Fix R/W references to random builtin function seeds (#8112)

src/V3LinkLValue.cpp

@@ -229,7 +229,7 @@ class LinkLValueVisitor final : public VNVisitor {
     }
     void visit(AstRand* nodep) override {
         VL_RESTORER(m_setRefLvalue);
-        if (!nodep->urandom()) m_setRefLvalue = VAccess::WRITE;
+        if (!nodep->urandom()) m_setRefLvalue = VAccess::READWRITE;
         iterateAndNextNull(nodep->seedp());
     }
     void visit(AstReadMem* nodep) override {
@@ -262,14 +262,14 @@ class LinkLValueVisitor final : public VNVisitor {
     }
     void visit(AstNodeDistBiop* nodep) override {
         VL_RESTORER(m_setRefLvalue);
-        m_setRefLvalue = VAccess::WRITE;
+        m_setRefLvalue = VAccess::READWRITE;
         iterateAndNextNull(nodep->lhsp());
         m_setRefLvalue = VAccess::NOCHANGE;
         iterateAndNextNull(nodep->rhsp());
     }
     void visit(AstNodeDistTriop* nodep) override {
         VL_RESTORER(m_setRefLvalue);
-        m_setRefLvalue = VAccess::WRITE;
+        m_setRefLvalue = VAccess::READWRITE;
         iterateAndNextNull(nodep->lhsp());
         m_setRefLvalue = VAccess::NOCHANGE;
         iterateAndNextNull(nodep->rhsp());

test_regress/t/t_cover_sys_line_expr.out

@@ -270,37 +270,37 @@
 -000000  point: type=branch comment=else hier=top.t
 ~000010     if (($dist_erlang(result, 2, 3) != 0) && foo) bump <= bump + 1;
 -000000  point: type=expr comment=(($dist_erlang(result, 32'sh2, 32'sh3) != 32'sh0)==0) => 0 hier=top.t
-+000010  point: type=expr comment=(($dist_erlang(result, 32'sh2, 32'sh3) != 32'sh0)==1 && foo==1) => 1 hier=top.t
+-000009  point: type=expr comment=(($dist_erlang(result, 32'sh2, 32'sh3) != 32'sh0)==1 && foo==1) => 1 hier=top.t
 -000000  point: type=expr comment=(foo==0) => 0 hier=top.t
 +000010  point: type=branch comment=if hier=top.t
 -000000  point: type=branch comment=else hier=top.t
 ~000010     if (($dist_normal(result, 2, 3) != 0) && foo) bump <= bump + 1;
--000000  point: type=expr comment=(($dist_normal(result, 32'sh2, 32'sh3) != 32'sh0)==0) => 0 hier=top.t
+-000002  point: type=expr comment=(($dist_normal(result, 32'sh2, 32'sh3) != 32'sh0)==0) => 0 hier=top.t
-+000010  point: type=expr comment=(($dist_normal(result, 32'sh2, 32'sh3) != 32'sh0)==1 && foo==1) => 1 hier=top.t
+-000009  point: type=expr comment=(($dist_normal(result, 32'sh2, 32'sh3) != 32'sh0)==1 && foo==1) => 1 hier=top.t
 -000000  point: type=expr comment=(foo==0) => 0 hier=top.t
 +000010  point: type=branch comment=if hier=top.t
 -000000  point: type=branch comment=else hier=top.t
-~000010     if (($dist_t(result, 2) != 0) && foo) bump <= bump + 1;
+%000007     if (($dist_t(result, 2) != 0) && foo) bump <= bump + 1;
--000000  point: type=expr comment=(($dist_t(result, 32'sh2) != 32'sh0)==0) => 0 hier=top.t
+-000005  point: type=expr comment=(($dist_t(result, 32'sh2) != 32'sh0)==0) => 0 hier=top.t
--000000  point: type=expr comment=(($dist_t(result, 32'sh2) != 32'sh0)==1 && foo==1) => 1 hier=top.t
+-000007  point: type=expr comment=(($dist_t(result, 32'sh2) != 32'sh0)==1 && foo==1) => 1 hier=top.t
 -000000  point: type=expr comment=(foo==0) => 0 hier=top.t
--000000  point: type=branch comment=if hier=top.t
+-000007  point: type=branch comment=if hier=top.t
-+000010  point: type=branch comment=else hier=top.t
+-000003  point: type=branch comment=else hier=top.t
-~000010     if (($dist_chi_square(result, 2) != 0) && foo) bump <= bump + 1;
+%000009     if (($dist_chi_square(result, 2) != 0) && foo) bump <= bump + 1;
 -000000  point: type=expr comment=(($dist_chi_square(result, 32'sh2) != 32'sh0)==0) => 0 hier=top.t
-+000010  point: type=expr comment=(($dist_chi_square(result, 32'sh2) != 32'sh0)==1 && foo==1) => 1 hier=top.t
+-000009  point: type=expr comment=(($dist_chi_square(result, 32'sh2) != 32'sh0)==1 && foo==1) => 1 hier=top.t
 -000000  point: type=expr comment=(foo==0) => 0 hier=top.t
-+000010  point: type=branch comment=if hier=top.t
+-000006  point: type=branch comment=if hier=top.t
--000000  point: type=branch comment=else hier=top.t
+-000004  point: type=branch comment=else hier=top.t
-~000010     if (($dist_exponential(result, 2) != 0) && foo) bump <= bump + 1;
+%000008     if (($dist_exponential(result, 2) != 0) && foo) bump <= bump + 1;
--000000  point: type=expr comment=(($dist_exponential(result, 32'sh2) != 32'sh0)==0) => 0 hier=top.t
+-000002  point: type=expr comment=(($dist_exponential(result, 32'sh2) != 32'sh0)==0) => 0 hier=top.t
--000000  point: type=expr comment=(($dist_exponential(result, 32'sh2) != 32'sh0)==1 && foo==1) => 1 hier=top.t
+-000006  point: type=expr comment=(($dist_exponential(result, 32'sh2) != 32'sh0)==1 && foo==1) => 1 hier=top.t
 -000000  point: type=expr comment=(foo==0) => 0 hier=top.t
-+000010  point: type=branch comment=if hier=top.t
+-000008  point: type=branch comment=if hier=top.t
--000000  point: type=branch comment=else hier=top.t
+-000002  point: type=branch comment=else hier=top.t
 ~000010     if (($dist_poisson(result, 2) != 0) && foo) bump <= bump + 1;
-+000010  point: type=expr comment=(($dist_poisson(result, 32'sh2) != 32'sh0)==0) => 0 hier=top.t
+-000002  point: type=expr comment=(($dist_poisson(result, 32'sh2) != 32'sh0)==0) => 0 hier=top.t
-+000010  point: type=expr comment=(($dist_poisson(result, 32'sh2) != 32'sh0)==1 && foo==1) => 1 hier=top.t
+-000009  point: type=expr comment=(($dist_poisson(result, 32'sh2) != 32'sh0)==1 && foo==1) => 1 hier=top.t
 -000000  point: type=expr comment=(foo==0) => 0 hier=top.t
 +000010  point: type=branch comment=if hier=top.t
 -000000  point: type=branch comment=else hier=top.t

