Replace the verifyUnusedValue directive with HasNoUseOf constraint

verifyUnusedValue is a bit strange given that it is specified in a
result pattern but used to generate match statements. Now we are
able to support multi-result ops better, we can retire it and replace
it with a HasNoUseOf constraint. This reduces the number of mechanisms.

PiperOrigin-RevId: 261166863

mlir/include/mlir/IR/OpBase.td

@@ -1173,9 +1173,17 @@ class Results<dag rets> {
   dag results = rets;
 }
 
+//===----------------------------------------------------------------------===//
+// Common value constraints
+//===----------------------------------------------------------------------===//
+
+def HasNoUseOf: Constraint<
+    CPred<"$_self->use_begin() == $_self->use_end()">, "has no use">;
+
 //===----------------------------------------------------------------------===//
 // Common op type constraints
 //===----------------------------------------------------------------------===//
+
 // These traits are for verifying properties of an op that require knowledge of
 // multiple arguments or results. For verifying properties of a single argument
 // or result, prefer operand type constraints.
@@ -1407,10 +1415,4 @@ class NativeCodeCall<string expr> {
 // so to replace the matched DAG with an existing SSA value.
 def replaceWithValue;
 
-// Directive used in result pattern to indicate that no replacement is generated
-// for the current result. Predicates are generated to make sure the
-// corresponding result in source pattern is unused.
-//   syntax: (verifyUnusedValue)
-def verifyUnusedValue;
-
 #endif // OP_BASE

mlir/include/mlir/TableGen/Constraint.h

@@ -74,9 +74,13 @@ private:
 
 // An constraint and the concrete entities to place the constraint on.
 struct AppliedConstraint {
-  AppliedConstraint(Constraint &&c, std::vector<std::string> &&e);
+  AppliedConstraint(Constraint &&constraint, StringRef self,
+                    std::vector<std::string> &&entities);
 
   Constraint constraint;
+  // The symbol to replace `$_self` special placeholder in the constraint.
+  std::string self;
+  // The symbols to replace `$N` positional placeholders in the constraint.
   std::vector<std::string> entities;
 };
 

mlir/include/mlir/TableGen/Pattern.h

@@ -166,9 +166,6 @@ public:
   // value.
   bool isReplaceWithValue() const;
 
-  // Returns true if this DAG node is the `verifyUnusedValue` directive.
-  bool isVerifyUnusedValue() const;
-
   // Returns true if this DAG node is wrapping native code call.
   bool isNativeCodeCall() const;
 

mlir/lib/TableGen/Constraint.cpp

@@ -63,6 +63,6 @@ llvm::StringRef Constraint::getDescription() const {
   return doc;
 }
 
-AppliedConstraint::AppliedConstraint(Constraint &&c,
-                                     std::vector<std::string> &&e)
-    : constraint(c), entities(std::move(e)) {}
+AppliedConstraint::AppliedConstraint(Constraint &&constraint, StringRef self,
+                                     std::vector<std::string> &&entities)
+    : constraint(constraint), self(self), entities(std::move(entities)) {}

mlir/lib/TableGen/Pattern.cpp

@@ -95,7 +95,7 @@ bool tblgen::DagNode::isNativeCodeCall() const {
 }
 
 bool tblgen::DagNode::isOperation() const {
-  return !(isNativeCodeCall() || isVerifyUnusedValue() || isReplaceWithValue());
+  return !(isNativeCodeCall() || isReplaceWithValue());
 }
 
 llvm::StringRef tblgen::DagNode::getNativeCodeTemplate() const {
@@ -151,11 +151,6 @@ bool tblgen::DagNode::isReplaceWithValue() const {
   return dagOpDef->getName() == "replaceWithValue";
 }
 
