Report UNUSED on parameters, localparam and genvars (#2627).

Changes

@@ -5,10 +5,14 @@ The contributors that suggested a given feature are shown in []. Thanks!
 
 * Verilator 4.107 devel
 
+**    Support randomize() class method and rand (#2607). [Krzysztof Bieganski]
+
 ***   Support $cast and new CASTCONST warning.
 
 ***   Add --top option as alias of --top-module.
 
+****  Report UNUSED on parameters, localparam and genvars (#2627). [Charles Eric LaForest]
+
 ****  Fix passing parameter type instantiations by position number.
 
 

bin/verilator

@@ -4973,10 +4973,10 @@ design simulate incorrectly; see the details under --bbox-unsup.
 
 =item UNUSED
 
-Warns that the specified signal is never used/consumed.  Verilator is
+Warns that the specified signal or parameter is never used/consumed.
-fairly liberal in the usage calculations; making a signal public, a signal
+Verilator is fairly liberal in the usage calculations; making a signal
-matching --unused-regexp ("*unused*") or accessing only a single array
+public, a signal matching --unused-regexp ("*unused*") or accessing only a
-element marks the entire signal as used.
+single array element marks the entire signal as used.
 
 Disabled by default as this is a code style warning; it will simulate
 correctly.

src/V3Dead.cpp

@@ -330,12 +330,6 @@ private:
         if (nodep->isSigPublic()) return false;  // Can't elim publics!
         if (nodep->isIO() || nodep->isClassMember()) return false;
         if (nodep->isTemp() && !nodep->isTrace()) return true;
-        if (nodep->isParam()) {
-            const bool overriddenForHierBlock
-                = m_modp && m_modp->hierBlock() && nodep->overriddenParam();
-            if (!nodep->isTrace() && !overriddenForHierBlock && !v3Global.opt.xmlOnly())
-                return true;
-        }
         return m_elimUserVars;  // Post-Trace can kill most anything
     }
 

src/V3LinkResolve.cpp

@@ -105,7 +105,7 @@ private:
 
     virtual void visit(AstNodeVarRef* nodep) override {
         // VarRef: Resolve its reference
-        if (nodep->varp()) { nodep->varp()->usedParam(true); }
+        if (nodep->varp()) nodep->varp()->usedParam(true);
         iterateChildren(nodep);
     }
 

