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verilator/src/V3SchedTiming.cpp

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// -*- mode: C++; c-file-style: "cc-mode" -*-
//*************************************************************************
// DESCRIPTION: Verilator: Code scheduling
//
// Code available from: https://verilator.org
//
//*************************************************************************
//
// Copyright 2003-2025 by Wilson Snyder. This program is free software; you
// can redistribute it and/or modify it under the terms of either the GNU
// Lesser General Public License Version 3 or the Perl Artistic License
// Version 2.0.
// SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
//
//*************************************************************************
//
// Functions defined in this file are used by V3Sched.cpp to properly integrate
// static scheduling with timing features. They create external domains for
// variables, remap them to trigger vectors, and create timing resume/commit
// calls for the global eval loop. There is also a function that transforms
// forks into emittable constructs.
//
// See the internals documentation docs/internals.rst for more details.
//
//*************************************************************************
#include "V3PchAstNoMT.h" // VL_MT_DISABLED_CODE_UNIT
#include "V3EmitCBase.h"
#include "V3Sched.h"
#include <unordered_map>
VL_DEFINE_DEBUG_FUNCTIONS;
namespace V3Sched {
//============================================================================
// Remaps external domains using the specified trigger map
std::map<const AstVarScope*, std::vector<AstSenTree*>>
TimingKit::remapDomains(const std::unordered_map<const AstSenTree*, AstSenTree*>& trigMap) const {
std::map<const AstVarScope*, std::vector<AstSenTree*>> remappedDomainMap;
for (const auto& vscpDomains : m_externalDomains) {
const AstVarScope* const vscp = vscpDomains.first;
const auto& domains = vscpDomains.second;
auto& remappedDomains = remappedDomainMap[vscp];
remappedDomains.reserve(domains.size());
for (AstSenTree* const domainp : domains) {
remappedDomains.push_back(trigMap.at(domainp));
}
}
return remappedDomainMap;
}
//============================================================================
// Creates a timing resume call (if needed, else returns null)
AstCCall* TimingKit::createResume(AstNetlist* const netlistp) {
if (!m_resumeFuncp) {
if (m_lbs.empty()) return nullptr;
// Create global resume function
AstScope* const scopeTopp = netlistp->topScopep()->scopep();
m_resumeFuncp = new AstCFunc{netlistp->fileline(), "_timing_resume", scopeTopp, ""};
m_resumeFuncp->dontCombine(true);
m_resumeFuncp->isLoose(true);
m_resumeFuncp->isConst(false);
m_resumeFuncp->declPrivate(true);
scopeTopp->addBlocksp(m_resumeFuncp);
// Put all the timing actives in the resume function
AstIf* dlyShedIfp = nullptr;
for (auto& p : m_lbs) {
AstActive* const activep = p.second;
// Hack to ensure that #0 delays will be executed after any other `act` events.
// Just handle delayed coroutines last.
AstVarRef* const schedrefp = VN_AS(
VN_AS(VN_AS(activep->stmtsp(), StmtExpr)->exprp(), CMethodHard)->fromp(), VarRef);
AstIf* const ifp = V3Sched::util::createIfFromSenTree(activep->sentreep());
ifp->addThensp(activep->stmtsp()->unlinkFrBackWithNext());
if (schedrefp->varScopep()->dtypep()->basicp()->isDelayScheduler()) {
dlyShedIfp = ifp;
} else {
m_resumeFuncp->addStmtsp(ifp);
}
}
if (dlyShedIfp) m_resumeFuncp->addStmtsp(dlyShedIfp);
// These are now spent, oispose of now empty AstActive instances
m_lbs.deleteActives();
}
AstCCall* const callp = new AstCCall{m_resumeFuncp->fileline(), m_resumeFuncp};
callp->dtypeSetVoid();
return callp;
}
//============================================================================
// Creates a timing commit call (if needed, else returns null)
