Add warning on dist in constraints (#5264)

src/V3AstNodeExpr.h

@@ -1142,6 +1142,39 @@ public:
     string emitC() override { V3ERROR_NA_RETURN(""); }
     bool cleanOut() const override { return true; }
 };
+class AstDist final : public AstNodeExpr {
+    // @astgen op1 := exprp : AstNodeExpr
+    // @astgen op2 := itemsp : List[AstDistItem]
+public:
+    AstDist(FileLine* fl, AstNodeExpr* exprp, AstDistItem* itemsp)
+        : ASTGEN_SUPER_Inside(fl) {
+        this->exprp(exprp);
+        this->addItemsp(itemsp);
+        dtypeSetBit();
+    }
+    ASTGEN_MEMBERS_AstDist;
+    string emitVerilog() override { return "%l dist { %r }"; }
+    string emitC() override { V3ERROR_NA_RETURN(""); }
+    bool cleanOut() const override { return false; }  // NA
+};
+class AstDistItem final : public AstNodeExpr {
+    // Constraint distribution item
+    // @astgen op1 := rangep : AstNodeExpr
+    // @astgen op2 := weightp : AstNodeExpr
+    bool m_isWhole = false;  // True for weight ':/', false for ':='
+public:
+    AstDistItem(FileLine* fl, AstNodeExpr* rangep, AstNodeExpr* weightp)
+        : ASTGEN_SUPER_DistItem(fl) {
+        this->rangep(rangep);
+        this->weightp(weightp);
+    }
+    ASTGEN_MEMBERS_AstDistItem;
+    string emitVerilog() override { return "%l "s + (m_isWhole ? ":/" : ":=") + " %r"; }
+    string emitC() override { V3ERROR_NA_RETURN(""); }
+    bool cleanOut() const override { return false; }  // NA
+    void isWhole(bool flag) { m_isWhole = flag; }
+    bool isWhole() const { return m_isWhole; }
+};
 class AstDot final : public AstNodeExpr {
     // A dot separating paths in an AstVarXRef, AstFuncRef or AstTaskRef
     // These are eliminated in the link stage

src/V3AstNodeOther.h

@@ -1064,24 +1064,6 @@ public:
     bool same(const AstNode*) const override { return true; }
     string path() const { return m_path; }
 };
-class AstDistItem final : public AstNode {
-    // Constraint distribution item
-    // @astgen op1 := rangep : AstNodeExpr
-    // @astgen op2 := weightp : AstNodeExpr
-    bool m_isWhole = false;  // True for weight ':/', false for ':='
-public:
-    AstDistItem(FileLine* fl, AstNodeExpr* rangep, AstNodeExpr* weightp)
-        : ASTGEN_SUPER_DistItem(fl) {
-        this->rangep(rangep);
-        this->weightp(weightp);
-    }
-    ASTGEN_MEMBERS_AstDistItem;
-    bool isGateOptimizable() const override { return false; }
-    bool isPredictOptimizable() const override { return false; }
-    bool same(const AstNode* /*samep*/) const override { return true; }
-    void isWhole(bool flag) { m_isWhole = flag; }
-    bool isWhole() const { return m_isWhole; }
-};
 class AstDpiExport final : public AstNode {
     // We could put an AstNodeFTaskRef instead of the verilog function name,
     // however we're not *calling* it, so that seems somehow wrong.

src/V3Randomize.cpp

@@ -328,6 +328,11 @@ class ConstraintExprVisitor final : public VNVisitor {
         // Fall back to "(ite cond then else)"
         visit(static_cast<AstNodeTriop*>(nodep));
     }
+    void visit(AstDist* nodep) override {
+        nodep->v3warn(CONSTRAINTIGN, "Constraint expression ignored (unsupported)");
+        nodep->replaceWith(new AstSFormatF{nodep->fileline(), "true", false, nullptr});
+        VL_DO_DANGLING(nodep->deleteTree(), nodep);
+    }
     void visit(AstReplicate* nodep) override {
         // Biop, but RHS is harmful
         if (editFormat(nodep)) return;

