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
The REPLACE_SHIFTL_SHIFTL and REPLACE_SHIFTR_SHIFTR peephole optimizations
fold '(a << b) << c' into 'a << (b + c)' (and likewise for '>>'), but computed
'b + c' in the width of the shift-amount operand. When 'b + c' overflows that
width it wraps around, producing a too-small shift amount and a wrong result.
Compute the sum one bit wider than the amounts so it cannot overflow.
Fixes#7955
PR #7902 uncovered a pre-existing bug in multi-threaded scheduling,
where we can end up with an un-ordered R-W hazard in the MTask graph,
resulting in non-deterministic runtime behaviour.
This is extremely hard to actually trigger on a small example, so using
ThreadSanitizer to flag it, which can identify the race reliably.
In this patch:
- Add configure and `verilator --get-supported TSAN` to check if the
configured compiler supports ThreadSanitizer
- Add a --tsan option to the test driver.py which builds the test with
thread sanitizer (similar idea to --gdbsim).
- Add a tests.enable_tsan() method to allow turning on TSan in the test
Python file.
- Add a suppressions file that waives TSan errors in the runtime library
- Finally add `t_sched_hybrid_hazard` that demonstrates the data race
triggered after #7902. This is currently expected failing, fix later.
With the suppression, there are 17 vltmt tests failing due races in the
generated code. (Using `driver.py --vltmt --tsan --quiet -j0`)
Geza Lore
BRDR LIFE
Yilou Wang
Artur Bieniek
Marco Bartoli
Gilberto Abram
spomatasmd
Wilson Snyder
Bartosz Skorowski
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Aisha
Jakub Michalski
Kornel Uriasz
Igor Zaworski
Pawel Klopotek
Philip Axer
Patrick Creighton
Mateusz Gancarz
Adam Kostrzewski
Andrii
Nick Brereton
Jeffrey Song
Yogish Sekhar