Fix incorrect temporary insertion in loop conditions with statements (#4873)

When the condition of an AstWhile loop contains a statement (e.g.
through an AstExprStmt), temporaries inserted in that statement need to
go before that statement, not in the AstWhile precondition.

src/V3Premit.cpp

@@ -176,8 +176,10 @@ class PremitVisitor final : public VNVisitor {
     if (stmtp->user1SetOnce()) return; \
     VL_RESTORER(m_assignLhs); \
     VL_RESTORER(m_stmtp); \
+    VL_RESTORER(m_inWhileCondp); \
     m_assignLhs = false; \
-    m_stmtp = stmtp
+    m_stmtp = stmtp; \
+    m_inWhileCondp = nullptr
 
     void visit(AstWhile* nodep) override {
         UINFO(4, "  WHILE  " << nodep << endl);

test_regress/t/t_while_cond_is_stmt.pl

@@ -0,0 +1,18 @@
+#!/usr/bin/env perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2024 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.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+scenarios(simulator => 1);
+
+compile();
+
+execute();
+
+ok(1);
+1;

test_regress/t/t_while_cond_is_stmt.v

@@ -0,0 +1,29 @@
+// DESCRIPTION: Verilator: Test of select from constant
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2024 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+module t;
+
+    function int unsigned nth_power_of_2(input int unsigned n);
+        nth_power_of_2 = 1;
+        while (n != 0) begin
+            n = n - 1;
+            nth_power_of_2 = nth_power_of_2 << 1;
+        end
+    endfunction
+
+    initial begin
+        // Evaluating the function call in the loop condition used
+        // to cause an infinite loop at run-time
+        while (nth_power_of_2(8) != 256) begin
+            $display("2**8 != 256 ?!");
+            $stop;
+        end
+
+        $write("*-* All Finished *-*\n");
+        $finish;
+    end
+
+endmodule