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verilator/src/V3Force.cpp

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// -*- mode: C++; c-file-style: "cc-mode" -*-
//*************************************************************************
// DESCRIPTION: Verilator: Covert forceable signals, process force/release
//
// 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
//
//*************************************************************************
// V3Force's Transformations:
//
// For each forceable net with name "<name>":
// add 3 extra signals:
// - <name>__VforceRd: a net with same type as signal
// - <name>__VforceEn: a var with same type as signal, which is the bitwise force enable
// - <name>__VforceVal: a var with same type as signal, which is the forced value
// add an initial statement:
// initial <name>__VforceEn = 0;
// add a continuous assignment:
// assign <name>__VforceRd = <name>__VforceEn ? <name>__VforceVal : <name>;
// replace all READ references to <name> with a read reference to <name>_VforceRd
//
// Replace each AstAssignForce with 3 assignments:
// - <lhs>__VforceEn = 1
// - <lhs>__VforceVal = <rhs>
// - <lhs>__VforceRd = <rhs>
//
// Replace each AstRelease with 1 or 2 assignments:
// - <lhs>__VforceEn = 0
// - <lhs>__VforceRd = <lhs> // iff lhs is a net
//
// After each WRITE of forced LHS
// reevaluate <lhs>__VforceRd to support immediate force/release
//
// After each WRITE of forced RHS
// reevaluate <lhs>__VforceVal to support VarRef rollback after release
//*************************************************************************
#include "V3PchAstNoMT.h" // VL_MT_DISABLED_CODE_UNIT
#include "V3Force.h"
#include "V3AstUserAllocator.h"
VL_DEFINE_DEBUG_FUNCTIONS;
//######################################################################
// Convert force/release statements and signals marked 'forceable'
class ForceState final {
// TYPES
struct ForceComponentsVar final {
AstVar* const m_rdVarp; // New variable to replace read references with
AstVar* const m_valVarp; // Forced value
AstVar* const m_enVarp; // Force enabled signal
explicit ForceComponentsVar(AstVar* varp)
: m_rdVarp{new AstVar{varp->fileline(), VVarType::WIRE, varp->name() + "__VforceRd",
varp->dtypep()}}
, m_valVarp{new AstVar{varp->fileline(), VVarType::VAR, varp->name() + "__VforceVal",
varp->dtypep()}}
, m_enVarp{new AstVar{
varp->fileline(), VVarType::VAR, varp->name() + "__VforceEn",
(ForceState::isRangedDType(varp) ? varp->dtypep() : varp->findBitDType())}} {
m_rdVarp->addNext(m_enVarp);
m_rdVarp->addNext(m_valVarp);
varp->addNextHere(m_rdVarp);
}
};
public:
struct ForceComponentsVarScope final {
AstVarScope* const m_rdVscp; // New variable to replace read references with
AstVarScope* const m_valVscp; // Forced value
AstVarScope* const m_enVscp; // Force enabled signal
explicit ForceComponentsVarScope(AstVarScope* vscp, ForceComponentsVar& fcv)
: m_rdVscp{new AstVarScope{vscp->fileline(), vscp->scopep(), fcv.m_rdVarp}}
, m_valVscp{new AstVarScope{vscp->fileline(), vscp->scopep(), fcv.m_valVarp}}
, m_enVscp{new AstVarScope{vscp->fileline(), vscp->scopep(), fcv.m_enVarp}} {
m_rdVscp->addNext(m_enVscp);
m_rdVscp->addNext(m_valVscp);
vscp->addNextHere(m_rdVscp);
FileLine* const flp = vscp->fileline();
{ // Add initialization of the enable signal
AstVarRef* const lhsp = new AstVarRef{flp, m_enVscp, VAccess::WRITE};
V3Number zero{m_enVscp, m_enVscp->width()};
zero.setAllBits0();
AstNodeExpr* const rhsp = new AstConst{flp, zero};
AstAssign* const assignp = new AstAssign{flp, lhsp, rhsp};
AstActive* const activep = new AstActive{
flp, "force-init",
new AstSenTree{flp, new AstSenItem{flp, AstSenItem::Static{}}}};
activep->senTreeStorep(activep->sentreep());
activep->addStmtsp(new AstInitial{flp, assignp});
vscp->scopep()->addBlocksp(activep);
}
{ // Add the combinational override
AstVarRef* const lhsp = new AstVarRef{flp, m_rdVscp, VAccess::WRITE};
AstNodeExpr* const rhsp = forcedUpdate(vscp);
// Explicitly list dependencies for update.