AstCCall* TimingKit::createCommit(AstNetlist* const netlistp) {
if (!m_commitFuncp) {
for (auto& p : m_lbs) {
AstActive* const activep = p.second;
auto* const resumep = VN_AS(VN_AS(activep->stmtsp(), StmtExpr)->exprp(), CMethodHard);
UASSERT_OBJ(!resumep->nextp(), resumep, "Should be the only statement here");
AstVarScope* const schedulerp = VN_AS(resumep->fromp(), VarRef)->varScopep();
UASSERT_OBJ(schedulerp->dtypep()->basicp()->isDelayScheduler()
|| schedulerp->dtypep()->basicp()->isTriggerScheduler()
|| schedulerp->dtypep()->basicp()->isDynamicTriggerScheduler(),
schedulerp, "Unexpected type");
if (!schedulerp->dtypep()->basicp()->isTriggerScheduler()) continue;
// Create the global commit function only if we have trigger schedulers
if (!m_commitFuncp) {
AstScope* const scopeTopp = netlistp->topScopep()->scopep();
m_commitFuncp
= new AstCFunc{netlistp->fileline(), "_timing_commit", scopeTopp, ""};
m_commitFuncp->dontCombine(true);
m_commitFuncp->isLoose(true);
m_commitFuncp->isConst(false);
m_commitFuncp->declPrivate(true);
scopeTopp->addBlocksp(m_commitFuncp);
}
// There is a somewhat complicate dance here. Given a suspendable
// process of the form:
// ->evntA;
// $display("Fired evntA");
// @(evntA or evntB);
// The firing of the event cannot trigger the event control
// following it, as the process is not yet sensitive to the event
// when it fires (same applies for change detects). The way the
// scheduling works, the @evnt will suspend the process before
// the firing of the event is recognized on the next iteration of
// the 'act' loop, and hence could incorrectly resume the @evnt
// statement. To make this work, whenever a process suspends, it
// goes into an "uncommitted" state, so it cannot be resumed
// immediately on the next iteration of the 'act' loop, which is
// what we want. The question then is, when should the suspended
// process be "committed" and hence possible to be resumed. This is
// done when it is know for sure the suspending expression was not
// triggered on the current iteration of the 'act' loop. With
// multiple events in the suspending expression, all events need
// to be not triggered to safely commit the suspended process.
//
// This is is consistent with IEEE scheduling semantics, and
// behaves as if the above was executed as:
// ->evntA;
// $display("Fired evnt");
// ... all other statements in the 'act' loop that might fire evntA or evntB ...
// @(evntA or evntB);
// which is a valid execution. Race conditions be fun to debug,
// but they are a responsibility of the user.
AstSenTree* const senTreep = activep->sentreep();
FileLine* const flp = senTreep->fileline();
// Create an 'AstIf' sensitive to the suspending triggers
AstIf* const ifp = V3Sched::util::createIfFromSenTree(senTreep);
m_commitFuncp->addStmtsp(ifp);
// Commit the processes suspended on this sensitivity expression
// in the **else** branch, when the event is known to be not fired.
AstVarRef* const refp = new AstVarRef{flp, schedulerp, VAccess::READWRITE};
AstCMethodHard* const callp = new AstCMethodHard{flp, refp, VCMethod::SCHED_COMMIT};
callp->dtypeSetVoid();
if (resumep->pinsp()) callp->addPinsp(resumep->pinsp()->cloneTree(false));
ifp->addElsesp(callp->makeStmt());
}
// We still haven't created a commit function (no trigger schedulers), return null
if (!m_commitFuncp) return nullptr;
}
AstCCall* const callp = new AstCCall{m_commitFuncp->fileline(), m_commitFuncp};
callp->dtypeSetVoid();
return callp;
}
//============================================================================
// Creates the timing kit and marks variables written by suspendables
class AwaitVisitor final : public VNVisitor {
// NODE STATE
// AstSenTree::user1() -> bool. Set true if the sentree has been visited.
const VNUser1InUse m_inuser1;
// STATE
bool m_inProcess = false; // Are we in a process?
bool m_gatherVars = false; // Should we gather vars in m_writtenBySuspendable?
