1.
SIL Optimizations
AllocBoxToStack
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

2.
Hi, I'm Yusuke
@kitasuke
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

3.
Why SIL?
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

4.
Why SIL?
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

5.
Why SIL?
→ Better idea of Swift type system !
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

6.
Why SIL?
→ Better idea of Swift type system !
→ Optimizations magic "✨
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

7.
Why SIL?
→ Better idea of Swift type system !
→ Optimizations magic "✨
→ Just for fun $
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

8.
SIL
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

9.
Swift
Intermediate
LanguageSIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

10.
SIL is a language specific
Intermediate
Representation
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

11.
Swift
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

12.
Swift Compiler
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

13.
Swift Compiler
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

14.
Swift Compiler
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

15.
SIL
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

16.
raw SIL
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

17.
canonical SIL
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

18.
Objective-C
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

19.
Clang
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

20.
Clang
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

21.
SIL
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

22.
Optimizations
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

23.
Optimization Passes
→ CapturePromotion
→ AllocBoxToStack
→ MandatoryInlining
→ DeadCodeElimination
→ Mem2Reg
...
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

24.
AllocBoxToStack
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

25.
Stack Promotion of
Box Objects
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

26.
Stack vs Heap
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

27.
Stack
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

28.
Stack
→ Very fast
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

29.
Stack
→ Very fast
→ No explicit memory management
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

30.
Stack
→ Very fast
→ No explicit memory management
→ Size limits
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

31.
Heap
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

32.
Heap
→ Slow
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

33.
Heap
→ Slow
→ Explicit memory management
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

34.
Heap
→ Slow
→ Explicit memory management
→ No size limits
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

35.
Stack vs Heap
Stack Heap
Value types Reference types
Pointers to reference
type
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

36.
How AllocBoxToStack
works?
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

37.
alloc_box ➡ alloc_stack
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

38.
stack.swift
func number() -> Int {
var x: Int
x = 1
return x
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

39.
raw SIL
$swiftc -emit-silgen stack.swift > stack.sil
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

40.
stack.sil
%0 = alloc_box ${ var Int }, var, name "x"
%1 = mark_uninitialized [var] %0 : ${ var Int }
%2 = project_box %1 : ${ var Int }, 0
...
%10 = begin_access [read] [unknown] %2 : $*Int
%11 = load [trivial] %10 : $*Int
end_access %10 : $*Int
destroy_value %1 : ${ var Int }
return %11 : $Int
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

41.
stack.sil
%0 = alloc_box ${ var Int }, var, name "x"
%1 = mark_uninitialized [var] %0 : ${ var Int }
%2 = project_box %1 : ${ var Int }, 0
...
%10 = begin_access [read] [unknown] %2 : $*Int
%11 = load [trivial] %10 : $*Int
end_access %10 : $*Int
destroy_value %1 : ${ var Int }
return %11 : $Int
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

42.
canonical SIL
$swiftc -emit-sil stack.swift > stack.sil
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

43.
stack.sil
%0 = alloc_stack $Int, var, name "x"
%1 = integer_literal $Builtin.Int64, 1
%2 = struct $Int (%1 : $Builtin.Int64)
...
return %2 : $Int
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

44.
stack.sil
%0 = alloc_stack $Int, var, name "x"
%1 = integer_literal $Builtin.Int64, 1
%2 = struct $Int (%1 : $Builtin.Int64)
...
return %2 : $Int
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

45.
alloc_box vs alloc_stack
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

46.
alloc_box
alloc_box allocates a reference counted box on
heap.
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

47.
alloc_stack
alloc_stack allocates a value on stack. All
allocations must be deallocated prior to returning
from a function.
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

48.
Stack Promotion of
Box Objects
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

49.
alloc_box ➡ alloc_stack
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

50.
alloc_box ➡ alloc_box
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

51.
box.swift
func closure(_ completion: @escaping () -> Void) {
completion()
}
func number() -> Int {
var i: Int
i = 0
closure { i = 10 }
return i
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

52.
box.swift
func closure(_ completion: @escaping () -> Void) {
completion()
}
func number() -> Int {
var i: Int
i = 0
closure { i = 10 }
return i
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

53.
box.swift
func closure(_ completion: @escaping () -> Void) {
completion()
}
func number() -> Int {
var i: Int
i = 0
closure { i = 10 }
return i
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

54.
raw SIL
$swiftc -emit-silgen box.swift > box.sil
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

