Fix zero-size parameter (#7387 repair) (#7411) (#7418)

Fixes #7411.

src/V3Param.cpp

@@ -1396,8 +1396,7 @@ class ParamProcessor final {
                 }
                 AstConst* const exprp = VN_CAST(pinp->exprp(), Const);
                 AstConst* const origp = VN_CAST(modvarp->valuep(), Const);
-                // Width the pin value to match the port type so that the same
+                // Width the pin to the port's type so equal values hash the same (#5479).
-                // logical value always produces the same specialization name.
                 AstConst* normedNamep = nullptr;
                 if (exprp && !exprp->num().isDouble() && !exprp->num().isString()) {
                     AstVar* cloneVarp = modvarp->cloneTree(false);
@@ -1406,21 +1405,41 @@ class ParamProcessor final {
                         VL_DO_DANGLING(oldValuep->deleteTree(), oldValuep);
                     }
                     cloneVarp->valuep(exprp->cloneTree(false));
-                    // Clone the dtype and resolve VarRefs to other parameters
-                    // with their already-constified pin values (e.g., N-1 in
-                    // logic [N-1:0] becomes Const-1 which can be folded).
                     if (AstNodeDType* const origDTypep = modvarp->subDTypep()) {
                         AstNodeDType* const dtypeClonep = origDTypep->cloneTree(false);
-                        dtypeClonep->foreach([&](AstVarRef* varrefp) {
+                        // Inline every param ref so widthing doesn't reach back into the template
-                            for (AstPin* pp = paramsp; pp; pp = VN_AS(pp->nextp(), Pin)) {
+                        // (#7411). Cycle detector for dependent parameters in the same module.
-                                if (pp->modVarp() == varrefp->varp()) {
+                        constexpr int maxSubstIters = 1000;
-                                    if (AstConst* const constp = VN_CAST(pp->exprp(), Const)) {
+                        for (int it = 0; it < maxSubstIters; ++it) {
-                                        varrefp->replaceWith(constp->cloneTree(false));
+                            bool any = false;
-                                        VL_DO_DANGLING(varrefp->deleteTree(), varrefp);
+                            dtypeClonep->foreach([&](AstVarRef* varrefp) {
+                                AstVar* const targetp = varrefp->varp();
+                                AstNode* replacep = nullptr;
+                                for (AstPin* pp = paramsp; pp; pp = VN_AS(pp->nextp(), Pin)) {
+                                    if (pp->modVarp() == targetp) {
+                                        if (AstConst* const constp = VN_CAST(pp->exprp(), Const)) {
+                                            replacep = constp->cloneTree(false);
+                                        }
+                                        break;
                                     }
-                                    break;
                                 }
-                            }
+                                if (!replacep && targetp->valuep()) {
+                                    replacep = targetp->valuep()->cloneTree(false);
+                                }
+                                if (replacep) {
+                                    varrefp->replaceWith(replacep);
+                                    VL_DO_DANGLING(varrefp->deleteTree(), varrefp);
+                                    any = true;
+                                }
+                            });
+                            if (!any) break;
+                        }
+                        // Bail if anything still points at the template.
+                        dtypeClonep->foreach([&](AstVarRef* varrefp) {
+                            varrefp->v3fatalSrc(
+                                "Unresolved VarRef '"
+                                << varrefp->prettyName() << "' in pin dtype clone.  Pin: "
+                                << pinp->prettyNameQ() << " of " << nodep->prettyNameQ());
                         });
                         if (cloneVarp->childDTypep())
                             cloneVarp->childDTypep()->unlinkFrBack()->deleteTree();
@@ -1429,8 +1448,7 @@ class ParamProcessor final {
                     }
                     V3Const::constifyParamsEdit(cloneVarp);
                     if (AstConst* const widthedp = VN_CAST(cloneVarp->valuep(), Const)) {
-                        // Set the constant's dtype to the port's widthed type
+                        // Stamp the port's type on the const so equal values hash the same.
-                        // so identical values hash the same in paramValueNumber.
                         if (cloneVarp->dtypep()) widthedp->dtypep(cloneVarp->dtypep());
                         widthedp->unlinkFrBack();
                         normedNamep = widthedp;

test_regress/t/t_param_localparam_recompute.py

@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# 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.
+# SPDX-FileCopyrightText: 2026 Wilson Snyder
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('simulator')
+
+test.compile(verilator_flags2=["--binary", "-Wno-WIDTHEXPAND"])
+
+test.execute()
+
+test.passes()

test_regress/t/t_param_localparam_recompute.v

@@ -0,0 +1,44 @@
+// DESCRIPTION: Verilator: Reproducer for issue #7411.
+//
+// when V3Param widths a pin value against the port dtype the widthing must not
+// edit any referenced template vars in place.  A dependent localparam like
+// dirs_lp = dims_p*2+1 must still recompute from the overridden dims_p on
+// each specialization.  (basically - don't poison the template)
+//
+// 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.
+// SPDX-FileCopyrightText: 2026 Wilson Snyder
+// SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+module sub #(
+    parameter int dims_p = 2,
+    parameter int dirs_lp = dims_p*2 + 1,
+    parameter bit [1:0][dirs_lp-1:0][dirs_lp-1:0] matrix_p = '0
+) ();
+endmodule
+
+module t;
+  localparam bit [1:0][4:0][4:0] big_matrix = '1;
+  localparam bit [1:0][2:0][2:0] small_matrix = '1;
+
+  // First instance processes matrix_p with the template's default dims_p=2.
+  // Before the fix, this froze dirs_lp on the template at 5.
+  sub #(.matrix_p(big_matrix)) s1 ();
+
+  // Second instance overrides dims_p=1, so dirs_lp must recompute to 3.
+  sub #(.dims_p(1), .matrix_p(small_matrix)) s2 ();
+
+  initial begin
+    if (s1.dirs_lp !== 5) begin
+      $write("%%Error: s1.dirs_lp=%0d expected 5\n", s1.dirs_lp);
+      $stop;
+    end
+    if (s2.dirs_lp !== 3) begin
+      $write("%%Error: s2.dirs_lp=%0d expected 3\n", s2.dirs_lp);
+      $stop;
+    end
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule