Internals: Swap lhs/rhs $cast args.

src/V3AstNodes.h

@@ -6025,6 +6025,7 @@ public:
     virtual bool cleanLhs() const { return true; }
     virtual bool sizeMattersLhs() const { return false; }
     AstNode* lhsp() const { return op1p(); }
+    AstNode* fromp() const { return lhsp(); }
     void lhsp(AstNode* nodep) { setOp1p(nodep); }
     virtual AstNodeDType* getChildDTypep() const override { return childDTypep(); }
     AstNodeDType* childDTypep() const { return VN_CAST(op2p(), NodeDType); }
@@ -6036,6 +6037,9 @@ class AstCastDynamic final : public AstNodeBiop {
     // Task usage of $cast is converted during parse to assert($cast(...))
     // Parents: MATH
     // Children: MATH
+    // lhsp() is value (we are converting FROM) to match AstCCast etc, this
+    // is opposite of $cast's order, because the first access is to the
+    // value reading from.  Suggest use fromp()/top() instead of lhsp/rhsp().
 public:
     AstCastDynamic(FileLine* fl, AstNode* lhsp, AstNode* rhsp)
         : ASTGEN_SUPER(fl, lhsp, rhsp) {}
@@ -6046,7 +6050,7 @@ public:
     virtual AstNode* cloneType(AstNode* lhsp, AstNode* rhsp) override {
         return new AstCastDynamic(this->fileline(), lhsp, rhsp);
     }
-    virtual string emitVerilog() override { return "%f$cast(%r, %l)"; }
+    virtual string emitVerilog() override { return "%f$cast(%l, %r)"; }
     // Non-existent filehandle returns EOF
     virtual string emitC() override { V3ERROR_NA_RETURN(""); }
     virtual bool cleanOut() const override { return true; }
@@ -6056,6 +6060,8 @@ public:
     virtual bool sizeMattersRhs() const override { return false; }
     virtual int instrCount() const override { return widthInstrs() * 20; }
     virtual bool isPure() const override { return true; }
+    AstNode* fromp() const { return lhsp(); }
+    AstNode* top() const { return rhsp(); }
 };
 
 class AstCastParse final : public AstNode {

src/V3LinkLValue.cpp

@@ -79,10 +79,10 @@ private:
     virtual void visit(AstCastDynamic* nodep) override {
         VL_RESTORER(m_setRefLvalue);
         {
-            m_setRefLvalue = VAccess::WRITE;
-            iterateAndNextNull(nodep->lhsp());
             m_setRefLvalue = VAccess::NOCHANGE;
-            iterateAndNextNull(nodep->rhsp());
+            iterateAndNextNull(nodep->fromp());
+            m_setRefLvalue = VAccess::WRITE;
+            iterateAndNextNull(nodep->top());
         }
     }
     virtual void visit(AstFOpen* nodep) override {

src/V3Width.cpp

@@ -1652,27 +1652,27 @@ private:
     virtual void visit(AstCast* nodep) override {
         nodep->dtypep(iterateEditMoveDTypep(nodep, nodep->subDTypep()));
         // if (debug()) nodep->dumpTree(cout, "  CastPre: ");
-        userIterateAndNext(nodep->lhsp(), WidthVP(SELF, PRELIM).p());
+        userIterateAndNext(nodep->fromp(), WidthVP(SELF, PRELIM).p());
 
         // When more general casts are supported, the cast elimination will be done later.
         // For now, replace it ASAP, so widthing can propagate easily
         // The cast may change signing, but we don't know the sign yet.  Make it so.
-        // Note we don't sign lhsp() that would make the algorithm O(n^2) if lots of casting.
+        // Note we don't sign fromp() that would make the algorithm O(n^2) if lots of casting.
         AstBasicDType* basicp = nodep->dtypep()->basicp();
         UASSERT_OBJ(basicp, nodep, "Unimplemented: Casting non-simple data type");
         if (m_vup->prelim()) {
-            userIterateAndNext(nodep->lhsp(), WidthVP(SELF, PRELIM).p());
+            userIterateAndNext(nodep->fromp(), WidthVP(SELF, PRELIM).p());
             // When implement more complicated types need to convert childDTypep to
             // dtypep() not as a child
-            if (!basicp->isDouble() && !nodep->lhsp()->isDouble()) {
+            if (!basicp->isDouble() && !nodep->fromp()->isDouble()) {
-                // Note castSized might modify nodep->lhsp()
+                // Note castSized might modify nodep->fromp()
                 int width = nodep->dtypep()->width();
-                castSized(nodep, nodep->lhsp(), width);
+                castSized(nodep, nodep->fromp(), width);
             } else {
-                iterateCheck(nodep, "value", nodep->lhsp(), SELF, FINAL, nodep->lhsp()->dtypep(),
+                iterateCheck(nodep, "value", nodep->fromp(), SELF, FINAL, nodep->fromp()->dtypep(),
                              EXTEND_EXP, false);
             }
-            AstNode* newp = nodep->lhsp()->unlinkFrBack();
+            AstNode* newp = nodep->fromp()->unlinkFrBack();
             if (basicp->isDouble() && !newp->isDouble()) {
                 if (newp->isSigned()) {
                     newp = new AstISToRD(nodep->fileline(), newp);

src/verilog.y

@@ -3667,7 +3667,7 @@ system_t_call<nodep>:		// IEEE: system_tf_call (as task)
 	|	yD_WRITEMEMH '(' expr ',' idClassSel ',' expr ',' expr ')'	{ $$ = new AstWriteMem($1, true,  $3, $5, $7, $9); }
 	//
 	|	yD_CAST '(' expr ',' expr ')'
-			{ $$ = new AstAssert($1, new AstCastDynamic($1, $3, $5), nullptr, nullptr, true); }
+			{ $$ = new AstAssert($1, new AstCastDynamic($1, $5, $3), nullptr, nullptr, true); }
 	//
 	// Any system function as a task
 	|	system_f_call_or_t			{ $$ = new AstSysFuncAsTask($<fl>1, $1); }
@@ -3677,7 +3677,7 @@ system_f_call<nodep>:		// IEEE: system_tf_call (as func)
 		yaD_PLI systemDpiArgsE			{ $$ = new AstFuncRef($<fl>1, *$1, $2); VN_CAST($$, FuncRef)->pli(true); }
 	//
 	|	yD_C '(' cStrList ')'			{ $$ = (v3Global.opt.ignc() ? nullptr : new AstUCFunc($1,$3)); }
-	|	yD_CAST '(' expr ',' expr ')'		{ $$ = new AstCastDynamic($1, $3, $5); }
+	|	yD_CAST '(' expr ',' expr ')'		{ $$ = new AstCastDynamic($1, $5, $3); }
 	|	yD_SYSTEM  '(' expr ')'			{ $$ = new AstSystemF($1,$3); }
 	//
 	|	system_f_call_or_t			{ $$ = $1; }