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//===--- SILSROA.cpp - Scalar Replacement of Aggregates ------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Change aggregate values into scalar values. Currently it takes every
// allocation and chops them up into their smallest non-captured pieces.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "sil-sroa"
#include "swift/Basic/LLVM.h"
#include "swift/Basic/Range.h"
#include "swift/SIL/DebugUtils.h"
#include "swift/SIL/Projection.h"
#include "swift/SIL/SILBuilder.h"
#include "swift/SIL/SILFunction.h"
#include "swift/SIL/SILModule.h"
#include "swift/SIL/SILUndef.h"
#include "swift/SILOptimizer/PassManager/Passes.h"
#include "swift/SILOptimizer/PassManager/Transforms.h"
#include "swift/SILOptimizer/Utils/InstOptUtils.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Debug.h"
#include <type_traits>
using namespace swift;
STATISTIC(NumEscapingAllocas, "Number of aggregate allocas not chopped up "
"due to uses.");
STATISTIC(NumChoppedAllocas, "Number of chopped up aggregate allocas.");
STATISTIC(NumUnhandledAllocas, "Number of non struct, tuple allocas.");
namespace {
class SROAMemoryUseAnalyzer {
// The allocation we are analyzing.
AllocStackInst *AI;
// Loads from AI.
llvm::SmallVector<LoadInst *, 4> Loads;
// Stores to AI.
llvm::SmallVector<StoreInst *, 4> Stores;
// Instructions which extract from aggregates.
llvm::SmallVector<SingleValueInstruction *, 4> ExtractInsts;
// TupleType if we are visiting a tuple.
TupleType *TT = nullptr;
// StructDecl if we are visiting a struct.
StructDecl *SD = nullptr;
public:
SROAMemoryUseAnalyzer(AllocStackInst *AI) : AI(AI) {
assert(AI && "AI should never be null here.");
}
bool analyze();
void chopUpAlloca(std::vector<AllocStackInst *> &Worklist);
private:
SILValue createAgg(SILBuilder &B, SILLocation Loc, SILType Ty,
ArrayRef<SILValue> Elements);
unsigned getEltNoForProjection(SILInstruction *Inst);
void createAllocas(llvm::SmallVector<AllocStackInst *, 4> &NewAllocations);
};
} // end anonymous namespace
SILValue
SROAMemoryUseAnalyzer::createAgg(SILBuilder &B, SILLocation Loc,
SILType Ty,
ArrayRef<SILValue> Elements) {
if (TT)
return B.createTuple(Loc, Ty, Elements);
assert(SD && "SD must not be null here since it or TT must be set to call"
" this method.");
return B.createStruct(Loc, Ty, Elements);
}
unsigned SROAMemoryUseAnalyzer::getEltNoForProjection(SILInstruction *Inst) {
if (TT)
return cast<TupleElementAddrInst>(Inst)->getFieldIndex();
assert(SD && "SD should not be null since either it or TT must be set at "
"this point.");
StructElementAddrInst *SEA = cast<StructElementAddrInst>(Inst);
VarDecl *Field = SEA->getField();
unsigned EltNo = 0;
for (auto *D : SD->getStoredProperties()) {
if (D == Field)
return EltNo;
++EltNo;
}
llvm_unreachable("Unknown field.");
}
bool SROAMemoryUseAnalyzer::analyze() {
// We only know how to split structs and tuples... So if we have a scalar or a
// different sort of aggregate, bail.
SILType Type = AI->getType();
TT = Type.getAs<TupleType>();
SD = Type.getStructOrBoundGenericStruct();
bool HasUnrefField = AI->getElementType().aggregateHasUnreferenceableStorage();
// Check that the allocated type is a struct or a tuple and that there are
// no unreferenced fields.
if (HasUnrefField || (!TT && !SD)) {
++NumUnhandledAllocas;
return false;
}
bool hasBenefit = false;
// Go through uses of the memory allocation of AI...
for (auto *Operand : getNonDebugUses(SILValue(AI))) {
SILInstruction *User = Operand->getUser();
LLVM_DEBUG(llvm::dbgs() << " Visiting use: " << *User);
// If we store the alloca pointer, we cannot analyze its uses so bail...