AstScope* const m_scopeTopp; // Scope at the top
LogicByScope& m_lbs; // Timing resume actives
AstNodeStmt*& m_postUpdatesr; // Post updates for the trigger eval function
// Additional var sensitivities
std::map<const AstVarScope*, std::set<AstSenTree*>>& m_externalDomains;
std::set<AstSenTree*> m_processDomains; // Sentrees from the current process
// Variables written by suspendable processes
std::vector<AstVarScope*> m_writtenBySuspendable;
// METHODS
// Add arguments to a resume() call based on arguments in the suspending call
void addResumePins(AstCMethodHard* const resumep, AstNodeExpr* pinsp) {
AstCExpr* const exprp = VN_CAST(pinsp, CExpr);
AstText* const textp = VN_CAST(exprp->nodesp(), Text);
if (textp) {
// The first argument, vlProcess, isn't used by any of resume() methods, skip it
if ((pinsp = VN_CAST(pinsp->nextp(), NodeExpr))) {
resumep->addPinsp(pinsp->cloneTree(false));
}
} else {
resumep->addPinsp(pinsp->cloneTree(false));
}
}
// Create an active with a timing scheduler resume() call
void createResumeActive(AstCAwait* const awaitp) {
auto* const methodp = VN_AS(awaitp->exprp(), CMethodHard);
AstVarScope* const schedulerp = VN_AS(methodp->fromp(), VarRef)->varScopep();
AstSenTree* const sentreep = awaitp->sentreep();
FileLine* const flp = sentreep->fileline();
// Create a resume() call on the timing scheduler
auto* const resumep = new AstCMethodHard{
flp, new AstVarRef{flp, schedulerp, VAccess::READWRITE}, VCMethod::SCHED_RESUME};
resumep->dtypeSetVoid();
if (schedulerp->dtypep()->basicp()->isTriggerScheduler()) {
UASSERT_OBJ(methodp->pinsp(), methodp,
"Trigger method should have pins from V3Timing");
// The first pin is the commit boolean, the rest (if any) should be debug info
// See V3Timing for details
if (AstNode* const dbginfop = methodp->pinsp()->nextp()) {
if (methodp->pinsp()) addResumePins(resumep, static_cast<AstNodeExpr*>(dbginfop));
}
} else if (schedulerp->dtypep()->basicp()->isDynamicTriggerScheduler()) {
auto* const postp = resumep->cloneTree(false);
postp->method(VCMethod::SCHED_DO_POST_UPDATES);
m_postUpdatesr = AstNode::addNext(m_postUpdatesr, postp->makeStmt());
}
// Put it in an active
AstActive* const activep = new AstActive{flp, "_timing", sentreep};
activep->addStmtsp(resumep->makeStmt());
m_lbs.emplace_back(m_scopeTopp, activep);
}
// VISITORS
void visit(AstNodeProcedure* const nodep) override {
UASSERT_OBJ(!m_inProcess && !m_gatherVars && m_processDomains.empty()
&& m_writtenBySuspendable.empty(),
nodep, "Process in process?");
m_inProcess = true;
m_gatherVars = nodep->isSuspendable(); // Only gather vars in a suspendable
const VNUser2InUse user2InUse; // AstVarScope -> bool: Set true if var has been added
// to m_writtenBySuspendable
iterateChildren(nodep);
for (AstVarScope* const vscp : m_writtenBySuspendable) {
m_externalDomains[vscp].insert(m_processDomains.begin(), m_processDomains.end());
vscp->varp()->setWrittenBySuspendable();
}
m_processDomains.clear();
m_writtenBySuspendable.clear();
m_inProcess = false;
m_gatherVars = false;
}
void visit(AstFork* nodep) override {
VL_RESTORER(m_gatherVars);
if (m_inProcess) m_gatherVars = true;
// If not in a process, we don't need to gather variables or domains
iterateChildren(nodep);
}
void visit(AstCAwait* nodep) override {
if (AstSenTree* const sentreep = nodep->sentreep()) {
if (!sentreep->user1SetOnce()) createResumeActive(nodep);
nodep->clearSentreep(); // Clear as these sentrees will get deleted later
if (m_inProcess) m_processDomains.insert(sentreep);
}
}
void visit(AstNodeVarRef* nodep) override {
