From 5fe539c707c88eedbb112f5c6bcea1dfe1d52169 Mon Sep 17 00:00:00 2001
From: Jack Koenig
Date: Thu, 1 Jul 2021 16:34:48 -0700
Subject: Add ChiselEnum.safe factory method and avoid warning

Previously, ChiselEnum would warn any time a UInt is converted to an
Enum. There was no way to suppress this warning. Now there is a factory
method (`.safe`) that does not warn and returns (Enum, Bool) where the
Bool is the result of calling .isValid on an Enum object. The regular
UInt cast is also now smarter and will not warn if all bitvectors of the
width of the Enum are legal states.
---
 core/src/main/scala/chisel3/StrongEnum.scala | 34 ++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

(limited to 'core/src')

diff --git a/core/src/main/scala/chisel3/StrongEnum.scala b/core/src/main/scala/chisel3/StrongEnum.scala
index 7d328eb7..1d0e04d3 100644
--- a/core/src/main/scala/chisel3/StrongEnum.scala
+++ b/core/src/main/scala/chisel3/StrongEnum.scala
@@ -131,7 +131,7 @@ abstract class EnumType(private val factory: EnumFactory, selfAnnotating: Boolea
     if (litOption.isDefined) {
       true.B
     } else {
-      factory.all.map(this === _).reduce(_ || _)
+      if (factory.isTotal) true.B else factory.all.map(this === _).reduce(_ || _)
     }
   }
 
@@ -233,6 +233,12 @@ abstract class EnumFactory {
 
   private[chisel3] val enumTypeName = getClass.getName.init
 
+  // Do all bitvectors of this Enum's width represent legal states?
+  private[chisel3] def isTotal: Boolean = {
+    (this.getWidth < 31) && // guard against Integer overflow
+      (enumRecords.size == (1 << this.getWidth))
+  }
+
   private[chisel3] def globalAnnotation: EnumDefChiselAnnotation =
     EnumDefChiselAnnotation(enumTypeName, (enumNames, enumValues).zipped.toMap)
 
@@ -277,7 +283,7 @@ abstract class EnumFactory {
 
   def apply(): Type = new Type
 
-  def apply(n: UInt)(implicit sourceInfo: SourceInfo, connectionCompileOptions: CompileOptions): Type = {
+  private def castImpl(n: UInt, warn: Boolean)(implicit sourceInfo: SourceInfo, connectionCompileOptions: CompileOptions): Type = {
     if (n.litOption.isDefined) {
       enumInstances.find(_.litValue == n.litValue) match {
         case Some(result) => result
@@ -288,8 +294,9 @@ abstract class EnumFactory {
     } else if (n.getWidth > this.getWidth) {
       throwException(s"The UInt being cast to $enumTypeName is wider than $enumTypeName's width ($getWidth)")
     } else {
-      Builder.warning(s"Casting non-literal UInt to $enumTypeName. You can check that its value is legal by calling isValid")
-
+      if (warn && !this.isTotal) {
+        Builder.warning(s"Casting non-literal UInt to $enumTypeName. You can use $enumTypeName.safe to cast without this warning.")
+      }
       val glue = Wire(new UnsafeEnum(width))
       glue := n
       val result = Wire(new Type)
@@ -297,6 +304,25 @@ abstract class EnumFactory {
       result
     }
   }
+
+  /** Cast an [[UInt]] to the type of this Enum
+    *
+    * @note will give a Chisel elaboration time warning if the argument could hit invalid states
+    * @param n the UInt to cast
+    * @return the equivalent Enum to the value of the cast UInt
+    */
+  def apply(n: UInt)(implicit sourceInfo: SourceInfo, connectionCompileOptions: CompileOptions): Type = castImpl(n, warn = true)
+
+  /** Safely cast an [[UInt]] to the type of this Enum
+    *
+    * @param n the UInt to cast
+    * @return the equivalent Enum to the value of the cast UInt and a Bool indicating if the
+    *         Enum is valid
+    */
+  def safe(n: UInt)(implicit sourceInfo: SourceInfo, connectionCompileOptions: CompileOptions): (Type, Bool) = {
+    val t = castImpl(n, warn = false)
+    (t, t.isValid)
+  }
 }
 
 
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