Support for arrays with swapped ranges within structs

This also corrects the implementation of C type arrays within structs.

Fixes #3550

frontends/ast/ast.h

@@ -203,7 +203,7 @@ namespace AST
 
 		// if this is a multirange memory then this vector contains offset and length of each dimension
 		std::vector<int> multirange_dimensions;
-		std::vector<bool> multirange_swapped; // true if range is swapped, not used for structs
+		std::vector<bool> multirange_swapped; // true if range is swapped
 
 		// this is set by simplify and used during RTLIL generation
 		AstNode *id2ast;

frontends/ast/simplify.cc

@@ -285,10 +285,16 @@ static void save_struct_array_width(AstNode *node, int width)
 
 }
 
+static void save_struct_range_swapped(AstNode *node, bool range_swapped)
+{
+	node->multirange_swapped.push_back(range_swapped);
+
+}
+
 static int get_struct_array_width(AstNode *node)
 {
 	// the stride for the array, 1 if not an array
-	return (node->multirange_dimensions.empty() ? 1 : node->multirange_dimensions.back());
+	return (node->multirange_dimensions.size() != 2 ? 1 : node->multirange_dimensions[1]);
 
 }
 
@@ -321,18 +327,22 @@ 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];
-						int array_count = range_width(node, rnode);
-						if (array_count == 1) {
-							// C-type array size e.g. bit [63:0] a [4]
-							array_count = rnode->range_left;
-						}
+						// C-type 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;
 					}
 					else {
 						// array element must be single bit for a packed array
 						struct_array_packing_error(node);
 					}
+				} else {
+					save_struct_array_width(node, width);
+					save_struct_range_swapped(node, node->children[0]->range_swapped);
 				}
 				// range nodes are now redundant
 				for (AstNode *child : node->children)
@@ -347,8 +357,11 @@ static int size_packed_struct(AstNode *snode, int base_offset)
 					struct_array_packing_error(node);
 				}
 				int array_count = range_width(node, rnode->children[0]);
+				save_struct_array_width(node, array_count);
+				save_struct_range_swapped(node, rnode->children[0]->range_swapped);
 				width = range_width(node, rnode->children[1]);
 				save_struct_array_width(node, width);
+				save_struct_range_swapped(node, rnode->children[1]->range_swapped);
 				width *= array_count;
 				// range nodes are now redundant
 				for (AstNode *child : node->children)
@@ -428,8 +441,16 @@ static AstNode *offset_indexed_range(int offset, int stride, AstNode *left_expr,
 	return new AstNode(AST_RANGE, left, right);
 }
 
-static AstNode *make_struct_index_range(AstNode *node, AstNode *rnode, int stride, int offset)
+static AstNode *make_struct_index_range(AstNode *node, AstNode *rnode, int stride, int offset, AstNode *member_node)
 {
+	if (member_node->multirange_swapped[0]) {
+		// The struct item has swapped range; swap index into the struct accordingly.
+		int msb = member_node->multirange_dimensions[0] - 1;
+		for (auto &expr : rnode->children) {
+			expr = new AstNode(AST_SUB, node_int(msb), expr);
+		}
+	}
+
 	// generate a range node to perform either bit or array indexing
 	if (rnode->children.size() == 1) {
 		// index e.g. s.a[i]
@@ -447,6 +468,7 @@ static AstNode *make_struct_index_range(AstNode *node, AstNode *rnode, int strid
 static AstNode *slice_range(AstNode *rnode, AstNode *snode)
 {
 	// apply the bit slice indicated by snode to the range rnode
+	// TODO: Check for swapped indexes - see make_struct_index_range
 	log_assert(rnode->type==AST_RANGE);
 	auto left  = rnode->children[0];
 	auto right = rnode->children[1];
@@ -474,13 +496,13 @@ AstNode *AST::make_struct_member_range(AstNode *node, AstNode *member_node)
 	int stride = get_struct_array_width(member_node);
 	if (node->children.size() == 1 && node->children[0]->type == AST_RANGE) {
 		// bit or array indexing e.g. s.a[2] or s.a[1:0]
-		return make_struct_index_range(node, node->children[0], stride, range_right);
+		return make_struct_index_range(node, node->children[0], stride, range_right, member_node);
 	}
 	else if (node->children.size() == 1 && node->children[0]->type == AST_MULTIRANGE) {
 		// multirange, i.e. bit slice after array index, e.g. s.a[i][p:q]
 		log_assert(stride > 1);
 		auto mrnode = node->children[0];
-		auto element_range = make_struct_index_range(node, mrnode->children[0], stride, range_right);
+		auto element_range = make_struct_index_range(node, mrnode->children[0], stride, range_right, member_node);
 		// then apply bit slice range
 		auto range = slice_range(element_range, mrnode->children[1]);
 		delete element_range;

