Skip to content

fix: use NLA to preserve externalized memory from being dropped #9012

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 1 commit into
base: main
Choose a base branch
from
Open

fix: use NLA to preserve externalized memory from being dropped #9012

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
35 changes: 33 additions & 2 deletions lib/Dialect/FIRRTL/Transforms/LayerSink.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@
#include "circt/Dialect/FIRRTL/FIRRTLInstanceGraph.h"
#include "circt/Dialect/FIRRTL/FIRRTLOps.h"
#include "circt/Dialect/FIRRTL/Passes.h"
#include "circt/Dialect/HW/HWOps.h"
#include "circt/Support/Debug.h"
#include "mlir/IR/Dominance.h"
#include "mlir/IR/Threading.h"
Expand All @@ -34,6 +35,9 @@ using namespace circt;
using namespace firrtl;
using namespace mlir;

static constexpr llvm::StringLiteral
kExtMemoryEffectNLAAttrName("circt.layerSink.externalMemoryEffect");

//===----------------------------------------------------------------------===//
// Helpers
//===----------------------------------------------------------------------===//
Expand Down Expand Up @@ -87,7 +91,10 @@ static bool cloneable(Operation *op) {
namespace {
class EffectInfo {
public:
EffectInfo(CircuitOp circuit, InstanceGraph &instanceGraph) {
EffectInfo(CircuitOp circuit, InstanceGraph &instanceGraph,
DenseSet<StringAttr> explicitEffectfulModules)
: explicitEffectfulModules(std::move(explicitEffectfulModules)) {
DenseSet<InstanceGraphNode *> visited;
instanceGraph.walkPostOrder(
[&](auto &node) { update(node.getModule().getOperation()); });
}
Expand All @@ -111,6 +118,7 @@ class EffectInfo {
}

private:
DenseSet<StringAttr> explicitEffectfulModules;
/// Record whether the module contains any effectful ops.
void update(FModuleOp moduleOp) {
moduleOp.getBodyBlock()->walk([&](Operation *op) {
Expand All @@ -130,6 +138,14 @@ class EffectInfo {
if (!annos.empty())
return markEffectful(moduleOp);

if (explicitEffectfulModules.contains(moduleOp.getModuleNameAttr()))
return markEffectful(moduleOp);

// Treat generated memory modules as effectful since they model stateful
// hardware even though they have no body.
if (isa<FMemModuleOp>(moduleOp.getOperation()))
return markEffectful(moduleOp);

for (auto annos : moduleOp.getPortAnnotations())
if (!cast<ArrayAttr>(annos).empty())
return markEffectful(moduleOp);
Expand Down Expand Up @@ -486,7 +502,19 @@ void LayerSinkPass::runOnOperation() {
<< "\n"
<< "Circuit: '" << circuit.getName() << "'\n";);
auto &instanceGraph = getAnalysis<InstanceGraph>();
EffectInfo effectInfo(circuit, instanceGraph);

DenseSet<StringAttr> explicitEffectModules;
SmallVector<hw::HierPathOp, 4> effectNLAs;
for (auto nla : circuit.getOps<hw::HierPathOp>()) {
if (!nla->hasAttr(kExtMemoryEffectNLAAttrName))
continue;
if (auto leaf = nla.leafMod())
explicitEffectModules.insert(leaf);
effectNLAs.push_back(nla);
}

EffectInfo effectInfo(circuit, instanceGraph,
std::move(explicitEffectModules));

std::atomic<bool> changed(false);
parallelForEach(&getContext(), circuit.getOps<FModuleOp>(),
Expand All @@ -495,6 +523,9 @@ void LayerSinkPass::runOnOperation() {
changed = true;
});

for (auto nla : effectNLAs)
nla.erase();

if (!changed)
markAllAnalysesPreserved();
else
Expand Down
19 changes: 19 additions & 0 deletions lib/Dialect/FIRRTL/Transforms/LowerMemory.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/STLFunctionalExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/Parallel.h"
#include <optional>
#include <set>
Expand Down Expand Up @@ -189,6 +190,9 @@ LowerMemoryPass::getMemoryModulePorts(const FirMemory &mem) {
return ports;
}

static constexpr llvm::StringLiteral
kExtMemoryEffectNLAAttrName("circt.layerSink.externalMemoryEffect");

FMemModuleOp
LowerMemoryPass::emitMemoryModule(MemOp op, const FirMemory &mem,
const SmallVectorImpl<PortInfo> &ports) {
Expand All @@ -208,6 +212,21 @@ LowerMemoryPass::emitMemoryModule(MemOp op, const FirMemory &mem,
mem.numReadWritePorts, mem.dataWidth, mem.maskBits, mem.readLatency,
mem.writeLatency, mem.depth,
*symbolizeRUWBehavior(static_cast<uint32_t>(mem.readUnderWrite)));
// Mark the generated external memory as effectful so downstream passes do not
// treat it as pure and drop the wrapper wiring around it. We create a
// temporary HierPathOp, which LayerSink will consume and erase.
auto circuit = op->getParentOfType<CircuitOp>();
OpBuilder nlaBuilder(circuit);
nlaBuilder.setInsertionPointToEnd(circuit.getBodyBlock());
auto pathAttr = nlaBuilder.getArrayAttr(SmallVector<Attribute, 1>{
FlatSymbolRefAttr::get(moduleOp.getModuleNameAttr())});
auto nlaName = circuitNamespace.newName(
(moduleOp.getModuleNameAttr().getValue() + "_effect_nla").str());
auto nla = nlaBuilder.create<hw::HierPathOp>(
mem.loc, StringAttr::get(&getContext(), nlaName), pathAttr);
nla->setAttr(kExtMemoryEffectNLAAttrName,
FlatSymbolRefAttr::get(moduleOp.getModuleNameAttr()));
SymbolTable::setSymbolVisibility(nla, SymbolTable::Visibility::Private);
SymbolTable::setSymbolVisibility(moduleOp, SymbolTable::Visibility::Private);
return moduleOp;
}
Expand Down