This commit makes reductions part of the terminator. Instead of
`scf.yield`, `scf.reduce` now terminates the body of `scf.parallel` ops.
`scf.reduce` may contain an arbitrary number of reductions, with one
region per reduction.
Example:
```mlir
%init = arith.constant 0.0 : f32
%r:2 = scf.parallel (%iv) = (%lb) to (%ub) step (%step) init (%init, %init)
-> f32, f32 {
%elem_to_reduce1 = load %buffer1[%iv] : memref<100xf32>
%elem_to_reduce2 = load %buffer2[%iv] : memref<100xf32>
scf.reduce(%elem_to_reduce1, %elem_to_reduce2 : f32, f32) {
^bb0(%lhs : f32, %rhs: f32):
%res = arith.addf %lhs, %rhs : f32
scf.reduce.return %res : f32
}, {
^bb0(%lhs : f32, %rhs: f32):
%res = arith.mulf %lhs, %rhs : f32
scf.reduce.return %res : f32
}
}
```
`scf.reduce` operations can no longer be interleaved with other ops in
the body of `scf.parallel`. This simplifies the op and makes it possible
to assign the `RecursiveMemoryEffects` trait to `scf.reduce`. (This was
not possible before because the op was not a terminator, causing the op
to be DCE'd.)
The scf.forall.in_parallel terminator operation has a nested graph region with the NoTerminator trait. Such regions are not supported by the default implementations. Therefore, this commit adds a specialized implementation for
this operation which only covers the case where the nested region is empty.
This is because after bufferization, ops like tensor.parallel_insert_slice were already converted to memref operations residing int the scf.forall only and the nested region of scf.forall.in_parallel ends up empty.
This reverts commit 1356e853d47723c1be6eee2368d95c514a1816d1.
This caused problems in downstream projects. We are reverting to give
them more time for integration.
The scf.forall.in_parallel terminator operation has a nested graph region with
the NoTerminator trait. Such regions are not supported by the default
implementations. Therefore, this commit adds a specialized implementation for
this operation which only covers the case where the nested region is empty.
This is because after bufferization, ops like tensor.parallel_insert_slice were
already converted to memref operations residing int the scf.forall only and the
nested region of scf.forall.in_parallel ends up empty.
Reviewed By: springerm
Differential Revision: https://reviews.llvm.org/D158979
