[MLIR][MemRef]-Add basic folding for memref ViewOp (llvm#146237)

Add a folding for MemRef::ViewOp where the source
memref type and the result memref type are similar.

Author: amirBish

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

@@ -2333,6 +2333,7 @@ def MemRef_ViewOp : MemRef_Op<"view", [
 
   let hasCanonicalizer = 1;
   let hasVerifier = 1;
+  let hasFolder = 1;
 }
 
 //===----------------------------------------------------------------------===//

mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp

@@ -3463,6 +3463,16 @@ LogicalResult ViewOp::verify() {
 
 Value ViewOp::getViewSource() { return getSource(); }
 
+OpFoldResult ViewOp::fold(FoldAdaptor adaptor) {
+  MemRefType sourceMemrefType = getSource().getType();
+  MemRefType resultMemrefType = getResult().getType();
+
+  if (resultMemrefType == sourceMemrefType && resultMemrefType.hasStaticShape())
+    return getViewSource();
+
+  return {};
+}
+
 namespace {
 
 struct ViewOpShapeFolder : public OpRewritePattern<ViewOp> {

mlir/test/Dialect/MemRef/canonicalize.mlir

@@ -1208,3 +1208,24 @@ func.func @fold_assume_alignment_chain(%0: memref<128xf32>) -> memref<128xf32> {
   // CHECK: return %[[ALIGN]]
   return %2 : memref<128xf32>
 }
+
+// -----
+
+// CHECK-LABEL: func @fold_view_same_source_result_types
+func.func @fold_view_same_source_result_types(%0: memref<128xi8>) -> memref<128xi8> {
+  %c0 = arith.constant 0: index
+  // CHECK-NOT: memref.view
+  %res = memref.view %0[%c0][] : memref<128xi8> to memref<128xi8>
+  return %res : memref<128xi8>
+}
+
+// -----
+
+// CHECK-LABEL: func @non_fold_view_same_source_res_types
+//  CHECK-SAME:   %[[ARG0:[a-zA-Z0-9]+]]
+func.func @non_fold_view_same_source_res_types(%0: memref<?xi8>, %arg0 : index) -> memref<?xi8> {
+  %c0 = arith.constant 0: index
+  // CHECK: memref.view
+  %res = memref.view %0[%c0][%arg0] : memref<?xi8> to memref<?xi8>
+  return %res : memref<?xi8>
+}