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Add a -emit-dead-strippable-symbols flag that emits functions/variable/metadata in a dead_strip-friendly way. #34281

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Add a -emit-dead-strippable-symbols flag that emits functions/variable/metadata in a dead_strip-friendly way. #34281

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30fa52b
Add a -emit-dead-strippable-symbols flag that emits functions/variabl…
kubamracek Oct 21, 2020
3817fcb
Mark the tests as requiring macosx
kubamracek Oct 22, 2020
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7 changes: 6 additions & 1 deletion include/swift/AST/IRGenOptions.h
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Original file line number Diff line number Diff line change
Expand Up @@ -250,6 +250,10 @@ class IRGenOptions {
/// Emit names of struct stored properties and enum cases.
unsigned EnableReflectionNames : 1;

/// Emit metadata, variables and functions in a way that a linker can remove
/// them if they're unused, even across modules (when linking statically).
unsigned EmitDeadStrippableSymbols : 1;

/// Emit mangled names of anonymous context descriptors.
unsigned EnableAnonymousContextMangledNames : 1;

Expand Down Expand Up @@ -348,7 +352,8 @@ class IRGenOptions {
PrintInlineTree(false), EmbedMode(IRGenEmbedMode::None),
LLVMLTOKind(IRGenLLVMLTOKind::None), HasValueNamesSetting(false),
ValueNames(false), EnableReflectionMetadata(true),
EnableReflectionNames(true), EnableAnonymousContextMangledNames(false),
EnableReflectionNames(true), EmitDeadStrippableSymbols(false),
EnableAnonymousContextMangledNames(false),
ForcePublicLinkage(false), LazyInitializeClassMetadata(false),
LazyInitializeProtocolConformances(false), DisableLegacyTypeInfo(false),
PrespecializeGenericMetadata(false), UseIncrementalLLVMCodeGen(true),
Expand Down
5 changes: 5 additions & 0 deletions include/swift/Option/FrontendOptions.td
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Expand Up @@ -604,6 +604,11 @@ def emit_sorted_sil : Flag<["-"], "emit-sorted-sil">,
HelpText<"When printing SIL, print out all sil entities sorted by name to "
"ease diffing">;

def emit_dead_strippable_symbols : Flag<["-"], "emit-dead-strippable-symbols">,
HelpText<"Emit metadata, variables and functions in a way that a linker can "
"remove them if they're unused, even across modules (when linking "
"statically).">;

def emit_syntax : Flag<["-"], "emit-syntax">,
HelpText<"Parse input file(s) and emit the Syntax tree(s) as JSON">, ModeOpt;

Expand Down
6 changes: 6 additions & 0 deletions lib/Frontend/CompilerInvocation.cpp
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Expand Up @@ -1546,6 +1546,12 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
Opts.EnableReflectionNames = false;
}

if (Args.hasArg(OPT_emit_dead_strippable_symbols)) {
if (!Opts.UseJIT) {
Opts.EmitDeadStrippableSymbols = true;
}
}

if (Args.hasArg(OPT_force_public_linkage)) {
Opts.ForcePublicLinkage = true;
}
Expand Down
194 changes: 139 additions & 55 deletions lib/IRGen/GenDecl.cpp
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Expand Up @@ -1991,8 +1991,9 @@ void irgen::updateLinkageForDefinition(IRGenModule &IGM,

// Everything externally visible is considered used in Swift.
// That mostly means we need to be good at not marking things external.
if (LinkInfo::isUsed(IRL))
IGM.addUsedGlobal(global);
if (LinkInfo::isUsed(IRL) && !IGM.IRGen.Opts.EmitDeadStrippableSymbols) {
IGM.addUsedGlobal(global);
}
}

LinkInfo LinkInfo::get(IRGenModule &IGM, const LinkEntity &entity,
Expand Down Expand Up @@ -2085,7 +2086,11 @@ llvm::Function *irgen::createFunction(IRGenModule &IGM,
// Everything externally visible is considered used in Swift.
// That mostly means we need to be good at not marking things external.
if (linkInfo.isUsed()) {
IGM.addUsedGlobal(fn);
// Don't allow dead_strip'ing for "main".
if (name == SWIFT_ENTRY_POINT_FUNCTION ||
!IGM.IRGen.Opts.EmitDeadStrippableSymbols) {
IGM.addUsedGlobal(fn);
}
}

return fn;
Expand Down Expand Up @@ -2132,7 +2137,7 @@ llvm::GlobalVariable *swift::irgen::createVariable(

// Everything externally visible is considered used in Swift.
// That mostly means we need to be good at not marking things external.
if (linkInfo.isUsed()) {
if (linkInfo.isUsed() && !IGM.IRGen.Opts.EmitDeadStrippableSymbols) {
IGM.addUsedGlobal(var);
}

