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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/V3Clock.cpp
+4 -14
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@@ -63,7 +63,7 @@ class ClockVisitor final : public VNVisitor {
// NODE STATE
// STATE
AstCFunc* m_sampleCFuncp = nullptr; // The CFunc to populate with sampled value assignments
AstCFunc* const m_sampleCFuncp; // The CFunc to populate with sampled value assignments
// VISITORS
void visit(AstCoverToggle* nodep) override {
@@ -106,11 +106,6 @@ class ClockVisitor final : public VNVisitor {
if (!varp->valuep()) return;
if (!varp->sampled()) return;
// Create the containing function on first encounter
if (!m_sampleCFuncp) {
m_sampleCFuncp = V3Sched::util::makeSubFunction(v3Global.rootp(), "_sample", false);
}
FileLine* const flp = nodep->fileline();
AstNodeExpr* const rhsp = VN_AS(varp->valuep()->unlinkFrBack(), NodeExpr);
AstVarRef* const lhsp = new AstVarRef{flp, nodep, VAccess::WRITE};
@@ -124,15 +119,10 @@ class ClockVisitor final : public VNVisitor {
public:
// CONSTRUCTORS
explicit ClockVisitor(AstNetlist* netlistp) {
explicit ClockVisitor(AstNetlist* netlistp)
: m_sampleCFuncp{netlistp->evalFuncp(VEval::SAMPLE)} {
iterate(netlistp);
// If we need a sample function, call it at the begining of eval
if (m_sampleCFuncp) {
V3Sched::util::splitCheck(m_sampleCFuncp);
AstCCall* const callp = new AstCCall{m_sampleCFuncp->fileline(), m_sampleCFuncp};
callp->dtypeSetVoid();
netlistp->evalp()->stmtsp()->addHereThisAsNext(callp->makeStmt());
}
V3Sched::util::splitCheck(m_sampleCFuncp);
}
~ClockVisitor() override = default;
};