Refactor TruthTable.apply and add factory method for Espresso (backport #2612) (#2620)

* Refactor TruthTable.apply and add factory method for Espresso (#2612)

Improves performance of creating TruthTables by processing entire BitPats
rather than individual bits. New TruthTable factory method enables
constructing TruthTables with semantics of OR-ing output BitPats together
rather than erroring when multiple terms have the same input BitPat.
This alternative factory method matches semantics for the output format
of Espresso.

Co-authored-by: Megan Wachs <megan@sifive.com>
Co-authored-by: Jack Koenig <koenig@sifive.com>
(cherry picked from commit 231f14e74f112a9f721e774561126b2bd1250039)

# Conflicts:
#	src/main/scala/chisel3/util/BitPat.scala

* Resolve backport conflicts

Co-authored-by: Aditya Naik <91489422+adkian-sifive@users.noreply.github.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/src/test/scala/chiselTests/util/experimental/TruthTableSpec.scala b/src/test/scala/chiselTests/util/experimental/TruthTableSpec.scala
index fa2c6f08..9b2dd600 100644
--- a/src/test/scala/chiselTests/util/experimental/TruthTableSpec.scala
+++ b/src/test/scala/chiselTests/util/experimental/TruthTableSpec.scala
@@ -104,4 +104,21 @@ class TruthTableSpec extends AnyFlatSpec {
     assert(t.toString contains "111->?")
     assert(t.toString contains "     0")
   }
+
+  "Using TruthTable.fromEspressoOutput" should "merge rows on conflict" in {
+    val mapping = List(
+      (BitPat("b110"), BitPat("b001")),
+      (BitPat("b111"), BitPat("b001")),
+      (BitPat("b111"), BitPat("b010")),
+      (BitPat("b111"), BitPat("b100"))
+    )
+
+    assert(
+      TruthTable.fromEspressoOutput(mapping, BitPat("b?")) ==
+        TruthTable.fromString("""110->001
+                                |111->111
+                                |?
+                                |""".stripMargin)
+    )
+  }
 }