All ops of the SCF dialect now use the `scf.` prefix instead of `loop.`. This
is a part of dialect renaming.
Differential Revision: https://reviews.llvm.org/D79844
The current lowering of loops to GPU only supports lowering of loop
nests where the loops mapped to workgroups and workitems are perfectly
nested. Here a new lowering is added to handle lowering of imperfectly
nested loop body with the following properties
1) The loops partitioned to workgroups are perfectly nested.
2) The loop body of the inner most loop partitioned to workgroups can
contain one or more loop nests that are to be partitioned across
workitems. Each individual loops nests partitioned to workitems should
also be perfectly nested.
3) The number of workgroups and workitems are not deduced from the
loop bounds but are passed in by the caller of the lowering as values.
4) For statements within the perfectly nested loop nest partitioned
across workgroups that are not loops, it is valid to have all threads
execute that statement. This is NOT verified.
PiperOrigin-RevId: 277958868
This CL introduces a simple loop utility function which rewrites the bounds and step of a loop so as to become mappable on a regular grid of processors whose identifiers are given by SSA values.
A corresponding unit test is added.
For example, using CUDA terminology, and assuming a 2-d grid with processorIds = [blockIdx.x, threadIdx.x] and numProcessors = [gridDim.x, blockDim.x], the loop:
```
loop.for %i = %lb to %ub step %step {
...
}
```
is rewritten into a version resembling the following pseudo-IR:
```
loop.for %i = %lb + threadIdx.x + blockIdx.x * blockDim.x to %ub
step %gridDim.x * blockDim.x {
...
}
```
PiperOrigin-RevId: 258945942
Alex Zinenko