Remove the present tcp.island.

The idea was half-baked and after some deep thought felt like a solution
looking for a problem. What we had here (and is removed in this patch)
just wasn't pulling its weight.

I cannot think of anything we would want to do with tcp.island as it is
removed here beyond just sinking and merging them within a basic block,
such that the witness argument is kind of pointless (only matters for
hoisting).

TCP compute ops like tcp.add and tcp.broadcast_to have the strong
invariant of "pure or undefined behavior", which means they are always
safe to sink. The island concept as removed here conferred no benefit.

Also, I'll note that "islands" are a trick you can only play once in a
system (unless they strictly nest). I have some early-stage thoughs on
having an island concept that helps with modeling tensor shapes
robustly which seems promising (the island would serve a similar role as
tie_shape).

include/npcomp/Dialect/TCP/IR/TCPOps.td

@@ -18,44 +18,6 @@ class TCP_Op<string mnemonic, list<OpTrait> traits = []>
     : Op<TCP_Dialect, mnemonic, traits> {
 }
 
-// TODO: Do islands belong inside this dialect?
-// It almost feels like they should be in an `error` dialect (containing
-// the witness type as well).
-// There would be no "shape.abort_if_error" because the aborting happens
-// inside the witness ops, with the island operating as a witness sink.
-def TCP_IslandOp : TCP_Op<"island"> {
-  let summary = "Island of no-side-effect ops.";
-  let description = [{
-Most ops in the `tcp` dialect have complex preconditions on their tensor 
-arguments (usually their shapes) so that they can be a good starting point
-for code generation compilation flows.
-We want an efficient way to understand which ops are related to which
-preconditions without cluttering the TCP ops themselves.
-To do this, we have this `tcp.island` op which takes as operands
-witness values establishing use-def edges between precondition assertions
-and this island op, and then restrict most other `tcp` ops to reside inside
-these islands. This makes code motion to rearrange `tcp` ops simpler
-by having the witness use-def edges, without needing for every `tcp` op
-to have extra operands.
-// TODO: Still unclear if this is really that useful. This mainly affects the
-// ability to hoist tcp ops. It should always be safe to sink TCP ops.
-  }];
-  let arguments = (ins Variadic<NoneType>:$witnesses);
-  let regions = (region AnyRegion:$body);
-  let results = (outs Variadic<AnyRankedTensor>:$results);
-  // TODO: verify return types match internal tcp.yield return ValueRange's.
-}
-
-def TCP_YieldOp
-    : TCP_Op<"yield", [NoSideEffect, HasParent<"IslandOp">, Terminator]> {
-  let summary = "yield-like terminator for tcp.island op.";
-  let description = [{
-Returns control and a variadic list of values to the parent tcp.island op.
-  }];
-  let arguments = (ins Variadic<AnyRankedTensor>:$operands);
-  let results = (outs);
-}
-
 // TODO: clarify allowed tensor element types.
 // TODO: HasParent is too restrictive? can't have an island with loop.for with
 // further ops inside it?
@@ -96,21 +58,23 @@ Allocates a memref of the given shape.
   let assemblyFormat = "$shape attr-dict `:`  type($memref)";
 }
 
-// TODO: Change to a more principled witness-based error handling mechanism.
+// TODO: Change to a more principled error handling mechanism.
 // This op probably doesn't need to exist eventually.
+// This op is also not correctly modeled right now, since it itself doesn't
+// produce the error in practice. The ops like shape.broadcast itself, when
+// lowered, immediately produce errors.
+// Right now, it's more of an "observe_error" which just keeps NoSideEffect
+// shape ops alive.
 def TCP_AbortIfErrorOp : TCP_Op<"abort_if_error",
     [DeclareOpInterfaceMethods<InferTypeOpInterface>]> {
   let summary = "Aborts the program if the argument is an error shape.";
   let description = [{
 Aborts the program if its `shape` argument is an error shape.
-TODO: can we do something better designed here then just abort?
-
-Returns `none`, which can be used as a witness value to establish a use-def
-relationship between this op and an op that requires the precondition
-established by this op.
   }];
   let arguments = (ins Shape_ShapeType:$shape);
-  let results = (outs NoneType:$result);
+  // TODO: ODS seems to create redeclared class members if we remove this,
+  // resulting in C++ compilation errors.
+  let results = (outs NoneType:$dummy);
 }
 
 // TODO: This probably belongs in the shape dialect.

lib/Conversion/TCFToTCP/TCFToTCP.cpp

@@ -33,15 +33,7 @@ public:
     Value rhsShape = rewriter.create<shape::ShapeOfOp>(op.getLoc(), op.rhs());
     Value broadcastedShape = rewriter.create<shape::BroadcastOp>(
         op.getLoc(), lhsShape, rhsShape, /*error=*/nullptr);
-    Value witness =
     rewriter.create<tcp::AbortIfErrorOp>(op.getLoc(), broadcastedShape);
-    tcp::IslandOp island =
-        rewriter.create<tcp::IslandOp>(op.getLoc(), op.getType(), witness);
-    Region &body = island.body();
-    Block *bodyBlock = new Block;
-    body.push_back(bodyBlock);
-    OpBuilder::InsertionGuard guard(rewriter);
-    rewriter.setInsertionPoint(bodyBlock, bodyBlock->begin());
     // TODO: It's annoying to do the dynamic broadcast above then
     // do the static transfer function here. Would be nice if they could
     // somehow be unified.
@@ -56,9 +48,7 @@ public:
         op.getLoc(), resultType, op.rhs(), broadcastedShape);
     Value add = rewriter.create<tcp::AddOp>(op.getLoc(), op.getType(),
                                             lhsBroadcasted, rhsBroadcasted);
-    rewriter.create<tcp::YieldOp>(op.getLoc(), add);
-
-    rewriter.replaceOp(op, island.getResults());
+    rewriter.replaceOp(op, add);
     return success();
   }
 };

lib/E2E/E2E.cpp

@@ -171,7 +171,7 @@ class ResolveTensorLoadStoreOps
     target.addLegalDialect<linalg::LinalgDialect>();
     target.addDynamicallyLegalOp<TensorLoadOp>([](TensorLoadOp op) {
       for (auto user : op.getResult().getUsers())
-        if (!isa<tcp::YieldOp>(user))
+        if (!isa<ReturnOp>(user))
           return false;
       return true;
     });

test/Dialect/TCP/ops.mlir

@@ -2,10 +2,6 @@
 
 func @f(%arg0: tensor<?xf32>, %arg1: tensor<?xf32>, %arg2: i32) {
   // CHECK: tcp.add
-  %result = "tcp.island"() ({
   %0 = "tcp.add"(%arg0, %arg1) : (tensor<?xf32>, tensor<?xf32>) -> tensor<?xf32>
-    "tcp.yield"(%0) : (tensor<?xf32>) -> ()
-  }) : () -> tensor<?xf32>
-
   return
 }