Guard against sign and overflow errors in rvalue array expressions

YosysHQ · Aug 12, 2023 · e06ab0f · e06ab0f
1 parent db4ba06
commit e06ab0f
Showing 1 changed file with 17 additions and 9 deletions.
diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
@@ -2358,6 +2358,10 @@ bool AstNode::simplify(bool const_fold, bool in_lvalue, int stage, int width_hin
 				input_error("Unsupported expression on dynamic range select on signal `%s'!\n", str.c_str());
 		}
 
+		int shift_expr_width_hint = -1;
+		bool shift_expr_sign_hint = true;
+		shift_expr->detectSignWidth(shift_expr_width_hint, shift_expr_sign_hint);
+
 		bool use_case_method = false;
 
 		if (id2ast->attributes.count(ID::nordshift)) {
@@ -2417,12 +2421,9 @@ bool AstNode::simplify(bool const_fold, bool in_lvalue, int stage, int width_hin
 			}
 
 			// Limit case conditions to possible index range.
-			int case_width_hint = -1;
-			bool case_sign_hint = true;
-			shift_expr->detectSignWidth(case_width_hint, case_sign_hint);
-			int max_bits = min(case_width_hint, 31 + case_sign_hint);
-			int max_offset = (1u << (max_bits - case_sign_hint)) - 1;
-			int min_offset = case_sign_hint ? -(1u << (max_bits - 1)) : 0;
+			int max_bits = min(shift_expr_width_hint, 31 + shift_expr_sign_hint);
+			int max_offset = (1u << (max_bits - shift_expr_sign_hint)) - 1;
+			int min_offset = shift_expr_sign_hint ? -(1u << (max_bits - 1)) : 0;
 
 			// New identifier to replace the current rvalue; used as lvalue in AST_COND assignments.
 			AstNode *wire = new AstNode(AST_WIRE, new AstNode(AST_RANGE, node_int(result_width - 1), node_int(0)));
@@ -2443,7 +2444,7 @@ bool AstNode::simplify(bool const_fold, bool in_lvalue, int stage, int width_hin
 				int end_bit = std::min(start_bit + result_width, source_offset + source_width) - 1;
 				if (start_bit/div_stride < min_offset || start_bit/div_stride > max_offset)
 					continue;
-				AstNode *cond = new AstNode(AST_COND, mkconst_int(start_bit/div_stride, case_sign_hint, case_width_hint));
+				AstNode *cond = new AstNode(AST_COND, mkconst_int(start_bit/div_stride, shift_expr_sign_hint, shift_expr_width_hint));
 				AstNode *rvalue = clone();
 				rvalue->delete_children();
 				if (member_node)
@@ -2474,7 +2475,14 @@ bool AstNode::simplify(bool const_fold, bool in_lvalue, int stage, int width_hin
 			if (member_node)
 				rvalue->attributes[ID::wiretype] = member_node->clone();
 
-			if (source_offset != 0) {
+			if (!shift_expr_sign_hint && (source_offset || id2ast->range_swapped)) {
+				// convert to signed while preserving the sign and value
+				shift_expr = new AstNode(AST_TO_SIGNED,
+							 new AstNode(AST_CAST_SIZE,
+								     node_int(shift_expr_width_hint + 1),
+								     shift_expr));
+			}
+			if (source_offset) {
 				// offset the shift amount by the lower bound of the dimension
 				shift_expr = new AstNode(AST_SUB, shift_expr, node_int(source_offset));
 			}
@@ -2485,7 +2493,7 @@ bool AstNode::simplify(bool const_fold, bool in_lvalue, int stage, int width_hin
 
 			// Shift rvalue to the right so that the bit slice starts at bit 0.
 			newNode = new AstNode(AST_CAST_SIZE,
-					      mkconst_int(result_width, true),
+					      node_int(result_width),
 					      new AstNode(AST_SHIFTX, rvalue, shift_expr));
 		}