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Optimize V3Scope to move nodes on the last instance of a module (#8417)

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Nodes were always cloned under the new scope, with the originals deleted
at the end of the pass. Count total module instantiations up front, then
move the nodes instead of cloning them when scoping the last instance.

Required to avoid a memory regression in a follow up, but also faster
and less peak memory overall.

Output is identical.
This commit is contained in:
Geza Lore
2026-09-20 14:15:29 +01:00
committed by GitHub
parent d30487e0f7
commit dfa4ace3dd
1 changed files with 52 additions and 30 deletions
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src/V3Scope.cpp
+52 -30
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@@ -38,8 +38,10 @@ class ScopeVisitor final : public VNVisitor {
// AstVar::user1p -> AstVarScope*. Replacement for this variable
// AstCell::user2p -> AstScope*. The scope created inside the cell
// AstTask::user2p -> AstTask*. Replacement task
// AstNodeModule::user3() -> uint64_t. Pending instantiations of this module
const VNUser1InUse m_inuser1;
const VNUser2InUse m_inuser2;
const VNUser3InUse m_inuser3;
// TYPES
// These cannot be unordered unless make a specialized hashing pair (gcc-8)
@@ -52,6 +54,7 @@ class ScopeVisitor final : public VNVisitor {
// STATE, for passing down one level of hierarchy (may need save/restore)
AstCell* m_aboveCellp = nullptr; // Cell that instantiates this module
AstScope* m_aboveScopep = nullptr; // Scope that instantiates this scope
bool m_last = false; // Scoping the last instantiation of the current module
std::unordered_map<AstNodeModule*, AstScope*>
m_classOrPackageScopes; // Scopes for each class or package
@@ -61,6 +64,32 @@ class ScopeVisitor final : public VNVisitor {
// METHODS
// Count module instantiations, visiting cells the same way the traversal below does
static void countInstantiations(AstNodeModule* modp) {
modp->user3Inc();
for (AstNode* stmtp = modp->stmtsp(); stmtp; stmtp = stmtp->nextp()) {
if (const AstCell* const cellp = VN_CAST(stmtp, Cell)) {
countInstantiations(cellp->modp());
}
}
}
// Copy, or move (on the last instantiation), the given node under
// the current scope, and return the version now under the scope
template <typename T_Node>
T_Node* cloneOrMove(T_Node* nodep) {
T_Node* clonep;
if (m_last) {
nodep->unlinkFrBack();
clonep = nodep;
} else {
clonep = nodep->cloneTree(false);
}
nodep->user2p(clonep);
m_scopep->addBlocksp(clonep);
return clonep;
}
void cleanupVarRefs() {
for (const auto& itr : m_varRefScopes) {
AstVarRef* const nodep = itr.first;
@@ -100,6 +129,7 @@ class ScopeVisitor final : public VNVisitor {
// Operate starting at the top of the hierarchy
m_aboveCellp = nullptr;
m_aboveScopep = nullptr;
countInstantiations(modp);
iterate(modp);
cleanupVarRefs();
}
@@ -157,8 +187,14 @@ class ScopeVisitor final : public VNVisitor {
}
// Copy blocks into this scope
// If this is the first usage of the block ever, we can move the reference
iterateChildren(nodep);
{
VL_RESTORER(m_last);
const uint64_t nInsts = nodep->user3();
UASSERT_OBJ(nInsts, nodep, "Module scoped more times than instantiated");
nodep->user3(nInsts - 1);
m_last = nInsts == 1;
iterateChildren(nodep);
}
// ***Note m_scopep is passed back to the caller of the routine (above)
}
@@ -208,41 +244,31 @@ class ScopeVisitor final : public VNVisitor {
VL_RESTORER(m_procedurep);
m_procedurep = nodep;
UINFO(4, " Move " << nodep);
AstNode* const clonep = nodep->cloneTree(false);
nodep->user2p(clonep);
m_scopep->addBlocksp(clonep);
iterateChildren(clonep); // We iterate under the *clone*
// We iterate under the *clone*
iterateChildren(cloneOrMove(nodep));
}
void visit(AstAlias* nodep) override {
// Add to list of blocks under this scope
UINFO(4, " Move " << nodep);
AstNode* const clonep = nodep->cloneTree(false);
nodep->user2p(clonep);
m_scopep->addBlocksp(clonep);
iterateChildren(clonep); // We iterate under the *clone*
// We iterate under the *clone*
iterateChildren(cloneOrMove(nodep));
}
void visit(AstAliasScope* nodep) override {
// Copy under the scope but don't recurse
UINFO(4, " Move " << nodep);
AstNode* const clonep = nodep->cloneTree(false);
nodep->user2p(clonep);
m_scopep->addBlocksp(clonep);
iterateChildren(clonep); // We iterate under the *clone*
// We iterate under the *clone*
iterateChildren(cloneOrMove(nodep));
}
void visit(AstCoverToggle* nodep) override {
// Add to list of blocks under this scope
UINFO(4, " Move " << nodep);
AstNode* const clonep = nodep->cloneTree(false);
nodep->user2p(clonep);
m_scopep->addBlocksp(clonep);
iterateChildren(clonep); // We iterate under the *clone*
// We iterate under the *clone*
iterateChildren(cloneOrMove(nodep));
}
void visit(AstCFunc* nodep) override {
// Add to list of blocks under this scope
UINFO(4, " CFUNC " << nodep);
AstCFunc* const clonep = nodep->cloneTree(false);
nodep->user2p(clonep);
m_scopep->addBlocksp(clonep);
AstCFunc* const clonep = cloneOrMove(nodep);
clonep->scopep(m_scopep);
// We iterate under the *clone*
iterateChildren(clonep);
@@ -250,17 +276,13 @@ class ScopeVisitor final : public VNVisitor {
void visit(AstNodeFTask* nodep) override {
// Add to list of blocks under this scope
UINFO(4, " FTASK " << nodep);
AstNodeFTask* clonep;
if (nodep->classMethod()) {
AstNodeFTask* const clonep = [&]() {
VL_RESTORER(m_last);
// Only one scope will be created, so avoid pointless cloning
nodep->unlinkFrBack();
clonep = nodep;
} else {
clonep = nodep->cloneTree(false);
}
nodep->user2p(clonep);
if (nodep->classMethod()) m_last = true;
return cloneOrMove(nodep);
}();
clonep->user2p(clonep); // For recursive self-references after cloneTree
m_scopep->addBlocksp(clonep);
// We iterate under the *clone*
iterateChildren(clonep);
}