Internals: Support linking recursive function calls (but not later st…

…ages)

src/V3Ast.h

@@ -2750,6 +2750,7 @@ class AstNodeFTask VL_NOT_FINAL : public AstNode {
     bool m_isHideProtected : 1;  // Verilog protected
     bool m_pure : 1;  // DPI import pure (vs. virtual pure)
     bool m_pureVirtual : 1;  // Pure virtual
+    bool m_recursive : 1;  // Recusive or part of recursion
     bool m_underGenerate : 1;  // Under generate (for warning)
     bool m_virtual : 1;  // Virtual method in class
     VLifetime m_lifetime;  // Lifetime
@@ -2774,6 +2775,7 @@ class AstNodeFTask VL_NOT_FINAL : public AstNode {
         , m_isHideProtected{false}
         , m_pure{false}
         , m_pureVirtual{false}
+        , m_recursive{false}
         , m_underGenerate{false}
         , m_virtual{false} {
         addNOp3p(stmtsp);
@@ -2843,6 +2845,8 @@ class AstNodeFTask VL_NOT_FINAL : public AstNode {
     bool pure() const { return m_pure; }
     void pureVirtual(bool flag) { m_pureVirtual = flag; }
     bool pureVirtual() const { return m_pureVirtual; }
+    void recursive(bool flag) { m_recursive = flag; }
+    bool recursive() const { return m_recursive; }
     void underGenerate(bool flag) { m_underGenerate = flag; }
     bool underGenerate() const { return m_underGenerate; }
     void isVirtual(bool flag) { m_virtual = flag; }

src/V3AstNodes.cpp

@@ -1802,12 +1802,13 @@ void AstNodeFTaskRef::dump(std::ostream& str) const {
 void AstNodeFTask::dump(std::ostream& str) const {
     this->AstNode::dump(str);
     if (classMethod()) str << " [METHOD]";
-    if (taskPublic()) str << " [PUBLIC]";
-    if (prototype()) str << " [PROTOTYPE]";
-    if (dpiImport()) str << " [DPII]";
     if (dpiExport()) str << " [DPIX]";
+    if (dpiImport()) str << " [DPII]";
     if (dpiOpenChild()) str << " [DPIOPENCHILD]";
     if (dpiOpenParent()) str << " [DPIOPENPARENT]";
+    if (prototype()) str << " [PROTOTYPE]";
+    if (recursive()) str << " [RECURSIVE]";
+    if (taskPublic()) str << " [PUBLIC]";
     if ((dpiImport() || dpiExport()) && cname() != name()) str << " [c=" << cname() << "]";
 }
 void AstNodeBlock::dump(std::ostream& str) const {

src/V3LinkDot.cpp

@@ -1860,7 +1860,7 @@ class LinkDotResolveVisitor final : public VNVisitor {
     VSymEnt* m_pinSymp = nullptr;  // SymEnt for pin lookups
     const AstCell* m_cellp = nullptr;  // Current cell
     AstNodeModule* m_modp = nullptr;  // Current module
-    const AstNodeFTask* m_ftaskp = nullptr;  // Current function/task
+    AstNodeFTask* m_ftaskp = nullptr;  // Current function/task
     int m_modportNum = 0;  // Uniqueify modport numbers
 
     struct DotStates {
@@ -2748,8 +2748,11 @@ class LinkDotResolveVisitor final : public VNVisitor {
                 if (foundp) {
                     if (VN_IS(foundp->nodep(), Var) && m_ds.m_dotText == "" && m_ftaskp
                         && m_ftaskp->name() == foundp->nodep()->name()) {
-                        nodep->v3warn(E_UNSUPPORTED, "Unsupported: Recursive function call "
-                                                         << nodep->prettyNameQ());
+                        // This is a recursive reference to the function itself, not to the var
+                        nodep->taskp(m_ftaskp);
+                        nodep->classOrPackagep(foundp->classOrPackagep());
+                        UINFO(7, "         Resolved recursive " << nodep
+                                                                << endl);  // Also prints taskp
                     } else {
                         nodep->v3error("Found definition of '"
                                        << m_ds.m_dotText << (m_ds.m_dotText == "" ? "" : ".")

src/V3Simulate.h

@@ -977,6 +977,13 @@ class SimulateVisitor VL_NOT_FINAL : public VNVisitor {
         VL_DANGLING(funcp);  // Make sure we've sized the function
         funcp = nodep->taskp();
         UASSERT_OBJ(funcp, nodep, "Not linked");
+        if (funcp->recursive()) {
+            // Because we attach values to nodes rather then making a stack, this is a mess
+            // When we do support this, we need a stack depth limit of 1K or something,
+            // and the t_func_recurse_param_bad.v test should check that limit's error message
+            clearOptimizable(funcp, "Unsupported: Recursive constant functions");
+            return;
+        }
         // Apply function call values to function
         V3TaskConnects tconnects = V3Task::taskConnects(nodep, nodep->taskp()->stmtsp());
         // Must do this in two steps, eval all params, then apply them

