From 219003c57565b836f5822daf2ab2082f811d77ab Mon Sep 17 00:00:00 2001
From: "Daniel R. Carvalho" <odanrc@yahoo.com.br>
Date: Sat, 13 Mar 2021 19:06:27 -0300
Subject: [PATCH] base-stats: Make Rate's compilation smarter

A Rate should be supplied units of different types.
Rates between units of the same type are Ratios,
and should be declared as such.

An exception is applied to Count and Unspecified,
since those units represent unknown underlying units.

Change-Id: I36ab7c73b239ccc86d866c5b38e14fd765bbbd0f
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/43008
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
---
 src/base/stats/units.hh | 67 +++++++++++++++++++++--------------------
 1 file changed, 35 insertions(+), 32 deletions(-)

diff --git a/src/base/stats/units.hh b/src/base/stats/units.hh
index b2dfefa19e..87e6025b69 100644
--- a/src/base/stats/units.hh
+++ b/src/base/stats/units.hh
@@ -272,38 +272,6 @@ class Count : public Base
     std::string getUnitString() const override { return Count::toString(); }
 };
 
-template <typename T1, typename T2>
-class Rate : public Base
-{
-  static_assert(std::is_base_of<Base, T1>::value,
-                "Rate(T1,T2) must have T1 and T2 derived from"
-                "Stats::Units::Base");
-  static_assert(std::is_base_of<Base, T2>::value,
-                "Rate(T1,T2) must have T1 and T2 derived from"
-                "Stats::Units::Base");
-  private:
-    Rate<T1,T2>() {}
-  public:
-    Rate<T1,T2>(Rate<T1,T2> const&) = delete;
-    void operator=(Rate<T1,T2> const&) = delete;
-    static Rate<T1,T2>*
-    get()
-    {
-        static Rate<T1,T2> instance;
-        return &instance;
-    }
-    static std::string
-    toString()
-    {
-        return csprintf("(%s/%s)", T1::toString(), T2::toString());
-    }
-    std::string
-    getUnitString() const override
-    {
-        return Rate<T1,T2>::toString();
-    }
-};
-
 class Ratio : public Base
 {
   private:
@@ -342,6 +310,41 @@ class Unspecified : public Base
     }
 };
 
+template <typename T1, typename T2>
+class Rate : public Base
+{
+    static_assert(std::is_base_of<Base, T1>::value,
+        "Rate(T1,T2) must have T1 and T2 derived from Stats::Units::Base");
+    static_assert(std::is_base_of<Base, T2>::value,
+        "Rate(T1,T2) must have T1 and T2 derived from Stats::Units::Base");
+    static_assert(!std::is_same<T1, T2>::value ||
+        std::is_same<T1, Count>::value || std::is_same<T1, Unspecified>::value,
+        "Rate(T1,T2) must have T1 and T2 of different types; "
+        "otherwise, it would be a Ratio");
+
+  private:
+    Rate<T1,T2>() {}
+  public:
+    Rate<T1,T2>(Rate<T1,T2> const&) = delete;
+    void operator=(Rate<T1,T2> const&) = delete;
+    static Rate<T1,T2>*
+    get()
+    {
+        static Rate<T1,T2> instance;
+        return &instance;
+    }
+    static std::string
+    toString()
+    {
+        return csprintf("(%s/%s)", T1::toString(), T2::toString());
+    }
+    std::string
+    getUnitString() const override
+    {
+        return Rate<T1,T2>::toString();
+    }
+};
+
 } // namespace Units
 
 } // namespace Stats