1 files changed, 37 insertions, 0 deletions
diff --git a/core/src/main/scala/chisel3/dontTouch.scala b/core/src/main/scala/chisel3/dontTouch.scala
new file mode 100644
index 00000000..5dfd9f19
--- /dev/null
+++ b/core/src/main/scala/chisel3/dontTouch.scala
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+package chisel3
+
+import chisel3.experimental.{ChiselAnnotation, annotate, requireIsHardware}
+import firrtl.transforms.DontTouchAnnotation
+
+/** Marks that a signal should not be removed by Chisel and Firrtl optimization passes
+  *
+  * @example {{{
+  * class MyModule extends Module {
+  *   val io = IO(new Bundle {
+  *     val a = Input(UInt(32.W))
+  *     val b = Output(UInt(32.W))
+  *   })
+  *   io.b := io.a
+  *   val dead = io.a +% 1.U // normally dead would be pruned by DCE
+  *   dontTouch(dead) // Marking it as such will preserve it
+  * }
+  * }}}
+  * @note Calling this on [[Data]] creates an annotation that Chisel emits to a separate annotations
+  * file. This file must be passed to FIRRTL independently of the `.fir` file. The execute methods
+  * in [[chisel3.Driver]] will pass the annotations to FIRRTL automatically.
+  */
+object dontTouch { // scalastyle:ignore object.name
+  /** Marks a signal to be preserved in Chisel and Firrtl
+    *
+    * @note Requires the argument to be bound to hardware
+    * @param data The signal to be marked
+    * @return Unmodified signal `data`
+    */
+  def apply[T <: Data](data: T)(implicit compileOptions: CompileOptions): T = {
+    if (compileOptions.checkSynthesizable) {
+      requireIsHardware(data, "Data marked dontTouch")
+    }
+    annotate(new ChiselAnnotation { def toFirrtl = DontTouchAnnotation(data.toNamed) })
+    data
+  }
+}