// It is ok if we store into the alloca pointer though.
if (auto *SI = dyn_cast<StoreInst>(User)) {
if (SI->getDest() == AI) {
LLVM_DEBUG(llvm::dbgs() << " Found a store into the "
"projection.\n");
Stores.push_back(SI);
SILValue Src = SI->getSrc();
if (isa<StructInst>(Src) || isa<TupleInst>(Src))
hasBenefit = true;
continue;
} else {
LLVM_DEBUG(llvm::dbgs() << " Found a store of the "
"projection pointer. Escapes!.\n");
++NumEscapingAllocas;
return false;
}
}
// If the use is a load, keep track of it for splitting later...
if (auto *LI = dyn_cast<LoadInst>(User)) {
LLVM_DEBUG(llvm::dbgs() << " Found a load of the projection.\n");
Loads.push_back(LI);
for (auto useIter = LI->use_begin(), End = LI->use_end();
!hasBenefit && useIter != End; ++useIter) {
hasBenefit = (isa<StructExtractInst>(useIter->get()) ||
isa<TupleExtractInst>(useIter->get()));
}
continue;
}
// If the use is a struct_element_addr, add it to the worklist so we check
// if it or one of its descendants escape.
if (auto *ASI = dyn_cast<StructElementAddrInst>(User)) {
LLVM_DEBUG(llvm::dbgs() << " Found a struct subprojection!\n");
ExtractInsts.push_back(ASI);
hasBenefit = true;
continue;
}
// If the use is a tuple_element_addr, add it to the worklist so we check
// if it or one of its descendants escape.
if (auto *TSI = dyn_cast<TupleElementAddrInst>(User)) {
LLVM_DEBUG(llvm::dbgs() << " Found a tuple subprojection!\n");
ExtractInsts.push_back(TSI);
hasBenefit = true;
continue;
}
if (isa<DeallocStackInst>(User)) {
// We can ignore the dealloc_stack.
continue;
}
// Otherwise we do not understand this instruction, so bail.
LLVM_DEBUG(llvm::dbgs() <<" Found unknown user, pointer escapes!\n");
++NumEscapingAllocas;
return false;
}
// Analysis was successful. We can break up this allocation!
++NumChoppedAllocas;
return hasBenefit;
}
void
SROAMemoryUseAnalyzer::
createAllocas(llvm::SmallVector<AllocStackInst *, 4> &NewAllocations) {
SILBuilderWithScope B(AI);
SILType Type = AI->getType().getObjectType();
// Intentionally dropping the debug info.
// FIXME: VarInfo needs to be extended with fragment info to support this.
SILLocation Loc = RegularLocation::getAutoGeneratedLocation();
if (TT) {
for (unsigned EltNo : indices(TT->getElementTypes())) {
SILType EltTy = Type.getTupleElementType(EltNo);
NewAllocations.push_back(B.createAllocStack(Loc, EltTy, {}));
}
} else {
assert(SD && "SD should not be null since either it or TT must be set at "
"this point.");
SILModule &M = AI->getModule();
for (auto *D : SD->getStoredProperties())
NewAllocations.push_back(B.createAllocStack(
Loc, Type.getFieldType(D, M, TypeExpansionContext(B.getFunction())),
{}));
}
}
void SROAMemoryUseAnalyzer::chopUpAlloca(std::vector<AllocStackInst *> &Worklist) {
// Create allocations for this instruction.
llvm::SmallVector<AllocStackInst *, 4> NewAllocations;
createAllocas(NewAllocations);
// Add the new allocations to the worklist for recursive processing.
