From e5f49baaac5817bff56f65cc59c261b71fffc351 Mon Sep 17 00:00:00 2001
From: Martin Whitaker <icarus@martin-whitaker.me.uk>
Date: Mon, 25 Aug 2014 20:27:22 +0100
Subject: [PATCH] Fix for GitHub issue #37 - bug in expression width pruning.

If an expression contains a division, remainder, or right shift operation,
set the expression min_width to UINT_MAX to flag that the expression width
cannot be pruned. Using UINT_MAX ensures that the min_width won't change
as we continue to elaborate the expression.
---
 elab_expr.cc |  4 ++--
 netmisc.cc   | 10 ++++++----
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/elab_expr.cc b/elab_expr.cc
index 11e7695ba..eeab59de9 100644
--- a/elab_expr.cc
+++ b/elab_expr.cc
@@ -310,7 +310,7 @@ unsigned PEBinary::test_width(Design*des, NetScope*scope, width_mode_t&mode)
 
                 case '%':
                 case '/':
-                  min_width_ = max(min_width_, expr_width_);
+                  min_width_ = UINT_MAX; // disable width pruning
                   break;
 
                 case 'l': // <<  Should be handled by PEBShift
@@ -816,7 +816,7 @@ unsigned PEBLeftWidth::test_width(Design*des, NetScope*scope, width_mode_t&mode)
       if (op_ == 'l')
             min_width_ = left_->min_width();
       else
-            min_width_ = expr_width_;
+            min_width_ = UINT_MAX; // disable width pruning
 
       return fix_width_(mode);
 }
diff --git a/netmisc.cc b/netmisc.cc
index ee69e8e6e..585388f06 100644
--- a/netmisc.cc
+++ b/netmisc.cc
@@ -20,6 +20,7 @@
 # include "config.h"
 
 # include  <cstdlib>
+# include  <climits>
 # include  "netlist.h"
 # include  "netvector.h"
 # include  "netmisc.h"
@@ -764,12 +765,13 @@ NetExpr* elab_and_eval(Design*des, NetScope*scope, PExpr*pe,
 
         // If we can get the same result using a smaller expression
         // width, do so.
-      if ((context_width > 0) && (pe->expr_type() != IVL_VT_REAL)
-          && (expr_width > pos_context_width)) {
-            expr_width = max(pe->min_width(), pos_context_width);
+      unsigned min_width = pe->min_width();
+      if ((min_width != UINT_MAX) && (pe->expr_type() != IVL_VT_REAL)
+          && (pos_context_width > 0) && (expr_width > pos_context_width)) {
+            expr_width = max(min_width, pos_context_width);
 
             if (debug_elaborate) {
-                  cerr << pe->get_fileline() << ":        "
+                  cerr << pe->get_fileline() << ":              : "
                        << "pruned to width=" << expr_width << endl;
             }
       }