Don't use ResolvedAnnotationPaths in ConstProp nor DCE (#1896)

Both use EliminateTargetPaths to duplicate modules based on annotations.
Currently, EliminateTargetPaths API is a little too limited so it
duplicates more than it should which effectively breaks Dedup whenever
DontTouchAnnotations are present.

Also, make ConstProp and DCE treat all HasDontTouches as local
annotations even if they are instance annotations. This is more
conservative but it is generally better to preserve deduplication than
to maximally optimize every instance.

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

1 files changed, 36 insertions, 0 deletions

diff --git a/src/test/scala/firrtlTests/DCETests.scala b/src/test/scala/firrtlTests/DCETests.scala
index a9084f0b..f1c0001a 100644
--- a/src/test/scala/firrtlTests/DCETests.scala
+++ b/src/test/scala/firrtlTests/DCETests.scala
@@ -491,6 +491,42 @@ class DCETests extends FirrtlFlatSpec {
     (verilog shouldNot include).regex("""fwrite""")
     (verilog shouldNot include).regex("""fatal""")
   }
+
+  "DCE" should "not duplicate unnecessarily" in {
+    val input =
+      """circuit Top :
+        |  module child :
+        |    input x : UInt<1>
+        |    output z : UInt<1>
+        |    z <= not(x)
+        |  module Top :
+        |    input x : UInt<1>
+        |    output z : UInt<1>
+        |    inst c of child
+        |    inst c_1 of child
+        |    c.x <= x
+        |    c_1.x <= x
+        |    z <= and(c.z, c_1.z)""".stripMargin
+    val check =
+      """circuit Top :
+        |  module child :
+        |    input x : UInt<1>
+        |    output z : UInt<1>
+        |    z <= not(x)
+        |  module Top :
+        |    input x : UInt<1>
+        |    output z : UInt<1>
+        |    inst c of child
+        |    inst c_1 of child
+        |    z <= and(c.z, c_1.z)
+        |    c.x <= x
+        |    c_1.x <= x""".stripMargin
+    val top = CircuitTarget("Top").module("Top")
+    val annos =
+      Seq(top.instOf("c", "child").ref("z"), top.instOf("c_1", "child").ref("z"))
+        .map(DontTouchAnnotation(_))
+    exec(input, check, annos)
+  }
 }
 
 class DCECommandLineSpec extends FirrtlFlatSpec {