From 0de1bbc85b281f811e3f539b2b297d39d2c31eac Mon Sep 17 00:00:00 2001
From: Geza Lore <gezalore@gmail.com>
Date: Tue, 5 Jul 2022 14:20:37 +0100
Subject: [PATCH] Add and use VL_CONSTEXPR_CXX17

---
 include/verilatedos.h    | 10 ++++++++++
 src/V3Ast.h              |  8 ++++----
 src/V3AstUserAllocator.h | 27 ++++++++++++---------------
 3 files changed, 26 insertions(+), 19 deletions(-)

diff --git a/include/verilatedos.h b/include/verilatedos.h
index 6bacfe27b..2b0cdd8ce 100644
--- a/include/verilatedos.h
+++ b/include/verilatedos.h
@@ -234,6 +234,16 @@
 # error "Verilator requires a C++11 or newer compiler"
 #endif
 
+//=========================================================================
+// C++-2017
+
+#if __cplusplus >= 201703L
+# define VL_CONSTEXPR_CXX17 constexpr
+#else
+# define VL_CONSTEXPR_CXX17
+#endif
+
+
 //=========================================================================
 // Optimization
 
diff --git a/src/V3Ast.h b/src/V3Ast.h
index dc4cf6d8e..868fc73f8 100644
--- a/src/V3Ast.h
+++ b/src/V3Ast.h
@@ -1948,7 +1948,7 @@ private:
             ASTNODE_PREFETCH(nodep->op2p());
             ASTNODE_PREFETCH(nodep->op3p());
             ASTNODE_PREFETCH(nodep->op4p());
-            if /* TODO: 'constexpr' in C++17 */ (VisitNext) ASTNODE_PREFETCH(nodep->nextp());
+            if VL_CONSTEXPR_CXX17 (VisitNext) ASTNODE_PREFETCH(nodep->nextp());
 
             // Apply function in pre-order
             if (privateTypeTest<typename std::remove_const<T_Arg>::type>(nodep)) {
@@ -1964,7 +1964,7 @@ private:
             }
 
             // Traverse 'nextp()' chain if requested
-            if /* TODO: 'constexpr' in C++17 */ (VisitNext) {
+            if VL_CONSTEXPR_CXX17 (VisitNext) {
                 nodep = nodep->nextp();
             } else {
                 break;
@@ -1987,7 +1987,7 @@ private:
             ASTNODE_PREFETCH(nodep->op2p());
             ASTNODE_PREFETCH(nodep->op3p());
             ASTNODE_PREFETCH(nodep->op4p());
-            if /* TODO: 'constexpr' in C++17 */ (VisitNext) ASTNODE_PREFETCH(nodep->nextp());
+            if VL_CONSTEXPR_CXX17 (VisitNext) ASTNODE_PREFETCH(nodep->nextp());
 
             // Apply function in pre-order
             if (privateTypeTest<typename std::remove_const<T_Arg>::type>(nodep)) {
@@ -2011,7 +2011,7 @@ private:
             }
 
             // Traverse 'nextp()' chain if requested
-            if /* TODO: 'constexpr' in C++17 */ (VisitNext) {
+            if VL_CONSTEXPR_CXX17 (VisitNext) {
                 nodep = nodep->nextp();
             } else {
                 break;
diff --git a/src/V3AstUserAllocator.h b/src/V3AstUserAllocator.h
index 8d63ad5a9..f8982bf16 100644
--- a/src/V3AstUserAllocator.h
+++ b/src/V3AstUserAllocator.h
@@ -35,17 +35,16 @@ private:
     std::vector<T_Data*> m_allocated;
 
     inline T_Data* getUserp(const T_Node* nodep) const {
-        // This simplifies statically as T_UserN is constant. In C++17, use 'if constexpr'.
-        if (T_UserN == 1) {
+        if VL_CONSTEXPR_CXX17 (T_UserN == 1) {
             const VNUser user = nodep->user1u();
             return user.to<T_Data*>();
-        } else if (T_UserN == 2) {
+        } else if VL_CONSTEXPR_CXX17 (T_UserN == 2) {
             const VNUser user = nodep->user2u();
             return user.to<T_Data*>();
-        } else if (T_UserN == 3) {
+        } else if VL_CONSTEXPR_CXX17 (T_UserN == 3) {
             const VNUser user = nodep->user3u();
             return user.to<T_Data*>();
-        } else if (T_UserN == 4) {
+        } else if VL_CONSTEXPR_CXX17 (T_UserN == 4) {
             const VNUser user = nodep->user4u();
             return user.to<T_Data*>();
         } else {
@@ -55,14 +54,13 @@ private:
     }
 
     inline void setUserp(T_Node* nodep, T_Data* userp) const {
-        // This simplifies statically as T_UserN is constant. In C++17, use 'if constexpr'.
-        if (T_UserN == 1) {
+        if VL_CONSTEXPR_CXX17 (T_UserN == 1) {
             nodep->user1u(VNUser(userp));
-        } else if (T_UserN == 2) {
+        } else if VL_CONSTEXPR_CXX17 (T_UserN == 2) {
             nodep->user2u(VNUser(userp));
-        } else if (T_UserN == 3) {
+        } else if VL_CONSTEXPR_CXX17 (T_UserN == 3) {
             nodep->user3u(VNUser(userp));
-        } else if (T_UserN == 4) {
+        } else if VL_CONSTEXPR_CXX17 (T_UserN == 4) {
             nodep->user4u(VNUser(userp));
         } else {
             nodep->user5u(VNUser(userp));
@@ -71,14 +69,13 @@ private:
 
 protected:
     AstUserAllocatorBase() {
-        // This simplifies statically as T_UserN is constant. In C++17, use 'if constexpr'.
-        if (T_UserN == 1) {
+        if VL_CONSTEXPR_CXX17 (T_UserN == 1) {
             VNUser1InUse::check();
-        } else if (T_UserN == 2) {
+        } else if VL_CONSTEXPR_CXX17 (T_UserN == 2) {
             VNUser2InUse::check();
-        } else if (T_UserN == 3) {
+        } else if VL_CONSTEXPR_CXX17 (T_UserN == 3) {
             VNUser3InUse::check();
-        } else if (T_UserN == 4) {
+        } else if VL_CONSTEXPR_CXX17 (T_UserN == 4) {
             VNUser4InUse::check();
         } else {
             VNUser5InUse::check();