55.
box.sil
%0 = alloc_box ${ var Int }, var, name "i"
%1 = mark_uninitialized [var] %0 : ${ var Int }
%2 = project_box %1 : ${ var Int }, 0
...
%16 = begin_access [read] [unknown] %2 : $*Int
%17 = load [trivial] %16 : $*Int
end_access %16 : $*Int
destroy_value %1 : ${ var Int }
return %17 : $Int
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

56.
box.sil
%0 = alloc_box ${ var Int }, var, name "i"
%1 = mark_uninitialized [var] %0 : ${ var Int }
%2 = project_box %1 : ${ var Int }, 0
...
%16 = begin_access [read] [unknown] %2 : $*Int
%17 = load [trivial] %16 : $*Int
end_access %16 : $*Int
destroy_value %1 : ${ var Int }
return %17 : $Int
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

57.
canonical SIL
$swiftc -emit-sil box.swift > box.sil
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

58.
box.sil
%0 = alloc_box ${ var Int }, var, name "i"
%1 = project_box %0 : ${ var Int }, 0
%2 = integer_literal $Builtin.Int64, 0
%3 = struct $Int (%2 : $Builtin.Int64)
...
%12 = begin_access [read] [dynamic] %1 : $*Int
%13 = load %12 : $*Int
end_access %12 : $*Int
strong_release %0 : ${ var Int }
return %13 : $Int
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

59.
box.sil
%0 = alloc_box ${ var Int }, var, name "i"
%1 = project_box %0 : ${ var Int }, 0
%2 = integer_literal $Builtin.Int64, 0
%3 = struct $Int (%2 : $Builtin.Int64)
...
%12 = begin_access [read] [dynamic] %1 : $*Int
%13 = load %12 : $*Int
end_access %12 : $*Int
strong_release %0 : ${ var Int }
return %13 : $Int
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

60.
How can promote
alloc_box?
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

61.
class AllocBoxToStack : public SILFunctionTransform {
void run() override {
...
AllocBoxToStackState pass(this);
for (auto &BB : *getFunction()) {
for (auto &I : BB)
if (auto *ABI = dyn_cast<AllocBoxInst>(&I))
if (canPromoteAllocBox(ABI, pass.PromotedOperands))
pass.Promotable.push_back(ABI);
}
if (!pass.Promotable.empty()) {
auto Count = rewritePromotedBoxes(pass);
...
}
...
}
};
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

62.
class AllocBoxToStack : public SILFunctionTransform {
void run() override {
...
AllocBoxToStackState pass(this);
for (auto &BB : *getFunction()) {
for (auto &I : BB)
if (auto *ABI = dyn_cast<AllocBoxInst>(&I))
if (canPromoteAllocBox(ABI, pass.PromotedOperands))
pass.Promotable.push_back(ABI);
}
if (!pass.Promotable.empty()) {
auto Count = rewritePromotedBoxes(pass);
...
}
...
}
};
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

63.
class AllocBoxToStack : public SILFunctionTransform {
void run() override {
...
AllocBoxToStackState pass(this);
for (auto &BB : *getFunction()) {
for (auto &I : BB)
if (auto *ABI = dyn_cast<AllocBoxInst>(&I))
if (canPromoteAllocBox(ABI, pass.PromotedOperands))
pass.Promotable.push_back(ABI);
}
if (!pass.Promotable.empty()) {
auto Count = rewritePromotedBoxes(pass);
...
}
...
}
};
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

64.
class AllocBoxToStack : public SILFunctionTransform {
void run() override {
...
AllocBoxToStackState pass(this);
for (auto &BB : *getFunction()) {
for (auto &I : BB)
if (auto *ABI = dyn_cast<AllocBoxInst>(&I))
if (canPromoteAllocBox(ABI, pass.PromotedOperands))
pass.Promotable.push_back(ABI);
}
if (!pass.Promotable.empty()) {
auto Count = rewritePromotedBoxes(pass);
...
}
...
}
};
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

