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//===- PackMetadataMarkerInserter.cpp - Add markers for metadata de/allocs ===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2023 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
//
//===----------------------------------------------------------------------===//
//
// IRGen initially assembles metadata and wtable packs on the stack. It then
// heapifies those packs.
//
// As an optimization, that heapification can be avoided some of the time:
// whenever the instructions which may result in such allocations are identified
// in functions which do not have instructions that obstruct StackNesting.
//
// Finds all instructions on behalf of which IRGen may emit on-stack pack
// metadata, looking for instructions which obstruct that optimization
//
// No code motion may occur after this pass: alloc_pack_metadata must directly
// precede the instruction on behalf of which metadata will actually be emitted
// (e.g. apply).
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "pack-metadata-dealloc-inserter"
#include "swift/AST/TypeWalker.h"
#include "swift/IRGen/IRGenSILPasses.h"
#include "swift/SIL/ApplySite.h"
#include "swift/SIL/Dominance.h"
#include "swift/SIL/SILBasicBlock.h"
#include "swift/SIL/SILBuilder.h"
#include "swift/SIL/SILInstruction.h"
#include "swift/SIL/SILNode.h"
#include "swift/SIL/StackList.h"
#include "swift/SILOptimizer/Analysis/DeadEndBlocksAnalysis.h"
#include "swift/SILOptimizer/Analysis/DominanceAnalysis.h"
#include "swift/SILOptimizer/PassManager/Transforms.h"
#include "swift/SILOptimizer/Utils/CFGOptUtils.h"
#include "swift/SILOptimizer/Utils/StackNesting.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/ErrorHandling.h"
using namespace swift;
namespace {
/// Finds and inserts marker instructions indicating where on-stack pack
/// metadata and wtables should be cleaned up.
///
/// Inserts alloc_pack_metadata before such instructions, and inserts
/// dealloc_pack_metadata on the dominance frontier. The client is responsible
/// for ensuring that critical edges have been split before inserting markers.
class Inserter {
SILFunction *function;
StackList<SILInstruction *> instructionsToCleanup;
public:
Inserter(SILFunction *function)
: function(function), instructionsToCleanup(function) {}
enum class FindResult {
None,
Some,
Unhandleable,
};
Inserter::FindResult find();
void insert(DominanceInfo *tree, DeadEndBlocks *deBlocks);
private:
FindResult shouldInsertMarkersForInstruction(SILInstruction *inst);
void insertMarkers(SILInstruction *instruction, DominanceInfo *tree,
DeadEndBlocks *deBlocks);
};
Inserter::FindResult
Inserter::shouldInsertMarkersForInstruction(SILInstruction *inst) {
switch (inst->getKind()) {
case SILInstructionKind::BuiltinInst: {
auto *bi = cast<BuiltinInst>(inst);
// Functions with async lets may use the stack, but that is not encoded in
// SIL. As a result, stack nesting is unable to properly nest async lets
// with on-stack pack metadata. rdar://109850951
if (bi->getBuiltinKind() ==
BuiltinValueKind::StartAsyncLetWithLocalBuffer ||
bi->getBuiltinKind() == BuiltinValueKind::StartAsyncLet)
return Inserter::FindResult::Unhandleable;
LLVM_FALLTHROUGH;
}
default:
return inst->mayRequirePackMetadata(*inst->getFunction())
? FindResult::Some
: FindResult::None;
}
}
void Inserter::insertMarkers(SILInstruction *instruction, DominanceInfo *tree,
DeadEndBlocks *deBlocks) {
SILBuilderWithScope builder(instruction);
auto *apmi = builder.createAllocPackMetadata(CleanupLocation(
RegularLocation::getAutoGeneratedLocation(instruction->getLoc())));
SmallVector<SILBasicBlock *, 4> boundary;
auto *block = apmi->getParent();
computeDominatedBoundaryBlocks(block, tree, boundary);
for (auto *block : boundary) {
if (deBlocks->isDeadEnd(block))
continue;
SILBuilderWithScope builder(&block->back());
builder.createDeallocPackMetadata(
CleanupLocation(RegularLocation::getAutoGeneratedLocation()), apmi);
}
}
/// Find instructions that may entail materializing a metadata pack and those
/// that will prevent stack allocation of metadata.
///
/// Found instructions are recorded in instructionsToCleanup.
Inserter::FindResult Inserter::find() {
auto collected = false;
for (auto &block : *function) {
for (auto &instruction : block) {
auto result = shouldInsertMarkersForInstruction(&instruction);
switch (result) {
case FindResult::None:
continue;
case FindResult::Some:
instructionsToCleanup.push_back(&instruction);
collected = true;
continue;
case FindResult::Unhandleable:
return FindResult::Unhandleable;
}
llvm_unreachable("covered switch");
}
}
return collected ? FindResult::Some : FindResult::None;
}
/// Insert the marker instructions around the instructions previously found.
void Inserter::insert(DominanceInfo *tree, DeadEndBlocks *deBlocks) {
for (auto *instruction : instructionsToCleanup) {
insertMarkers(instruction, tree, deBlocks);
}
}
class PackMetadataMarkerInserter : public SILFunctionTransform {
void run() override {
auto *function = getFunction();
// If on-stack metadata is disabled, this pass does nothing.
auto options = function->getModule().getOptions();
if (!options.EnablePackMetadataStackPromotion)
return;
Inserter inserter(function);
auto found = inserter.find();
switch (found) {
case Inserter::FindResult::None:
return;
case Inserter::FindResult::Unhandleable:
LLVM_DEBUG(llvm::dbgs() << "Found obstructive instructions in "
<< function->getName() << ".\n");
/// The function contains some unhandleable instruction. Record that on
/// the function.
function->setUseStackForPackMetadata(DoNotUseStackForPackMetadata);
return;
case Inserter::FindResult::Some:
LLVM_DEBUG(llvm::dbgs() << "Found potential pack metadata emitters in "
<< function->getName() << ".\n");
break;
}
auto *dominance = getAnalysis<DominanceAnalysis>();
auto *tree = dominance->get(function);
auto split = splitAllCriticalEdges(*function, /*domInfo=*/tree,
/*loopInfo=*/nullptr);
auto *deadEnds = getAnalysis<DeadEndBlocksAnalysis>();
if (split) {
deadEnds->invalidateFunction(function);
}
auto *deBlocks = deadEnds->get(function);
inserter.insert(tree, deBlocks);
auto changes = StackNesting::fixNesting(function);
invalidateAnalysis(
(split || changes == StackNesting::Changes::CFG)
? SILAnalysis::InvalidationKind::BranchesAndInstructions
: SILAnalysis::InvalidationKind::Instructions);
}
};
} // end anonymous namespace
SILTransform *irgen::createPackMetadataMarkerInserter() {
return new PackMetadataMarkerInserter();
}
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