src/V3Width.cpp

@@ -2150,8 +2150,11 @@ class WidthVisitor final : public VNVisitor {
         userIterateAndNext(nodep->rangesp(), WidthVP{SELF, BOTH}.p());
     }
     void visit(AstDistItem* nodep) override {
-        userIterate(nodep->rangep(), WidthVP{SELF, BOTH}.p());
-        userIterate(nodep->weightp(), WidthVP{SELF, BOTH}.p());
+        userIterate(nodep->rangep(), m_vup);
+        if (m_vup->prelim()) {  // First stage evaluation
+            userIterate(nodep->weightp(), WidthVP{SELF, BOTH}.p());
+        }
+        nodep->dtypep(nodep->rangep()->dtypep());
     }
     void visit(AstVar* nodep) override {
         // if (debug()) nodep->dumpTree("-  InitPre: ");
@@ -2574,6 +2577,46 @@ class WidthVisitor final : public VNVisitor {
             }
         }
     }
+    void visit(AstDist* nodep) override {
+        userIterateAndNext(nodep->exprp(), WidthVP{CONTEXT_DET, PRELIM}.p());
+        for (AstNode *nextip, *itemp = nodep->itemsp(); itemp; itemp = nextip) {
+            nextip = itemp->nextp();  // iterate may cause the node to get replaced
+            VL_DO_DANGLING(userIterate(itemp, WidthVP{CONTEXT_DET, PRELIM}.p()), itemp);
+        }
+
+        AstBasicDType* dtype = VN_CAST(nodep->exprp()->dtypep(), BasicDType);
+        AstNodeDType* subDTypep = nullptr;
+        nodep->dtypeSetBit();
+
+        if (dtype && dtype->isString()) {
+            nodep->dtypeSetString();
+            subDTypep = nodep->findStringDType();
+        } else if (dtype && dtype->isDouble()) {
+            nodep->dtypeSetDouble();
+            subDTypep = nodep->findDoubleDType();
+        } else {
+            // Take width as maximum across all items
+            int width = nodep->exprp()->width();
+            int mwidth = nodep->exprp()->widthMin();
+            for (const AstNode* itemp = nodep->itemsp(); itemp; itemp = itemp->nextp()) {
+                width = std::max(width, itemp->width());
+                mwidth = std::max(mwidth, itemp->widthMin());
+            }
+            subDTypep = nodep->findLogicDType(width, mwidth, nodep->exprp()->dtypep()->numeric());
+        }
+
+        iterateCheck(nodep, "Dist expression", nodep->exprp(), CONTEXT_DET, FINAL, subDTypep,
+                     EXTEND_EXP);
+        for (AstDistItem *nextip, *itemp = nodep->itemsp(); itemp; itemp = nextip) {
+            nextip
+                = VN_AS(itemp->nextp(), DistItem);  // iterate may cause the node to get replaced
+            iterateCheck(nodep, "Dist Item", itemp, CONTEXT_DET, FINAL, subDTypep, EXTEND_EXP);
+        }
+
+        if (debug() >= 9) nodep->dumpTree("-  dist-out: ");
+        nodep->dtypep(subDTypep);
+    }
+
     void visit(AstInside* nodep) override {
         userIterateAndNext(nodep->exprp(), WidthVP{CONTEXT_DET, PRELIM}.p());
         for (AstNode *nextip, *itemp = nodep->itemsp(); itemp; itemp = nextip) {

src/verilog.y

@@ -5057,7 +5057,7 @@ expr<nodeExprp>:                // IEEE: part of expression/constant_expression/
         //
         //                      // IEEE: expression_or_dist - here to avoid reduce problems
         //                      // "expr yDIST '{' dist_list '}'"
-        |       ~l~expr yDIST '{' dist_list '}'         { $$ = $1; $4->deleteTree(); }
+        |       ~l~expr yDIST '{' dist_list '}'         { $$ = new AstDist{$2, $1, $4}; }
         ;
 
 fexpr<nodeExprp>:                   // For use as first part of statement (disambiguates <=)
@@ -7383,7 +7383,7 @@ constraint_set<nodep>:  // ==IEEE: constraint_set
         |       '{' constraint_expressionList '}'       { $$ = $2; }
         ;
 
-dist_list<nodep>:  // ==IEEE: dist_list
+dist_list<distItemp>:  // ==IEEE: dist_list
                 dist_item                               { $$ = $1; }
         |       dist_list ',' dist_item                 { $$ = addNextNull($1, $3); }
         ;