65.
static SILInstruction * findUnexpectedBoxUse(SILValue Box, bool examinePartialApply,
bool inAppliedFunction, llvm::SmallVectorImpl<Operand *> &PromotedOperands) {
llvm::SmallVector<Operand *, 4> LocalPromotedOperands;
llvm::SmallVector<Operand *, 32> Worklist(Box->use_begin(), Box->use_end());
while (!Worklist.empty()) {
auto *Op = Worklist.pop_back_val();
auto *User = Op->getUser();
if (isa<StrongRetainInst>(User) || isa<StrongReleaseInst>(User) ||
isa<ProjectBoxInst>(User) || isa<DestroyValueInst>(User) ||
(!inAppliedFunction && isa<DeallocBoxInst>(User)))
continue;
if (isa<MarkUninitializedInst>(User) || isa<CopyValueInst>(User)) {
copy(cast<SingleValueInstruction>(User)->getUses(), std::back_inserter(Worklist));
continue;
}
if (auto *PAI = dyn_cast<PartialApplyInst>(User))
if (examinePartialApply && checkPartialApplyBody(Op) &&
!partialApplyEscapes(PAI, /* examineApply = */ true)) {
LocalPromotedOperands.push_back(Op);
continue;
}
return User;
}
...
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

66.
static SILInstruction * findUnexpectedBoxUse(SILValue Box, bool examinePartialApply,
bool inAppliedFunction, llvm::SmallVectorImpl<Operand *> &PromotedOperands) {
llvm::SmallVector<Operand *, 4> LocalPromotedOperands;
llvm::SmallVector<Operand *, 32> Worklist(Box->use_begin(), Box->use_end());
while (!Worklist.empty()) {
auto *Op = Worklist.pop_back_val();
auto *User = Op->getUser();
if (isa<StrongRetainInst>(User) || isa<StrongReleaseInst>(User) ||
isa<ProjectBoxInst>(User) || isa<DestroyValueInst>(User) ||
(!inAppliedFunction && isa<DeallocBoxInst>(User)))
continue;
if (isa<MarkUninitializedInst>(User) || isa<CopyValueInst>(User)) {
copy(cast<SingleValueInstruction>(User)->getUses(), std::back_inserter(Worklist));
continue;
}
if (auto *PAI = dyn_cast<PartialApplyInst>(User))
if (examinePartialApply && checkPartialApplyBody(Op) &&
!partialApplyEscapes(PAI, /* examineApply = */ true)) {
LocalPromotedOperands.push_back(Op);
continue;
}
return User;
}
...
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

67.
static SILInstruction * findUnexpectedBoxUse(SILValue Box, bool examinePartialApply,
bool inAppliedFunction, llvm::SmallVectorImpl<Operand *> &PromotedOperands) {
llvm::SmallVector<Operand *, 4> LocalPromotedOperands;
llvm::SmallVector<Operand *, 32> Worklist(Box->use_begin(), Box->use_end());
while (!Worklist.empty()) {
auto *Op = Worklist.pop_back_val();
auto *User = Op->getUser();
if (isa<StrongRetainInst>(User) || isa<StrongReleaseInst>(User) ||
isa<ProjectBoxInst>(User) || isa<DestroyValueInst>(User) ||
(!inAppliedFunction && isa<DeallocBoxInst>(User)))
continue;
if (isa<MarkUninitializedInst>(User) || isa<CopyValueInst>(User)) {
copy(cast<SingleValueInstruction>(User)->getUses(), std::back_inserter(Worklist));
continue;
}
if (auto *PAI = dyn_cast<PartialApplyInst>(User))
if (examinePartialApply && checkPartialApplyBody(Op) &&
!partialApplyEscapes(PAI, /* examineApply = */ true)) {
LocalPromotedOperands.push_back(Op);
continue;
}
return User;
}
...
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

68.
static SILInstruction * findUnexpectedBoxUse(SILValue Box, bool examinePartialApply,
bool inAppliedFunction, llvm::SmallVectorImpl<Operand *> &PromotedOperands) {
llvm::SmallVector<Operand *, 4> LocalPromotedOperands;
llvm::SmallVector<Operand *, 32> Worklist(Box->use_begin(), Box->use_end());
while (!Worklist.empty()) {
auto *Op = Worklist.pop_back_val();
auto *User = Op->getUser();
if (isa<StrongRetainInst>(User) || isa<StrongReleaseInst>(User) ||
isa<ProjectBoxInst>(User) || isa<DestroyValueInst>(User) ||
(!inAppliedFunction && isa<DeallocBoxInst>(User)))
continue;
if (isa<MarkUninitializedInst>(User) || isa<CopyValueInst>(User)) {
copy(cast<SingleValueInstruction>(User)->getUses(), std::back_inserter(Worklist));
continue;
}
if (auto *PAI = dyn_cast<PartialApplyInst>(User))
if (examinePartialApply && checkPartialApplyBody(Op) &&
!partialApplyEscapes(PAI, /* examineApply = */ true)) {
LocalPromotedOperands.push_back(Op);
continue;
}
return User;
}
...
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

