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//===--- AccessMarkerElimination.cpp - Eliminate access markers. ----------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
///
/// This pass eliminates the instructions that demarcate memory access regions.
/// If no memory access markers exist, then the pass does nothing. Otherwise, it
/// unconditionally eliminates all non-dynamic markers (plus any dynamic markers
/// if dynamic exclusivity checking is disabled).
///
/// This is an always-on pass for temporary bootstrapping. It allows running
/// test cases through the pipeline and exercising SIL verification before all
/// passes support access markers.
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "access-marker-elim"
#include "swift/Basic/Range.h"
#include "swift/SIL/MemAccessUtils.h"
#include "swift/SIL/SILFunction.h"
#include "swift/SILOptimizer/PassManager/Transforms.h"
#include "llvm/Support/CommandLine.h"
using namespace swift;
// This temporary option allows markers during optimization passes. Enabling
// this flag causes this pass to preserve all access markers. Otherwise, it only
// preserved "dynamic" markers.
llvm::cl::opt<bool> EnableOptimizedAccessMarkers(
"sil-optimized-access-markers", llvm::cl::init(false),
llvm::cl::desc("Enable memory access markers during optimization passes."));
namespace {
struct AccessMarkerElimination {
SILModule *Mod;
SILFunction *F;
bool removedAny = false;
AccessMarkerElimination(SILFunction *F)
: Mod(&F->getModule()), F(F) {}
void notifyErased(SILInstruction *inst) {
LLVM_DEBUG(llvm::dbgs() << "Erasing access marker: " << *inst);
removedAny = true;
}
SILBasicBlock::iterator eraseInst(SILInstruction *inst) {
auto nextIter = std::next(inst->getIterator());
notifyErased(inst);
return nextIter;
};
bool shouldPreserveAccess(SILAccessEnforcement enforcement);
// Check if the instruction is a marker that should be eliminated. If so,
// updated the SIL, short of erasing the marker itself, and return true.
SILBasicBlock::iterator checkAndEliminateMarker(SILInstruction *inst);
// Entry point called either by the pass by the same name
// or as a utility (e.g. during deserialization).
bool stripMarkers();
};
bool AccessMarkerElimination::shouldPreserveAccess(
SILAccessEnforcement enforcement) {
if (EnableOptimizedAccessMarkers || Mod->getOptions().VerifyExclusivity)
return true;
switch (enforcement) {
case SILAccessEnforcement::Static:
case SILAccessEnforcement::Unsafe:
return false;
// Signed access should be preserved until IRGen
case SILAccessEnforcement::Signed:
return true;
case SILAccessEnforcement::Unknown:
case SILAccessEnforcement::Dynamic:
return Mod->getOptions().EnforceExclusivityDynamic;
}
llvm_unreachable("unhandled enforcement");
}
// Check if the instruction is a marker that should be eliminated. If so, delete
// the begin_access along with all associated end_access and a valid instruction
// iterator pointing to the first remaining instruction following the
// begin_access. If the marker is not eliminated, return an iterator pointing to
// the marker.
SILBasicBlock::iterator
AccessMarkerElimination::checkAndEliminateMarker(SILInstruction *inst) {
if (auto beginAccess = dyn_cast<BeginAccessInst>(inst)) {
// Builtins used by the standard library must emit markers regardless of the
// current compiler options so that any user code that initiates access via
// the standard library is fully enforced.
if (beginAccess->isFromBuiltin())
return inst->getIterator();
// Leave dynamic and signed accesses in place, but delete all others.
if (shouldPreserveAccess(beginAccess->getEnforcement()))
return inst->getIterator();
notifyErased(beginAccess);
return removeBeginAccess(beginAccess);
}
// end_access instructions will be handled when we process the
// begin_access.
// begin_unpaired_access instructions will be directly removed and
// simply replaced with their operand.
if (auto BUA = dyn_cast<BeginUnpairedAccessInst>(inst)) {
// Builtins used by the standard library must emit markers regardless of the
// current compiler options.
if (BUA->isFromBuiltin())
return inst->getIterator();
if (shouldPreserveAccess(BUA->getEnforcement()))
return inst->getIterator();
return eraseInst(BUA);
}
// end_unpaired_access instructions will be directly removed and
// simply replaced with their operand.
if (auto EUA = dyn_cast<EndUnpairedAccessInst>(inst)) {
// Builtins used by the standard library must emit markers regardless of the
// current compiler options.
if (EUA->isFromBuiltin())
return inst->getIterator();
if (shouldPreserveAccess(EUA->getEnforcement()))
return inst->getIterator();
return eraseInst(EUA);
}
return inst->getIterator();
}
// Top-level per-function entry-point.
// Return `true` if any markers were removed.
bool AccessMarkerElimination::stripMarkers() {
// Iterating in reverse eliminates more begin_access users before they
// need to be replaced.
for (auto &BB : llvm::reverse(*F)) {
// Don't cache the begin iterator since we're reverse iterating.
for (auto II = BB.end(); II != BB.begin();) {
SILInstruction *inst = &*(--II);
// checkAndEliminateMarker returns the next non-deleted instruction. The
// following iteration moves the iterator backward.
II = checkAndEliminateMarker(inst);
}
}
return removedAny;
}
} // end anonymous namespace
// Implement a SILModule::SILFunctionBodyCallback that strips all access
// markers from newly deserialized function bodies.
static void prepareSILFunctionForOptimization(ModuleDecl *, SILFunction *F) {
LLVM_DEBUG(llvm::dbgs() << "Stripping all markers in: " << F->getName()
<< "\n");
AccessMarkerElimination(F).stripMarkers();
}
namespace {
struct AccessMarkerEliminationPass : SILModuleTransform {
void run() override {
auto &M = *getModule();
for (auto &F : M) {
bool removedAny = AccessMarkerElimination(&F).stripMarkers();
// Only invalidate analyses if we removed some markers.
if (removedAny) {
auto InvalidKind = SILAnalysis::InvalidationKind::Instructions;
invalidateAnalysis(&F, InvalidKind);
}
}
// Markers from all current SIL functions are stripped. Register a
// callback to strip an subsequently loaded functions on-the-fly.
if (!EnableOptimizedAccessMarkers && !M.checkHasAccessMarkerHandler()) {
using NotificationHandlerTy =
FunctionBodyDeserializationNotificationHandler;
auto *n = new NotificationHandlerTy(prepareSILFunctionForOptimization);
std::unique_ptr<DeserializationNotificationHandler> ptr(n);
M.registerDeserializationNotificationHandler(std::move(ptr));
M.setHasAccessMarkerHandler();
}
}
};
} // end anonymous namespace
SILTransform *swift::createAccessMarkerElimination() {
return new AccessMarkerEliminationPass();
}
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