[mlir] Add check for ViewLikeOpInterface that creates additional aliases.

[dfki-jugr]

Summary

ViewLikeOpInterfaces introduce new aliases that need to be added to the alias
list. This is necessary to place deallocs in the right positions.

[pifon2a]

mlir/lib/Transforms/BufferPlacement.cpp

149

What would be the difference between aliasing-operation-effects interface and already existing ViewLikeOpInterface ?

[bondhugula]

mlir/lib/Transforms/BufferPlacement.cpp

149

Nit: memRefCastOp.source()

[herhut]

Thanks for trying this! As @pifon suggests, you could use the ViewLikeOpInterface today and cover some ops (like ViewOp and SubviewOp) in std. That would definitely be worth adding. So please rewrite using that interface and change the test to use SubviewOp. Then this can land!

mlir/lib/Transforms/BufferPlacement.cpp

149

Maybe we should evolve ViewLikeOpInterface in that direction. @nicolasvasilache Would you say that memref_cast should implement that interface? Or do you have some other semantic meaning in mind?

mlir/test/Transforms/buffer-placement.mlir

929

Should the others be CHECK-NEXT too?

[pifon2a]

mlir/lib/Transforms/BufferPlacement.cpp

149

Would it make sense to add ViewLikeOpInterface to MemrefcastOp?

[dfki-jugr]

Changed from a specialized MemRefCastOp version to a more general ViewLikeOpInterface version.
Adapt test case, since MemRefCastOp is currently not a ViewLikeOp.

[herhut]

Looks good to me. Thanks!

mlir/lib/Transforms/BufferPlacement.cpp

private:
   /// regions and branch-like return operations from nested regions.
   void build(Operation *op) {
     // Registers all aliases of the given values.
     auto registerAliases = [&](auto values, auto aliases) {
       for (auto entry : llvm::zip(values, aliases))
         this->aliases[std::get<0>(entry)].insert(std::get<1>(entry));
     };
 
+    // TODO: After providing an aliasing-operation-effects interface, this can
+    // be removed.
+    // Add an alias created by a MemRefCastOp to the alias list.
+    op->walk([&](MemRefCastOp memRefCastOp) {
+      aliases[memRefCastOp.getOperand()].insert(memRefCastOp);
+    });
+
     // Query all branch interfaces to link block argument aliases.
     op->walk([&](BranchOpInterface branchInterface) {
       Block *parentBlock = branchInterface.getOperation()->getBlock();
       for (auto it = parentBlock->succ_begin(), e = parentBlock->succ_end();
            it != e; ++it) {
         // Query the branch op interface to get the successor operands.
         auto successorOperands =
             branchInterface.getSuccessorOperands(it.getIndex());

mlir/test/Transforms/buffer-placement.mlir

 // CHECK-NEXT: test.region_if_yield %[[ALLOC6]]
 //      CHECK: ^bb0(%[[ALLOC7:.*]]:{{.*}}):
 //      CHECK: %[[ALLOC8:.*]] = alloc
 // CHECK-NEXT: linalg.copy(%[[ALLOC7]], %[[ALLOC8]])
 // CHECK-NEXT: dealloc %[[ALLOC7]]
 // CHECK-NEXT: test.region_if_yield %[[ALLOC8]]
 //      CHECK: dealloc %[[ALLOC0]]
 // CHECK-NEXT: return %[[ALLOC1]]
+
+// -----
+
+// CHECK-LABEL: func @memref_cast_op
+func @memref_cast_op(%arg0: memref<2xf32>) {
+  %0 = alloc() : memref<2xf32>
+  %1 = memref_cast %0 : memref<2xf32> to memref<?xf32>
+  "linalg.copy"(%1, %arg0) : (memref<?xf32>, memref<2xf32>) -> ()
+  return
+}
+
+// CHECK-NEXT: %[[ALLOC:.*]] = alloc()
+//      CHECK: memref_cast
+//      CHECK: linalg.copy
+// CHECK-NEXT: dealloc %[[ALLOC]]
+// CHECK-NEXT: return