// Note: rdVscp is also needed to retrigger assignment for the first time.
AstSenItem* const itemsp = new AstSenItem{
flp, VEdgeType::ET_CHANGED, new AstVarRef{flp, m_rdVscp, VAccess::READ}};
itemsp->addNext(new AstSenItem{flp, VEdgeType::ET_CHANGED,
new AstVarRef{flp, m_valVscp, VAccess::READ}});
itemsp->addNext(new AstSenItem{flp, VEdgeType::ET_CHANGED,
new AstVarRef{flp, m_enVscp, VAccess::READ}});
AstVarRef* const origp = new AstVarRef{flp, vscp, VAccess::READ};
ForceState::markNonReplaceable(origp);
itemsp->addNext(new AstSenItem{flp, VEdgeType::ET_CHANGED, origp});
AstActive* const activep
= new AstActive{flp, "force-update", new AstSenTree{flp, itemsp}};
activep->senTreeStorep(activep->sentreep());
activep->addStmtsp(new AstAlways{flp, VAlwaysKwd::ALWAYS, nullptr,
new AstAssign{flp, lhsp, rhsp}});
vscp->scopep()->addBlocksp(activep);
}
}
AstNodeExpr* forcedUpdate(AstVarScope* const vscp) const {
FileLine* const flp = vscp->fileline();
AstVarRef* const origp = new AstVarRef{flp, vscp, VAccess::READ};
ForceState::markNonReplaceable(origp);
if (ForceState::isRangedDType(vscp)) {
return new AstOr{
flp,
new AstAnd{flp, new AstVarRef{flp, m_enVscp, VAccess::READ},
new AstVarRef{flp, m_valVscp, VAccess::READ}},
new AstAnd{flp, new AstNot{flp, new AstVarRef{flp, m_enVscp, VAccess::READ}},
origp}};
}
return new AstCond{flp, new AstVarRef{flp, m_enVscp, VAccess::READ},
new AstVarRef{flp, m_valVscp, VAccess::READ}, origp};
}
};
private:
// NODE STATE
// AstVar::user1p -> ForceComponentsVar* instance (via m_forceComponentsVar)
// AstVarScope::user1p -> ForceComponentsVarScope* instance (via m_forceComponentsVarScope)
// AstVarRef::user2 -> Flag indicating not to replace reference
// AstVarScope::user3p -> AstAssign*, the assignment <lhs>__VforceVal = <rhs>
const VNUser1InUse m_user1InUse;
const VNUser2InUse m_user2InUse;
const VNUser3InUse m_user3InUse;
AstUser1Allocator<AstVar, ForceComponentsVar> m_forceComponentsVar;
AstUser1Allocator<AstVarScope, ForceComponentsVarScope> m_forceComponentsVarScope;
std::unordered_map<const AstVarScope*,
std::pair<std::unordered_set<AstVarScope*>, std::vector<AstVarScope*>>>
m_valVscps;
// `valVscp` force components of a forced RHS
public:
// CONSTRUCTORS
ForceState() = default;
VL_UNCOPYABLE(ForceState);
// STATIC METHODS
static bool isRangedDType(AstNode* nodep) {
// If ranged we need a multibit enable to support bit-by-bit part-select forces,
// otherwise forcing a real or other opaque dtype and need a single bit enable.