src/V3Undriven.cpp

@@ -149,7 +149,7 @@ public:
     void reportViolations() {
         // Combine bits into overall state
         AstVar* nodep = m_varp;
-        if (!nodep->isParam() && !nodep->isGenVar()) {
+        {
             bool allU = true;
             bool allD = true;
             bool anyU = m_wholeFlags[FLAG_USED];
@@ -168,8 +168,12 @@ public:
                 anyDnotU |= !used && driv;
                 anynotDU |= !used && !driv;
             }
+            if ((nodep->isGenVar() || nodep->isParam()) && nodep->isUsedParam())
+                allD = allU = true;
             if (allU) m_wholeFlags[FLAG_USED] = true;
             if (allD) m_wholeFlags[FLAG_DRIVEN] = true;
+            const char* const what
+                = nodep->isParam() ? "parameter" : nodep->isGenVar() ? "genvar" : "signal";
             // Test results
             if (nodep->isIfaceRef()) {
                 // For interface top level we don't do any tracking
@@ -181,35 +185,39 @@ public:
                 // UNDRIVEN is considered more serious - as is more likely a bug,
                 // thus undriven+unused bits get UNUSED warnings, as they're not as buggy.
                 if (!unusedMatch(nodep)) {
-                    nodep->v3warn(UNUSED,
+                    nodep->v3warn(UNUSED, ucfirst(what) << " is not driven, nor used: "
-                                  "Signal is not driven, nor used: " << nodep->prettyNameQ());
+                                                        << nodep->prettyNameQ());
                     nodep->fileline()->modifyWarnOff(V3ErrorCode::UNUSED, true);  // Warn only once
                 }
             } else if (allD && !anyU) {
                 if (!unusedMatch(nodep)) {
-                    nodep->v3warn(UNUSED, "Signal is not used: " << nodep->prettyNameQ());
+                    nodep->v3warn(UNUSED, ucfirst(what)
+                                              << " is not used: " << nodep->prettyNameQ());
                     nodep->fileline()->modifyWarnOff(V3ErrorCode::UNUSED, true);  // Warn only once
                 }
             } else if (!anyD && allU) {
-                nodep->v3warn(UNDRIVEN, "Signal is not driven: " << nodep->prettyNameQ());
+                nodep->v3warn(UNDRIVEN, ucfirst(what)
+                                            << " is not driven: " << nodep->prettyNameQ());
                 nodep->fileline()->modifyWarnOff(V3ErrorCode::UNDRIVEN, true);  // Warn only once
             } else {
                 // Bits have different dispositions
                 bool setU = false;
                 bool setD = false;
                 if (anynotDU && !unusedMatch(nodep)) {
-                    nodep->v3warn(UNUSED, "Bits of signal are not driven, nor used: "
+                    nodep->v3warn(UNUSED, "Bits of " << what << " are not driven, nor used: "
-                                              << nodep->prettyNameQ() << bitNames(BN_BOTH));
+                                                     << nodep->prettyNameQ() << bitNames(BN_BOTH));
                     setU = true;
                 }
                 if (anyDnotU && !unusedMatch(nodep)) {
-                    nodep->v3warn(UNUSED, "Bits of signal are not used: " << nodep->prettyNameQ()
+                    nodep->v3warn(UNUSED, "Bits of " << what
-                                                                          << bitNames(BN_UNUSED));
+                                                     << " are not used: " << nodep->prettyNameQ()
+                                                     << bitNames(BN_UNUSED));
                     setU = true;
                 }
                 if (anyUnotD) {
-                    nodep->v3warn(UNDRIVEN, "Bits of signal are not driven: "
+                    nodep->v3warn(UNDRIVEN,
-                                                << nodep->prettyNameQ() << bitNames(BN_UNDRIVEN));
+                                  "Bits of " << what << " are not driven: " << nodep->prettyNameQ()
+                                             << bitNames(BN_UNDRIVEN));
                     setD = true;
                 }
                 if (setU) {  // Warn only once

test_regress/t/t_delay.v

@@ -8,7 +8,6 @@ module t (/*AUTOARG*/
    // Inputs
    clk
    );
-   parameter PAR = 3;
 
    input clk;
    integer cyc=1;