Expand Down Expand Up @@ -3350,6 +3355,47 @@ llvm::Constant *IRGenModule::emitSwiftProtocols() {
if (SwiftProtocols.empty())
return nullptr;

StringRef sectionName;
switch (TargetInfo.OutputObjectFormat) {
case llvm::Triple::UnknownObjectFormat:
llvm_unreachable("Don't know how to emit protocols for "
"the selected object format.");
case llvm::Triple::MachO:
sectionName = IRGen.Opts.EmitDeadStrippableSymbols
? "__TEXT, __swift5_protos, regular, live_support"
: "__TEXT, __swift5_protos, regular, no_dead_strip";
break;
case llvm::Triple::ELF:
case llvm::Triple::Wasm:
sectionName = "swift5_protocols";
break;
case llvm::Triple::XCOFF:
case llvm::Triple::COFF:
sectionName = ".sw5prt$B";
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One question I have is if this information around sectionName is something that is also somewhere else. Seems like we should have that centralized so it isn't out of sync, no?

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I guess it was just below? Nm.

break;
}

if (IRGen.Opts.EmitDeadStrippableSymbols) {
for (auto *protocol : SwiftProtocols) {
auto ref = getTypeEntityReference(protocol);
auto name = "\x01l_protocol_" + std::string(ref.getValue()->getName());
auto var = new llvm::GlobalVariable(
Module, ProtocolRecordTy, /*isConstant*/ true,
llvm::GlobalValue::PrivateLinkage, /*initializer*/ nullptr, name);

llvm::Constant *relativeAddr =
emitDirectRelativeReference(ref.getValue(), var, {0});
llvm::Constant *recordFields[] = {relativeAddr};
auto record = llvm::ConstantStruct::get(ProtocolRecordTy, recordFields);
var->setInitializer(record);
var->setSection(sectionName);
var->setAlignment(llvm::MaybeAlign(4));

disableAddressSanitizer(*this, var);
}
return nullptr;
}

// Define the global variable for the protocol list.
ConstantInitBuilder builder(*this);
auto recordsArray = builder.beginArray(ProtocolRecordTy);
Expand All @@ -3374,24 +3420,6 @@ llvm::Constant *IRGenModule::emitSwiftProtocols() {
/*isConstant*/ true,
llvm::GlobalValue::PrivateLinkage);

StringRef sectionName;
switch (TargetInfo.OutputObjectFormat) {
case llvm::Triple::UnknownObjectFormat:
llvm_unreachable("Don't know how to emit protocols for "
"the selected object format.");
case llvm::Triple::MachO:
sectionName = "__TEXT, __swift5_protos, regular, no_dead_strip";
break;
case llvm::Triple::ELF:
case llvm::Triple::Wasm:
sectionName = "swift5_protocols";
break;
case llvm::Triple::XCOFF:
case llvm::Triple::COFF:
sectionName = ".sw5prt$B";
break;
}

var->setSection(sectionName);

disableAddressSanitizer(*this, var);
Expand All @@ -3413,6 +3441,49 @@ llvm::Constant *IRGenModule::emitProtocolConformances() {
if (ProtocolConformances.empty())
return nullptr;

StringRef sectionName;
switch (TargetInfo.OutputObjectFormat) {
case llvm::Triple::UnknownObjectFormat:
llvm_unreachable("Don't know how to emit protocol conformances for "
"the selected object format.");
case llvm::Triple::MachO:
sectionName = IRGen.Opts.EmitDeadStrippableSymbols
? "__TEXT, __swift5_proto, regular, live_support"
: "__TEXT, __swift5_proto, regular, no_dead_strip";
break;
case llvm::Triple::ELF:
case llvm::Triple::Wasm:
sectionName = "swift5_protocol_conformances";
break;
case llvm::Triple::XCOFF:
case llvm::Triple::COFF:
sectionName = ".sw5prtc$B";
break;
}

if (IRGen.Opts.EmitDeadStrippableSymbols) {
for (const auto &record : ProtocolConformances) {
auto conformance = record.conformance;
auto entity = LinkEntity::forProtocolConformanceDescriptor(conformance);
auto name =
"\x01l_protocol_conformance_" + std::string(entity.mangleAsString());
auto var = new llvm::GlobalVariable(
Module, RelativeAddressTy, /*isConstant*/ true,
llvm::GlobalValue::PrivateLinkage, /*initializer*/ nullptr, name);

auto descriptor =
getAddrOfLLVMVariable(entity, ConstantInit(), DebugTypeInfo());
llvm::Constant *relativeAddr =
emitDirectRelativeReference(descriptor, var, {});
var->setInitializer(relativeAddr);
var->setSection(sectionName);
var->setAlignment(llvm::MaybeAlign(4));

disableAddressSanitizer(*this, var);
}
return nullptr;
}

// Define the global variable for the conformance list.
ConstantInitBuilder builder(*this);
auto descriptorArray = builder.beginArray(RelativeAddressTy);
Expand All @@ -3434,24 +3505,6 @@ llvm::Constant *IRGenModule::emitProtocolConformances() {
/*isConstant*/ true,
llvm::GlobalValue::PrivateLinkage);

