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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/V3EmitCModel.cpp
+77 -30
View File
@@ -31,9 +31,12 @@ class EmitCModel final : public EmitCFunc {
using CFuncVector = std::vector<const AstCFunc*>;
// MEMBERS
// Needed to emit references to functions of the model, e.g. entry points
const EmitCParentModule m_emitCParentModule;
V3UniqueNames m_uniqueNames; // For generating unique file names
// METHODS
CFuncVector findFuncps(std::function<bool(const AstCFunc*)> cb) {
CFuncVector funcps;
for (AstNode* nodep = m_modp->stmtsp(); nodep; nodep = nodep->nextp()) {
@@ -91,11 +94,16 @@ class EmitCModel final : public EmitCFunc {
puts("public ::sc_core::sc_module, ");
}
puts("public VerilatedModel {\n");
// The symbol table references the model's evaluation state
puts("friend class " + EmitCUtil::symClassName() + ";\n");
ofp()->resetPrivate();
ofp()->putsPrivate(true); // private:
puts("// Symbol table holding complete model state (owned by this class)\n");
puts(EmitCUtil::symClassName() + "* const vlSymsp;\n");
puts("// Evaluation loop\n");
puts("VerilatedEvalLoop m_evalLoop;\n");
puts("\n");
ofp()->putsPrivate(false); // public:
@@ -258,7 +266,23 @@ class EmitCModel final : public EmitCFunc {
}
ofp()->putsPrivate(true); // private:
puts("// Internal functions - trace registration\n");
puts("\n// Internal functions - the model's evaluation entry points\n");
puts("void evalBegin() override final;\n");
puts("void evalEnd() override final;\n");
for (int i = 0; i < VEval::_ENUM_END; ++i) {
const VEval eval{i};
// Only the iterated regions report whether they did any work
puts(eval.isIterated() ? "bool "s : "void "s);
puts(eval.evalMethod() + (eval.firstIteration() ? "(bool firstIteration)"s : "()"s));
puts(" override final;\n");
}
for (int i = 0; i < VEval::_ENUM_END; ++i) {
const VEval eval{i};
if (!eval.hasTriggers()) continue;
puts("void " + eval.dumpTriggersMethod() + "() override final;\n");
}
puts("\n// Internal functions - trace registration\n");
puts("void traceBaseModel(VerilatedTraceBaseC* tfp, int levels, int options);\n");
puts("};\n");
@@ -279,11 +303,13 @@ class EmitCModel final : public EmitCFunc {
puts(" , vlSymsp{new " + EmitCUtil::symClassName()
+ "(contextp(), name(), this)}\n");
} else {
puts(+"(VerilatedContext* _vcontextp__, const char* _vcname__)\n");
puts("(VerilatedContext* _vcontextp__, const char* _vcname__)\n");
puts(" : VerilatedModel{*_vcontextp__}\n");
puts(" , vlSymsp{new " + EmitCUtil::symClassName()
+ "(contextp(), _vcname__, this)}\n");
}
puts(" , m_evalLoop{*this, /*convergeLimit:*/ "s
+ cvtToStr(v3Global.opt.convergeLimit()) + "}\n");
// Set up IO references
for (const AstNode* nodep = modp->stmtsp(); nodep; nodep = nodep->nextp()) {
@@ -311,6 +337,12 @@ class EmitCModel final : public EmitCFunc {
puts("{\n");
puts("// Register model with the context\n");
puts("contextp()->addModel(this);\n");
if (v3Global.opt.profExec()) {
putsDecoration(nullptr, "// Profile the evaluation loop's region loops\n");
const bool topLevel = !v3Global.opt.hierChild() && v3Global.opt.libCreate().empty();
puts("m_evalLoop.profiler(vlSymsp->__Vm_executionProfilerp, /*topLevel:*/ "s
+ (topLevel ? "true" : "false") + ");\n");
}
if (v3Global.opt.trace())
puts("contextp()->traceBaseModelCbAdd(\n"
"[this](VerilatedTraceBaseC* tfp, int levels, int options) {"
@@ -382,10 +414,14 @@ class EmitCModel final : public EmitCFunc {
puts("void " + topModNameProtected + "__" + protect("_eval_debug_assertions") + selfDecl
+ ";\n");
puts("#endif // VL_DEBUG\n");
puts("void " + topModNameProtected + "__" + protect("_eval_static") + selfDecl + ";\n");
puts("void " + topModNameProtected + "__" + protect("_eval_initial") + selfDecl + ";\n");
puts("void " + topModNameProtected + "__" + protect("_eval_settle") + selfDecl + ";\n");
puts("void " + topModNameProtected + "__" + protect("_eval") + selfDecl + ";\n");
const AstNetlist* const netlistp = v3Global.rootp();
