This is a reboot of the original design and implementation by
Nicolai Haehnle <nicolai.haehnle@amd.com>:
https://reviews.llvm.org/D85603
This change also obsoletes an earlier attempt at restarting the work on
convergence tokens:
https://reviews.llvm.org/D104504
Changes relative to D85603:
1. Clean up the definition of a "convergent operation", a convergent
call and convergent function.
2. Clean up the relationship between dynamic instances, sets of threads and
convergence tokens.
3. Redistribute the formal rules into the definitions of the convergence
intrinsics.
4. Expand on the semantics of entering a function from outside LLVM,
and the environment-defined outcome of the entry intrinsic.
5. Replace the term "cycle" with "closed path". The static rules are defined
in terms of closed paths, and then a relation is established with cycles.
6. Specify that if a function contains a controlled convergent operation, then
all convergent operations in that function must be controlled.
7. Describe an optional procedure to infer tokens for uncontrolled convergent
operations.
8. Introduce controlled maximal convergence-before and controlled m-converged
property as an update to the original properties in UniformityAnalysis.
9. Additional constraint that a cycle heart can only occur in the header of a
reducible cycle (natural loop).
Reviewed By: nhaehnle
Differential Revision: https://reviews.llvm.org/D147116
UniformityAnalysis offers all of the same features and much more, there is no reason left to use the legacy DAs.
See RFC: https://discourse.llvm.org/t/rfc-deprecate-divergenceanalysis-legacydivergenceanalysis/69538
- Remove LegacyDivergenceAnalysis.h/.cpp
- Remove DivergenceAnalysis.h/.cpp + Unit tests
- Remove SyncDependenceAnalysis - it was not a real registered analysis and was only used by DAs
- Remove/adjust references to the passes in the docs where applicable
- Remove TTI hook associated with those passes.
- Move tests to UniformityAnalysis folder.
- Remove RUN lines for the DA, leave only the UA ones.
- Some tests had to be adjusted/removed depending on how they used the legacy DAs.
Reviewed By: foad, sameerds
Differential Revision: https://reviews.llvm.org/D148116
An instruction that is "always uniform" is so even if it occurs in an
irreducible cycle. The output produced by such an instruction may depend on the
implementation defined cycle hierarchy, but that does not affect the uniformity
of the output. In other words, an "always uniform" instruction is uniform even
if it is not m-converged.
Reviewed By: ruiling, ronlieb
Differential Revision: https://reviews.llvm.org/D145572
Uniformity analysis is a generalization of divergence analysis to
include irreducible control flow:
1. The proposed spec presents a notion of "maximal convergence" that
captures the existing convention of converging threads at the
headers of natual loops.
2. Maximal convergence is then extended to irreducible cycles. The
identity of irreducible cycles is determined by the choices made
in a depth-first traversal of the control flow graph. Uniformity
analysis uses criteria that depend only on closed paths and not
cycles, to determine maximal convergence. This makes it a
conservative analysis that is independent of the effect of DFS on
CycleInfo.
3. The analysis is implemented as a template that can be
instantiated for both LLVM IR and Machine IR.
Validation:
- passes existing tests for divergence analysis
- passes new tests with irreducible control flow
- passes equivalent tests in MIR and GMIR
Based on concepts originally outlined by
Nicolai Haehnle <nicolai.haehnle@amd.com>
With contributions from Ruiling Song <ruiling.song@amd.com> and
Jay Foad <jay.foad@amd.com>.
Support for GMIR and lit tests for GMIR/MIR added by
Yashwant Singh <yashwant.singh@amd.com>.
Differential Revision: https://reviews.llvm.org/D130746
