* Fix $fgets being mis-optimized away (#7976).

Fixes #7976.

Changes

@@ -66,6 +66,7 @@ Verilator 5.051 devel
 * Fix lost writes when select width exceeds variable width (#7975). [Bartosz Skorowski]
 * Fix variable scope in unique on dynamic array (#7981). [Kornel Uriasz, Antmicro Ltd.]
 * Fix table optimization causing not contextually convertible to bool error (#7983). [Jakub Michalski]
+* Fix $fgets being mis-optimized away (#7976). [G-A. Kamendje]
 
 
 Verilator 5.050 2026-07-01

src/V3AstNodeExpr.h

@@ -3259,6 +3259,7 @@ public:
     bool sizeMattersRhs() const override { return false; }
     bool isSystemFunc() const override { return true; }
     int instrCount() const override { return widthInstrs() * 64; }
+    bool isPure() override { return false; }  // SPECIAL: $display has 'visual' ordering
 };
 class AstFUngetC final : public AstNodeBiop {
 public:

test_regress/t/t_sys_fgets_loop.dat

@@ -0,0 +1,11 @@
+This is line 0 in test file
+This is line 1 in test file
+This is line 2 in test file
+This is line 3 in test file
+This is line 4 in test file
+This is line 5 in test file
+This is line 6 in test file
+This is line 7 in test file
+This is line 8 in test file
+This is line 8 in test file
+This is line 9 in test file

test_regress/t/t_sys_fgets_loop.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'])
+
+test.execute()
+
+test.passes()

test_regress/t/t_sys_fgets_loop.v

@@ -0,0 +1,57 @@
+// 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
+
+module t;
+
+  task test_read(input integer f, output string l);
+    automatic string line;
+    automatic string buffer = "";
+    automatic integer code;
+
+    if (f == 0) $stop;
+    while (1) begin
+      code = $fgets(line, f);
+      // Uncomment for issue #7976 workaround
+      // $display("code %d => content: %s", code, line);
+      buffer = {buffer, line};
+      if (line == "") begin
+        break;
+      end
+    end
+    l = buffer;
+  endtask
+
+  task test_eof_tsk;
+    automatic integer fd;
+    automatic string test_file_name = "t/t_sys_fgets_loop.dat";
+    automatic string output_line;
+    // Open files
+    fd = $fopen(test_file_name, "r");
+    if (fd == 0) begin
+      $display("ERROR ould not open file '%s' for reading aborting", test_file_name);
+      $fatal(0);
+    end
+
+    while (!$feof(
+        fd
+    )) begin
+      test_read(fd, output_line);
+    end
+    $fclose(fd);
+  endtask
+
+  initial begin
+    test_eof_tsk;
+  end
+
+  initial begin
+    #100;
+
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+
+endmodule