[mlir] Remove ReferTo attr constraint

[jpienaar]

Summary

The current generation is unsafe as it is evaluated during verify
invocation rather than during verifySymbolUses. Remove until this is
safely generated.

mlir/include/mlir/IR/OpBase.td

And<[
       CPred<"$_self.cast<::mlir::ArrayAttr>()[" # index # "]"
         ".cast<::mlir::IntegerAttr>().getInt() >= " # min>
         ]>,
     "whose " # index # "-th element must be at least " # min>;
 
 def IsNullAttr : AttrConstraint<
     CPred<"!$_self">, "empty attribute (for optional attributes)">;
 
-// An attribute constraint on FlatSymbolRefAttr that requires that the
-// reference point to an op of `opClass` within the closest parent with a symbol
-// table.
-// TODO: Add support for nested symbol references.
-class ReferToOp<string opClass> : AttrConstraint<
-    CPred<"isa_and_nonnull<" # opClass # ">("
-            "::mlir::SymbolTable::lookupNearestSymbolFrom("
-              "&$_op, $_self.cast<::mlir::FlatSymbolRefAttr>().getAttr()))">,
-    "referencing to a '" # opClass # "' symbol">;
-
 //===----------------------------------------------------------------------===//
 // Region definitions
 //===----------------------------------------------------------------------===//
 
 class Region<Pred condition, string descr = ""> :
     RegionConstraint<condition, descr>;
 
 // Any region.

mlir/test/IR/attribute.mlir

 
 func.func @fn() { return }
 
 // CHECK: test.symbol_ref_attr
 "test.symbol_ref_attr"() {symbol = @fn} : () -> ()
 
 // -----
 
-// expected-error @+1 {{referencing to a 'func::FuncOp' symbol}}
-"test.symbol_ref_attr"() {symbol = @foo} : () -> ()
-
-// -----
-
 //===----------------------------------------------------------------------===//
 // Test IntElementsAttr
 //===----------------------------------------------------------------------===//
 
 func.func @correct_int_elements_attr_pass() {
   "test.int_elements_attr"() {
     // CHECK: any_i32_attr = dense<5> : tensor<1x2x3x4xui32>,
     any_i32_attr = dense<5> : tensor<1x2x3x4xui32>,

mlir/test/lib/Dialect/Test/TestOps.td

 // Define an op that contains the enum attribute.
 def OpWithBitEnumVerticalBar : TEST_Op<"op_with_bit_enum_vbar"> {
   let arguments = (ins TestBitEnumVerticalBarAttr:$value,
                    OptionalAttr<AnyAttr>:$tag);
   let assemblyFormat = "$value (`tag` $tag^)? attr-dict";
 }
 
 //===----------------------------------------------------------------------===//
-// Test Attribute Constraints
-//===----------------------------------------------------------------------===//
-
-def SymbolRefOp : TEST_Op<"symbol_ref_attr"> {
-  let arguments = (ins
-    ConfinedAttr<FlatSymbolRefAttr, [ReferToOp<"func::FuncOp">]>:$symbol
-  );
-}
-
-//===----------------------------------------------------------------------===//
 // Test Regions
 //===----------------------------------------------------------------------===//
 
 def OneRegionOp : TEST_Op<"one_region_op", []> {
   let regions = (region AnyRegion);
 }
 
 def TwoRegionOp : TEST_Op<"two_region_op", []> {