if (m_gatherVars && nodep->access().isWriteOrRW() && !nodep->varp()->ignoreSchedWrite()
&& !nodep->varScopep()->user2SetOnce()) {
m_writtenBySuspendable.push_back(nodep->varScopep());
}
}
void visit(AstExprStmt* nodep) override { iterateChildren(nodep); }
//--------------------
void visit(AstNode* nodep) override { iterateChildren(nodep); }
public:
// CONSTRUCTORS
explicit AwaitVisitor(AstNetlist* nodep, LogicByScope& lbs, AstNodeStmt*& postUpdatesr,
std::map<const AstVarScope*, std::set<AstSenTree*>>& externalDomains)
: m_scopeTopp{nodep->topScopep()->scopep()}
, m_lbs{lbs}
, m_postUpdatesr{postUpdatesr}
, m_externalDomains{externalDomains} {
iterate(nodep);
}
~AwaitVisitor() override = default;
};
TimingKit prepareTiming(AstNetlist* const netlistp) {
if (!v3Global.usesTiming()) return {};
LogicByScope lbs;
AstNodeStmt* postUpdates = nullptr;
std::map<const AstVarScope*, std::set<AstSenTree*>> externalDomains;
AwaitVisitor{netlistp, lbs, postUpdates, externalDomains};
return {std::move(lbs), postUpdates, std::move(externalDomains)};
}
//============================================================================
// Visits all forks and transforms their sub-statements into separate functions.
// Transform all forked processes into functions
class TransformForksVisitor final : public VNVisitor {
// NODE STATE
// AstVar::user1() -> bool. Set true if the variable was declared before the current fork.
const VNUser1InUse m_inuser1;
// STATE
bool m_inClass = false; // Are we in a class?
bool m_beginHasAwaits = false; // Does the current begin have awaits?
AstFork* m_forkp = nullptr; // Current fork
AstCFunc* m_funcp = nullptr; // Current function
// METHODS
// Remap local vars referenced by the given fork function
// TODO: We should only pass variables to the fork that are
// live in the fork body, but for that we need a proper data
// flow analysis framework which we don't have at the moment
void remapLocals(AstCFunc* const funcp, AstCCall* const callp) {
const VNUser2InUse user2InUse; // AstVarScope -> AstVarScope: var to remap to
funcp->foreach([&](AstNodeVarRef* refp) {
AstVar* const varp = refp->varp();
AstBasicDType* const dtypep = varp->dtypep()->basicp();
// If not a fork..join, copy. All write refs should've been handled by V3Fork
bool passByValue = !m_forkp->joinType().join();
if (!varp->isFuncLocal()) {
// Not func local. Its lifetime is longer than the forked process. Skip
return;
} else if (!varp->user1()) {
// Not declared before the fork. It cannot outlive the forked process
return;
} else if (dtypep && dtypep->isForkSync()) {
// We can just pass it by value to the new function
passByValue = true;
}
// Remap the reference
AstVarScope* const vscp = refp->varScopep();
if (!vscp->user2p()) {
// Clone the var to the new function
AstVar* const newvarp
= new AstVar{varp->fileline(), VVarType::BLOCKTEMP, varp->name(), varp};
newvarp->funcLocal(true);
newvarp->direction(passByValue ? VDirection::INPUT : VDirection::REF);
funcp->addArgsp(newvarp);
AstVarScope* const newvscp
= new AstVarScope{newvarp->fileline(), funcp->scopep(), newvarp};
funcp->scopep()->addVarsp(newvscp);
vscp->user2p(newvscp);
callp->addArgsp(new AstVarRef{refp->fileline(), vscp,
passByValue ? VAccess::READ : VAccess::READWRITE});
}
AstVarScope* const newvscp = VN_AS(vscp->user2p(), VarScope);
refp->varScopep(newvscp);
refp->varp(newvscp->varp());
});
}
// VISITORS
void visit(AstNodeModule* nodep) override {
VL_RESTORER(m_inClass);
m_inClass = VN_IS(nodep, Class);
iterateChildren(nodep);
}
void visit(AstCFunc* nodep) override {
VL_RESTORER(m_funcp);
