Add IGNOREDRETURN warning.

Changes

@@ -8,6 +8,8 @@ The contributors that suggested a given feature are shown in []. Thanks!
 
 ***   Support $fread.  [Leendert van Doorn]
 
+***   Add IGNOREDRETURN warning.
+
 ****  Report PORTSHORT errors on concat constants, bug 1400. [Will Korteland]
 
 ****  Fix VERILATOR_GDB being ignored, msg2860. [Yu Sheng Lin]

bin/verilator

@@ -3580,6 +3580,14 @@ code to a case statement, or a SystemVerilog 'unique if' or 'priority if'.
 Disabled by default as this is a code style warning; it will simulate
 correctly.
 
+=item IGNOREDRETURN
+
+Warns that a non-void function is being called as a task, and hence the
+return value is being ignored. This warning is required by IEEE.
+
+Ignoring this warning will only suppress the lint check, it will simulate
+correctly.
+
 =item IMPERFECTSCH
 
 Warns that the scheduling of the model is not absolutely perfect, and some

src/V3Error.h

@@ -78,7 +78,8 @@ public:
 	ENDLABEL,	// End lable name mismatch
 	GENCLK,		// Generated Clock
 	IFDEPTH,	// If statements too deep
-	IMPERFECTSCH,	// Imperfect schedule (disabled by default)
+        IGNOREDRETURN,  // Ignoring return value (funcation as task)
+        IMPERFECTSCH,   // Imperfect schedule (disabled by default)
         IMPLICIT,       // Implicit wire
         IMPORTSTAR,     // Import::* in $unit
         IMPURE,         // Impure function not being inlined
@@ -139,7 +140,8 @@ public:
             "CMPCONST", "COLONPLUS", "COMBDLY", "CONTASSREG",
             "DEFPARAM", "DECLFILENAME",
             "ENDLABEL", "GENCLK",
-            "IFDEPTH", "IMPERFECTSCH", "IMPLICIT", "IMPORTSTAR", "IMPURE",
+            "IFDEPTH", "IGNOREDRETURN",
+            "IMPERFECTSCH", "IMPLICIT", "IMPORTSTAR", "IMPURE",
             "INCABSPATH", "INFINITELOOP", "INITIALDLY",
             "LITENDIAN", "MODDUP",
             "MULTIDRIVEN",

src/V3Task.cpp

@@ -1170,11 +1170,15 @@ private:
 	    nodep->replaceWith(outrefp);
 	    // Insert new statements
             visitp = insertBeforeStmt(nodep, beginp);
-	} else {
-	    // outvscp maybe non-NULL if calling a function in a taskref,
-	    // but if so we want to simply ignore the function result
-	    nodep->replaceWith(beginp);
-	}
+        } else {
+            if (nodep->taskp()->isFunction()) {
+                nodep->v3warn(IGNOREDRETURN,
+                              "Ignoring return value of non-void function (IEEE 2017 13.4.1)");
+            }
+            // outvscp maybe non-NULL if calling a function in a taskref,
+            // but if so we want to simply ignore the function result
+            nodep->replaceWith(beginp);
+        }
 	// Cleanup
 	nodep->deleteTree(); VL_DANGLING(nodep);
 	UINFO(4,"  FTask REF Done.\n");

test_regress/t/t_dpi_shortcircuit2.v

@@ -46,7 +46,9 @@ module t (/*AUTOARG*/);
    // Test loop
    initial begin
       // bug963
+      // verilator lint_off IGNOREDRETURN
       dpii_clear();
+      // verilator lint_on IGNOREDRETURN
       j = 0;
       for (i=0; i<64; i++) begin
 	 if (i[0])

test_regress/t/t_func.v

@@ -50,12 +50,15 @@ module t;
       if (n !== 10) $stop;
 
       // Functions called as tasks
+      // verilator lint_off IGNOREDRETURN
       rglobal = 32'h4;
       if (inc_and_return(32'h2) != 32'h6) $stop;
       if (rglobal !== 32'h6) $stop;
       rglobal = 32'h6;
+
       inc_and_return(32'h3);
       if (rglobal !== 32'h9) $stop;
+      // verilator lint_on IGNOREDRETURN
 
       $write("*-* All Finished *-*\n");
       $finish;

test_regress/t/t_func_tie_bad.v

@@ -6,6 +6,7 @@
 module t (/*AUTOARG*/);
 
    initial begin
+      // verilator lint_off IGNOREDRETURN
       func(0, 1'b1);
    end
 

test_regress/t/t_func_void.pl

@@ -0,0 +1,20 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you can
+# redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+
+scenarios(simulator => 1);
+
+compile(
+    );
+
+execute(
+    check_finished => 1,
+    );
+
+ok(1);
+1;

test_regress/t/t_func_void.v

@@ -0,0 +1,36 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2003 by Wilson Snyder.
+
+module t (clk);
+   input clk;
+
+   int side_effect;
+
+   function int f1;
+      input int in;
+      f1 = in + 1;
+      side_effect += in + 1;
+   endfunction
+
+   initial begin
+      int got;
+      side_effect = 1;
+      //
+      got = f1(10);
+      if (got != 11) $stop;
+      if (side_effect != 12) $stop;
+      // verilator lint_off IGNOREDRETURN
+      f1(20);
+      // verilator lint_on IGNOREDRETURN
+      if (side_effect != 33) $stop;
+      //
+//      void'f1(30);
+//      if (side_effect != 64) $stop;
+      //
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+
+endmodule

test_regress/t/t_func_void_bad.out

@@ -0,0 +1,3 @@
+%Warning-IGNOREDRETURN: t/t_func_void_bad.v:25: Ignoring return value of non-void function (IEEE 2017 13.4.1)
+%Warning-IGNOREDRETURN: Use "/* verilator lint_off IGNOREDRETURN */" and lint_on around source to disable this message.
+%Error: Exiting due to

test_regress/t/t_func_void_bad.pl

@@ -0,0 +1,18 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you can
+# redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+
+scenarios(simulator => 1);
+
+compile(
+    fails => 1,
+    expect_filename => $Self->{golden_filename},
+    );
+
+ok(1);
+1;

test_regress/t/t_func_void_bad.v

@@ -0,0 +1,35 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2003 by Wilson Snyder.
+
+module t (clk);
+   input clk;
+
+   int side_effect;
+
+   function int f1;
+      input int in;
+      f1 = in + 1;
+      side_effect += in + 1;
+   endfunction
+
+   initial begin
+      int got;
+      side_effect = 1;
+      //
+      got = f1(10);
+      if (got != 11) $stop;
+      if (side_effect != 12) $stop;
+      //
+      f1(20);
+      if (side_effect != 33) $stop;
+      //
+//      void'f1(30);
+//      if (side_effect != 64) $stop;
+      //
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+
+endmodule