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Fix slow compilation of generated sampled value code (#6652)

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For handling $past and similar functions, we used to collect sampled
values of variables at the beginning of the main _eval function. If we
have many of these, this can grow _eval very large which can make C++
compilation very slow. Apply usual fix of emitting the necessary code in
a separate function and then splitting it based on size.
This commit is contained in:
Geza Lore
2025-11-06 13:31:40 +00:00
committed by GitHub
parent 47b52800bf
commit f7e12e9219
3 changed files with 26 additions and 17 deletions
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src/V3Clock.cpp
+23 -15
View File
@@ -24,6 +24,7 @@
#include "V3Clock.h"
#include "V3Const.h"
#include "V3Sched.h"
VL_DEFINE_DEBUG_FUNCTIONS;
@@ -62,7 +63,7 @@ class ClockVisitor final : public VNVisitor {
// NODE STATE
// STATE
AstCFunc* const m_evalp = nullptr; // The '_eval' function
AstCFunc* m_sampleCFuncp = nullptr; // The CFunc to populate with sampled value assignments
// VISITORS
void visit(AstCoverToggle* nodep) override {
@@ -98,19 +99,20 @@ class ClockVisitor final : public VNVisitor {
//========== Move sampled assignments
void visit(AstVarScope* nodep) override {
AstVar* const varp = nodep->varp();
if (varp->valuep() && varp->name().substr(0, strlen("__Vsampled")) == "__Vsampled") {
FileLine* const flp = nodep->fileline();
AstNodeExpr* const rhsp = VN_AS(varp->valuep()->unlinkFrBack(), NodeExpr);
AstVarRef* const lhsp = new AstVarRef{flp, nodep, VAccess::WRITE};
AstAssign* const assignp = new AstAssign{flp, lhsp, rhsp};
if (AstNode* const stmtsp = m_evalp->stmtsp()) {
stmtsp->addHereThisAsNext(assignp);
} else {
m_evalp->addStmtsp(assignp);
}
varp->direction(VDirection::NONE); // Restore defaults
varp->primaryIO(false);
if (!varp->valuep()) return;
if (!VString::startsWith(varp->name(), "__Vsampled")) 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};
m_sampleCFuncp->addStmtsp(new AstAssign{flp, lhsp, rhsp});
varp->direction(VDirection::NONE); // Restore defaults
varp->primaryIO(false);
}
//--------------------
@@ -118,9 +120,15 @@ class ClockVisitor final : public VNVisitor {
public:
// CONSTRUCTORS
explicit ClockVisitor(AstNetlist* netlistp)
: m_evalp{netlistp->evalp()} {
explicit ClockVisitor(AstNetlist* netlistp) {
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());
}
}
~ClockVisitor() override = default;
};