Add Expression Fuzzer (#1741)

Includes:
* Random generator of FIRRTL Expressions (UInt and SInt types)
* JQF SBT plugin and CLI
* Documentation in README.md

Co-authored-by: Jack Koenig <koenig@sifive.com>

2 files changed, 84 insertions, 0 deletions

diff --git a/fuzzer/src/test/scala/Example.scala b/fuzzer/src/test/scala/Example.scala
new file mode 100644
index 00000000..9779f7b0
--- /dev/null
+++ b/fuzzer/src/test/scala/Example.scala
@@ -0,0 +1,63 @@
+package firrtl.fuzzer
+
+import org.scalacheck.{Gen, Prop, Properties}
+import firrtl.{ChirrtlForm, CircuitState, CustomTransformException, LowFirrtlCompiler, Namespace}
+import firrtl.passes.CheckWidths
+import ExprGen._
+import ScalaCheckGenMonad._
+
+object FirrtlCompileProperties extends Properties("FirrtlCompile") {
+  property("compile") = {
+    val gen = Gen.sized { size =>
+      val params = ExprGenParams(
+        maxDepth = size / 3,
+        maxWidth = math.min(size + 1, CheckWidths.MaxWidth),
+        generators = Seq(
+          1 -> AddDoPrimGen,
+          1 -> SubDoPrimGen,
+          1 -> MulDoPrimGen,
+          1 -> DivDoPrimGen,
+          1 -> LtDoPrimGen,
+          1 -> LeqDoPrimGen,
+          1 -> GtDoPrimGen,
+          1 -> GeqDoPrimGen,
+          1 -> EqDoPrimGen,
+          1 -> NeqDoPrimGen,
+          1 -> PadDoPrimGen,
+          1 -> ShlDoPrimGen,
+          1 -> ShrDoPrimGen,
+          1 -> DshlDoPrimGen,
+          1 -> CvtDoPrimGen,
+          1 -> NegDoPrimGen,
+          1 -> NotDoPrimGen,
+          1 -> AndDoPrimGen,
+          1 -> OrDoPrimGen,
+          1 -> XorDoPrimGen,
+          1 -> AndrDoPrimGen,
+          1 -> OrrDoPrimGen,
+          1 -> XorrDoPrimGen,
+          1 -> CatDoPrimGen,
+          1 -> BitsDoPrimGen,
+          1 -> HeadDoPrimGen,
+          1 -> TailDoPrimGen,
+          1 -> AsUIntDoPrimGen,
+          1 -> AsSIntDoPrimGen,
+        )
+      )
+      params.generateSingleExprCircuit[Gen]()
+    }
+    val lowFirrtlCompiler = new firrtl.LowFirrtlCompiler()
+    Prop.forAll(gen) { circuit =>
+      val state = CircuitState(circuit, ChirrtlForm, Seq())
+      //val compiler = new LowFirrtlCompiler()
+      val compiler = lowFirrtlCompiler
+      try {
+        val res = compiler.compile(state, Seq())
+        true
+      } catch {
+        case e: CustomTransformException => false
+        case any : Throwable => false
+      }
+    }
+  }
+}
diff --git a/fuzzer/src/test/scala/GenMonad.scala b/fuzzer/src/test/scala/GenMonad.scala
new file mode 100644
index 00000000..0eaadd13
--- /dev/null
+++ b/fuzzer/src/test/scala/GenMonad.scala
@@ -0,0 +1,21 @@
+package firrtl.fuzzer
+
+import org.scalacheck.{Gen, Properties}
+
+object ScalaCheckGenMonad {
+  implicit def scalaCheckGenMonadInstance: GenMonad[Gen] = new GenMonad[Gen] {
+    def flatMap[A, B](a: Gen[A])(f: A => Gen[B]): Gen[B] = a.flatMap(f)
+
+    def map[A, B](a: Gen[A])(f: A => B): Gen[B] = a.map(f)
+
+    def choose(min: Int, max: Int): Gen[Int] = Gen.choose(min, max)
+
+    def oneOf[A](items: A*): Gen[A] = Gen.oneOf(items)
+
+    def const[A](c: A): Gen[A] = Gen.const(c)
+
+    def widen[A, B >: A](ga: Gen[A]): Gen[B] = ga
+
+    def generate[A](ga: Gen[A]): A = ga.sample.get
+  }
+}