Apart from adding required AstCUse, V3CUse also used to create some
standard methods for classes. This is now done in a separate pass
V3Common. Note that this is not a performance issue, as V3Common just
iterates through each module, which are stored in a simple linked list
under the netlist, and does not need to traverse the whole netlist.
Internal AstNodeModule headers (.h) and implementation (.cpp) files are
now emitted separately in V3EmitC::emitcHeaders() and
V3EmitC::emitcImp() respectively. No functional change intended
A separate V3VariableOrder pass is now used to order module variables
before Emit. All variables are now ordered together, without
consideration for whether they are ports, signals form the design, or
additional internal variables added by Verilator (which used to be
ordered and emitted as separate groups in Emit). For single threaded
models, this is performance neutral. For multi-threaded models, the
MTask affinity based sorting was slightly modified, so variables with no
MTask affinity are emitted last, otherwise the MTask affinity sets are
sorted using the TSP sorter as before, but again, ports, signals, and
internal variables are not differentiated. This yields a 2%+ speedup for
the multithreaded model on OpenTitan.
This patch implements #3032. Verilator creates a module representing the
SystemVerilog $root scope (V3LinkLevel::wrapTop). Until now, this was
called the "TOP" module, which also acted as the user instantiated model
class. Syms used to hold a pointer to this root module, but hold
instances of any submodule. This patch renames this root scope module
from "TOP" to "$root", and introduces a separate model class which is
now an interface class. As the root module is no longer the user
interface class, it can now be made an instance of Syms, just like any
other submodule. This allows absolute references into the root module to
avoid an additional pointer indirection resulting in a potential speedup
(about 1.5% on OpenTitan). The model class now also contains all non
design specific generated code (e.g.: eval loops, trace config, etc),
which additionally simplifies Verilator internals.
Please see the updated documentation for the model interface changes.
Factored out bits from V3EmitC.cpp that is required to emit a whole
(non-trace) AstCFunc. This is mostly what used to be the EmitCStmts
class plus relevant bits from EmitCImp. These now live in EmitCFunc,
which is reusable by anything that needs to emit a regular AstCFunc
(differences in tracing to be addressed later). EmitCImp now extends
EmitCFunc instead of EmitCStmts. No functional change intended.
What previously used to be per module static constants created in
V3Table and V3Prelim are now merged globally within the whole model and
emitted as part of a separate constant pool. Members of the constant
pool are global variables which are declared lazily when used (similar to
loose methods).
Check the C++ compiler for -Og via configure and use it if available.
Per the GCC manual:
-Og should be the optimization level of choice for the standard
edit-compile-debug cycle, offering a reasonable level of optimization
while maintaining fast compilation and a good debugging experience. It
is a better choice than -O0 for producing debuggable code because some
compiler passes that collect debug information are disabled at -O0.
The debug exe is painfully slow on large designs, hopefully this is an
improvement.
Similarly, check for and use -gz to compress the debug info as it is
huge otherwise. This should help with distribution and caching on CI.
Also checks for -ggdb via configure for compatibility.
Rework Ast hashing to be stable
Eliminated reliance on pointer values in AstNode hashes in order to make
them stable. This requires moving the sameHash functions into a visitor,
as nodes pointed to via members (and not child nodes) need to be hashed
themselves.
The hashes are now stable (as far as I could test them), and the impact
on verilation time is small enough not to be reliably measurable.
V3Hasher is responsible for computing AstNode hashes, while V3DupFinder
can be used to find duplicate trees based on hashes. Interface of
V3DupFinder simplified somewhat. No functional change intended at this
point, but hash computation might differ in minor details, this however
should have no perceivable effect on output/runtime.
Implements (#2964)
This provides minor simulation performance benefit, but can provide
large C++ compilation time improvement, notably with Clang (4x).
This patch implements #2366 .
This adds the flag --generate-waivefile <filename>. This will generate
a verilator config file with the proper lint_off statemens to turn off
warnings emitted during this particular run.
This feature can be used to start with using Verilator as linter and
systematically capture all known lint warning for further
elimination. It hopefully helps people turning of -Wno-fatal or
-Wno-lint and gradually improve their code base.
Signed-off-by: Stefan Wallentowitz <stefan.wallentowitz@hm.edu>
The build is now by default configured to link performance critical
libraries (libgcc, libstdc++, libtcmalloc) statically. This improves
Verilation speed by between 4.5-7% based on my measurements as it
eliminates approx 20% of the mispredicted branches from the execution.
With partial static linking, the size of the .text section in
verilator_bin is increased by about 14%, and the binary is itself only
about 800KB bigger on disk, so hopefully this is not a big issue in
exchange for the faster compilation speed. A configure option
"--disable-partial-static" is provided to restore the old behaviour of
linking everything dynamically.
Note: This patch also changes to use libtcmalloc_minimal, which is all
we really need and itself has fewer dependencies.
As Verilator continuously allocates and releases small objects (e.g.:
AstNode, V3GraphVertex, V3GraphEdge), it spends a significant amount of
time in malloc/free and friends. This patch adds the --enable-tcmalloc
configure option to link Verilator against the high performance malloc
implementation library libtcmalloc. The default is to use libtcmalloc if
available on the system. Note that there are no source code change, we
are simply replacing the standard library memory allocation functions.
Measured major compilation speed improvement of 27% when running
Verilator with -O3 on a large design.
