Fix width inferencing issue (#952)

* Fix width propagation of non-literals in WireInit and RegInit
* Change .getWidth to throw an exception instead of calling .get
* Add utilities for checking inferred vs. known widths
* Add tests for Wire, WireInit, Reg, and RegInit width inference
* Add ScalaDoc for Reg, Wire, RegInit, and WireInit

2 files changed, 251 insertions, 1 deletions

diff --git a/src/test/scala/chiselTests/ChiselSpec.scala b/src/test/scala/chiselTests/ChiselSpec.scala
index 661cf00e..ff75c1a3 100644
--- a/src/test/scala/chiselTests/ChiselSpec.scala
+++ b/src/test/scala/chiselTests/ChiselSpec.scala
@@ -31,6 +31,33 @@ trait ChiselRunners extends Assertions with BackendCompilationUtilities {
   }
   def elaborate(t: => RawModule): Unit = Driver.elaborate(() => t)
 
+  def assertKnownWidth(expected: Int)(gen: => Data): Unit = {
+    assertTesterPasses(new BasicTester {
+      val x = gen
+      assert(x.getWidth === expected)
+      // Sanity check that firrtl doesn't change the width
+      x := 0.U.asTypeOf(chiselTypeOf(x))
+      val (_, done) = chisel3.util.Counter(true.B, 2)
+      when (done) {
+        chisel3.assert(~(x.asUInt) === -1.S(expected.W).asUInt)
+        stop()
+      }
+    })
+  }
+
+  def assertInferredWidth(expected: Int)(gen: => Data): Unit = {
+    assertTesterPasses(new BasicTester {
+      val x = gen
+      assert(!x.isWidthKnown, s"Asserting that width should be inferred yet width is known to Chisel!")
+      x := 0.U.asTypeOf(chiselTypeOf(x))
+      val (_, done) = chisel3.util.Counter(true.B, 2)
+      when (done) {
+        chisel3.assert(~(x.asUInt) === -1.S(expected.W).asUInt)
+        stop()
+      }
+    })
+  }
+
   /** Given a generator, return the Firrtl that it generates.
     *
     * @param t Module generator
@@ -63,7 +90,59 @@ trait ChiselRunners extends Assertions with BackendCompilationUtilities {
 }
 
 /** Spec base class for BDD-style testers. */
-class ChiselFlatSpec extends FlatSpec with ChiselRunners with Matchers
+abstract class ChiselFlatSpec extends FlatSpec with ChiselRunners with Matchers
+
+class ChiselTestUtilitiesSpec extends ChiselFlatSpec {
+  import org.scalatest.exceptions.TestFailedException
+  // Who tests the testers?
+  "assertKnownWidth" should "error when the expected width is wrong" in {
+    a [TestFailedException] shouldBe thrownBy {
+      assertKnownWidth(7) {
+        Wire(UInt(8.W))
+      }
+    }
+  }
+
+  it should "error when the width is unknown" in {
+    a [ChiselException] shouldBe thrownBy {
+      assertKnownWidth(7) {
+        Wire(UInt())
+      }
+    }
+  }
+
+  it should "work if the width is correct" in {
+    assertKnownWidth(8) {
+      Wire(UInt(8.W))
+    }
+  }
+
+  "assertInferredWidth" should "error if the width is known" in {
+    a [TestFailedException] shouldBe thrownBy {
+      assertInferredWidth(8) {
+        Wire(UInt(8.W))
+      }
+    }
+  }
+
+  it should "error if the expected width is wrong" in {
+    a [TestFailedException] shouldBe thrownBy {
+      assertInferredWidth(8) {
+        val w = Wire(UInt())
+        w := 2.U(2.W)
+        w
+      }
+    }
+  }
+
+  it should "pass if the width is correct" in {
+    assertInferredWidth(4) {
+      val w = Wire(UInt())
+      w := 2.U(4.W)
+      w
+    }
+  }
+}
 
 /** Spec base class for property-based testers. */
 class ChiselPropSpec extends PropSpec with ChiselRunners with PropertyChecks with Matchers {
diff --git a/src/test/scala/chiselTests/WidthSpec.scala b/src/test/scala/chiselTests/WidthSpec.scala
index 9a5b1860..0011c532 100644
--- a/src/test/scala/chiselTests/WidthSpec.scala
+++ b/src/test/scala/chiselTests/WidthSpec.scala
@@ -4,6 +4,19 @@ package chiselTests
 