test_regress/t/t_delay_stmtdly_bad.out

@@ -1,26 +1,26 @@
-%Warning-ASSIGNDLY: t/t_delay.v:23:13: Unsupported: Ignoring delay on this assignment/primitive.
+%Warning-ASSIGNDLY: t/t_delay.v:22:13: Unsupported: Ignoring delay on this assignment/primitive.
-   23 |    assign #(1.2000000000000000) dly1 = dly0 + 32'h1;
+   22 |    assign #(1.2000000000000000) dly1 = dly0 + 32'h1;
       |             ^~~~~~~~~~~~~~~~~~
                     ... Use "/* verilator lint_off ASSIGNDLY */" and lint_on around source to disable this message.
-%Warning-ASSIGNDLY: t/t_delay.v:28:19: Unsupported: Ignoring delay on this assignment/primitive.
+%Warning-ASSIGNDLY: t/t_delay.v:27:19: Unsupported: Ignoring delay on this assignment/primitive.
-   28 |          dly0 <= #0 32'h11;
+   27 |          dly0 <= #0 32'h11;
       |                   ^
-%Warning-ASSIGNDLY: t/t_delay.v:31:19: Unsupported: Ignoring delay on this assignment/primitive.
+%Warning-ASSIGNDLY: t/t_delay.v:30:19: Unsupported: Ignoring delay on this assignment/primitive.
-   31 |          dly0 <= #0.12 dly0 + 32'h12;
+   30 |          dly0 <= #0.12 dly0 + 32'h12;
       |                   ^~~~
-%Warning-ASSIGNDLY: t/t_delay.v:39:25: Unsupported: Ignoring delay on this assignment/primitive.
+%Warning-ASSIGNDLY: t/t_delay.v:38:25: Unsupported: Ignoring delay on this assignment/primitive.
-   39 |          dly0 <= #(dly_s.dly) 32'h55;
+   38 |          dly0 <= #(dly_s.dly) 32'h55;
       |                         ^
-%Warning-STMTDLY: t/t_delay.v:44:11: Unsupported: Ignoring delay on this delayed statement.
+%Warning-STMTDLY: t/t_delay.v:43:11: Unsupported: Ignoring delay on this delayed statement.
                                    : ... In instance t
-   44 |          #100 $finish;
+   43 |          #100 $finish;
       |           ^~~
-%Warning-UNUSED: t/t_delay.v:21:12: Signal is not used: 'dly_s'
+%Warning-UNUSED: t/t_delay.v:20:12: Signal is not used: 'dly_s'
                                   : ... In instance t
-   21 |    dly_s_t dly_s;
+   20 |    dly_s_t dly_s;
       |            ^~~~~
-%Warning-BLKSEQ: t/t_delay.v:38:20: Blocking assignments (=) in sequential (flop or latch) block
+%Warning-BLKSEQ: t/t_delay.v:37:20: Blocking assignments (=) in sequential (flop or latch) block
                                   : ... Suggest delayed assignments (<=)
-   38 |          dly_s.dly = 55;
+   37 |          dly_s.dly = 55;
       |                    ^
 %Error: Exiting due to

test_regress/t/t_lint_defparam.v

@@ -13,4 +13,5 @@ endmodule
 
 module sub;
    parameter P = 6;
+   if (P != 0) ;  // Prevent unused
 endmodule

test_regress/t/t_lint_unused.v

@@ -44,8 +44,6 @@ module sub;
 
    wire pub /*verilator public*/;   // Ignore publics
 
-   localparam THREE = 3;
-
 endmodule
 
 primitive udp_mux2 (q, a, b, s);

test_regress/t/t_lint_unused_bad.out

@@ -23,4 +23,16 @@
                                               : ... In instance t.sub
    28 |    wire [3:0] mixed;   
       |               ^~~~~
+%Warning-UNUSED: t/t_lint_unused_bad.v:37:14: Parameter is not used: 'UNUSED_P'
+                                            : ... In instance t.sub
+   37 |    parameter UNUSED_P = 1;
+      |              ^~~~~~~~
+%Warning-UNUSED: t/t_lint_unused_bad.v:38:15: Parameter is not used: 'UNUSED_LP'
+                                            : ... In instance t.sub
+   38 |    localparam UNUSED_LP = 2;
+      |               ^~~~~~~~~
+%Warning-UNUSED: t/t_lint_unused_bad.v:40:15: Genvar is not driven, nor used: 'unused_gv'
+                                            : ... In instance t.sub
+   40 |    genvar     unused_gv;
+      |               ^~~~~~~~~
 %Error: Exiting due to

test_regress/t/t_lint_unused_bad.v

@@ -34,9 +34,21 @@ module sub;
 
    localparam THREE = 3;
 
+   parameter UNUSED_P = 1;
+   localparam UNUSED_LP = 2;
+
+   genvar     unused_gv;
+   genvar     ok_gv;
+
    initial begin
       if (0 && assunu1[0] != 0 && udrb2 != 0) begin end
       if (0 && assunub2[THREE] && assunub2[1:0]!=0) begin end
       if (0 && mixed[1:0] != 0) begin end
    end
+
+   generate
+      if (0)
+        for (ok_gv = 0; ok_gv < 1; ++ok_gv) begin end
+   endgenerate
+
 endmodule