add RemoveUnreachableBlocks pass to clean up padding blocks

Author: katrinafyi

src/main/scala/ir/transforms/RemoveUnreachableBlocks.scala

@@ -0,0 +1,57 @@
+package ir.transforms
+
+import ir.*
+import ir.cilvisitor.*
+
+import analysis.{LatticeSet}
+
+import collection.immutable
+
+/**
+ * Find blocks which are mentioned syntactically within a given procedure.
+ *
+ * Includes the entry block, and overapproximates in the presence of indirect calls.
+ */
+class FindGotoTargets extends CILVisitor {
+
+  var keep: LatticeSet[Block] = LatticeSet.Bottom()
+
+  override def vproc(p: Procedure) = {
+    keep = keep ++ p.entryBlock
+    DoChildren()
+  }
+
+  override def vstmt(s: Statement) = {
+    s match {
+      case IndirectCall(_, _) => keep = LatticeSet.Top()
+      case _ => ()
+    }
+    SkipChildren()
+  }
+
+  override def vjump(s: Jump) = {
+    s match {
+      case GoTo(targs, _) => keep = keep ++ targs
+      case _ => ()
+    }
+    SkipChildren()
+  }
+}
+
+/**
+ * Very coarse transform pass to remove obviously unreachable blocks.
+ *
+ * This only removes in the most simple cases.
+ * Does NOT remove:
+ * - mutually-recursive unreachable blocks,
+ * - blocks only reachable from unreachable blocks.
+ * - any blocks in the presence of indirect calls.
+ */
+object RemoveUnreachableBlocks {
+  def apply(p: Procedure) = {
+    val vis = FindGotoTargets()
+    visit_proc(vis, p)
+    val keepBlocks = vis.keep
+    p.blocks.toList.filterNot(keepBlocks.contains).foreach(p.removeBlocks)
+  }
+}

src/main/scala/util/RunUtils.scala

@@ -894,7 +894,8 @@ object RunUtils {
 
     if (!q.loading.keepPC) {
       visit_prog(transforms.RemovePCStatements(), ctx.program)
-      Logger.info(s"[!] Removed PC-related statements")
+      ctx.program.procedures.foreach(transforms.RemoveUnreachableBlocks.apply)
+      Logger.info(s"[!] Removed PC-related statements and unreachable blocks")
     }
 
     if (q.loading.parameterForm && !q.simplify) {