const AstBasicDType* const basicp = nodep->dtypep()->skipRefp()->basicp();
return basicp && basicp->isRanged();
}
static bool isNotReplaceable(const AstVarRef* const nodep) { return nodep->user2(); }
static void markNonReplaceable(AstVarRef* const nodep) { nodep->user2SetOnce(); }
// Get all ValVscps for a VarScope
const std::vector<AstVarScope*>* getValVscps(AstVarRef* const refp) const {
auto it = m_valVscps.find(refp->varScopep());
if (it != m_valVscps.end()) return &(it->second.second);
return nullptr;
}
// Add a ValVscp for a VarScope
void addValVscp(AstVarRef* const refp, AstVarScope* const valVscp) {
if (m_valVscps[refp->varScopep()].first.find(valVscp)
!= m_valVscps[refp->varScopep()].first.end())
return;
m_valVscps[refp->varScopep()].first.emplace(valVscp);
m_valVscps[refp->varScopep()].second.push_back(valVscp);
}
// METHODS
const ForceComponentsVarScope& getForceComponents(AstVarScope* vscp) {
AstVar* const varp = vscp->varp();
return m_forceComponentsVarScope(vscp, vscp, m_forceComponentsVar(varp, varp));
}
ForceComponentsVarScope* tryGetForceComponents(AstVarRef* nodep) const {
return m_forceComponentsVarScope.tryGet(nodep->varScopep());
}
void setValVscpAssign(AstVarScope* valVscp, AstAssign* rhsExpr) { valVscp->user3p(rhsExpr); }
AstAssign* getValVscpAssign(AstVarScope* valVscp) const {
return VN_CAST(valVscp->user3p(), Assign);
}
};
class ForceConvertVisitor final : public VNVisitor {
// STATE
ForceState& m_state;
// STATIC METHODS
// Replace each AstNodeVarRef in the given 'nodep' that writes a variable by transforming the
// referenced AstVarScope with the given function.
static void transformWritenVarScopes(AstNode* nodep,
std::function<AstVarScope*(AstVarScope*)> f) {
UASSERT_OBJ(nodep->backp(), nodep, "Must have backp, otherwise will be lost if replaced");
nodep->foreach([&f](AstNodeVarRef* refp) {
if (refp->access() != VAccess::WRITE) return;
// TODO: this is not strictly speaking safe for some complicated lvalues, eg.:
// 'force foo[a(cnt)] = 1;', where 'cnt' is an out parameter, but it will
// do for now...
refp->replaceWith(
new AstVarRef{refp->fileline(), f(refp->varScopep()), VAccess::WRITE});
VL_DO_DANGLING(refp->deleteTree(), refp);
});
}
// VISITORS
void visit(AstNode* nodep) override { iterateChildren(nodep); }
void visit(AstAssignForce* nodep) override {
// The AstAssignForce node will be removed for sure
FileLine* const flp = nodep->fileline();
AstNodeExpr* const lhsp = nodep->lhsp(); // The LValue we are forcing
AstNodeExpr* const rhsp = nodep->rhsp(); // The value we are forcing it to
VNRelinker relinker;
nodep->unlinkFrBack(&relinker);
VL_DO_DANGLING(pushDeletep(nodep), nodep);
// Set corresponding enable signals to ones
V3Number ones{lhsp, ForceState::isRangedDType(lhsp) ? lhsp->width() : 1};
ones.setAllBits1();
AstAssign* const setEnp
= new AstAssign{flp, lhsp->cloneTreePure(false), new AstConst{rhsp->fileline(), ones}};
transformWritenVarScopes(setEnp->lhsp(), [this](AstVarScope* vscp) {
return m_state.getForceComponents(vscp).m_enVscp;
});
// Set corresponding value signals to the forced value
AstAssign* const setValp
= new AstAssign{flp, lhsp->cloneTreePure(false), rhsp->cloneTreePure(false)};