 import chisel3._
 
+class SimpleBundle extends Bundle {
+  val x = UInt(4.W)
+  val y = UInt()
+}
+object SimpleBundle {
+  def intoWire(): SimpleBundle = {
+    val w = Wire(new SimpleBundle)
+    w.x := 0.U(4.W)
+    w.y := 0.U(4.W)
+    w
+  }
+}
+
 class WidthSpec extends ChiselFlatSpec {
   "Literals without specified widths" should "get the minimum legal width" in {
     "hdeadbeef".U.getWidth should be (32)
@@ -15,3 +28,161 @@ class WidthSpec extends ChiselFlatSpec {
     1.S.getWidth should be (2)
   }
 }
+
+abstract class WireRegWidthSpecImpl extends ChiselFlatSpec {
+  def name: String
+  def builder[T <: Data](x: T): T
+
+  behavior of name
+
+  it should "set the width if the template type has a set width" in {
+    assertKnownWidth(4) {
+      builder(UInt(4.W))
+    }
+    assertKnownWidth(4) {
+      val w = builder(new SimpleBundle)
+      w := SimpleBundle.intoWire()
+      w.x
+    }
+    assertKnownWidth(4) {
+      val x = builder(Vec(1, UInt(4.W)))
+      x(0)
+    }
+  }
+
+  it should "infer the width if the template type has no width" in {
+    assertInferredWidth(4) {
+      val w = builder(UInt())
+      w := 0.U(4.W)
+      w
+    }
+    assertInferredWidth(4) {
+      val w = builder(new SimpleBundle)
+      w := SimpleBundle.intoWire()
+      w.y
+    }
+    assertInferredWidth(4) {
+      val w = builder(Vec(1, UInt()))
+      w(0) := 0.U(4.W)
+      w(0)
+    }
+  }
+}
+
+class WireWidthSpec extends WireRegWidthSpecImpl {
+  def name = "Wire"
+  def builder[T <: Data](x: T): T = Wire(x)
+}
+class RegWidthSpec extends WireRegWidthSpecImpl {
+  def name = "Reg"
+  def builder[T <: Data](x: T): T = Reg(x)
+}
+
+abstract class WireInitRegInitSpecImpl extends ChiselFlatSpec {
+  def name: String
+  def builder1[T <: Data](x: T): T
+  def builder2[T <: Data](x: T, y: T): T
+
+  behavior of s"$name (Single Argument)"
+
+  it should "set width if passed a literal with forced width" in {
+    assertKnownWidth(4) {
+      builder1(3.U(4.W))
+    }
+  }
+
+  it should "NOT set width if passed a literal without a forced width" in {
+    assertInferredWidth(4) {
+      val w = builder1(3.U)
+      w := 3.U(4.W)
+      w
+    }
+  }
+
+  it should "NOT set width if passed a non-literal" in {
+    assertInferredWidth(4) {
+      val w = WireInit(3.U(4.W))
+      builder1(w)
+    }
+  }
+
+  it should "copy the widths of aggregates" in {
+    assertInferredWidth(4) {
+      val w = builder1(SimpleBundle.intoWire())
+      w.y
+    }
+    assertKnownWidth(4) {
+      val w = builder1(SimpleBundle.intoWire())
+      w.x
+    }
+    assertInferredWidth(4) {
+      val x = Wire(Vec(1, UInt()))
+      x(0) := 0.U(4.W)
+      val w = builder1(x)
+      w(0)
+    }
+    assertKnownWidth(4) {
+      val x = Wire(Vec(1, UInt(4.W)))
+      x(0) := 0.U(4.W)
+      val w = builder1(x)
+      w(0)
+    }
+  }
+
+  behavior of s"$name (Double Argument)"
+
+  it should "set the width if the template type has a set width" in {
+    assertKnownWidth(4) {
+      WireInit(UInt(4.W), 0.U)
+    }
+    assertKnownWidth(4) {
+      WireInit(UInt(4.W), 0.U(2.W))
+    }
+    assertKnownWidth(4) {
+      val w = WireInit(new SimpleBundle, SimpleBundle.intoWire())
+      w.x
+    }
+    assertKnownWidth(4) {
+      val x = Wire(Vec(1, UInt()))
+      x(0) := 0.U(4.W)
+      val w = WireInit(Vec(1, UInt(4.W)), x)
+      w(0)
+    }
+  }
+
+  it should "infer the width if the template type has no width" in {
+    val templates = Seq(
+      () => 0.U, () => 0.U(2.W), () => WireInit(0.U), () => WireInit(0.U(2.W))
+    )
+    for (gen <- templates) {
+      assertInferredWidth(4) {
+        val w = WireInit(UInt(), gen())
+        w := 0.U(4.W)
+        w
+      }
+    }
+    assertInferredWidth(4) {
+      val w = WireInit(new SimpleBundle, SimpleBundle.intoWire())
+      w.y
+    }
+    assertInferredWidth(4) {
+      val x = Wire(Vec(1, UInt()))
+      x(0) := 0.U(4.W)
+      val w = WireInit(Vec(1, UInt()), x)
+      w(0)
+    }
+  }
+}
+
+class WireInitWidthSpec extends WireInitRegInitSpecImpl {
+  def name = "WireInit"
+  def builder1[T <: Data](x: T): T = WireInit(x)
+  def builder2[T <: Data](x: T, y: T): T = WireInit(x, y)
+}
+
+class RegInitWidthSpec extends WireInitRegInitSpecImpl {
+  def name = "RegInit"
+  def builder1[T <: Data](x: T): T = RegInit(x)
+  def builder2[T <: Data](x: T, y: T): T = RegInit(x, y)
+}
+