tests/svtypes/struct_array.sv

@@ -1,7 +1,6 @@
 // test for array indexing in structures
 
 module top;
-
 	struct packed {
 		bit [5:0] [7:0] a;	// 6 element packed array of bytes
 		bit [15:0] b;		// filler for non-zero offset
@@ -39,4 +38,90 @@ module top;
 
 	always_comb assert(s2==80'hFC00_4200_0012_3400_FFFC);
 
+	// Same as s2, but with little endian addressing
+	struct packed {
+		bit [0:7] [7:0] a;	// 8 element packed array of bytes
+		bit [0:15] b;		// filler for non-zero offset
+	} s3;
+
+	initial begin
+		s3 = '0;
+
+		s3.a[5:6] = 16'h1234;
+		s3.a[2] = 8'h42;
+
+		s3.a[0] = '1;
+		s3.a[0][1:0] = '0;
+
+		s3.b = '1;
+		s3.b[14:15] = '0;
+	end
+
+	always_comb assert(s3==80'hFC00_4200_0012_3400_FFFC);
+
+	// Note that the tests below for unpacked arrays in structs rely on the
+	// fact that they are actually packed in Yosys.
+
+	// Same as s2, but using unpacked array syntax
+	struct packed {
+		bit [7:0] a [7:0];	// 8 element unpacked array of bytes
+		bit [15:0] b;		// filler for non-zero offset
+	} s4;
+
+	initial begin
+		s4 = '0;
+
+		s4.a[2:1] = 16'h1234;
+		s4.a[5] = 8'h42;
+
+		s4.a[7] = '1;
+		s4.a[7][1:0] = '0;
+
+		s4.b = '1;
+		s4.b[1:0] = '0;
+	end
+
+	always_comb assert(s4==80'hFC00_4200_0012_3400_FFFC);
+
+	// Same as s3, but using unpacked array syntax
+	struct packed {
+		bit [7:0] a [0:7];	// 8 element unpacked array of bytes
+		bit [0:15] b;		// filler for non-zero offset
+	} s5;
+
+	initial begin
+		s5 = '0;
+
+		s5.a[5:6] = 16'h1234;
+		s5.a[2] = 8'h42;
+
+		s5.a[0] = '1;
+		s5.a[0][1:0] = '0;
+
+		s5.b = '1;
+		s5.b[14:15] = '0;
+	end
+
+	always_comb assert(s5==80'hFC00_4200_0012_3400_FFFC);
+
+	// Same as s5, but using C-type unpacked array syntax
+	struct packed {
+		bit [7:0] a [8];	// 8 element unpacked array of bytes
+		bit [0:15] b;		// filler for non-zero offset
+	} s6;
+
+	initial begin
+		s6 = '0;
+
+		s6.a[5:6] = 16'h1234;
+		s6.a[2] = 8'h42;
+
+		s6.a[0] = '1;
+		s6.a[0][1:0] = '0;
+
+		s6.b = '1;
+		s6.b[14:15] = '0;
+	end
+
+	always_comb assert(s6==80'hFC00_4200_0012_3400_FFFC);
 endmodule