Miscellaneous improvements and fixes to shift elaboration (v0.9).

This patch ensures that the result of a shift is an undefined value
if the right operand is an undefined value. It also improves the
code generated for right shifts where the right operand is constant
(which fixes the compiler crash on pr3098439b in the test suite).

elab_expr.cc

@@ -509,9 +509,11 @@ NetExpr* PEBinary::elaborate_expr_base_lshift_(Design*des,
 
       if (NetEConst*lpc = dynamic_cast<NetEConst*> (lp)) {
 
-	      // Special case: The left expression is zero. No matter
+	      // Special case: The left expression is zero. If the
-	      // what the shift, the result is going to be zero.
+	      // shift value contains no 'x' or 'z' bits, the result
-	    if (lpc->value().is_defined() && lpc->value().is_zero()) {
+              // is going to be zero.
+	    if (lpc->value().is_defined() && lpc->value().is_zero()
+                && (rp->expr_type() == IVL_VT_BOOL)) {
 
 		  if (debug_elaborate)
 			cerr << get_fileline() << ": debug: "
@@ -527,6 +529,11 @@ NetExpr* PEBinary::elaborate_expr_base_lshift_(Design*des,
 		    // Handle the super-special case that both
 		    // operands are constants. Precalculate the
 		    // entire value here.
+                  if (!rpc->value().is_defined()) {
+		        tmp = make_const_x(use_wid);
+		        tmp->set_line(*this);
+		        return tmp;
+                  }
 		  verinum lpval = lpc->value();
 		  unsigned shift = rpc->value().as_ulong();
 		  verinum result = lpc->value() << shift;
@@ -566,6 +573,20 @@ NetExpr* PEBinary::elaborate_expr_base_lshift_(Design*des,
 	    }
 
       } else if (NetEConst*rpc = dynamic_cast<NetEConst*> (rp)) {
+              // Special case: The shift value contains 'x' or 'z' bits.
+              // Elaborate as a constant-x.
+            if (!rpc->value().is_defined()) {
+
+                  if (debug_elaborate)
+                        cerr << get_fileline() << ": debug: " 
+                             << "Shift by undefined value. "
+                             << "Elaborate as constant 'x'." << endl;
+      
+                  tmp = make_const_x(expr_wid);
+                  tmp->set_line(*this);
+                  return tmp;
+            }
+
 	    long shift = rpc->value().as_long();
 	    use_wid = lp->expr_width();
 	    if (expr_wid > 0)
@@ -594,6 +615,11 @@ NetExpr* PEBinary::elaborate_expr_base_lshift_(Design*des,
 	      // default way.
 	    if (expr_wid >= 0)
 		  lp = pad_to_width(lp, expr_wid, *this);
+
+            rp = new NetESelect(rp, 0, rp->expr_width());
+            rp->cast_signed(false);
+            rp->set_line(*this);
+
 	    tmp = new NetEBShift(op_, lp, rp);
       }
 
@@ -631,9 +657,11 @@ NetExpr* PEBinary::elaborate_expr_base_rshift_(Design*des,
 
       if (NetEConst*lpc = dynamic_cast<NetEConst*> (lp)) {
 
-	      // Special case: The left expression is zero. No matter
+	      // Special case: The left expression is zero. If the
-	      // what the shift, the result is going to be zero.
+	      // shift value contains no 'x' or 'z' bits, the result
-	    if (lpc->value().is_defined() && lpc->value().is_zero()) {
+              // is going to be zero.
+	    if (lpc->value().is_defined() && lpc->value().is_zero()
+                && (rp->expr_type() == IVL_VT_BOOL)) {
 
 		  if (debug_elaborate)
 			cerr << get_fileline() << ": debug: "
@@ -647,6 +675,20 @@ NetExpr* PEBinary::elaborate_expr_base_rshift_(Design*des,
       }
 
       if (NetEConst*rpc = dynamic_cast<NetEConst*> (rp)) {
+              // Special case: The shift value contains 'x' or 'z' bits.
+              // Elaborate as a constant-x.
+            if (!rpc->value().is_defined()) {
+
+                  if (debug_elaborate)
+                        cerr << get_fileline() << ": debug: " 
+                             << "Shift by undefined value. "
+                             << "Elaborate as constant 'x'." << endl;
+      
+                  tmp = make_const_x(expr_wid);
+                  tmp->set_line(*this);
+                  return tmp;
+            }
+
 	    unsigned long shift = rpc->value().as_ulong();
 
