Improved rewrite code for writing to bit slice (disabled for now)

This adds the new rewrite rule. But it's still missing a check that makes
sure the new rewrite rule is actually a valid substitute in the always
block being processed. Therefore the new rewrite rule is just disabled
for now.

Signed-off-by: Claire Wolf <claire@symbioticeda.com>

1 files changed, 64 insertions, 12 deletions

diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
index cb89f58ba..e181af140 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -1721,8 +1721,10 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
 	}
 
 	// replace dynamic ranges in left-hand side expressions (e.g. "foo[bar] <= 1'b1;") with
-	// a big case block that selects the correct single-bit assignment.
-	if (type == AST_ASSIGN_EQ || type == AST_ASSIGN_LE) {
+	// either a big case block that selects the correct single-bit assignment, or mask and
+	// shift operations.
+	if (type == AST_ASSIGN_EQ || type == AST_ASSIGN_LE)
+	{
 		if (children[0]->type != AST_IDENTIFIER || children[0]->children.size() == 0)
 			goto skip_dynamic_range_lvalue_expansion;
 		if (children[0]->children[0]->range_valid || did_something)
@@ -1731,10 +1733,13 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
 			goto skip_dynamic_range_lvalue_expansion;
 		if (!children[0]->id2ast->range_valid)
 			goto skip_dynamic_range_lvalue_expansion;
+
 		int source_width = children[0]->id2ast->range_left - children[0]->id2ast->range_right + 1;
 		int result_width = 1;
+
 		AstNode *shift_expr = NULL;
 		AstNode *range = children[0]->children[0];
+
 		if (range->children.size() == 1) {
 			shift_expr = range->children[0]->clone();
 		} else {
@@ -1747,19 +1752,66 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
 				log_file_error(filename, location.first_line, "Unsupported expression on dynamic range select on signal `%s'!\n", str.c_str());
 			result_width = abs(int(left_at_zero_ast->integer - right_at_zero_ast->integer)) + 1;
 		}
-		did_something = true;
-		newNode = new AstNode(AST_CASE, shift_expr);
-		for (int i = 0; i < source_width; i++) {
-			int start_bit = children[0]->id2ast->range_right + i;
-			AstNode *cond = new AstNode(AST_COND, mkconst_int(start_bit, true));
+
+		if (1)
+		{
+			// big case block
+
+			did_something = true;
+			newNode = new AstNode(AST_CASE, shift_expr);
+			for (int i = 0; i < source_width; i++) {
+				int start_bit = children[0]->id2ast->range_right + i;
+				AstNode *cond = new AstNode(AST_COND, mkconst_int(start_bit, true));
+				AstNode *lvalue = children[0]->clone();
+				lvalue->delete_children();
+				int end_bit = std::min(start_bit+result_width,source_width) - 1;
+				lvalue->children.push_back(new AstNode(AST_RANGE,
+						mkconst_int(end_bit, true), mkconst_int(start_bit, true)));
+				cond->children.push_back(new AstNode(AST_BLOCK, new AstNode(type, lvalue, children[1]->clone())));
+				newNode->children.push_back(cond);
+			}
+		}
+		else
+		{
+			// mask and shift operations, disabled for now
+
+			AstNode *wire_mask = new AstNode(AST_WIRE, new AstNode(AST_RANGE, mkconst_int(source_width-1, true), mkconst_int(0, true)));
+			wire_mask->str = stringf("$bitselwrite$mask$%s:%d$%d", filename.c_str(), location.first_line, autoidx++);
+			wire_mask->attributes["\\nosync"] = AstNode::mkconst_int(1, false);
+			wire_mask->is_logic = true;
+			while (wire_mask->simplify(true, false, false, 1, -1, false, false)) { }
+			current_ast_mod->children.push_back(wire_mask);
+
+			AstNode *wire_data = new AstNode(AST_WIRE, new AstNode(AST_RANGE, mkconst_int(source_width-1, true), mkconst_int(0, true)));
+			wire_data->str = stringf("$bitselwrite$data$%s:%d$%d", filename.c_str(), location.first_line, autoidx++);
+			wire_data->attributes["\\nosync"] = AstNode::mkconst_int(1, false);
+			wire_data->is_logic = true;
+			while (wire_data->simplify(true, false, false, 1, -1, false, false)) { }
+			current_ast_mod->children.push_back(wire_data);
+
+			did_something = true;
+			newNode = new AstNode(AST_BLOCK);
+
 			AstNode *lvalue = children[0]->clone();
 			lvalue->delete_children();
-			int end_bit = std::min(start_bit+result_width,source_width) - 1;
-			lvalue->children.push_back(new AstNode(AST_RANGE,
-					mkconst_int(end_bit, true), mkconst_int(start_bit, true)));
-			cond->children.push_back(new AstNode(AST_BLOCK, new AstNode(type, lvalue, children[1]->clone())));
-			newNode->children.push_back(cond);
+
+			AstNode *ref_mask = new AstNode(AST_IDENTIFIER);
+			ref_mask->str = wire_mask->str;
+			ref_mask->was_checked = true;
+
+			AstNode *ref_data = new AstNode(AST_IDENTIFIER);
+			ref_data->str = wire_data->str;
+			ref_data->was_checked = true;
+
+			AstNode *shamt = shift_expr;
+
+			newNode->children.push_back(new AstNode(AST_ASSIGN_EQ, ref_mask->clone(),
+					new AstNode(AST_SHIFT_LEFT, mkconst_bits(std::vector<RTLIL::State>(result_width, State::S1), false), shamt->clone())));
+			newNode->children.push_back(new AstNode(AST_ASSIGN_EQ, ref_data->clone(),
+					new AstNode(AST_SHIFT_LEFT, new AstNode(AST_BIT_AND, mkconst_bits(std::vector<RTLIL::State>(result_width, State::S1), false), children[1]->clone()), shamt)));
+			newNode->children.push_back(new AstNode(type, lvalue, new AstNode(AST_BIT_OR, new AstNode(AST_BIT_AND, lvalue->clone(), new AstNode(AST_BIT_NOT, ref_mask)), ref_data)));
 		}
+
 		goto apply_newNode;
 	}
 skip_dynamic_range_lvalue_expansion:;