Add AttrConstraint to enable generating verification for attribute values.

Change MinMaxAttr to match hasValidMinMaxAttribute behavior. Post rewriting the other users of that function it could be removed too. The currently generated error message is:

error: 'tfl.fake_quant' op attribute 'minmax' failed to satisfy constraint of MinMaxAttr
PiperOrigin-RevId: 229775631

mlir/include/mlir/IR/op_base.td

@@ -218,8 +218,16 @@ def FloatLike : TypeConstraint<AnyOf<[Float.predicate,
 // Attributes
 //===----------------------------------------------------------------------===//
 
+// A constraint on attributes. This can be used to check the validity of
+// instruction attributes.
+class AttrConstraint<Pred condition> {
+  // The predicates that this type satisfies.
+  // Format: {0} will be expanded to the attribute.
+  Pred predicate = condition;
+}
+
 // Base class for all attributes.
-class Attr {
+class Attr<Pred condition = CPred<"true">> : AttrConstraint<condition> {
   code storageType = ?; // The backing mlir::Attribute type
   code returnType = ?;  // The underlying C++ value type
 

mlir/include/mlir/TableGen/Attribute.h

@@ -24,6 +24,7 @@
 #define MLIR_TABLEGEN_ATTRIBUTE_H_
 
 #include "mlir/Support/LLVM.h"
+#include "mlir/TableGen/Predicate.h"
 #include "llvm/ADT/StringRef.h"
 
 namespace llvm {
@@ -77,6 +78,15 @@ public:
   // derived attribute.
   StringRef getDerivedCodeBody() const;
 
+  // Returns the predicate that can be used to check if a attribute satisfies
+  // this attribute's constraint.
+  Pred getPredicate() const;
+
+  // Returns the template that can be used to verify that an attribute satisfies
+  // the constraints for its declared attribute type.
+  // Syntax: {0} should be replaced with the attribute.
+  std::string getConditionTemplate() const;
+
 private:
   // The TableGen definition of this attribute.
   const llvm::Record *def;

mlir/include/mlir/TableGen/Predicate.h

@@ -40,6 +40,8 @@ namespace tblgen {
 // TableGen class 'Pred'.
 class Pred {
 public:
+  // Constructs the null Predicate (e.g., always true).
+  explicit Pred() : def(nullptr) {}
   // Construct a Predicate from a record.
   explicit Pred(const llvm::Record *record);
   // Construct a Predicate from an initializer.

mlir/lib/TableGen/Attribute.cpp

@@ -90,3 +90,18 @@ StringRef tblgen::Attribute::getDerivedCodeBody() const {
   assert(isDerivedAttr() && "only derived attribute has 'body' field");
   return def->getValueAsString("body");
 }
+
+tblgen::Pred tblgen::Attribute::getPredicate() const {
+  auto *val = def->getValue("predicate");
+  // If no predicate is specified, then return the null predicate (which
+  // corresponds to true).
+  if (!val)
+    return Pred();
+
+  const auto *pred = dyn_cast<llvm::DefInit>(val->getValue());
+  return Pred(pred);
+}
+
+std::string tblgen::Attribute::getConditionTemplate() const {
+  return getPredicate().getCondition();
+}

mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp

@@ -369,6 +369,15 @@ void OpEmitter::emitVerifier() {
     OUT(4) << "if (!this->getAttr(\"" << name << "\").dyn_cast_or_null<"
            << attr.getStorageType() << ">()) return emitOpError(\"requires "
            << attr.getReturnType() << " attribute '" << name << "'\");\n";
+
+    auto attrPred = attr.getPredicate();
+    if (!attrPred.isNull()) {
+      OUT(4) << formatv("if (!({0})) return emitOpError(\"attribute '{1}' "
+                        "failed to satisfy constraint of {2}\");\n",
+                        formatv(attrPred.getCondition(),
+                                formatv("this->getAttr(\"{0}\")", name)),
+                        name, attr.getTableGenDefName());
+    }
   }
 
   // TODO: Handle variadic.