diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
index 945f286a1..51ed95621 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -2966,96 +2966,67 @@ bool AstNode::simplify(bool const_fold, int stage, int width_hint, bool sign_hin
}
} else {
// mask and shift operations
-
- AstNode *wire_mask = new AstNode(AST_WIRE, new AstNode(AST_RANGE, mkconst_int(wire_width-1, true), mkconst_int(0, true)));
- wire_mask->str = stringf("$bitselwrite$mask$%s:%d$%d", RTLIL::encode_filename(filename).c_str(), location.first_line, autoidx++);
- wire_mask->set_attribute(ID::nosync, AstNode::mkconst_int(1, false));
- wire_mask->is_logic = true;
- while (wire_mask->simplify(true, 1, -1, false)) { }
- current_ast_mod->children.push_back(wire_mask);
-
- AstNode *wire_data = new AstNode(AST_WIRE, new AstNode(AST_RANGE, mkconst_int(wire_width-1, true), mkconst_int(0, true)));
- wire_data->str = stringf("$bitselwrite$data$%s:%d$%d", RTLIL::encode_filename(filename).c_str(), location.first_line, autoidx++);
- wire_data->set_attribute(ID::nosync, AstNode::mkconst_int(1, false));
- wire_data->is_logic = true;
- while (wire_data->simplify(true, 1, -1, false)) { }
- current_ast_mod->children.push_back(wire_data);
-
- int shamt_width_hint = -1;
- bool shamt_sign_hint = true;
- shift_expr->detectSignWidth(shamt_width_hint, shamt_sign_hint);
-
- AstNode *wire_sel = new AstNode(AST_WIRE, new AstNode(AST_RANGE, mkconst_int(shamt_width_hint-1, true), mkconst_int(0, true)));
- wire_sel->str = stringf("$bitselwrite$sel$%s:%d$%d", RTLIL::encode_filename(filename).c_str(), location.first_line, autoidx++);
- wire_sel->set_attribute(ID::nosync, AstNode::mkconst_int(1, false));
- wire_sel->is_logic = true;
- wire_sel->is_signed = shamt_sign_hint;
- while (wire_sel->simplify(true, 1, -1, false)) { }
- current_ast_mod->children.push_back(wire_sel);
-
- did_something = true;
- newNode = new AstNode(AST_BLOCK);
+ // dst = (dst & ~(width'1 << lsb)) | unsigned'(width'(src)) << lsb)
AstNode *lvalue = children[0]->clone();
lvalue->delete_children();
if (member_node)
lvalue->set_attribute(ID::wiretype, member_node->clone());
- AstNode *ref_mask = new AstNode(AST_IDENTIFIER);
- ref_mask->str = wire_mask->str;
- ref_mask->id2ast = wire_mask;
- ref_mask->was_checked = true;
-
- AstNode *ref_data = new AstNode(AST_IDENTIFIER);
- ref_data->str = wire_data->str;
- ref_data->id2ast = wire_data;
- ref_data->was_checked = true;
-
- AstNode *ref_sel = new AstNode(AST_IDENTIFIER);
- ref_sel->str = wire_sel->str;
- ref_sel->id2ast = wire_sel;
- ref_sel->was_checked = true;
-
AstNode *old_data = lvalue->clone();
if (type == AST_ASSIGN_LE)
old_data->lookahead = true;
- AstNode *s = new AstNode(AST_ASSIGN_EQ, ref_sel->clone(), shift_expr);
- newNode->children.push_back(s);
+ int shift_width_hint;
+ bool shift_sign_hint;
+ shift_expr->detectSignWidth(shift_width_hint, shift_sign_hint);
- AstNode *shamt = ref_sel;
+ // All operations are carried out in a new block.
+ newNode = new AstNode(AST_BLOCK);
- // convert to signed while preserving the sign and value
- shamt = new AstNode(AST_CAST_SIZE, mkconst_int(shamt_width_hint + 1, true), shamt);
- shamt = new AstNode(AST_TO_SIGNED, shamt);
+ // Temporary register holding the result of the bit- or part-select position expression.
+ AstNode *pos = mktemp_logic("$bitselwrite$pos$", current_ast_mod, true, shift_width_hint - 1, 0, shift_sign_hint);
+ newNode->children.push_back(new AstNode(AST_ASSIGN_EQ, pos, shift_expr));
+
+ // Calculate lsb from position.
+ AstNode *shift_val = pos->clone();
+
+ // If the expression is signed, we must add an extra bit for possible negation of the most negative number.
+ // If the expression is unsigned, we must add an extra bit for sign.
+ shift_val = new AstNode(AST_CAST_SIZE, mkconst_int(shift_width_hint + 1, true), shift_val);
+ if (!shift_sign_hint)
+ shift_val = new AstNode(AST_TO_SIGNED, shift_val);
// offset the shift amount by the lower bound of the dimension
- int start_bit = wire_offset;
- shamt = new AstNode(AST_SUB, shamt, mkconst_int(start_bit, true));
+ if (wire_offset != 0)
+ shift_val = new AstNode(AST_SUB, shift_val, mkconst_int(wire_offset, true));
// reflect the shift amount if the dimension is swapped
if (children[0]->id2ast->range_swapped)
- shamt = new AstNode(AST_SUB, mkconst_int(wire_width - result_width, true), shamt);
+ shift_val = new AstNode(AST_SUB, mkconst_int(wire_width - result_width, true), shift_val);
// AST_SHIFT uses negative amounts for shifting left
- shamt = new AstNode(AST_NEG, shamt);
+ shift_val = new AstNode(AST_NEG, shift_val);
- AstNode *t;
-
- t = mkconst_bits(std::vector<RTLIL::State>(result_width, State::S1), false);
- t = new AstNode(AST_SHIFT, t, shamt->clone());
- t = new AstNode(AST_ASSIGN_EQ, ref_mask->clone(), t);
- newNode->children.push_back(t);
-
- t = new AstNode(AST_BIT_AND, mkconst_bits(std::vector<RTLIL::State>(result_width, State::S1), false), children[1]->clone());
- t = new AstNode(AST_SHIFT, t, shamt);
- t = new AstNode(AST_ASSIGN_EQ, ref_data->clone(), t);
- newNode->children.push_back(t);
-
- t = new AstNode(AST_BIT_AND, old_data, new AstNode(AST_BIT_NOT, ref_mask));
- t = new AstNode(AST_BIT_OR, t, ref_data);
- t = new AstNode(type, lvalue, t);
- newNode->children.push_back(t);
+ // dst = (dst & ~(width'1 << lsb)) | unsigned'(width'(src)) << lsb)
+ did_something = true;
+ AstNode *bitmask = mkconst_bits(std::vector<RTLIL::State>(result_width, State::S1), false);
+ newNode->children.push_back(
+ new AstNode(type,
+ lvalue,
+ new AstNode(AST_BIT_OR,
+ new AstNode(AST_BIT_AND,
+ old_data,
+ new AstNode(AST_BIT_NOT,
+ new AstNode(AST_SHIFT,
+ bitmask,
+ shift_val->clone()))),
+ new AstNode(AST_SHIFT,
+ new AstNode(AST_TO_UNSIGNED,
+ new AstNode(AST_CAST_SIZE,
+ mkconst_int(result_width, true),
+ children[1]->clone())),
+ shift_val))));
newNode->fixup_hierarchy_flags(true);
}