StringRef sectionName;
switch (TargetInfo.OutputObjectFormat) {
case llvm::Triple::UnknownObjectFormat:
llvm_unreachable("Don't know how to emit protocol conformances for "
"the selected object format.");
case llvm::Triple::MachO:
sectionName = "__TEXT, __swift5_proto, regular, no_dead_strip";
break;
case llvm::Triple::ELF:
case llvm::Triple::Wasm:
sectionName = "swift5_protocol_conformances";
break;
case llvm::Triple::XCOFF:
case llvm::Triple::COFF:
sectionName = ".sw5prtc$B";
break;
}

var->setSection(sectionName);

disableAddressSanitizer(*this, var);
Expand All @@ -3466,7 +3519,9 @@ llvm::Constant *IRGenModule::emitTypeMetadataRecords() {
std::string sectionName;
switch (TargetInfo.OutputObjectFormat) {
case llvm::Triple::MachO:
sectionName = "__TEXT, __swift5_types, regular, no_dead_strip";
sectionName = IRGen.Opts.EmitDeadStrippableSymbols
? "__TEXT, __swift5_types, regular, live_support"
: "__TEXT, __swift5_types, regular, no_dead_strip";
break;
case llvm::Triple::ELF:
case llvm::Triple::Wasm:
Expand All @@ -3485,6 +3540,45 @@ llvm::Constant *IRGenModule::emitTypeMetadataRecords() {
if (RuntimeResolvableTypes.empty())
return nullptr;

auto generateRecord = [this](TypeEntityReference ref,
llvm::GlobalVariable *var,
ArrayRef<unsigned> baseIndices) {
// Form the relative address, with the type reference kind in the low bits.
llvm::Constant *relativeAddr =
emitDirectRelativeReference(ref.getValue(), var, baseIndices);
unsigned lowBits = static_cast<unsigned>(ref.getKind());
if (lowBits != 0) {
relativeAddr = llvm::ConstantExpr::getAdd(
relativeAddr, llvm::ConstantInt::get(RelativeAddressTy, lowBits));
}

llvm::Constant *recordFields[] = {relativeAddr};
auto record = llvm::ConstantStruct::get(TypeMetadataRecordTy, recordFields);
return record;
};

if (IRGen.Opts.EmitDeadStrippableSymbols) {
for (auto type : RuntimeResolvableTypes) {
auto ref = getTypeEntityReference(type);
auto name =
"\x01l_type_metadata_" + std::string(ref.getValue()->getName());
auto var = new llvm::GlobalVariable(
Module, TypeMetadataRecordTy, /*isConstant*/ true,
llvm::GlobalValue::PrivateLinkage, /*initializer*/ nullptr, name);

auto record = generateRecord(ref, var, {0});
var->setInitializer(record);
var->setSection(sectionName);
var->setAlignment(llvm::MaybeAlign(4));

disableAddressSanitizer(*this, var);

addCompilerUsedGlobal(var);
}

return nullptr;
}

// Define the global variable for the conformance list.
// We have to do this before defining the initializer since the entries will
// contain offsets relative to themselves.
Expand All @@ -3502,20 +3596,8 @@ llvm::Constant *IRGenModule::emitTypeMetadataRecords() {
SmallVector<llvm::Constant *, 8> elts;
for (auto type : RuntimeResolvableTypes) {
auto ref = getTypeEntityReference(type);

// Form the relative address, with the type reference kind in the low bits.
unsigned arrayIdx = elts.size();
llvm::Constant *relativeAddr =
emitDirectRelativeReference(ref.getValue(), var, { arrayIdx, 0 });
unsigned lowBits = static_cast<unsigned>(ref.getKind());
if (lowBits != 0) {
relativeAddr = llvm::ConstantExpr::getAdd(relativeAddr,
llvm::ConstantInt::get(RelativeAddressTy, lowBits));
}

llvm::Constant *recordFields[] = { relativeAddr };
auto record = llvm::ConstantStruct::get(TypeMetadataRecordTy,
recordFields);
auto record = generateRecord(ref, var, { arrayIdx, 0 });
elts.push_back(record);
}

Expand Down Expand Up @@ -3890,7 +3972,9 @@ llvm::GlobalValue *IRGenModule::defineAlias(LinkEntity entity,
ApplyIRLinkage({link.getLinkage(), link.getVisibility(), link.getDLLStorage()})
.to(alias);

if (link.isUsed()) {
// Everything externally visible is considered used in Swift.
// That mostly means we need to be good at not marking things external.
if (link.isUsed() && !IRGen.Opts.EmitDeadStrippableSymbols) {
addUsedGlobal(alias);
}

Expand Down
71 changes: 71 additions & 0 deletions test/IRGen/dead_strip.swift
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Original file line number Diff line number Diff line change
@@ -0,0 +1,71 @@
// Checks that applying -dead_strip linker flag actually removes unused classes and functions from static libraries.