for (int i = 0; i < VEval::_ENUM_END; ++i) {
emitCFuncDecl(netlistp->evalFuncp(VEval{i}), modp);
}
for (int i = 0; i < VEval::_ENUM_END; ++i) {
const AstCFunc* const funcp = netlistp->dumpTriggersFuncp(VEval{i});
if (funcp) emitCFuncDecl(funcp, modp);
}
if (optSystemC() && v3Global.usesTiming()) {
// ::eval
@@ -399,11 +435,15 @@ class EmitCModel final : public EmitCFunc {
puts("}\n");
}
// ::eval_step
// ::eval_step - the run-time library drives the whole time step
puts("\nvoid " + EmitCUtil::topClassName() + "::eval_step() {\n");
puts("VL_DEBUG_IF(VL_DBG_MSGF(\"+++++TOP Evaluate " + EmitCUtil::topClassName()
+ "::eval_step\\n\"); );\n");
puts("m_evalLoop.eval();\n");
puts("}\n");
// ::evalBegin - prepare the model for a time step
puts("\nvoid " + EmitCUtil::topClassName() + "::evalBegin() {\n");
puts("#ifdef VL_DEBUG\n");
putsDecoration(nullptr, "// Debug assertions\n");
puts(topModNameProtected + "__" + protect("_eval_debug_assertions")
@@ -415,32 +455,42 @@ class EmitCModel final : public EmitCFunc {
if (v3Global.hasEvents()) puts("vlSymsp->clearTriggeredEvents();\n");
if (v3Global.hasClasses()) puts("vlSymsp->__Vm_deleter.deleteAll();\n");
puts("if (VL_UNLIKELY(!vlSymsp->__Vm_didInit)) {\n");
puts("VL_DEBUG_IF(VL_DBG_MSGF(\"+ Initial\\n\"););\n");
puts(topModNameProtected + "__" + protect("_eval_static") + "(&(vlSymsp->TOP));\n");
puts(topModNameProtected + "__" + protect("_eval_initial") + "(&(vlSymsp->TOP));\n");
puts(topModNameProtected + "__" + protect("_eval_settle") + "(&(vlSymsp->TOP));\n");
puts("vlSymsp->__Vm_didInit = true;\n");
puts("}\n");
if (v3Global.opt.profExec() && !v3Global.opt.hierChild()
&& v3Global.opt.libCreate().empty()) {
puts("vlSymsp->__Vm_executionProfilerp->configure();\n");
}
puts("VL_DEBUG_IF(VL_DBG_MSGF(\"+ Eval\\n\"););\n");
puts(topModNameProtected + "__" + protect("_eval") + "(&(vlSymsp->TOP));\n");
// ::evalEnd - the time step is complete
puts("\nvoid " + EmitCUtil::topClassName() + "::evalEnd() {\n");
putsDecoration(nullptr, "// Evaluate cleanup\n");
puts("Verilated::endOfEval(vlSymsp->__Vm_evalMsgQp);\n");
puts("}\n");
// Evaluation entry points
for (int i = 0; i < VEval::_ENUM_END; ++i) {
const VEval eval{i};
AstCFunc* const funcp = v3Global.rootp()->evalFuncp(eval);
puts(eval.isIterated() ? "\nbool " : "\nvoid ");
puts(EmitCUtil::topClassName() + "::" + eval.evalMethod() + "(");
if (eval.firstIteration()) puts("bool firstIteration");
puts(") {\n");
if (eval.isIterated()) puts("return ");
puts(funcNameProtect(funcp, m_modp) + "(&(vlSymsp->TOP)");
if (eval.firstIteration()) puts(", firstIteration");
puts(");\n");
puts("}\n");
}
// The trigger dump of each region
for (int i = 0; i < VEval::_ENUM_END; ++i) {
const VEval eval{i};
if (!eval.hasTriggers()) continue;
puts("\nVL_ATTR_COLD void " + EmitCUtil::topClassName()
+ "::" + eval.dumpTriggersMethod() + "() {\n");
puts(funcNameProtect(v3Global.rootp()->dumpTriggersFuncp(eval), m_modp)
+ "(&(vlSymsp->TOP));\n");
puts("}\n");
}
}
void emitStandardMethods2(AstNodeModule* modp) {
const string topModNameProtected = EmitCUtil::prefixNameProtect(modp);
const string selfDecl = "(" + topModNameProtected + "* vlSelf)";
// ::eval_end_step
if (v3Global.needTraceDumper() && !optSystemC()) {
puts("\n");
@@ -485,14 +535,10 @@ class EmitCModel final : public EmitCFunc {
}
putSectionDelimiter("Invoke final blocks");
// Forward declarations
puts("\n");
putns(modp,
"void " + topModNameProtected + "__" + protect("_eval_final") + selfDecl + ";\n");
// ::final
puts("\nVL_ATTR_COLD void " + EmitCUtil::topClassName() + "::final() {\n");
puts("contextp()->executingFinal(true);\n");
puts(/**/ topModNameProtected + "__" + protect("_eval_final") + "(&(vlSymsp->TOP));\n");
puts("evalFinal();\n");
puts("contextp()->executingFinal(false);\n");
puts("}\n");
@@ -710,5 +756,6 @@ public:
void V3EmitC::emitcModel() {
UINFO(2, __FUNCTION__ << ":");
v3Global.rootp()->addEvalStats("emitc");
{ EmitCModel{v3Global.rootp()->topModulep()}; }
}