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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/V3SchedUtil.cpp
+14 -21
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@@ -46,6 +46,19 @@ AstCFunc* makeSubFunction(AstNetlist* netlistp, const string& name, bool slow) {
return funcp;
}
AstVarScope* newArgument(AstCFunc* funcp, AstNodeDType* dtypep, const string& name,
VDirection direction) {
FileLine* const flp = funcp->fileline();
AstScope* const scopep = funcp->scopep();
AstVar* const varp = new AstVar{flp, VVarType::BLOCKTEMP, name, dtypep};
varp->funcLocal(true);
varp->direction(direction);
funcp->addArgsp(varp);
AstVarScope* const vscp = new AstVarScope{flp, scopep, varp};
scopep->addVarsp(vscp);
return vscp;
}
AstCFunc* makeTopFunction(AstNetlist* netlistp, const string& name, bool slow) {
AstCFunc* const funcp = makeSubFunction(netlistp, name, slow);
funcp->entryPoint(true);
@@ -77,27 +90,6 @@ AstNodeStmt* callVoidFunc(AstCFunc* funcp) {
return callp->makeStmt();
}
AstNodeStmt* checkIterationLimit(AstNetlist* netlistp, const string& name, AstVarScope* counterp,
AstNodeStmt* dumpCallp) {
FileLine* const flp = netlistp->fileline();
// If we exceeded the iteration limit, die
const uint32_t limit = v3Global.opt.convergeLimit();
AstVarRef* const counterRefp = new AstVarRef{flp, counterp, VAccess::READ};
AstConst* const constp = new AstConst{flp, AstConst::DTyped{}, counterp->dtypep()};
constp->num().setLong(limit);
AstNodeExpr* const condp = new AstGt{flp, counterRefp, constp};
AstIf* const ifp = new AstIf{flp, condp};
ifp->branchPred(VBranchPred::BP_UNLIKELY);
if (dumpCallp) ifp->addThensp(dumpCallp);
AstCStmt* const stmtp = new AstCStmt{flp};
ifp->addThensp(stmtp);
stmtp->add("VL_FATAL_MT(\"\", 0, \"\", \"DIDNOTCONVERGE: " + name
+ " region did not converge after '--converge-limit' of " + std::to_string(limit)
+ " tries\");");
return ifp;
}
static AstCFunc* splitCheckCreateNewSubFunc(AstCFunc* ofuncp) {
static std::map<AstCFunc*, uint32_t> s_funcNums; // What split number to attach to a function
const uint32_t funcNum = s_funcNums[ofuncp]++;
@@ -256,4 +248,5 @@ AstIf* createIfFromSenTree(AstSenTree* senTreep) {
}
} // namespace util
} // namespace V3Sched