69.
static SILInstruction * findUnexpectedBoxUse(SILValue Box, bool examinePartialApply,
bool inAppliedFunction, llvm::SmallVectorImpl<Operand *> &PromotedOperands) {
llvm::SmallVector<Operand *, 4> LocalPromotedOperands;
llvm::SmallVector<Operand *, 32> Worklist(Box->use_begin(), Box->use_end());
while (!Worklist.empty()) {
auto *Op = Worklist.pop_back_val();
auto *User = Op->getUser();
if (isa<StrongRetainInst>(User) || isa<StrongReleaseInst>(User) ||
isa<ProjectBoxInst>(User) || isa<DestroyValueInst>(User) ||
(!inAppliedFunction && isa<DeallocBoxInst>(User)))
continue;
if (isa<MarkUninitializedInst>(User) || isa<CopyValueInst>(User)) {
copy(cast<SingleValueInstruction>(User)->getUses(), std::back_inserter(Worklist));
continue;
}
if (auto *PAI = dyn_cast<PartialApplyInst>(User))
if (examinePartialApply && checkPartialApplyBody(Op) &&
!partialApplyEscapes(PAI, /* examineApply = */ true)) {
LocalPromotedOperands.push_back(Op);
continue;
}
return User;
}
...
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

70.
Recap
→ Promotes @noescape values to stack
→ @escaping values with a reference count
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

71.
Optimization Flags
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

72.
optimized.swift
func closure(_ completion: @escaping () -> Void) {
completion()
}
func number() -> Int {
var i: Int
i = 0
closure { i = 10 }
return i
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

73.
canonical SIL with -O
$swiftc -emit-sil -O optimized.swift > optimized.sil
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

74.
optimized.sil
%0 = integer_literal $Builtin.Int64, 10
%1 = struct $Int (%0 : $Builtin.Int64)
return %1 : $Int
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

75.
No alloc_box or
alloc_stack
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

76.
Mem2Reg
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

77.
Register Promotion of
Stack Allocations
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

78.
How can promote stack
allocation?
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

79.
class SILMem2Reg : public SILFunctionTransform {
void run() override {
SILFunction *F = getFunction();
DominanceAnalysis* DA = PM->getAnalysis<DominanceAnalysis>();
bool Changed = MemoryToRegisters(*F, DA->get(F)).run();
...
}
};
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

80.
class SILMem2Reg : public SILFunctionTransform {
void run() override {
SILFunction *F = getFunction();
DominanceAnalysis* DA = PM->getAnalysis<DominanceAnalysis>();
bool Changed = MemoryToRegisters(*F, DA->get(F)).run();
...
}
};
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

81.
class SILMem2Reg : public SILFunctionTransform {
void run() override {
SILFunction *F = getFunction();
DominanceAnalysis* DA = PM->getAnalysis<DominanceAnalysis>();
bool Changed = MemoryToRegisters(*F, DA->get(F)).run();
...
}
};
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

82.
class SILMem2Reg : public SILFunctionTransform {
void run() override {
SILFunction *F = getFunction();
DominanceAnalysis* DA = PM->getAnalysis<DominanceAnalysis>();
bool Changed = MemoryToRegisters(*F, DA->get(F)).run();
...
}
};
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

83.
bool MemoryToRegisters::promoteSingleAllocation(AllocStackInst *alloc, DomTreeLevelMap &DomTreeLevels){
NumAllocStackFound++;
bool inSingleBlock = false;
if (isCaptured(alloc, inSingleBlock)) {
NumAllocStackCaptured++;
return false;
}
if (isWriteOnlyAllocation(alloc)) {
eraseUsesOfInstruction(alloc);
return true;
}
if (inSingleBlock) {
removeSingleBlockAllocation(alloc);
if (!alloc->use_empty()) {
B.setInsertionPoint(std::next(alloc->getIterator()));
B.createDeallocStack(alloc->getLoc(), alloc);
}
return true;
}
StackAllocationPromoter(alloc, DT, DomTreeLevels, B).run();
eraseUsesOfInstruction(alloc);
return true;
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

