Allow Side Effecting Statement to have Names (#2057)

* firrtl: add optional statement labels for stop, printf, assert, assume and cover

* test: parsing of statement labels

* ir: ensure that name is properly retained

* SymbolTable: add support for labled statements

* test: parsing statement labels

* test: lower types name collisions with named statements

* ignore empty names

* Inline: deal with named and unnamed statements

* RemoveWires: treat stop, printf and verification statements as "others"

* test: fix InlineInstance tests

* DeadCodeEliminations: statements are now als declarations

* CheckHighForm: ensure that statement names are not used as references

* CheckSpec: throw error if statement name collides

* add pass to automatically add missing statement names

* check: make sure that two statements cannot have the same name

* stmtLabel -> stmtName

* scalafmt

* add statement names to spec

* spec: meta data -> metadata

* EnsureStatementNames: explain naming algorithm

* remove returns

* better namespace use

* ir: add CanBeReferenced trait

* ir: add newline as jack requested

2 files changed, 38 insertions, 16 deletions

diff --git a/src/main/scala/firrtl/passes/CheckHighForm.scala b/src/main/scala/firrtl/passes/CheckHighForm.scala
index e3468c4e..05635d00 100644
--- a/src/main/scala/firrtl/passes/CheckHighForm.scala
+++ b/src/main/scala/firrtl/passes/CheckHighForm.scala
@@ -22,6 +22,10 @@ trait CheckHighFormLike { this: Pass =>
       moduleNS += name
       scopes.head += name
     }
+    // ensures that the name cannot be used again, but prevent references to this name
+    def addToNamespace(name: String): Unit = {
+      moduleNS += name
+    }
     def expandMPortVisibility(port: CDefMPort): Unit = {
       // Legacy CHIRRTL ports are visible in any scope where their parent memory is visible
       scopes.find(_.contains(port.mem)).getOrElse(scopes.head) += port.name
@@ -250,10 +254,19 @@ trait CheckHighFormLike { this: Pass =>
       e.foreach(checkHighFormE(info, mname, names))
     }
 
-    def checkName(info: Info, mname: String, names: ScopeView)(name: String): Unit = {
-      if (!names.legalDecl(name))
-        errors.append(new NotUniqueException(info, mname, name))
-      names.declare(name)
+    def checkName(info: Info, mname: String, names: ScopeView, canBeReference: Boolean)(name: String): Unit = {
+      // Empty names are allowed for backwards compatibility reasons and
+      // indicate that the entity has essentially no name.
+      if (name.isEmpty) { assert(!canBeReference, "A statement with an empty name cannot be used as a reference!") }
+      else {
+        if (!names.legalDecl(name))
+          errors.append(new NotUniqueException(info, mname, name))
+        if (canBeReference) {
+          names.declare(name)
+        } else {
+          names.addToNamespace(name)
+        }
+      }
     }
 
     def checkInstance(info: Info, child: String, parent: String): Unit = {
@@ -270,7 +283,11 @@ trait CheckHighFormLike { this: Pass =>
         case NoInfo => minfo
         case x      => x
       }
-      s.foreach(checkName(info, mname, names))
+      val canBeReference = s match {
+        case _: CanBeReferenced => true
+        case _ => false
+      }
+      s.foreach(checkName(info, mname, names, canBeReference))
       s match {
         case DefRegister(info, name, tpe, _, reset, init) =>
           if (hasFlip(tpe))
diff --git a/src/main/scala/firrtl/passes/Inline.scala b/src/main/scala/firrtl/passes/Inline.scala
index 4eba5d59..912acf8e 100644
--- a/src/main/scala/firrtl/passes/Inline.scala
+++ b/src/main/scala/firrtl/passes/Inline.scala
@@ -187,18 +187,23 @@ class InlineInstances extends Transform with DependencyAPIMigration with Registe
       renameMap:     RenameMap
     )(s:             Statement
     ): Statement = {
-      def onName(ofModuleOpt: Option[String])(name: String) = {
-        if (prefix.nonEmpty && !ns.tryName(prefix + name)) {
-          throw new Exception(s"Inlining failed. Inlined name '${prefix + name}' already exists")
-        }
-        ofModuleOpt match {
-          case None =>
-            renameMap.record(currentModule.ref(name), nextModule.ref(prefix + name))
-          case Some(ofModule) =>
-            renameMap.record(currentModule.instOf(name, ofModule), nextModule.instOf(prefix + name, ofModule))
+      def onName(ofModuleOpt: Option[String])(name: String): String = {
+        // Empty names are allowed for backwards compatibility reasons and
+        // indicate that the entity has essentially no name and thus cannot be prefixed.
+        if (name.isEmpty) { name }
+        else {
+          if (prefix.nonEmpty && !ns.tryName(prefix + name)) {
+            throw new Exception(s"Inlining failed. Inlined name '${prefix + name}' already exists")
+          }
+          ofModuleOpt match {
+            case None =>
+              renameMap.record(currentModule.ref(name), nextModule.ref(prefix + name))
+            case Some(ofModule) =>
+              renameMap.record(currentModule.instOf(name, ofModule), nextModule.instOf(prefix + name, ofModule))
+          }
+          renames(name) = prefix + name
+          prefix + name
         }
-        renames(name) = prefix + name
-        prefix + name
       }
 
       s match {