Recognize "decoder" case statements (where every case item only assigns
constants to a fixed set of left-hand sides) and replace them with a
single packed constant lookup table indexed by the case expression.
Small tables are materialized inline in the generated code, and are
always optimized. Larger ones are placed in the constant pool and only
optimized if deemed beneficial over branches.
While this slightly conflicts with V3Table, and is not worth that much
on it's own, there will be a follow up patch that converts more cases of
this form which will be much more valuable. This patch does the
necessary analysis and the simple table conversion when possible.
Split -fcase into -fcase-table (this new conversion) and -fcase-tree (the
existing bitwise branch-tree conversion); -fno-case is now an alias for
both.
Default branches, assignments preceding the case (used as default values),
casez wildcards, multiple and partial left-hand sides, and both blocking and
non-blocking assignments are handled. Cases that cannot be safely tabled (e.g.
non-exhaustive with no default, overlapping writes to one variable, or mixed
blocking/non-blocking assignments) fall back to the existing if/else lowering.
Consequently disabled re-inlining of constant pool variables in V3Const,
and rebuild the constant pool hash in V3Dead (previously we didn't
create constant pool entries early enough for this to matter)
When a lot of combinational logic is driven from top level inputs,
work can be wasted evaluating that logic if the top level inputs don't
change.
This change adds an optimization by performing a change detect on the
top level inputs, and evaluate 'ico' logic only if the top level input
actually changed. This especially helps with --hierarchical/--lib-create
which runs the 'ico' of each sub-model in the eval settle loop.
This was observed to yield 40%+ run-time speedup on some partitioned
designs.
The added change detection is cheap, so it is emitted even if the 'ico'
region is small, and is on by default.
The optimization is only sound if the model itself does not write to the
top level inputs (otherwise the 'previous value' variables would be out
of sync, which are not updated by internal writes.). If we can detect a
top level input is written within the design, then for that input, we
fall back on always running the relevant logic. With --vpi we cannot
prove safety statically, so --vpi will disable this optimisation unless
explicitly enabled. (In which case it's the user's responsibility to not
write to top level inputs via the VPI.)
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
Relax the live variable analysis performed by Dfg to bail on fewer
cases. This analysis was already conservative (meaning it might think
variables are live when they are not), which is good enough for Dfg use.
This change in particular enables synthesizing more complex logic
involving arrays, e.g. those introduce by V3Table creating lookup
tables.
AstCAwait is only ever uses in statement position, so model it as a
statement. We should never ever have a coroutine that returns a value.
There is no need for it in SV, nor should we rely on it for internals.
Also reworks the fix for V3Life incorrectly constant propagating the
beforeTrig functions (#7072). The property that upsets V3Life is that
a function:
1. Is called from multiple static call sites (multiple AstCCall)
2. Reads model state directly (AstVarRef to non-locals/arguments)
Such function can only be created internally after scheduling (V3Task
throws an unsupported error on a non-inlined function that reads model
state), so added a flag to AstCFunc to mark the dangerous ones for
V3Life.
Igor Zaworski
Geza Lore
Artur Bieniek
Matthew Ballance
Muzaffer Kal
em2machine
Yogish Sekhar
Wilson Snyder
anonkey
Jakub Michalski
github action
Bartłomiej Chmiel
Todd Strader
Ryszard Rozak
Yilou Wang
Nick Brereton
Geza Lore
Krzysztof Bieganski