[mlir][memref] Clarify the documentation for memref.clone [NFC]

[herhut]

Summary

The wording was wrong and suggested that operands to memref.clone may not be mutated.

[bondhugula]

mlir/include/mlir/Dialect/MemRef/IR/MemRefOps.td

428–431

This is just completely twisting and directly contradicting the statement above "Clones the data in the input view into an implicitly defined output view.". Is this op misnamed? clone_read_only_view? Even with that it doesn't explain disallowing mutations to the source.

[mehdi_amini]

mlir/include/mlir/Dialect/MemRef/IR/MemRefOps.td

428–431

Yes the naming is very misleading, I'm very supportive of a renaming (if you want to send a patch @bondhugula ?)

[bondhugula]

mlir/include/mlir/Dialect/MemRef/IR/MemRefOps.td

428–431

I just posted on the discord: https://llvm.discourse.group/t/reasoning-about-memref-mutability/3830/24?u=bondhugula The best I could think of based on my undertsanding is freeze_and_clone_read_only --- as in it freezes the source memref and makes a read-only clone. Pretty awkward but the semantics are as well!

mlir/include/mlir/Dialect/MemRef/IR/MemRefOps.td

let description = [{
     Clones the data in the input view into an implicitly defined output view.
 
     Usage:
 
     ```mlir
     %arg1 = memref.clone %arg0 : memref<?xf32> to memref<?xf32>
     ```
 
-    Note, that mutating the source or result of the clone operation leads to
-    undefined behavior.
+    Valid implementations of this operation may alias the input and output
+    views or create an actual copy. Mutating the source or result
+    of the clone operation after the clone operation thus leads to undefined
+    behavior.
   }];
 
   let arguments = (ins Arg<AnyRankedOrUnrankedMemRef, "", []>:$input);
   let results = (outs Arg<AnyRankedOrUnrankedMemRef, "", []>:$output);
 
   let extraClassDeclaration = [{
     Value getSource() { return input();}
     Value getTarget() { return output(); }