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Fix cross-hierarchy tristate drivers of interface nets (#7339) (#7801)

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Closes #7339.
This commit is contained in:
Yilou Wang
2026-06-18 19:07:37 -04:00
committed by GitHub
parent 51022d6152
commit 129cfc19c0
6 changed files with 270 additions and 2 deletions
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src/V3Tristate.cpp
+41 -2
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@@ -352,7 +352,9 @@ class TristatePinVisitor final : public TristateBaseVisitor {
TristateGraph& m_tgraph;
const bool m_lvalue; // Flip to be an LVALUE
// VISITORS
void visit(AstVarRef* nodep) override {
// AstNodeVarRef, not just AstVarRef: a cross-hierarchy pin expression into an
// interface (.pin(iface.net)) is an AstVarXRef and needs the same access flip.
void visit(AstNodeVarRef* nodep) override {
UASSERT_OBJ(!nodep->access().isRW(), nodep, "Tristate unexpected on R/W access flip");
if (m_lvalue && !nodep->access().isWriteOrRW()) {
UINFO(9, " Flip-to-LValue " << nodep);
@@ -405,6 +407,11 @@ class TristateVisitor final : public TristateBaseVisitor {
struct AuxAstVar final {
AstPull* pullp = nullptr; // pullup/pulldown direction (whole variable)
AstVar* outVarp = nullptr; // output __out var
bool ifaceTristate = false; // Interface var known to be tristate (set when the
// interface module is processed). Lets a module that
// drives this var across hierarchy with a plain (non-Z)
// assign be recognised as a tristate contributor even
// though that module's own graph has no Z on the net.
std::unordered_map<int, int>
bitPulls; // Per-bit pull: bit_index -> direction (1=up, 0=down)
};
@@ -439,6 +446,7 @@ class TristateVisitor final : public TristateBaseVisitor {
int m_unique = 0;
bool m_alhs = false; // On LHS of assignment
bool m_inAlias = false; // Inside alias statement
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
const AstNode* m_logicp = nullptr; // Current logic being built
@@ -755,6 +763,9 @@ class TristateVisitor final : public TristateBaseVisitor {
}
}
} else if (isIfaceTri) {
// Mark here too, so a net made tristate only by an external 'z driver
// still captures a plain cross-hierarchy driver processed later.
m_varAux(invarp).ifaceTristate = true;
// Interface tristate vars: drivers from different interface instances
// (different VarXRef dotted paths) must be processed separately.
// E.g. io_ifc.d and io_ifc_local.d both target the same AstVar d in
@@ -780,7 +791,11 @@ class TristateVisitor final : public TristateBaseVisitor {
}
} else if (VN_IS(nodep, Iface) && !invarp->isIO()) {
// Local driver in an interface module - use contribution mechanism
// so it can be combined with any external drivers later
// so it can be combined with any external drivers later. Record that
// this interface net is tristate, so a module that drives it across
// hierarchy with a plain (non-Z) assign is also routed through the
// contribution mechanism (its own graph has no Z to mark it tristate).
m_varAux(invarp).ifaceTristate = true;
insertTristatesSignal(nodep, invarp, refsp, true, "", "", nullptr);
} else {
insertTristatesSignal(nodep, invarp, refsp, false, "", "", nullptr);
@@ -2080,6 +2095,15 @@ class TristateVisitor final : public TristateBaseVisitor {
if (m_graphing) {
if (nodep->access().isWriteOrRW()) associateLogic(nodep, nodep->varp());
if (nodep->access().isReadOrRW()) associateLogic(nodep->varp(), nodep);
// Only interface tristate nets need this: a plain (non-Z) cross-hierarchy
// driver has no Z in its own module's graph, so mark the net tristate here to
// collect the driver as a contribution. The ifaceTristate flag is only set for
// interface nets; a non-interface cross-module tri driver does nothing here and
// is instead rejected (E_UNSUPPORTED) later in insertTristates.
if (nodep->access().isWriteOrRW() && VN_IS(nodep, VarXRef)
&& m_varAux(nodep->varp()).ifaceTristate) {
m_tgraph.setTristate(nodep->varp());
}
} else {
if (nodep->user2() & U2_NONGRAPH) return; // Processed
nodep->user2Or(U2_NONGRAPH);
@@ -2160,6 +2184,9 @@ class TristateVisitor final : public TristateBaseVisitor {
}
void visit(AstNodeModule* nodep) override {
// Interfaces are processed first in the constructor; skip the duplicate visit
// during the later iterateChildrenBackwardsConst() pass over all modules.
if (m_processedIfaces && VN_IS(nodep, Iface)) return;
UINFO(8, dbgState() << nodep);
VL_RESTORER(m_modp);
VL_RESTORER(m_graphing);
@@ -2296,6 +2323,18 @@ public:
// CONSTRUCTORS
explicit TristateVisitor(AstNetlist* netlistp) {
m_tgraph.clearAndCheck();
// Process interface modules first, so an interface tristate net is recorded
// (AuxAstVar::ifaceTristate) before any module that drives it across hierarchy is
// graphed. A module driving such a net with a plain (non-Z) assign has no Z in its
// own graph to mark the net tristate, so without this its driver would be dropped.
// Collect only the interfaces (reverse declaration order to match the pass below).
std::vector<AstNodeModule*> ifacesp;
for (AstNode* modp = netlistp->modulesp(); modp; modp = modp->nextp()) {
if (VN_IS(modp, Iface)) ifacesp.push_back(VN_AS(modp, NodeModule));
}
for (auto it = ifacesp.rbegin(); it != ifacesp.rend(); ++it) iterate(*it);
m_processedIfaces = true;
// Then the rest in the historical order; interfaces are skipped (already done).
iterateChildrenBackwardsConst(netlistp);
// Combine interface tristate contributions after all modules processed