Support $sampled.

src/V3Assert.cpp

@@ -326,6 +326,10 @@ private:
         }
         nodep->replaceWith(inp);
     }
+    virtual void visit(AstSampled* nodep) VL_OVERRIDE {
+        nodep->replaceWith(nodep->exprp()->unlinkFrBack());
+        VL_DO_DANGLING(pushDeletep(nodep), nodep);
+    }
 
     //========== Statements
     virtual void visit(AstDisplay* nodep) VL_OVERRIDE {

src/V3AstNodes.h

@@ -6265,6 +6265,24 @@ public:
     virtual bool same(const AstNode* samep) const { return true; }
 };
 
+class AstSampled : public AstNodeMath {
+    // Verilog $sampled
+    // Parents: math
+    // Children: expression
+public:
+    AstSampled(FileLine* fl, AstNode* exprp)
+        : ASTGEN_SUPER(fl) { addOp1p(exprp); }
+    ASTNODE_NODE_FUNCS(Sampled)
+    virtual string emitVerilog() { return "$sampled(%l)"; }
+    virtual string emitC() { V3ERROR_NA; return "";}
+    virtual string emitSimpleOperator() { V3ERROR_NA; return ""; }
+    virtual bool cleanOut() const { V3ERROR_NA; return ""; }
+    virtual int instrCount() const { return 0; }
+    AstNode* exprp() const { return op1p(); }  // op1 = expression
+    virtual V3Hash sameHash() const { return V3Hash(); }
+    virtual bool same(const AstNode* samep) const { return true; }
+};
+
 class AstPattern : public AstNodeMath {
     // Verilog '{a,b,c,d...}
     // Parents: AstNodeAssign, AstPattern, ...

src/V3Width.cpp

@@ -947,6 +947,12 @@ private:
             }
         }
     }
+    virtual void visit(AstSampled* nodep) VL_OVERRIDE {
+        if (m_vup->prelim()) {
+            iterateCheckSizedSelf(nodep, "LHS", nodep->exprp(), SELF, BOTH);
+            nodep->dtypeFrom(nodep->exprp());
+        }
+    }
     virtual void visit(AstRand* nodep) VL_OVERRIDE {
         if (m_vup->prelim()) {
             nodep->dtypeSetSigned32();  // Says the spec

src/verilog.l

@@ -234,6 +234,7 @@ vnum    {vnum1}|{vnum2}|{vnum3}|{vnum4}|{vnum5}
   "$rtoi"               { FL; return yD_RTOI; }
   "$setup"              { FL; return yaTIMINGSPEC; }
   "$setuphold"          { FL; return yaTIMINGSPEC; }
+  "$sampled"            { FL; return yD_SAMPLED; }
   "$sformat"            { FL; return yD_SFORMAT; }
   "$sformatf"           { FL; return yD_SFORMATF; }
   "$shortrealtobits"    { FL; return yD_SHORTREALTOBITS; }

src/verilog.y

@@ -591,6 +591,7 @@ class AstSenTree;
 %token<fl>		yD_REWIND	"$rewind"
 %token<fl>		yD_RIGHT	"$right"
 %token<fl>		yD_RTOI		"$rtoi"
+%token<fl>		yD_SAMPLED	"$sampled"
 %token<fl>		yD_SFORMAT	"$sformat"
 %token<fl>		yD_SFORMATF	"$sformatf"
 %token<fl>		yD_SHORTREALTOBITS "$shortrealtobits"
@@ -3264,6 +3265,7 @@ system_f_call_or_t<nodep>:	// IEEE: part of system_tf_call (can be task or func)
 	|	yD_RIGHT '(' exprOrDataType ')'		{ $$ = new AstAttrOf($1,AstAttrType::DIM_RIGHT,$3,NULL); }
 	|	yD_RIGHT '(' exprOrDataType ',' expr ')'	{ $$ = new AstAttrOf($1,AstAttrType::DIM_RIGHT,$3,$5); }
 	|	yD_RTOI '(' expr ')'			{ $$ = new AstRToIS($1,$3); }
+	|	yD_SAMPLED '(' expr ')'			{ $$ = new AstSampled($1, $3); }
 	|	yD_SFORMATF '(' str commaEListE ')'	{ $$ = new AstSFormatF($1,*$3,false,$4); }
 	|	yD_SHORTREALTOBITS '(' expr ')'		{ $$ = new AstRealToBits($1,$3); UNSUPREAL($1); }
 	|	yD_SIGNED '(' expr ')'			{ $$ = new AstSigned($1,$3); }

test_regress/t/t_past.v

@@ -75,6 +75,8 @@ module Test (/*AUTOARG*/
       if (dly0 != $past(in)) $stop;
       if (dly0 != $past(in,1)) $stop;
       if (dly1 != $past(in,2)) $stop;
+      // $sampled(expression) -> expression
+      if (in != $sampled(in)) $stop;
    end
 
    assert property (@(posedge clk) dly0 == $past(in));