//
// TODO: Change this into an assert. For some reason I am running into compile
// issues when I try it now.
for (auto *AI : NewAllocations)
Worklist.push_back(AI);
// Change any aggregate loads into field loads + aggregate structure.
for (auto *LI : Loads) {
SILBuilderWithScope B(LI);
llvm::SmallVector<SILValue, 4> Elements;
for (auto *NewAI : NewAllocations) {
Elements.push_back(B.emitLoadValueOperation(LI->getLoc(), NewAI,
LI->getOwnershipQualifier()));
}
SILValue Agg = createAgg(B, LI->getLoc(), LI->getType().getObjectType(),
Elements);
LI->replaceAllUsesWith(Agg);
LI->eraseFromParent();
}
// Change any aggregate stores into extracts + field stores.
for (auto *SI : Stores) {
SILBuilderWithScope builder(SI);
SmallVector<SILValue, 8> destructured;
builder.emitDestructureValueOperation(SI->getLoc(), SI->getSrc(),
destructured);
for (unsigned eltNo : indices(NewAllocations)) {
builder.emitStoreValueOperation(SI->getLoc(), destructured[eltNo],
NewAllocations[eltNo],
SI->getOwnershipQualifier());
}
SI->eraseFromParent();
}
// Forward any field extracts to the new allocation.
for (auto *Ext : ExtractInsts) {
AllocStackInst *NewValue = NewAllocations[getEltNoForProjection(Ext)];
Ext->replaceAllUsesWith(NewValue);
Ext->eraseFromParent();
}
// Find all dealloc instructions for AI and then chop them up.
llvm::SmallVector<DeallocStackInst *, 4> ToRemove;
for (auto *Operand : getNonDebugUses(SILValue(AI))) {
SILInstruction *User = Operand->getUser();
SILBuilderWithScope B(User);
// If the use is a DSI, add it to our memory analysis so that if we can chop
// up allocas, we also chop up the relevant dealloc stack insts.
if (auto *DSI = dyn_cast<DeallocStackInst>(User)) {
LLVM_DEBUG(llvm::dbgs() << " Found DeallocStackInst!\n");
// Create the allocations in reverse order.
for (auto *NewAI : llvm::reverse(NewAllocations))
B.createDeallocStack(DSI->getLoc(), SILValue(NewAI));
ToRemove.push_back(DSI);
}
}
// Remove the old DeallocStackInst instructions.
for (auto *DSI : ToRemove) {
DSI->eraseFromParent();
}
eraseFromParentWithDebugInsts(AI);
}
/// Returns true, if values of \ty should be ignored, because \p ty is known
/// by a high-level SIL optimization. Values of that type must not be split
/// so that those high-level optimizations can analyze the code.
static bool isSemanticType(ASTContext &ctxt, SILType ty) {
NominalTypeDecl *stringDecl = ctxt.getStringDecl();
if (ty.getStructOrBoundGenericStruct() == stringDecl)
return true;
return false;
}
static bool runSROAOnFunction(SILFunction &Fn, bool splitSemanticTypes) {
std::vector<AllocStackInst *> Worklist;
bool Changed = false;
ASTContext &ctxt = Fn.getModule().getASTContext();
// For each basic block BB in Fn...
for (auto &BB : Fn)
// For each instruction in BB...
for (auto &I : BB)
// If the instruction is an alloc stack inst, add it to the worklist.
if (auto *AI = dyn_cast<AllocStackInst>(&I)) {
if (!splitSemanticTypes && isSemanticType(ctxt, AI->getElementType()))
continue;
if (shouldExpand(Fn.getModule(), AI->getElementType()))
Worklist.push_back(AI);
}
while (!Worklist.empty()) {
AllocStackInst *AI = Worklist.back();
Worklist.pop_back();
SROAMemoryUseAnalyzer Analyzer(AI);
if (!Analyzer.analyze())
continue;
Changed = true;
Analyzer.chopUpAlloca(Worklist);
}
return Changed;
}
namespace {
class SILSROA : public SILFunctionTransform {
bool splitSemanticTypes;
public:
SILSROA(bool splitSemanticTypes) : splitSemanticTypes(splitSemanticTypes) { }
/// The entry point to the transformation.
void run() override {
SILFunction *F = getFunction();
LLVM_DEBUG(llvm::dbgs() << "***** SROA on function: " << F->getName()
<< " *****\n");
if (runSROAOnFunction(*F, splitSemanticTypes))
invalidateAnalysis(SILAnalysis::InvalidationKind::Instructions);
}
};
} // end anonymous namespace
SILTransform *swift::createSROA() {
return new SILSROA(/*splitSemanticTypes*/ true);
}
SILTransform *swift::createEarlySROA() {
return new SILSROA(/*splitSemanticTypes*/ false);
}