84.
bool MemoryToRegisters::promoteSingleAllocation(AllocStackInst *alloc, DomTreeLevelMap &DomTreeLevels){
NumAllocStackFound++;
bool inSingleBlock = false;
if (isCaptured(alloc, inSingleBlock)) {
NumAllocStackCaptured++;
return false;
}
if (isWriteOnlyAllocation(alloc)) {
eraseUsesOfInstruction(alloc);
return true;
}
if (inSingleBlock) {
removeSingleBlockAllocation(alloc);
if (!alloc->use_empty()) {
B.setInsertionPoint(std::next(alloc->getIterator()));
B.createDeallocStack(alloc->getLoc(), alloc);
}
return true;
}
StackAllocationPromoter(alloc, DT, DomTreeLevels, B).run();
eraseUsesOfInstruction(alloc);
return true;
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

85.
bool MemoryToRegisters::promoteSingleAllocation(AllocStackInst *alloc, DomTreeLevelMap &DomTreeLevels){
NumAllocStackFound++;
bool inSingleBlock = false;
if (isCaptured(alloc, inSingleBlock)) {
NumAllocStackCaptured++;
return false;
}
if (isWriteOnlyAllocation(alloc)) {
eraseUsesOfInstruction(alloc);
return true;
}
if (inSingleBlock) {
removeSingleBlockAllocation(alloc);
if (!alloc->use_empty()) {
B.setInsertionPoint(std::next(alloc->getIterator()));
B.createDeallocStack(alloc->getLoc(), alloc);
}
return true;
}
StackAllocationPromoter(alloc, DT, DomTreeLevels, B).run();
eraseUsesOfInstruction(alloc);
return true;
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

86.
bool MemoryToRegisters::promoteSingleAllocation(AllocStackInst *alloc, DomTreeLevelMap &DomTreeLevels){
NumAllocStackFound++;
bool inSingleBlock = false;
if (isCaptured(alloc, inSingleBlock)) {
NumAllocStackCaptured++;
return false;
}
if (isWriteOnlyAllocation(alloc)) {
eraseUsesOfInstruction(alloc);
return true;
}
if (inSingleBlock) {
removeSingleBlockAllocation(alloc);
if (!alloc->use_empty()) {
B.setInsertionPoint(std::next(alloc->getIterator()));
B.createDeallocStack(alloc->getLoc(), alloc);
}
return true;
}
StackAllocationPromoter(alloc, DT, DomTreeLevels, B).run();
eraseUsesOfInstruction(alloc);
return true;
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

87.
bool MemoryToRegisters::promoteSingleAllocation(AllocStackInst *alloc, DomTreeLevelMap &DomTreeLevels){
NumAllocStackFound++;
bool inSingleBlock = false;
if (isCaptured(alloc, inSingleBlock)) {
NumAllocStackCaptured++;
return false;
}
if (isWriteOnlyAllocation(alloc)) {
eraseUsesOfInstruction(alloc);
return true;
}
if (inSingleBlock) {
removeSingleBlockAllocation(alloc);
if (!alloc->use_empty()) {
B.setInsertionPoint(std::next(alloc->getIterator()));
B.createDeallocStack(alloc->getLoc(), alloc);
}
return true;
}
StackAllocationPromoter(alloc, DT, DomTreeLevels, B).run();
eraseUsesOfInstruction(alloc);
return true;
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

88.
optimized.swift
func closure(_ completion: @escaping () -> Void) {
completion()
}
func number() -> Int {
var i: Int
i = 0
closure { i = 10 }
return i
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

89.
optimized.swift
func number() -> Int {
return 10
}
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

90.
Optimization Flags
→ -Onone
→ -O
→ -Ounchecked
→ -Osize
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

91.
Tips for Debug
→ -Xllvm -sil-print-all
→ -Xllvm -sil-print-only-functions
→ -Xllvm -sil-print-before/after/around
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

92.
Summary
→ Optimize, optimize and optimize !
→ Better ideas of how Swift Compiler works "
→ Definitely worth learning #
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

93.
References
→ var vs let in SIL
→ swift/docs/SIL.rst
→ Debugging the Swift Compiler
→ Swift's High-Level IR: A Case Study of
Complementing LLVM IR with Language-Specific
Optimization
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018

94.
Thank you!
SIL Optimizations - AllocBoxToStack, Yusuke Kita (@kitasuke), iOSDC 2018