transformWritenVarScopes(setValp->lhsp(), [this, rhsp, setValp](AstVarScope* vscp) {
AstVarScope* const valVscp = m_state.getForceComponents(vscp).m_valVscp;
m_state.setValVscpAssign(valVscp, setValp);
rhsp->foreach([valVscp, this](AstVarRef* refp) { m_state.addValVscp(refp, valVscp); });
return valVscp;
});
// Set corresponding read signal directly as well, in case something in the same
// process reads it later
AstAssign* const setRdp = new AstAssign{flp, lhsp->unlinkFrBack(), rhsp->unlinkFrBack()};
transformWritenVarScopes(setRdp->lhsp(), [this](AstVarScope* vscp) {
return m_state.getForceComponents(vscp).m_rdVscp;
});
setEnp->addNext(setValp);
setEnp->addNext(setRdp);
relinker.relink(setEnp);
}
void visit(AstRelease* nodep) override {
FileLine* const flp = nodep->fileline();
AstNodeExpr* const lhsp = nodep->lhsp(); // The LValue we are releasing
// The AstRelease node will be removed for sure
VNRelinker relinker;
nodep->unlinkFrBack(&relinker);
VL_DO_DANGLING(pushDeletep(nodep), nodep);
// Set corresponding enable signals to zero
V3Number zero{lhsp, ForceState::isRangedDType(lhsp) ? lhsp->width() : 1};
zero.setAllBits0();
AstAssign* const resetEnp
= new AstAssign{flp, lhsp->cloneTreePure(false), new AstConst{lhsp->fileline(), zero}};
transformWritenVarScopes(resetEnp->lhsp(), [this](AstVarScope* vscp) {
return m_state.getForceComponents(vscp).m_enVscp;
});
// IEEE 1800-2023 10.6.2: When released, then if the variable is not driven by a continuous
// assignment and does not currently have an active procedural continuous assignment, the
// variable shall not immediately change value and shall maintain its current value until
// the next procedural assignment to the variable is executed. Releasing a variable that is
// driven by a continuous assignment or currently has an active assign procedural
// continuous assignment shall reestablish that assignment and schedule a reevaluation in
// the continuous assignment's scheduling region.
AstAssign* const resetRdp
= new AstAssign{flp, lhsp->cloneTreePure(false), lhsp->unlinkFrBack()};
// Replace write refs on the LHS
resetRdp->lhsp()->foreach([this](AstNodeVarRef* refp) {
if (refp->access() != VAccess::WRITE) return;
AstVarScope* const vscp = refp->varScopep();
AstVarScope* const newVscp = vscp->varp()->isContinuously()
? m_state.getForceComponents(vscp).m_rdVscp
: vscp;
AstVarRef* const newpRefp = new AstVarRef{refp->fileline(), newVscp, VAccess::WRITE};
refp->replaceWith(newpRefp);
VL_DO_DANGLING(refp->deleteTree(), refp);
});
// Replace write refs on RHS
resetRdp->rhsp()->foreach([this](AstNodeVarRef* refp) {
if (refp->access() != VAccess::WRITE) return;
AstVarScope* const vscp = refp->varScopep();
if (vscp->varp()->isContinuously()) {
AstVarRef* const newpRefp = new AstVarRef{refp->fileline(), vscp, VAccess::READ};
ForceState::markNonReplaceable(newpRefp);
refp->replaceWith(newpRefp);
} else {
refp->replaceWith(m_state.getForceComponents(vscp).forcedUpdate(vscp));
}
VL_DO_DANGLING(refp->deleteTree(), refp);
});
resetRdp->addNext(resetEnp);
relinker.relink(resetRdp);
}
void visit(AstVarScope* nodep) override {
// If this signal is marked externally forceable, create the public force signals
if (nodep->varp()->isForceable()) {
