Handle range offsets in packed arrays within packed structs

This brings the metadata for packed arrays in packed structs
in line with the metadata for unpacked arrays, and correctly
handles the case when both lsb and msb in an address range are
non-zero.

frontends/ast/simplify.cc

@@ -278,17 +278,21 @@ static int range_width(AstNode *node, AstNode *rnode)
 	log_file_error(node->filename, node->location.first_line, "Unpacked array in packed struct/union member %s\n", node->str.c_str());
 }
 
-static void save_struct_array_width(AstNode *node, int width)
+static void save_struct_range_dimensions(AstNode *node, AstNode *rnode)
 {
-	// stash the stride for the array
-	node->multirange_dimensions.push_back(width);
-
+	node->multirange_dimensions.push_back(rnode->range_right);
+	node->multirange_dimensions.push_back(range_width(node, rnode));
+	node->multirange_swapped.push_back(rnode->range_swapped);
 }
 
-static void save_struct_range_swapped(AstNode *node, bool range_swapped)
+static int get_struct_range_offset(AstNode *node, int dimension)
 {
-	node->multirange_swapped.push_back(range_swapped);
+	return node->multirange_dimensions[2*dimension];
+}
 
+static int get_struct_range_width(AstNode *node, int dimension)
+{
+	return node->multirange_dimensions[2*dimension + 1];
 }
 
 static int size_packed_struct(AstNode *snode, int base_offset)
@@ -322,14 +326,17 @@ static int size_packed_struct(AstNode *snode, int base_offset)
 					if (node->children[1]->type == AST_RANGE) {
 						// Unpacked array, e.g. bit [63:0] a [0:3]
 						auto rnode = node->children[1];
-						// C-style array size, e.g. bit [63:0] a [4]
-						bool c_type = rnode->children.size() == 1;
-						int array_count = c_type ? rnode->range_left : range_width(node, rnode);
-						save_struct_array_width(node, array_count);
-						save_struct_range_swapped(node, rnode->range_swapped || c_type);
-						save_struct_array_width(node, width);
-						save_struct_range_swapped(node, node->children[0]->range_swapped);
-						width *= array_count;
+						if (rnode->children.size() == 1) {
+							// C-style array size, e.g. bit [63:0] a [4]
+							node->multirange_dimensions.push_back(0);
+							node->multirange_dimensions.push_back(rnode->range_left);
+							node->multirange_swapped.push_back(true);
+							width *= rnode->range_left;
+						} else {
+							save_struct_range_dimensions(node, rnode);
+							width *= range_width(node, rnode);
+						}
+						save_struct_range_dimensions(node, node->children[0]);
 					}
 					else {
 						// The Yosys extension for unpacked arrays in packed structs / unions
@@ -338,8 +345,7 @@ static int size_packed_struct(AstNode *snode, int base_offset)
 					}
 				} else {
 					// Vector
-					save_struct_array_width(node, width);
-					save_struct_range_swapped(node, node->children[0]->range_swapped);
+					save_struct_range_dimensions(node, node->children[0]);
 				}
 				// range nodes are now redundant
 				for (AstNode *child : node->children)
@@ -355,10 +361,8 @@ static int size_packed_struct(AstNode *snode, int base_offset)
 				}
 				width = 1;
 				for (auto rnode : node->children[0]->children) {
-					int rwidth = range_width(node, rnode);
-					save_struct_array_width(node, rwidth);
-					save_struct_range_swapped(node, rnode->range_swapped);
-					width *= rwidth;
+					save_struct_range_dimensions(node, rnode);
+					width *= range_width(node, rnode);
 				}
 				// range nodes are now redundant
 				for (AstNode *child : node->children)
@@ -422,9 +426,14 @@ static AstNode *normalize_struct_index(AstNode *expr, AstNode *member_node, int
 {
 	expr = expr->clone();
 
+	int offset = get_struct_range_offset(member_node, dimension);
+	if (offset) {
+		expr = new AstNode(AST_SUB, expr, node_int(offset));
+	}
+
 	if (member_node->multirange_swapped[dimension]) {
 		// The dimension has swapped range; swap index into the struct accordingly.
-		int msb = member_node->multirange_dimensions[dimension] - 1;
+		int msb = get_struct_range_width(member_node, dimension) - 1;
 		expr = new AstNode(AST_SUB, node_int(msb), expr);
 	}
 
@@ -433,7 +442,7 @@ static AstNode *normalize_struct_index(AstNode *expr, AstNode *member_node, int
 
 static AstNode *struct_index_lsb_offset(AstNode *lsb_offset, AstNode *rnode, AstNode *member_node, int dimension, int &stride)
 {
-	stride /= member_node->multirange_dimensions[dimension];
+	stride /= get_struct_range_width(member_node, dimension);
 	auto right = normalize_struct_index(rnode->children.back(), member_node, dimension);
 	auto offset = stride > 1 ? multiply_by_const(right, stride) : right;
 	return new AstNode(AST_ADD, lsb_offset, offset);

tests/svtypes/struct_array.sv

@@ -141,6 +141,26 @@ module top;
 
 	always_comb assert(s3_llb==80'hFC00_4200_0012_3400_FFFC);
 
+	struct packed {
+		bit [-10:-3] [-2:-1] [5:2] a;
+		bit [0:15] b;		// filler for non-zero offset
+	} s3_off;
+
+	initial begin
+		s3_off = '0;
+
+		s3_off.a[-5:-4] = 16'h1234;
+		s3_off.a[-8] = 8'h42;
+
+		s3_off.a[-10] = '1;
+		s3_off.a[-10][-1][3:0] = '0;
+
+		s3_off.b = '1;
+		s3_off.b[14:15] = '0;
+	end
+
+	always_comb assert(s3_off==80'hFC00_4200_0012_3400_FFFC);
+
 `ifndef VERIFIC
 	// Note that the tests below for unpacked arrays in structs rely on the
 	// fact that they are actually packed in Yosys.