From 891edad53a799332db481767b198af2780a9b23c Mon Sep 17 00:00:00 2001
From: Wilson Snyder <wsnyder@wsnyder.org>
Date: Mon, 5 Nov 2007 14:09:22 +0000
Subject: [PATCH] Fixed generate for loops with constant zero conditions.

git-svn-id: file://localhost/svn/verilator/trunk/verilator@968 77ca24e4-aefa-0310-84f0-b9a241c72d87
---
 Changes                      |  4 ++-
 src/V3Unroll.cpp             | 15 ++++++++---
 test_regress/t/t_gen_for0.pl | 18 ++++++++++++++
 test_regress/t/t_gen_for0.v  | 48 ++++++++++++++++++++++++++++++++++++
 4 files changed, 81 insertions(+), 4 deletions(-)
 create mode 100755 test_regress/t/t_gen_for0.pl
 create mode 100644 test_regress/t/t_gen_for0.v

diff --git a/Changes b/Changes
index 3b7e34195..ebf56a9db 100644
--- a/Changes
+++ b/Changes
@@ -7,7 +7,9 @@ indicates the contributor was also the author of the fix; Thanks!
 
 ***  Support "#delay <statement>;" with associated STMTDLY warning.
 
-**** Fixed divide-by-zero errors in constant propagator.  [Rodney Sinclair]
+**** Fixed generate for loops with constant zero conditions. [Rodney Sinclair]
+
+**** Fixed divide-by-zero errors in constant propagator. [Rodney Sinclair]
 
 **** Fixed wrong result with obscure signed-shift underneath a "? :".
 
diff --git a/src/V3Unroll.cpp b/src/V3Unroll.cpp
index a2ba56324..e5f1733c2 100644
--- a/src/V3Unroll.cpp
+++ b/src/V3Unroll.cpp
@@ -313,9 +313,18 @@ private:
 	    if (nodep->initsp()) V3Const::constifyTree(nodep->initsp());
 	    if (nodep->condp()) V3Const::constifyTree(nodep->condp());
 	    if (nodep->incsp()) V3Const::constifyTree(nodep->incsp());
-	    if (forUnrollCheck(nodep, nodep->initsp(),
-			       NULL, nodep->condp(),
-			       nodep->incsp(), nodep->bodysp())) {
+	    if (nodep->condp()->isZero()) {
+		// We don't need to do any loops.  Remove the GenFor,
+		// Genvar's don't care about any initial assignments.
+		//
+		// Note normal For's can't do exactly this deletion, as
+		// we'd need to initialize the variable to the initial
+		// condition, but they'll become while's which can be
+		// deleted by V3Const.
+		nodep->unlinkFrBack()->deleteTree(); nodep=NULL;
+	    } else if (forUnrollCheck(nodep, nodep->initsp(),
+				      NULL, nodep->condp(),
+				      nodep->incsp(), nodep->bodysp())) {
 		pushDeletep(nodep); nodep=NULL; // Did replacement
 	    } else {
 		nodep->v3error("For loop doesn't have genvar index, or is misformed");
diff --git a/test_regress/t/t_gen_for0.pl b/test_regress/t/t_gen_for0.pl
new file mode 100755
index 000000000..7bfdbe852
--- /dev/null
+++ b/test_regress/t/t_gen_for0.pl
@@ -0,0 +1,18 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("./driver.pl", @ARGV, $0); die; }
+# $Id$
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you can
+# redistribute it and/or modify it under the terms of either the GNU
+# General Public License or the Perl Artistic License.
+
+compile (
+	 );
+
+execute (
+	 check_finished=>1,
+     );
+
+ok(1);
+1;
diff --git a/test_regress/t/t_gen_for0.v b/test_regress/t/t_gen_for0.v
new file mode 100644
index 000000000..79be997b7
--- /dev/null
+++ b/test_regress/t/t_gen_for0.v
@@ -0,0 +1,48 @@
+// $Id$
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2007 by Wilson Snyder.
+
+module t (/*AUTOARG*/
+   // Inputs
+   clk
+   );
+   input clk;
+
+   integer 	cyc=0;
+
+   Testit testit (/*AUTOINST*/
+		  // Inputs
+		  .clk			(clk));
+
+   always @ (posedge clk) begin
+      cyc <= cyc + 1;
+      if (cyc==0) begin
+      end
+      else if (cyc<10) begin
+      end
+      else if (cyc<90) begin
+      end
+      else if (cyc==99) begin
+	 $write("*-* All Finished *-*\n");
+	 $finish;
+      end
+   end
+
+endmodule
+
+module Testit (clk);
+   input clk;
+
+   genvar igen;
+   generate
+      for (igen=0; igen<0; igen=igen+1) begin : test_gen
+	 always @ (posedge clk) begin
+	    $display("igen1 = %d", igen);
+	    $stop;
+	 end
+      end
+   endgenerate
+   
+endmodule