const ForceState::ForceComponentsVarScope& fc = m_state.getForceComponents(nodep);
fc.m_enVscp->varp()->sigUserRWPublic(true);
fc.m_valVscp->varp()->sigUserRWPublic(true);
}
}
public:
// CONSTRUCTOR
// cppcheck-suppress constParameterCallback
ForceConvertVisitor(AstNetlist* nodep, ForceState& state)
: m_state{state} {
// Transform all force and release statements
iterateAndNextNull(nodep->modulesp());
}
};
class ForceReplaceVisitor final : public VNVisitor {
// STATE
const ForceState& m_state;
AstNodeStmt* m_stmtp = nullptr;
bool m_inLogic = false;
// METHODS
void iterateLogic(AstNode* logicp) {
VL_RESTORER(m_inLogic);
m_inLogic = true;
iterateChildren(logicp);
}
// VISITORS
void visit(AstNodeStmt* nodep) override {
VL_RESTORER(m_stmtp);
m_stmtp = nodep;
iterateChildren(nodep);
}
void visit(AstCFunc* nodep) override { iterateLogic(nodep); }
void visit(AstCoverToggle* nodep) override { iterateLogic(nodep); }
void visit(AstNodeProcedure* nodep) override { iterateLogic(nodep); }
void visit(AstSenItem* nodep) override { iterateLogic(nodep); }
void visit(AstVarRef* nodep) override {
if (ForceState::isNotReplaceable(nodep)) return;
switch (nodep->access()) {
case VAccess::READ: {
// Replace VarRef from forced LHS with rdVscp.
if (ForceState::ForceComponentsVarScope* const fcp
= m_state.tryGetForceComponents(nodep)) {
nodep->varp(fcp->m_rdVscp->varp());
nodep->varScopep(fcp->m_rdVscp);
}
break;
}
case VAccess::WRITE: {
if (!m_inLogic) return;
// Emit rdVscp update after each write to any VarRef on forced LHS.
if (ForceState::ForceComponentsVarScope* const fcp
= m_state.tryGetForceComponents(nodep)) {
FileLine* const flp = nodep->fileline();
AstVarRef* const lhsp = new AstVarRef{flp, fcp->m_rdVscp, VAccess::WRITE};
AstNodeExpr* const rhsp = fcp->forcedUpdate(nodep->varScopep());
m_stmtp->addNextHere(new AstAssign{flp, lhsp, rhsp});
}
// Emit valVscp update after each write to any VarRef on forced RHS.
if (!m_state.getValVscps(nodep)) break;
for (AstVarScope* const valVscp : *m_state.getValVscps(nodep)) {
FileLine* const flp = nodep->fileline();
AstAssign* assignp = m_state.getValVscpAssign(valVscp);
UASSERT_OBJ(assignp, flp, "Missing stored assignment for forced valVscp");
assignp = assignp->cloneTreePure(false);
assignp->rhsp()->foreach(
[](AstVarRef* refp) { ForceState::markNonReplaceable(refp); });
m_stmtp->addNextHere(assignp);
}
break;
}
default:
if (!m_inLogic) return;
if (m_state.tryGetForceComponents(nodep) || m_state.getValVscps(nodep)) {
nodep->v3warn(
E_UNSUPPORTED,
"Unsupported: Signals used via read-write reference cannot be forced");
}
break;
}
}
void visit(AstNode* nodep) override { iterateChildren(nodep); }
public:
// CONSTRUCTOR
explicit ForceReplaceVisitor(AstNetlist* nodep, const ForceState& state)
: m_state{state} {
iterateChildren(nodep);
}
};
//######################################################################
//
void V3Force::forceAll(AstNetlist* nodep) {
UINFO(2, __FUNCTION__ << ":");
if (!v3Global.hasForceableSignals()) return;
{
ForceState state;
{ ForceConvertVisitor{nodep, state}; }
{ ForceReplaceVisitor{nodep, state}; }
V3Global::dumpCheckGlobalTree("force", 0, dumpTreeEitherLevel() >= 3);
}
}
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