Instead of op-specific cleanup patterns for region branch ops to remove
unused results / block arguments, etc., add a set of patterns that can
handle all `RegionBranchOpInterface` ops. These patterns are enabled
only for selected SCF dialect ops at the moment:
* `scf.execute_region`
* `scf.for`
* `scf.if`
* `scf.index_switch`
* `scf.while`
It is currently not possible to register canoncalization patterns for op
interfaces and some ops have incorrect interface implementations. In
follow-up PRs, the set of ops will be gradually extended within the SCF
dialect (`scf.forall`) and across other dialects
(`gpu.warp_execute_on_lane0`, (maybe) various affine dialect ops, ...),
and maybe eventually to apply to all `RegionBranchOpInterface` ops.
This commit removes many similar canonicalization patterns from the SCF
dialect. The newly added canonicalization patterns allow users to get
the same canonicalizations for free for their own ops. And even a few
additional new canonicalizations
([example](https://github.com/llvm/llvm-project/pull/174094/files#diff-54318cd685386d5519c42be49818e388b09d934edcbe4280548baa3601802977R2241),
[example](https://github.com/llvm/llvm-project/pull/174094/files#diff-54318cd685386d5519c42be49818e388b09d934edcbe4280548baa3601802977R1101),
...).
Implementation outline: This commit adds 3 canonicalization patterns.
* `MakeRegionBranchOpSuccessorInputsDead`: Remove uses of successor
inputs, by swapping them for successor operand values.
* `RemoveDuplicateSuccessorInputUses`: Remove uses of successor inputs
that are duplicates. (Similar to `WhileRemoveDuplicatedResults` in the
SCF dialect.)
* `RemoveDeadRegionBranchOpSuccessorInputs`: Remove dead successor
inputs if all of their "tied" successor inputs are also dead. (Similar
to `WhileUnusedResult` in the SCF dialect.)
c4750d0575