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Support delayed tristate gates (#7960) (#7961)

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Fixes #7960.
This commit is contained in:
Patrick Creighton
2026-07-20 09:21:23 -04:00
committed by GitHub
parent 176e333774
commit cdfff86c2d
2 changed files with 67 additions and 9 deletions
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src/V3Tristate.cpp
+16 -5
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@@ -422,9 +422,11 @@ class TristateVisitor final : public TristateBaseVisitor {
struct RefStrength final {
AstNodeVarRef* m_varrefp;
VStrength m_strength;
RefStrength(AstNodeVarRef* varrefp, VStrength strength)
AstDelay* m_delayp; // Explicit delay on the continuous assignment
RefStrength(AstNodeVarRef* varrefp, VStrength strength, AstDelay* delayp)
: m_varrefp{varrefp}
, m_strength{strength} {}
, m_strength{strength}
, m_delayp{delayp} {}
};
using RefStrengthVec = std::vector<RefStrength>;
using VarMap = std::map<AstVar*, RefStrengthVec*>;
@@ -449,6 +451,7 @@ class TristateVisitor final : public TristateBaseVisitor {
bool m_processedIfaces = false; // Interface modules already processed (interfaces-first pass)
VStrength m_currentStrength = VStrength::STRONG; // Current strength of assignment,
// Used only on LHS of assignment
AstDelay* m_currentDelayp = nullptr; // Delay of assignment currently collecting LHS drivers
const AstNode* m_logicp = nullptr; // Current logic being built
TristateGraph m_tgraph; // Logic graph
// Map: interface AstVar* -> list of per-module (enVarp, outVarp) contribution pairs
@@ -635,7 +638,7 @@ class TristateVisitor final : public TristateBaseVisitor {
AstVar* const key = nodep->varp();
const auto pair = m_lhsmap.emplace(key, nullptr);
if (pair.second) pair.first->second = new RefStrengthVec;
pair.first->second->push_back(RefStrength{nodep, m_currentStrength});
pair.first->second->push_back(RefStrength{nodep, m_currentStrength, m_currentDelayp});
}
AstNodeExpr* newEnableDeposit(AstSel* selp, AstNodeExpr* enp) {
@@ -854,6 +857,7 @@ class TristateVisitor final : public TristateBaseVisitor {
AstAssignW* const enLhspAssignp = new AstAssignW{
refp->fileline(), new AstVarRef{refp->fileline(), newEnLhsp, VAccess::WRITE},
getEnp(refp)};
if (it->m_delayp) { enLhspAssignp->timingControlp(it->m_delayp->cloneTree(false)); }
UINFO(9, " newenlhspAssignp " << enLhspAssignp);
nodep->addStmtsp(new AstAlways{enLhspAssignp});
@@ -1567,11 +1571,18 @@ class TristateVisitor final : public TristateBaseVisitor {
void visitAssign(AstNodeAssign* nodep) {
VL_RESTORER(m_alhs);
VL_RESTORER(m_currentStrength);
VL_RESTORER(m_currentDelayp);
if (VN_IS(nodep->rhsp(), CReset)) return;
if (AstAssignW* const assignWp = VN_CAST(nodep, AssignW)) {
m_currentDelayp = VN_CAST(assignWp->timingControlp(), Delay);
}
if (m_graphing) {
if (AstAssignW* assignWp = VN_CAST(nodep, AssignW)) {
if (assignWp->timingControlp() || assignWp->getLhsNetDelay()) return;
addToAssignmentList(assignWp);
if (assignWp->getLhsNetDelay()) return;
if (assignWp->timingControlp() && !m_currentDelayp) return;
// Separate data and enable assignments cannot preserve distinct rise/fall delays.
if (m_currentDelayp && m_currentDelayp->fallDelay()) return;
if (!assignWp->timingControlp()) addToAssignmentList(assignWp);
}
if (nodep->user2() & U2_GRAPHING) return;