-bool tblgen::DagNode::isVerifyUnusedValue() const {
-  auto *dagOpDef = cast<llvm::DefInit>(node->getOperator())->getDef();
-  return dagOpDef->getName() == "verifyUnusedValue";
-}
-
 tblgen::Pattern::Pattern(const llvm::Record *def, RecordOperatorMap *mapper)
     : def(*def), recordOpMap(mapper) {
   collectBoundSymbols(getSourcePattern(), srcBoundOps, /*isSrcPattern=*/true);
@@ -225,7 +220,7 @@ std::vector<tblgen::AppliedConstraint> tblgen::Pattern::getConstraints() const {
       entities.push_back(argName->getValue());
 
     ret.emplace_back(cast<llvm::DefInit>(dagInit->getOperator())->getDef(),
-                     std::move(entities));
+                     dagInit->getNameStr(), std::move(entities));
   }
   return ret;
 }

mlir/test/lib/TestDialect/TestOps.td

@@ -475,13 +475,11 @@ def : Pattern<(ThreeResultOp MultiResultOpKind4),
                (TwoResultOp:$res2__1 MultiResultOpKind4)]>;
 
 // Test referencing a single value in the value pack
-def HasNoUse: Constraint<
-    CPred<"$0->use_begin() == $0->use_end()">, "has no use">;
 // This rule only matches TwoResultOp if its second result has no use.
 def : Pattern<(TwoResultOp:$res MultiResultOpKind5),
               [(OneResultOp2 MultiResultOpKind5),
                (OneResultOp1 MultiResultOpKind5)],
-              [(HasNoUse $res__1)]>;
+              [(HasNoUseOf:$res__1)]>;
 
 // Test using auxiliary ops for replacing multi-result op
 def : Pattern<
@@ -494,20 +492,6 @@ def : Pattern<
         (AnotherTwoResultOp MultiResultOpKind6)
     ]>;
 
-//===----------------------------------------------------------------------===//
-// Test Directives
-//===----------------------------------------------------------------------===//
-
-// Test 'verifyUnusedValue'
-def VUVTwoResultOp : TEST_Op<"vuv_two_result_op", []> {
-  let arguments = (ins I32:$input);
-  let results = (outs I32:$r1, I32:$r2);
-}
-def VUVFoldTwoResultOp : Pattern<(VUVTwoResultOp $input), [
-        (verifyUnusedValue),
-        (replaceWithValue $input)
-      ]>;
-
 //===----------------------------------------------------------------------===//
 // Test Legalization
 //===----------------------------------------------------------------------===//

mlir/test/mlir-tblgen/verify-unused-value.mlir

@@ -1,20 +0,0 @@
-// RUN: mlir-opt -test-patterns %s | FileCheck %s
-
-//===----------------------------------------------------------------------===//
-// Test 'verifyUnusedValue'
-//===----------------------------------------------------------------------===//
-
-// CHECK-LABEL: @match_success_on_unused_first_result
-func @match_success_on_unused_first_result(%arg0 : i32) -> i32 {
-  // CHECK-NEXT: return {{.*}} : i32
-  %result:2 = "test.vuv_two_result_op"(%arg0) : (i32) -> (i32, i32)
-  return %result#1 : i32
-}
-
-// CHECK-LABEL: @match_fail_on_used_first_result
-func @match_fail_on_used_first_result(%arg0 : i32) -> i32 {
-  // CHECK-NEXT: "test.vuv_two_result_op"(%arg0) : (i32) -> (i32, i32)
-  %result:2 = "test.vuv_two_result_op"(%arg0) : (i32) -> (i32, i32)
-  "foo.unknown_op"(%result#0) : (i32) -> ()
-  return %result#1 : i32
-}

mlir/tools/mlir-tblgen/RewriterGen.cpp

@@ -274,10 +274,6 @@ private:
   // replacement.
   std::string handleReplaceWithValue(DagNode tree);
 
-  // Handles the `verifyUnusedValue` directive: emitting C++ statements to check
-  // the `index`-th result of the source op is not used.
-  void handleVerifyUnusedValue(DagNode tree, int index);
-
   // Emits the C++ statement to build a new op out of the given DAG `tree` and
   // returns the variable name that this op is assigned to. If the root op in
   // DAG `tree` has a specified name, the created op will be assigned to a
@@ -502,15 +498,6 @@ void PatternEmitter::emitMatchMethod(DagNode tree) {
     s.autogeneratedRewritePatternOps[0] = op0;
 )";
 
