreakCycles.cpp and V3DfgDecomposition.cpp used to contain an
implementation of the same algorithm to color strongly connected
components. Now there is only one, and it lives in V3DfgColorSCCs.cpp.
Added an algorithm that can break some combinational cycles in DFG, by
attempting to trace driver logic until we escape the cycle. This can
eliminate a decent portion of UNOPTFLAT warnings. E.g. due to this code:
```systemverilog
assign a[0] = .....;
assign a[1] = ~a[0];
```
Jared Bold
Marco Bartoli
Geza Lore
Matthew Ballance
Igor Zaworski
Sumanth Kadiyala
Shashvat
Yogish Sekhar
Yilou Wang
Wilson Snyder
Geza Lore
em2machine
Jose Drowne
Dan Ruelas-Petrisko
Bartłomiej Chmiel
Andrew Voznytsa