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Internals: Move the eval loop into the runtime library (#8225)

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The loops modelling the SystemVerilog scheduling regions are no longer
generated. They now live in 'VerilatedEvalLoop' in the runtime library.
The generated model holds one as a member, passing itself to it, and
exposes each evaluation entry point to it as a pure virtual method on
VerilatedModel. The model's 'eval' and 'eval_step' remain the top level
entry points, and are backward compatible.

V3Sched no longer emits '_eval' or '_eval_settle', etc.. Instead every
evaluation entry point called from the runtime is enumerated by 'VEval',

Scheduling creates all entry points, for all scheduling regions, even if
they are empty, and the runtime eval loop calls everything
unconditionally. If regions are empty, this is simply a call to an empty
function. This will hurt performance on very small models, but should
not be noticeable on anything meaningful, so it is likely best to keep
to reduce complexity.

A scheduling entry points evaluate a single iteration and returns
whether it did any work, they are effectively the previous
`_eval_phase_*` functions.
This commit is contained in:
Geza Lore
2026-08-27 07:53:02 -04:00
committed by GitHub
parent 59f221986c
commit 8546d5db06
44 changed files with 2204 additions and 1418 deletions
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src/V3AstNodes.cpp
+25 -2
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@@ -22,6 +22,8 @@
#include "V3Global.h"
#include "V3Graph.h"
#include "V3Hasher.h"
#include "V3InstrCount.h"
#include "V3Stats.h"
#include "V3String.h"
#include "V3Ast__gen_impl.h" // Generated by 'astgen'
@@ -602,6 +604,15 @@ const char* AstNetlist::broken() const {
for (const AstVar* const varp : m_deferredParamVarps) {
BROKEN_RTN(!varp || !varp->brokeExists());
}
for (int i = 0; i < VEval::_ENUM_END; ++i) {
const AstCFunc* const funcp = m_evalFuncps[i];
const AstCFunc* const dumpp = m_dumpTriggersFuncps[i];
BROKEN_RTN(funcp && !funcp->brokeExists());
BROKEN_RTN(dumpp && !dumpp->brokeExists());
// Once created, an entry point has a trigger dump iff it has triggers
BROKEN_RTN(funcp && VEval{i}.hasTriggers() && !dumpp);
BROKEN_RTN(dumpp && !VEval{i}.hasTriggers());
}
return nullptr;
}
@@ -2964,13 +2975,13 @@ void AstNetlist::deleteContents() {
m_constPoolp = nullptr;
m_dollarUnitPkgp = nullptr;
m_stdPackagep = nullptr;
m_evalp = nullptr;
m_evalNbap = nullptr;
m_dpiExportTriggerp = nullptr;
m_delaySchedulerp = nullptr;
m_nbaEventp = nullptr;
m_nbaEventTriggerp = nullptr;
m_topScopep = nullptr;
m_evalFuncps.fill(nullptr);
m_dumpTriggersFuncps.fill(nullptr);
if (op1p()) op1p()->unlinkFrBackWithNext()->deleteTree();
if (op2p()) op2p()->unlinkFrBackWithNext()->deleteTree();
if (op3p()) op3p()->unlinkFrBackWithNext()->deleteTree();
@@ -3014,6 +3025,18 @@ AstFuncRef* AstNetlist::stdPackageProcessSelfp(FileLine* flp) const {
processSelfp->classOrPackagep(v3Global.rootp()->stdPackageProcessp());
return processSelfp;
}
void AstNetlist::addEvalStats(const std::string& phase) {
if (!v3Global.opt.stats()) return;
for (int i = 0; i < VEval::_ENUM_END; ++i) {
VEval eval{i};
AstCFunc* const funcp = m_evalFuncps[i];
if (!funcp) continue;
const uint32_t nodes = funcp->nodeCount();
const uint32_t instr = V3InstrCount::count(funcp, false);
V3Stats::addStat("Size of eval, nodes - '" + eval.tag() + "', " + phase, nodes);
V3Stats::addStat("Size of eval, instr - '" + eval.tag() + "', " + phase, instr);
}
}
void AstNodeModule::dump(std::ostream& str) const {
this->AstNode::dump(str);
str << " L" << level();