-  // The rewrite pattern may specify that certain outputs should be unused in
-  // the source IR. Check it here.
-  for (int i = 0, e = pattern.getNumResultPatterns(); i < e; ++i) {
-    DagNode resultTree = pattern.getResultPattern(i);
-    if (resultTree.isVerifyUnusedValue()) {
-      handleVerifyUnusedValue(resultTree, i);
-    }
-  }
-
   emitOpMatch(tree, 0);
 
   for (auto &appliedConstraint : pattern.getConstraints()) {
@@ -528,7 +515,7 @@ void PatternEmitter::emitMatchMethod(DagNode tree) {
       PrintFatalError(
           loc, "cannot use AttrConstraint in Pattern multi-entity constraints");
     } else {
-      // TODO(fengliuai): replace formatv arguments with the exact specified
+      // TODO(b/138794486): replace formatv arguments with the exact specified
       // args.
       if (entities.size() > 4) {
         PrintFatalError(loc, "only support up to 4-entity constraints now");
@@ -537,10 +524,14 @@ void PatternEmitter::emitMatchMethod(DagNode tree) {
       int i = 0;
       for (int e = entities.size(); i < e; ++i)
         names.push_back(resolveSymbol(entities[i]));
+      std::string self = appliedConstraint.self;
+      if (!self.empty())
+        self = resolveSymbol(self);
       for (; i < 4; ++i)
         names.push_back("<unused>");
-      os.indent(4) << formatv(cmd, tgfmt(condition, &matchCtx, names[0],
-                                         names[1], names[2], names[3]));
+      os.indent(4) << formatv(cmd,
+                              tgfmt(condition, &matchCtx.withSelf(self),
+                                    names[0], names[1], names[2], names[3]));
     }
   }
 
@@ -678,25 +669,6 @@ std::string PatternEmitter::handleRewritePattern(DagNode resultTree,
   if (resultTree.isNativeCodeCall())
     return emitReplaceWithNativeCodeCall(resultTree);
 
-  if (resultTree.isVerifyUnusedValue()) {
-    if (depth > 0) {
-      // TODO: Revisit this when we have use cases of matching an intermediate
-      // multi-result op with no uses of its certain results.
-      PrintFatalError(loc, "verifyUnusedValue directive can only be used to "
-                           "verify top-level result");
-    }
-
-    if (!resultTree.getSymbol().empty()) {
-      PrintFatalError(loc, "cannot bind symbol to verifyUnusedValue");
-    }
-
-    // The C++ statements to check that this result value is unused are already
-    // emitted in the match() method. So returning a nullptr here directly
-    // should be safe because the C++ RewritePattern harness will use it to
-    // replace nothing.
-    return "nullptr";
-  }
-
   if (resultTree.isReplaceWithValue())
     return handleReplaceWithValue(resultTree);
 
@@ -718,19 +690,12 @@ std::string PatternEmitter::handleReplaceWithValue(DagNode tree) {
   }
 
   if (!tree.getSymbol().empty()) {
-    PrintFatalError(loc, "cannot bind symbol to verifyUnusedValue");
+    PrintFatalError(loc, "cannot bind symbol to replaceWithValue");
   }
 
   return resolveSymbol(tree.getArgName(0));
 }
 
-void PatternEmitter::handleVerifyUnusedValue(DagNode tree, int index) {
-  assert(tree.isVerifyUnusedValue());
-
-  os.indent(4) << "if (!op0->getResult(" << index
-               << ")->use_empty()) return matchFailure();\n";
-}
-
 std::string PatternEmitter::handleOpArgument(DagLeaf leaf, StringRef argName) {
   if (leaf.isConstantAttr()) {
     auto constAttr = leaf.getAsConstantAttr();
@@ -759,7 +724,7 @@ std::string PatternEmitter::handleOpArgument(DagLeaf leaf, StringRef argName) {
 
 std::string PatternEmitter::emitReplaceWithNativeCodeCall(DagNode tree) {
   auto fmt = tree.getNativeCodeTemplate();
-  // TODO(fengliuai): replace formatv arguments with the exact specified args.
+  // TODO(b/138794486): replace formatv arguments with the exact specified args.
   SmallVector<std::string, 8> attrs(8);
   if (tree.getNumArgs() > 8) {
     PrintFatalError(loc, "unsupported NativeCodeCall argument numbers: " +