src/V3Width.cpp

@@ -4538,8 +4538,10 @@ class WidthVisitor final : public VNVisitor {
         // Grab width from the output variable (if it's a function)
         if (nodep->didWidth()) return;
         if (nodep->doingWidth()) {
-            nodep->v3warn(E_UNSUPPORTED, "Unsupported: Recursive function or task call");
-            nodep->dtypeSetBit();
+            UINFO(5, "Recursive function or task call: " << nodep);
+            nodep->v3warn(E_UNSUPPORTED, "Unsupported: Recursive function or task call: "
+                                             << nodep->prettyNameQ());
+            nodep->recursive(true);
             nodep->didWidth(true);
             return;
         }
@@ -4554,7 +4556,8 @@ class WidthVisitor final : public VNVisitor {
         // Would use user1 etc, but V3Width called from too many places to spend a user
         nodep->doingWidth(true);
         m_ftaskp = nodep;
-        userIterateChildren(nodep, nullptr);
+        // First width the function variable, as if is a recursive function we need data type
+        if (nodep->fvarp()) userIterate(nodep->fvarp(), nullptr);
         if (nodep->isConstructor()) {
             // Pretend it's void so less special casing needed when look at dtypes
             nodep->dtypeSetVoid();
@@ -4563,6 +4566,7 @@ class WidthVisitor final : public VNVisitor {
             UASSERT_OBJ(m_funcp, nodep, "FTask with function variable, but isn't a function");
             nodep->dtypeFrom(nodep->fvarp());  // Which will get it from fvarp()->dtypep()
         }
+        userIterateChildren(nodep, nullptr);
         nodep->didWidth(true);
         nodep->doingWidth(false);
         m_funcp = nullptr;

test_regress/t/t_func_recurse.out

@@ -1,5 +1,6 @@
-%Error-UNSUPPORTED: t/t_func_recurse.v:12:31: Unsupported: Recursive function call 'recurse_self'
-   12 |       else recurse_self = i + recurse_self(i - 1) * 2;
-      |                               ^~~~~~~~~~~~
+%Error-UNSUPPORTED: t/t_func_recurse.v:9:27: Unsupported: Recursive function or task call: 'recurse_self'
+                                           : ... In instance t
+    9 |    function automatic int recurse_self;
+      |                           ^~~~~~~~~~~~
                     ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
 %Error: Exiting due to

test_regress/t/t_func_recurse2.out

@@ -1,4 +1,4 @@
-%Error-UNSUPPORTED: t/t_func_recurse2.v:9:27: Unsupported: Recursive function or task call
+%Error-UNSUPPORTED: t/t_func_recurse2.v:9:27: Unsupported: Recursive function or task call: 'recurse_1'
                                             : ... In instance t
     9 |    function automatic int recurse_1;
       |                           ^~~~~~~~~

test_regress/t/t_func_recurse_param.out

@@ -1,5 +1,16 @@
-%Error-UNSUPPORTED: t/t_func_recurse_param.v:12:31: Unsupported: Recursive function call 'recurse_self'
-   12 |       else recurse_self = i + recurse_self(i - 1) * 2;
-      |                               ^~~~~~~~~~~~
+%Error-UNSUPPORTED: t/t_func_recurse_param.v:9:27: Unsupported: Recursive function or task call: 'recurse_self'
+                                                 : ... In instance t
+    9 |    function automatic int recurse_self;
+      |                           ^~~~~~~~~~~~
                     ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
+%Error: t/t_func_recurse_param.v:15:26: Expecting expression to be constant, but can't determine constant for FUNCREF 'recurse_self'
+                                      : ... In instance t
+        t/t_func_recurse_param.v:9:27: ... Location of non-constant FUNC 'recurse_self': Unsupported: Recursive constant functions
+   15 |    localparam int ZERO = recurse_self(0);
+      |                          ^~~~~~~~~~~~
+%Error: t/t_func_recurse_param.v:16:28: Expecting expression to be constant, but can't determine constant for FUNCREF 'recurse_self'
+                                      : ... In instance t
+        t/t_func_recurse_param.v:9:27: ... Location of non-constant FUNC 'recurse_self': Unsupported: Recursive constant functions
+   16 |    localparam int ELEVEN = recurse_self(3);
+      |                            ^~~~~~~~~~~~
 %Error: Exiting due to

test_regress/t/t_func_recurse_param_bad.out

@@ -1,5 +1,11 @@
-%Error-UNSUPPORTED: t/t_func_recurse_param_bad.v:12:31: Unsupported: Recursive function call 'recurse_self'
-   12 |       else recurse_self = i + recurse_self(i - 1) * 2;
-      |                               ^~~~~~~~~~~~
+%Error-UNSUPPORTED: t/t_func_recurse_param_bad.v:9:27: Unsupported: Recursive function or task call: 'recurse_self'
+                                                     : ... In instance t
+    9 |    function automatic int recurse_self;
+      |                           ^~~~~~~~~~~~
                     ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
+%Error: t/t_func_recurse_param_bad.v:15:26: Expecting expression to be constant, but can't determine constant for FUNCREF 'recurse_self'
+                                          : ... In instance t
+        t/t_func_recurse_param_bad.v:9:27: ... Location of non-constant FUNC 'recurse_self': Unsupported: Recursive constant functions
+   15 |    localparam int HUGE = recurse_self(10000);   
+      |                          ^~~~~~~~~~~~
 %Error: Exiting due to