 	      // Special case: The shift is the size of the entire
@@ -692,36 +734,16 @@ NetExpr* PEBinary::elaborate_expr_base_rshift_(Design*des,
 		  tmp = pad_to_width(tmp, use_wid, *this);
 		  return tmp;
 	    }
-
-	      // If this is lossless, then pad the left expression
-	      // enough to cover the right shift.
-	    if (expr_wid == -2 && use_wid+shift > lp->expr_width()) {
-	          lp->cast_signed(lp->has_sign() && op_=='R');
-		  lp = pad_to_width(lp, use_wid + shift, *this);
-	    }
-
-	    tmp = new NetEConst(verinum(shift));
-	    tmp->set_line(*this);
-	    long tmp_wid = lp->expr_width() - shift;
-	    if (tmp_wid > use_wid)
-		  tmp_wid = use_wid;
-
-	    ivl_assert(*this, tmp_wid > 0);
-	    ivl_assert(*this, use_wid > 0);
-
-	      // Implement the right-shift by part-selecting the low
-	      // bits out. Pad the result of the part select back out
-	      // to the desired size.
-	    tmp = new NetESelect(lp, tmp, tmp_wid);
-	    tmp->set_line(*this);
-	    tmp->cast_signed(lp->has_sign() && op_=='R');
-	    tmp = pad_to_width(tmp, use_wid, *this);
-	    return tmp;
       }
 
 	// Fallback, handle the general case.
       if (expr_wid > 0)
 	    lp = pad_to_width(lp, expr_wid, *this);
+
+      rp = new NetESelect(rp, 0, rp->expr_width());
+      rp->cast_signed(false);
+      rp->set_line(*this);
+
       tmp = new NetEBShift(op_, lp, rp);
       tmp->set_line(*this);
       return tmp;

tgt-vvp/eval_expr.c

@@ -1157,8 +1157,9 @@ static struct vector_info draw_binary_expr_lrs(ivl_expr_t expr, unsigned wid)
 	  case 'l': /* << (left shift) */
 	    lv = draw_eval_expr_wid(le, wid, 0);
 
-	      /* shifting 0 gets 0. */
+	      /* Shifting 0 gets 0, if we can be sure the shift value
-	    if (lv.base == 0)
+                 contains no 'x' or 'z' bits. */
+	    if ((lv.base == 0) && (ivl_expr_value(re) == IVL_VT_BOOL))
 		  return lv;
 
 	    if (lv.base < 4) {
@@ -1193,8 +1194,9 @@ static struct vector_info draw_binary_expr_lrs(ivl_expr_t expr, unsigned wid)
 		  lv = draw_eval_expr_wid(le, ivl_expr_width(le), 0);
 	    }
 
-	      /* shifting 0 gets 0. */
+	      /* Shifting 0 gets 0, if we can be sure the shift value
-	    if (lv.base == 0)
+                 contains no 'x' or 'z' bits. */
+	    if ((lv.base == 0) && (ivl_expr_value(re) == IVL_VT_BOOL))
 		  return lv;
 
 	    if (lv.base < 4) {
@@ -1229,13 +1231,15 @@ static struct vector_info draw_binary_expr_lrs(ivl_expr_t expr, unsigned wid)
 		  lv = draw_eval_expr_wid(le, ivl_expr_width(le), 0);
 	    }
 
-	      /* shifting 0 gets 0. */
+	      /* Shifting 0 gets 0, if we can be sure the shift value
-	    if (lv.base == 0)
+                 contains no 'x' or 'z' bits. */
+	    if ((lv.base == 0) && (ivl_expr_value(re) == IVL_VT_BOOL))
 		  return lv;
 
-	      /* Sign extend any constant begets itself, if this
+	      /* Similarly, sign extending any constant bit begets itself,
-		 expression is signed. */
+                 if this expression is signed. */
-	    if ((lv.base < 4) && (ivl_expr_signed(expr)))
+	    if ((lv.base < 4) && ivl_expr_signed(expr)
+                && (ivl_expr_value(re) == IVL_VT_BOOL))
 		  return lv;
 
 	    if (lv.base < 4) {