This is intended as a fast pattern rewrite driver for the cases when a
simple walk gets the job done but we would still want to implement it in
terms of rewrite patterns (that can be used with the greedy pattern
rewrite driver downstream).
The new driver is inspired by the discussion in
https://github.com/llvm/llvm-project/pull/112454 and the LLVM Dev
presentation from @matthias-springer earlier this week.
This limitation comes with some limitations:
* It does not repeat until a fixpoint or revisit ops modified in place
or newly created ops. In general, it only walks forward (in the
post-order).
* `matchAndRewrite` can only erase the matched op or its descendants.
This is verified under expensive checks.
* It does not perform folding / DCE.
We could probably relax some of these in the future without sacrificing
too much performance.
`UnsignedWhenEquivalent` doesn't really need any dialect conversion
features and switching it normal patterns makes it more composable with
other patterns-based transformations (and probably faster).
`CeilDivUIOp` seemed to have been added by mistake to the list of
dynamically
illegal operations in `arith-unsigned-when-equivalent`. The only illegal
operations
should be the signed operations that can be converted to their unsigned
counterpart.
The pass was not checking for uninitialized states due to dead code.
This patch also makes LLVMFuncOp correctly return a null body when it is
external.
Fixes#58807
Depends on D139388
Reviewed By: rriddle
Differential Revision: https://reviews.llvm.org/D139389
