Use of i1 outside of the cycle, both uniform and divergent,
is lane mask(in sgpr) that contains i1 at iteration that lane
exited the cycle.
Create phi that merges lane mask across all iterations.
Record all uses outside cycle with divergent exit during
propagateTemporalDivergence in Uniformity analysis.
With this list of candidates for temporal divergence lowering,
excluding known lane masks from control flow intrinsics,
find sources from inside the cycle that are not i1 and uniform.
Temporal divergence lowering (non i1):
create copy(v_mov) to vgpr, with implicit exec (to stop other
passes from moving this copy outside of the cycle) and use this
vgpr outside of the cycle instead of original uniform source.
Prepare for new pass manager version of `MachineDominatorTreeAnalysis`.
We may need a machine dominator tree version of `DomTreeUpdater` to
handle `SplitCriticalEdge` in some CodeGen passes.
Basic implementation of lane mask merging for GlobalISel.
Lane masks on GlobalISel are registers with sgpr register class
and S1 LLT - required by machine uniformity analysis.
Implements equivalent of lowerPhis from SILowerI1Copies.cpp in:
patch 1: https://github.com/llvm/llvm-project/pull/75340
patch 2: https://github.com/llvm/llvm-project/pull/75349
patch 3: https://github.com/llvm/llvm-project/pull/80003
patch 4: https://github.com/llvm/llvm-project/pull/78431
patch 5: is in this commit:
AMDGPU/GlobalISelDivergenceLowering: constrain incoming registers
Previously, in PHIs that represent lane masks, incoming registers
taken as-is were not selected as lane masks. Such registers are not
being merged with another lane mask and most often only have S1 LLT.
Implement constrainAsLaneMask by constraining incoming registers
taken as-is with lane mask attributes, essentially transforming them
to lane masks. This is final step in having PHI instructions created
in this pass to be fully instruction-selected.
Implement PhiLoweringHelper for GlobalISel in DivergenceLoweringHelper.
Use machine uniformity analysis to find divergent i1 phis and select
them as lane mask phis in same way SILowerI1Copies select VReg_1 phis.
Note that divergent i1 phis include phis created by LCSSA and all cases
of uses outside of cycle are actually covered by "lowering LCSSA phis".
GlobalISel lane masks are registers with sgpr register class and S1 LLT.
TODO: General goal is that instructions created in this pass are fully
instruction-selected so that selection of lane mask phis is not split
across multiple passes.
patch 3 from: https://github.com/llvm/llvm-project/pull/73337
Implement PhiLoweringHelper for GlobalISel in DivergenceLoweringHelper.
Use machine uniformity analysis to find divergent i1 phis and select
them as lane mask phis in same way SILowerI1Copies select VReg_1 phis.
Note that divergent i1 phis include phis created by LCSSA and all cases
of uses outside of cycle are actually covered by "lowering LCSSA phis".
GlobalISel lane masks are registers with sgpr register class and S1 LLT.
TODO: General goal is that instructions created in this pass are fully
instruction-selected so that selection of lane mask phis is not split
across multiple passes.
patch 3 from: https://github.com/llvm/llvm-project/pull/73337
Implement PhiLoweringHelper for GlobalISel in DivergenceLoweringHelper.
Use machine uniformity analysis to find divergent i1 phis and select
them as lane mask phis in same way SILowerI1Copies select VReg_1 phis.
Note that divergent i1 phis include phis created by LCSSA and all cases
of uses outside of cycle are actually covered by "lowering LCSSA phis".
GlobalISel lane masks are registers with sgpr register class and S1 LLT.
TODO: General goal is that instructions created in this pass are fully
instruction-selected so that selection of lane mask phis is not split
across multiple passes.
patch 3 from: https://github.com/llvm/llvm-project/pull/73337
Add empty AMDGPUGlobalISelDivergenceLowering pass. This pass will
implement
- selection of divergent i1 phis as lane mask phis, requires lane mask
merging in some cases
- lower uses of divergent i1 values outside of the cycle using lane mask
merging
- lowering of all cases of temporal divergence:
- lower uses of uniform i1 values outside of the cycle using lane mask
merging
- lower uses of uniform non-i1 values outside of the cycle using a copy
to vgpr inside of the cycle
Add very detailed set of regression tests for cases mentioned above.
patch 1 from: https://github.com/llvm/llvm-project/pull/73337