test_regress/t/t_rand_dist_seed.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('vlt')
+
+test.compile(verilator_flags2=["--binary"])
+
+test.execute()
+
+test.passes()

test_regress/t/t_rand_dist_seed.v

@@ -0,0 +1,83 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain.
+// SPDX-FileCopyrightText: 2026 Wilson Snyder
+// SPDX-License-Identifier: CC0-1.0
+
+// verilog_format: off
+`define stop $stop
+`define checkd(gotv,expv) do if ((gotv) !== (expv)) begin $write("%%Error: %s:%0d:  got=%0d exp=%0d (%s !== %s)\n", `__FILE__,`__LINE__, (gotv), (expv), `"gotv`", `"expv`"); `stop; end while(0);
+// verilog_format: on
+
+module t;
+
+  logic clk = 0;
+  always #5 clk = ~clk;
+
+  localparam CYCLES = 10;
+
+  int cyc = 0;
+
+  wire logic last = cyc == CYCLES - 1;
+
+  // Reports and returns zero if any two of the samples are the same
+  function automatic bit all_different(input int samples[CYCLES]);
+    for (int i = 0; i < CYCLES; ++i) begin
+      for (int j = i + 1; j < CYCLES; ++j) begin
+        if (samples[i] === samples[j]) begin
+          $write("%%Error: samples %0d and %0d are both %0d\n", i, j, samples[i]);
+          return 1'b0;
+        end
+      end
+    end
+    return 1'b1;
+  endfunction
+
+  // A seed must be referred to by the call only for this test to be effective
+
+  // 2 operand $dist_*
+  int dist_bi_seed;
+  int dist_bi_values[CYCLES];
+
+  // 3 operand $dist_*
+  int dist_tri_seed;
+  int dist_tri_values[CYCLES];
+
+  // $random
+  int random_seed;
+  int random_values[CYCLES];
+
+  // $urandom - seed or this is input, not inout
+  int urandom_seed = 32'h4567_89ab;
+
+  always @(posedge clk) begin
+    cyc <= cyc + 1;
+
+    // 2 operand $dist_*
+    dist_bi_values[cyc] = $dist_exponential(dist_bi_seed, 1000000);
+    if (last) begin
+      `checkd(all_different(dist_bi_values), 1'b1);
+    end
+
+    // 3 operand $dist_*
+    dist_tri_values[cyc] = $dist_normal(dist_tri_seed, 100, 1000000);
+    if (last) begin
+      `checkd(all_different(dist_tri_values), 1'b1);
+    end
+
+    // $random
+    random_values[cyc] = $random(random_seed);
+    if (last) begin
+      `checkd(all_different(random_values), 1'b1);
+    end
+
+    // $urandom - seed must not change
+    void'($urandom(urandom_seed));
+    `checkd(urandom_seed, 32'h4567_89ab);
+
+    if (last) begin
+      $write("*-* All Finished *-*\n");
+      $finish;
+    end
+  end
+endmodule