m_funcp = nodep;
iterateChildren(nodep);
}
void visit(AstVar* nodep) override {
if (!m_forkp) nodep->user1(true);
}
void visit(AstFork* nodep) override {
if (m_forkp) return; // Handle forks in forks after moving them to new functions
VL_RESTORER(m_forkp);
m_forkp = nodep;
iterateChildrenConst(nodep); // Const, so we don't iterate the calls twice
// Replace self with the function calls (no co_await, as we don't want the main
// process to suspend whenever any of the children do)
// V3Dead could have removed all statements from the fork, so guard against it
// Inline begins now that they are not needed
AstNode* resp = nullptr;
if (AstNode* const declsp = nodep->declsp()) {
resp = AstNode::addNext(resp, declsp->unlinkFrBackWithNext());
}
if (AstNode* const stmtsp = nodep->stmtsp()) {
resp = AstNode::addNext(resp, stmtsp->unlinkFrBackWithNext());
}
while (AstBegin* const beginp = nodep->forksp()) {
if (AstNode* const declsp = beginp->declsp()) {
resp = AstNode::addNext(resp, declsp->unlinkFrBackWithNext());
}
if (AstNode* const stmtsp = beginp->stmtsp()) {
resp = AstNode::addNext(resp, stmtsp->unlinkFrBackWithNext());
}
VL_DO_DANGLING(pushDeletep(beginp->unlinkFrBack()), beginp);
}
if (resp) {
nodep->replaceWith(resp);
} else {
nodep->unlinkFrBack();
}
VL_DO_DANGLING(pushDeletep(nodep), nodep);
}
void visit(AstBegin* nodep) override {
UASSERT_OBJ(m_forkp, nodep, "Begin outside of a fork");
// Start with children, so later we only find awaits that are actually in this begin
m_beginHasAwaits = false;
iterateChildrenConst(nodep);
if (!nodep->stmtsp()) return;
if (!m_beginHasAwaits && !nodep->needProcess()) return;
UASSERT_OBJ(!nodep->name().empty(), nodep, "Begin needs a name");
// Create a function to put this begin's statements in
FileLine* const flp = nodep->fileline();
AstCFunc* const newfuncp = new AstCFunc{flp, m_funcp->name() + "__" + nodep->name(),
m_funcp->scopep(), "VlCoroutine"};
m_funcp->addNextHere(newfuncp);
newfuncp->isLoose(m_funcp->isLoose());
newfuncp->slow(m_funcp->slow());
newfuncp->isConst(m_funcp->isConst());
newfuncp->declPrivate(true);
// Create the call to the function
AstCCall* const callp = new AstCCall{flp, newfuncp};
callp->dtypeSetVoid();
// If we're in a class, add a vlSymsp arg
if (m_inClass) {
newfuncp->addStmtsp(new AstCStmt{flp, "VL_KEEP_THIS;"});
newfuncp->argTypes(EmitCUtil::symClassVar());
callp->argTypes("vlSymsp");
}
// Put the begin's statements in the function
if (AstNode* const declsp = nodep->declsp()) {
newfuncp->addStmtsp(declsp->unlinkFrBackWithNext());
}
if (AstNode* const stmtsp = nodep->stmtsp()) {
newfuncp->addStmtsp(stmtsp->unlinkFrBackWithNext());
}
// Replace the body of the begin with a call to the newly created function
nodep->addStmtsp(callp->makeStmt());
// Propagate if needs process
if (nodep->needProcess()) {
newfuncp->setNeedProcess();
newfuncp->addStmtsp(new AstCStmt{flp, "vlProcess->state(VlProcess::FINISHED);"});
}
remapLocals(newfuncp, callp);
}
void visit(AstCAwait* nodep) override {
m_beginHasAwaits = true;
iterateChildrenConst(nodep);
}
//--------------------
void visit(AstNode* nodep) override { iterateChildren(nodep); }
public:
// CONSTRUCTORS
explicit TransformForksVisitor(AstNetlist* nodep) { iterate(nodep); }
~TransformForksVisitor() override = default;
};
void transformForks(AstNetlist* const netlistp) {
if (!v3Global.usesTiming()) return;
TransformForksVisitor{netlistp};
V3Global::dumpCheckGlobalTree("transform_forks", 0, dumpTreeEitherLevel() >= 3);
}
} // namespace V3Sched
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