Internals: Refactor generate construct Ast handling (#6280)
We introduce AstNodeGen, the common base class of AstGenBlock,
AstGenCase, AstGenFor, and AstGenIf, which together represent all SV
generate constructs. Subsequently remove AstNodeFor, AstNodeCase
(AstCase is now directly derived from AstNodeStmt) and adjust internals
to work on the new representation.
Output is identical modulo hashes do to changed AstNode type ids, no
functional change intended.
Step towards #6280.
The only use for the clocker attribute and the AstVar::isUsedClock that
is actually necessary today for correctness is to mark top level inputs
of --lib-create blocks as being (or driving) a clock signal. Correctness
of --lib-create (and hence hierarchical blocks) actually used to depend
on having the right optimizations eliminate intermediate clocks (e.g.:
V3Gate), when the top level port was not used directly in a sensitivity
list, or marking top level signals manually via --clk or the clocker
attribute. However V3Sched::partition already needs to trace through the
logic to figure out what signals might drive a sensitivity list, so it
can very easily mark all top level inputs as such.
In this patch we remove the AstVar::attrClocker and AstVar::isUsedClock
attributes, and replace them with AstVar::isPrimaryClock, automatically
set by V3Sched::partition. This eliminates all need for manual
annotation so we are deprecating the --clk/--no-clk options and the
clocker/no_clocker attributes.
This also eliminates the opportunity for any further mis-optimization
similar to #6453.
Regarding the other uses of the removed AstVar attributes:
- As of 5.000, initial edges are triggered via a separate mechanism
applied in V3Sched, so the use in V3EmitCFunc.cpp is redundant
- Also as of 5.000, we can handle arbitrary sensitivity expressions, so
the restriction on eliminating clock signals in V3Gate is unnecessary
- Since the recent change when Dfg is applied after V3Scope, it does
perform the equivalent of GateClkDecomp, so we can delete that pass.
Added cppcheck-suppressions.txt in the repo root. You can add new
patterns in there instead of having to parse the XML output.
Also configure to add the -D__GNUC__ preprocessor macro, which makes it
understand UASSERT (it understands the 'noreturn' function attribute).
Added some case by case specific suppressions and fixed up other code,
especially in V3Ast*h and V3Dfg*.h, including code generated by astgen
that had some no-ops that irks cppcheck.
One thing it does not seem to like is `const` class members with default
initializers in the class. It will assume that's always the value, even
if overridden in the constructor. We had few so removed them.
With that a lot of files in `src/` are now clean or only have a handful
of issues. Therefore, I have also deleted cppcheck_filtered, and made it
produce human readable output straight to the terminal.
Regarding cleaning up the reported nits, I kind of got bored after
V3[A-E] so pausing here. Apologies for the merge conflicts.
Tested with cppcheck 2.13.0
Remove AstJumpLabel
AstJumpGo now references one if its enclosing AstJumpBlocks, and
branches straight after the referenced block.
That is:
```
JumpBlock a {
...
JumpGo(a);
...
}
// <--- the JumpGo(a) goes here
```
This is sufficient for all use cases and makes control flow much easier to
reason about. As a result, V3Const can optimize a bit more aggressively.
Second half of, and fixes#6216
Somewhat commonly, there is code out there that compares an expression (or
variable) against many different constants, e.g. a one-hot decoder:
```systemverilog
assign oneHot = {x == 3, x == 2, x == 1, x == 0};
```
If the width of the expression is sufficiently large, this can blow up
a GCC pass and take an egregious amount of memory and time to compile.
Adding a new DFG pass that will generate a cheap one-hot decoder:
to compute:
```systemverilog
wire [$bits(x)-1:0] idx = <the expression being compared many times>
reg tab [1<<$bits(x)] = '{default: 0};
reg [$bits(x)-1:0] pre = '0;
always_comb begin
tab[pre] = 0;
tab[idx] = 1;
pre = idx ; // This assignment marked to avoid a false UNOPFTLAT
end
```
We then replace the comparisons `x == CONST` with `tab[CONST]`.
This is generally performance neutral, but avoids the compile time and memory
blowup with GCC (128GB+ -> 1GB in one example).
We do not apply this if the comparisons seem to be part of a `COMPARE ?
val : COND` conditional tree, which the C++ compilers can turn into jump
tables.
This enables all XiangShan configurations from RTLMeter to now build with GCC,
so in this patch we enabled those in the nightly runs.
Having many triggers still hits a bottleneck in LLVM leading to long
compile times.
Instead of setting triggers bit-wise, set them as a whole 64-bit word
when possible. This improves C++ compile times by ~4x on some large
designs and has minor run-time performance benefit.
* Support 2D dynamic array initialization (#4700)
- new[] on sub arrays (as per original issue)
- Built-in methods for sub-arrays
- Initialization and literals assignmensts
- Dynamic array as an element for other arrays and queues
For NBAs that might execute a dynamic number of times in a single
evaluation (specifically: those that assign to array elements inside
loops), we introduce a new run-time VlNBACommitQueue data-structure
(currently a vector), which stores all pending updates and the necessary
info to reconstruct the LHS reference of the AstAssignDly at run-time.
All variables needing a commit queue has their corresponding unique
commit queue.
All NBAs to a variable that requires a commit queue go through the
commit queue. This is necessary to preserve update order in sequential
code, e.g.:
a[7] <= 10
for (int i = 1 ; i < 10; ++i) a[i] <= i;
a[2] <= 10
needs to end with array elements 1..9 being 1, 10, 3, 4, 5, 6, 7, 8, 9.
This enables supporting common forms of NBAs to arrays on the left hand
side of <= in non-suspendable/non-fork code. (Suspendable/fork
implementation is unclear to me so I left it unchanged, see #5084).
Any NBA that does not need a commit queue (i.e.: those that were
supported before), use the same scheme as before, and this patch should
have no effect on the generated code for those NBAs.
There is no strong need to re-map LogicMTask IDs and it just adds extra
processing. Instead we just allocate a separate set of ExecMTask IDs as
they are created, which can also be used as the unique profiling ID as
well. The only effect on the output of this is the change in mtask IDs
emitted, which was fairly arbitrary to begin with.
This saves about 5% memory. V3AstUserAllocator is appropriate for most use
cases, performance is marginally up as we are mostly D-cache bound on
large designs.
The typical find/if-not-exists-insert pattern can be achieved with 1
lookup instead of 2 using emplace with a sentinel value. Also maps value
initialize their values when inserted with the [] operator, this is
defined and so there is no need to explicitly insert zeroes for integer
values.
Wilson Snyder
Geza Lore
Artur Bieniek
Ryszard Rozak
Krzysztof Bieganski
Igor Zaworski
Paul Swirhun
Paul Swirhun
George Polack
Yilou Wang
github action
Krzysztof Starecki
Arkadiusz Kozdra
Bartłomiej Chmiel
Valentin Atepalikhin
Bartłomiej Chmiel
Andrew Nolte
Kefa Chen
Yutetsu TAKATSUKASA
Szymon Gizler
Krzysztof Boroński
Chih-Mao Chen
Marlon James
Aleksander Kiryk
Anthony Donlon