[Mlir-commits] [mlir] [mlir][scf] Extend consumer fuse to nested loop structure (PR #94190)

[llvmlistbot at llvm.org]

MaheshRavishankar wrote:

> Seems to me like this should be done by multiple application of existing transformations and not by creating a new custom transformation that unrolls both in C++

I agree with Nicolas' comment here. This is the way tile and fuse is supposed to work. You start with

```
%0 = <producer>
%1 = <consumer>(...%0...)
```

First tile the consumer

```
%0 = <producer>
%1 = scf.for ... shared_outs/init(%arg0 =...) {
   %2 = scf.for ... shared_outs/init(%arg1 = %arg0) {
      %3 = <consumer>(...%0...)
       %4 = ... insert_slice %3 into %arg1 ...
       scf.yield %4 
   }
   scf.yield %2
}
```

then you fuse `%0` within the `scf.for` nest that is created during tiling of consumer to get 

```
%1 = scf.for ... shared_outs/init(%arg0 =...) {
   %2 = scf.for ... shared_outs/init(%arg1 = %arg0) {
     %0 = <producer>
      %3 = <consumer>(...%0...)
       %4 = ... insert_slice %3 into %arg1 ...
       scf.yield %4 
   }
   scf.yield %2
}
```        

So you are fusing the operation into an "immediately created" tiled loop nest. The more general case you are looking for can be done through repeated application.

https://github.com/llvm/llvm-project/pull/94190