// REQUIRES: OS=macosx

// RUN: echo "-target x86_64-apple-macos11.0 -swift-version 5 -parse-as-library -working-directory %t" >> %t-commonflags
// RUN: echo "-Xfrontend -disable-objc-interop" >> %t-commonflags
// RUN: echo "-Xfrontend -disable-reflection-metadata -Xfrontend -disable-reflection-names" >> %t-commonflags

// RUN: %empty-directory(%t)
// RUN: %target-swiftc_driver @%t-commonflags -emit-library -static -DMODULE -emit-module %s -module-name MyModule
// RUN: %target-swiftc_driver @%t-commonflags %s -I%t -L%t -lMyModule -Xlinker -dead_strip -module-name main -o %t/main
// RUN: %llvm-nm --defined-only %t/main | %FileCheck %s

// RUN: %empty-directory(%t)
// RUN: %target-swiftc_driver @%t-commonflags -emit-library -static -DMODULE -emit-module %s -module-name MyModule -Xfrontend -emit-dead-strippable-symbols
// RUN: %target-swiftc_driver @%t-commonflags %s -I%t -L%t -lMyModule -Xlinker -dead_strip -module-name main -o %t/main
// RUN: %llvm-nm --defined-only %t/main | %FileCheck %s -check-prefix CHECK-DEADSTRIPPABLE

#if MODULE

public protocol MyProtocol {
}
public class MyClass: MyProtocol {
}

public func fooFromModule() { print("fooFromModule") }
public func barFromModule() { print("barFromModule") }

#else

import MyModule

@_cdecl("main")
func main() {
print("Hello!")
fooFromModule()
}

#endif

// CHECK: _$s8MyModule07barFromB0yyF
// CHECK: _$s8MyModule07fooFromB0yyF
// CHECK: _$s8MyModule0A5ClassCAA0A8ProtocolAAMc
// CHECK: _$s8MyModule0A5ClassCAA0A8ProtocolAAWP
// CHECK: _$s8MyModule0A5ClassCACycfC
// CHECK: _$s8MyModule0A5ClassCACycfCTq
// CHECK: _$s8MyModule0A5ClassCACycfc
// CHECK: _$s8MyModule0A5ClassCMa
// CHECK: _$s8MyModule0A5ClassCMf
// CHECK: _$s8MyModule0A5ClassCMn
// CHECK: _$s8MyModule0A5ClassCN
// CHECK: _$s8MyModule0A5ClassCfD
// CHECK: _$s8MyModule0A5ClassCfd
// CHECK: _$s8MyModule0A8ProtocolMp
// CHECK: _$s8MyModuleMXM

// CHECK-DEADSTRIPPABLE-NOT: _$s8MyModule07barFromB0yyF
// CHECK-DEADSTRIPPABLE: _$s8MyModule07fooFromB0yyF
// CHECK-DEADSTRIPPABLE-NOT: _$s8MyModule0A5ClassCAA0A8ProtocolAAMc
// CHECK-DEADSTRIPPABLE-NOT: _$s8MyModule0A5ClassCAA0A8ProtocolAAWP
// CHECK-DEADSTRIPPABLE-NOT: _$s8MyModule0A5ClassCACycfC
// CHECK-DEADSTRIPPABLE-NOT: _$s8MyModule0A5ClassCACycfCTq
// CHECK-DEADSTRIPPABLE-NOT: _$s8MyModule0A5ClassCACycfc
// CHECK-DEADSTRIPPABLE-NOT: _$s8MyModule0A5ClassCMa
// CHECK-DEADSTRIPPABLE-NOT: _$s8MyModule0A5ClassCMf
// CHECK-DEADSTRIPPABLE-NOT: _$s8MyModule0A5ClassCMn
// CHECK-DEADSTRIPPABLE-NOT: _$s8MyModule0A5ClassCN
// CHECK-DEADSTRIPPABLE-NOT: _$s8MyModule0A5ClassCfD
// CHECK-DEADSTRIPPABLE-NOT: _$s8MyModule0A5ClassCfd
// CHECK-DEADSTRIPPABLE-NOT: _$s8MyModule0A8ProtocolMp
// CHECK-DEADSTRIPPABLE-NOT: _$s8MyModuleMXM
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