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cxxrtl: split processes into sync and case nodes. 

Similar to the treatment of black boxes, splitting processes into two
scheduling nodes adds sufficient freedom so that netlists with
well-behaved processes (e.g. those emitted by nMigen) can immediately
converge.

Because processes are not emitted into edge-triggered regions, this
approach has comparable performance to -O5 (without -noproc), which
is substantially slower than -O6.
This commit is contained in:
whitequark 2020-12-22 00:07:45 +00:00
parent ac988cfac5
commit 7378194169
1 changed files with 26 additions and 11 deletions
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37
backends/cxxrtl/cxxrtl_backend.cc
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@ -272,7 +272,8 @@ struct FlowGraph {
CONNECT,
CELL_SYNC,
CELL_EVAL,
PROCESS
PROCESS_SYNC,
PROCESS_CASE,
};
Type type;
@ -458,7 +459,7 @@ struct FlowGraph {
}
// Processes
void add_case_defs_uses(Node *node, const RTLIL::CaseRule *case_)
void add_case_rule_defs_uses(Node *node, const RTLIL::CaseRule *case_)
{
for (auto &action : case_->actions) {
add_defs(node, action.first, /*is_ff=*/false, /*inlinable=*/false);
@ -469,14 +470,13 @@ struct FlowGraph {
for (auto sub_case : sub_switch->cases) {
for (auto &compare : sub_case->compare)
add_uses(node, compare);
add_case_defs_uses(node, sub_case);
add_case_rule_defs_uses(node, sub_case);
}
}
}
void add_process_defs_uses(Node *node, const RTLIL::Process *process)
void add_sync_rules_defs_uses(Node *node, const RTLIL::Process *process)
{
add_case_defs_uses(node, &process->root_case);
for (auto sync : process->syncs)
for (auto action : sync->actions) {
if (sync->type == RTLIL::STp || sync->type == RTLIL::STn || sync->type == RTLIL::STe)
@ -490,10 +490,16 @@ struct FlowGraph {
Node *add_node(const RTLIL::Process *process)
{
Node *node = new Node;
node->type = Node::Type::PROCESS;
node->type = Node::Type::PROCESS_SYNC;
node->process = process;
nodes.push_back(node);
add_process_defs_uses(node, process);
add_sync_rules_defs_uses(node, process);
node = new Node;
node->type = Node::Type::PROCESS_CASE;
node->process = process;
nodes.push_back(node);
add_case_rule_defs_uses(node, &process->root_case);
return node;
}
};
@ -1481,13 +1487,19 @@ struct CxxrtlWorker {
f << indent << "}\n";
}
void dump_process(const RTLIL::Process *proc)
void dump_process_case(const RTLIL::Process *proc)
{
dump_attrs(proc);
f << indent << "// process " << proc->name.str() << "\n";
f << indent << "// process " << proc->name.str() << " case\n";
// The case attributes (for root case) are always empty.
log_assert(proc->root_case.attributes.empty());
dump_case_rule(&proc->root_case);
}
void dump_process_syncs(const RTLIL::Process *proc)
{
dump_attrs(proc);
f << indent << "// process " << proc->name.str() << " syncs\n";
for (auto sync : proc->syncs) {
RTLIL::SigBit sync_bit;
if (!sync->signal.empty()) {
@ -1702,8 +1714,11 @@ struct CxxrtlWorker {
case FlowGraph::Node::Type::CELL_EVAL:
dump_cell_eval(node.cell);
break;
case FlowGraph::Node::Type::PROCESS:
dump_process(node.process);
case FlowGraph::Node::Type::PROCESS_SYNC:
dump_process_syncs(node.process);
break;
case FlowGraph::Node::Type::PROCESS_CASE:
dump_process_case(node.process);
break;
}
}