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Use AstDelay nodes for intra-assignment delays (#3672)

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Also fix messy implementation of net delays.

Signed-off-by: Krzysztof Bieganski <[email protected]>
This commit is contained in:
Krzysztof Bieganski
2022-10-14 09:35:26 +02:00
committed by GitHub
parent caed086516
commit 8a347248f5
16 changed files with 119 additions and 104 deletions
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src/V3Timing.cpp
+25 -17
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@@ -135,14 +135,17 @@ private:
return nodep->user3u().to<DependencyVertex*>();
}
// Find net delay on the LHS of an assignment
AstNode* getLhsNetDelay(AstNodeAssign* nodep) const {
AstDelay* getLhsNetDelay(AstNodeAssign* nodep) const {
bool foundWrite = false;
AstNode* delayp = nullptr;
AstDelay* delayp = nullptr;
nodep->lhsp()->foreach<AstNodeVarRef>([&](const AstNodeVarRef* const refp) {
if (!refp->access().isWriteOrRW()) return;
UASSERT_OBJ(!foundWrite, nodep, "Should only be one variable written to on the LHS");
foundWrite = true;
if (refp->varp()->delayp()) delayp = refp->varp()->delayp()->cloneTree(false);
if (refp->varp()->delayp()) {
delayp = refp->varp()->delayp();
delayp->unlinkFrBack();
}
});
return delayp;
}
@@ -150,20 +153,25 @@ private:
// assignment under it
AstNodeStmt* factorOutTimingControl(AstNodeAssign* nodep) const {
AstNodeStmt* stmtp = nodep;
AstNode* delayp = getLhsNetDelay(nodep);
AstDelay* delayp = getLhsNetDelay(nodep);
FileLine* const flp = nodep->fileline();
AstNode* const controlp = nodep->timingControlp();
if (controlp) {
controlp->unlinkFrBack();
if (!VN_IS(controlp, SenTree)) {
delayp = delayp ? new AstAdd{flp, delayp, controlp} : controlp;
if (auto* const assignDelayp = VN_CAST(controlp, Delay)) {
if (delayp) {
delayp->lhsp(new AstAdd{flp, delayp->lhsp()->unlinkFrBack(),
assignDelayp->lhsp()->unlinkFrBack()});
VL_DO_DANGLING(assignDelayp->deleteTree(), nodep);
} else {
delayp = assignDelayp;
}
}
}
if (delayp) {
auto* const delayStmtp = new AstDelay{flp, delayp, nullptr};
stmtp->replaceWith(delayStmtp);
delayStmtp->addStmtsp(stmtp);
stmtp = delayStmtp;
stmtp->replaceWith(delayp);
delayp->addStmtsp(stmtp);
stmtp = delayp;
}
if (auto* const sensesp = VN_CAST(controlp, SenTree)) {
auto* const eventControlp = new AstEventControl{flp, sensesp, nullptr};
@@ -493,7 +501,6 @@ private:
VL_DO_DANGLING(nodep->deleteTree(), nodep);
}
void visit(AstNodeAssign* nodep) override {
iterateChildren(nodep);
// Only process once to avoid infinite loops (due to the net delay)
if (nodep->user1SetOnce()) return;
AstNode* const controlp = factorOutTimingControl(nodep);
@@ -536,14 +543,14 @@ private:
replaceWithIntermediate(nodep->rhsp(), m_intraValueNames.get(nodep));
}
void visit(AstAssignW* nodep) override {
iterateChildren(nodep);
auto* const netDelayp = getLhsNetDelay(nodep);
AstDelay* const netDelayp = getLhsNetDelay(nodep);
if (!netDelayp && !nodep->timingControlp()) return;
// This assignment will be converted to an always. In some cases this may generate an
// UNOPTFLAT, e.g.: assign #1 clk = ~clk. We create a temp var for the LHS of this assign,
// to disable the UNOPTFLAT warning for it.
// TODO: Find a way to do this without introducing this var. Perhaps make V3SchedAcyclic
// recognize awaits and prevent it from treating this kind of logic as cyclic
// UNOPTFLAT, e.g.: assign #1 clk = ~clk. We create a temp var for the LHS of this
// assign, to disable the UNOPTFLAT warning for it.
// TODO: Find a way to do this without introducing this var. Perhaps make
// V3SchedAcyclic recognize awaits and prevent it from treating this kind of logic as
// cyclic
AstNode* const lhsp = nodep->lhsp()->unlinkFrBack();
std::string varname;
if (auto* const refp = VN_CAST(lhsp, VarRef)) {
@@ -631,6 +638,7 @@ private:
//--------------------
void visit(AstNodeMath*) override {} // Accelerate
void visit(AstVar*) override {}
void visit(AstNode* nodep) override { iterateChildren(nodep); }
public: