[mlir] Separate enum information from attributes, improve EnumProp

This commit pulls apart the inherent attribute dependence of classes
like EnumAttrInfo and EnumAttrCase, factoring them out into simpler
EnumCase and EnumInfo variants. This allows specifying the cases of an
enum without needing to make the cases, or the EnumInfo itself, a
subclass of SignlessIntegerAttrBase.

The existing classes are retained as subclasses of the new ones, both
for backwards compatibility and to allow attribute-specific
information.

In addition, the new BitEnum class changes its default printer/parser
behavior: cases when multiple keywords appear, like having both nuw
and nsw in overflow flags, will no longer be quoted by the operator<<,
and the FieldParser instance will now expect multiple keywords. All
instances of BitEnumAttr retain the old behavior.

Finally, this commit improves the `EnumProp` class, causing it to wrap
around an `EnumInfo` just like `EnumAttr` does, and introducing logic
for converting to/from attributes and bitcode (while using
autogenerated parsers and printers). The commit also provides the
`NamedEnumProp` class for the common pattern of `name<enum_value>` in
MLIR code, and provides `EnumPropWithAttrForm` to allow upgrading enum
attributes to properties without breaking the generic form of
assembly.

(Sadly, bitcode auto-upgrade is hampered by the lack of the ability to
optionally parse an attribute.)

Author: krzysz00

mlir/include/mlir/Dialect/LLVMIR/LLVMEnums.td

@@ -485,17 +485,16 @@ def DISubprogramFlags : I32BitEnumAttr<
 // IntegerOverflowFlags
 //===----------------------------------------------------------------------===//
 
-def IOFnone : I32BitEnumAttrCaseNone<"none">;
-def IOFnsw  : I32BitEnumAttrCaseBit<"nsw", 0>;
-def IOFnuw  : I32BitEnumAttrCaseBit<"nuw", 1>;
+def IOFnone : I32BitEnumCaseNone<"none">;
+def IOFnsw  : I32BitEnumCaseBit<"nsw", 0>;
+def IOFnuw  : I32BitEnumCaseBit<"nuw", 1>;
 
-def IntegerOverflowFlags : I32BitEnumAttr<
+def IntegerOverflowFlags : I32BitEnum<
     "IntegerOverflowFlags",
     "LLVM integer overflow flags",
     [IOFnone, IOFnsw, IOFnuw]> {
   let separator = ", ";
   let cppNamespace = "::mlir::LLVM";
-  let genSpecializedAttr = 0;
   let printBitEnumPrimaryGroups = 1;
 }
 
@@ -504,6 +503,11 @@ def LLVM_IntegerOverflowFlagsAttr :
   let assemblyFormat = "`<` $value `>`";
 }
 
+def LLVM_IntegerOverflowFlagsProp :
+    NamedEnumPropWithAttrForm<IntegerOverflowFlags, "overflow", LLVM_IntegerOverflowFlagsAttr> {
+  let defaultValue = enum.cppType # "::" # "none";
+}
+
 //===----------------------------------------------------------------------===//
 // FastmathFlags
 //===----------------------------------------------------------------------===//

mlir/include/mlir/Dialect/LLVMIR/LLVMOps.td

@@ -60,7 +60,7 @@ class LLVM_IntArithmeticOpWithOverflowFlag<string mnemonic, string instName,
                                    list<Trait> traits = []> :
     LLVM_ArithmeticOpBase<AnySignlessInteger, mnemonic, instName,
     !listconcat([DeclareOpInterfaceMethods<IntegerOverflowFlagsInterface>], traits)> {
-  dag iofArg = (ins EnumProp<"IntegerOverflowFlags", "", "IntegerOverflowFlags::none">:$overflowFlags);
+  dag iofArg = (ins LLVM_IntegerOverflowFlagsProp:$overflowFlags);
   let arguments = !con(commonArgs, iofArg);
 
   string mlirBuilder = [{
@@ -69,7 +69,7 @@ class LLVM_IntArithmeticOpWithOverflowFlag<string mnemonic, string instName,
     $res = op;
   }];
   let assemblyFormat = [{
-    $lhs `,` $rhs `` custom<OverflowFlags>($overflowFlags) attr-dict `:` type($res)
+    $lhs `,` $rhs ($overflowFlags^)? attr-dict `:` type($res)
   }];
   string llvmBuilder =
     "$res = builder.Create" # instName #
@@ -563,10 +563,10 @@ class LLVM_CastOpWithOverflowFlag<string mnemonic, string instName, Type type,
                   Type resultType, list<Trait> traits = []> :
     LLVM_Op<mnemonic, !listconcat([Pure], [DeclareOpInterfaceMethods<IntegerOverflowFlagsInterface>], traits)>,
     LLVM_Builder<"$res = builder.Create" # instName # "($arg, $_resultType, /*Name=*/\"\", op.hasNoUnsignedWrap(), op.hasNoSignedWrap());"> {
-  let arguments = (ins type:$arg, EnumProp<"IntegerOverflowFlags", "", "IntegerOverflowFlags::none">:$overflowFlags);
+  let arguments = (ins type:$arg, LLVM_IntegerOverflowFlagsProp:$overflowFlags);
   let results = (outs resultType:$res);
   let builders = [LLVM_OneResultOpBuilder];
-  let assemblyFormat = "$arg `` custom<OverflowFlags>($overflowFlags) attr-dict `:` type($arg) `to` type($res)";
+  let assemblyFormat = "$arg ($overflowFlags^)? attr-dict `:` type($arg) `to` type($res)";
   string llvmInstName = instName;
   string mlirBuilder = [{
     auto op = $_builder.create<$_qualCppClassName>(