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[LTO] Handles commons in monolithic LTO
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The gold-plugin was doing this internally, now the API is handling
commons correctly based on the given resolution.

Differential Revision: https://reviews.llvm.org/D23739

llvm-svn: 279417
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@joker-eph
joker-eph committed Aug 22, 2016
1 parent d310b47 commit dc4c8cf
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Showing 5 changed files with 111 additions and 58 deletions.
5 changes: 5 additions & 0 deletions llvm/include/llvm/LTO/LTO.h
View file
Expand Up @@ -306,6 +306,11 @@ class LTO {

struct RegularLTOState {
RegularLTOState(unsigned ParallelCodeGenParallelismLevel, Config &Conf);
struct CommonResolution {
uint64_t Size = 0;
unsigned Align = 0;
};
std::map<std::string, CommonResolution> Commons;

unsigned ParallelCodeGenParallelismLevel;
LTOLLVMContext Ctx;
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33 changes: 33 additions & 0 deletions llvm/lib/LTO/LTO.cpp
View file
Expand Up @@ -292,6 +292,14 @@ Error LTO::addRegularLTO(std::unique_ptr<InputFile> Input,
break;
}
}
// Common resolution: collect the maximum size/alignment.
// FIXME: right now we ignore the prevailing information, it is not clear
// what is the "right" behavior here.
if (Sym.getFlags() & object::BasicSymbolRef::SF_Common) {
auto &CommonRes = RegularLTO.Commons[Sym.getIRName()];
CommonRes.Size = std::max(CommonRes.Size, Sym.getCommonSize());
CommonRes.Align = std::max(CommonRes.Align, Sym.getCommonAlignment());
}

// FIXME: use proposed local attribute for FinalDefinitionInLinkageUnit.
}
Expand Down Expand Up @@ -361,6 +369,31 @@ Error LTO::run(AddOutputFn AddOutput) {
}

Error LTO::runRegularLTO(AddOutputFn AddOutput) {
// Make sure commons have the right size/alignment: we kept the largest from
// all the prevailing when adding the inputs, and we apply it here.
for (auto &I : RegularLTO.Commons) {
ArrayType *Ty =
ArrayType::get(Type::getInt8Ty(RegularLTO.Ctx), I.second.Size);
GlobalVariable *OldGV = RegularLTO.CombinedModule->getNamedGlobal(I.first);
if (OldGV && OldGV->getType()->getElementType() == Ty) {
// Don't create a new global if the type is already correct, just make
// sure the alignment is correct.
OldGV->setAlignment(I.second.Align);
continue;
}
auto *GV = new GlobalVariable(*RegularLTO.CombinedModule, Ty, false,
GlobalValue::CommonLinkage,
ConstantAggregateZero::get(Ty), "");
GV->setAlignment(I.second.Align);
if (OldGV) {
OldGV->replaceAllUsesWith(ConstantExpr::getBitCast(GV, OldGV->getType()));
GV->takeName(OldGV);
OldGV->eraseFromParent();
} else {
GV->setName(I.first);
}
}

if (Conf.PreOptModuleHook &&
!Conf.PreOptModuleHook(0, *RegularLTO.CombinedModule))
return Error();
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7 changes: 7 additions & 0 deletions llvm/test/tools/llvm-lto2/Inputs/common.ll
View file
@@ -0,0 +1,7 @@
target triple = "x86_64-apple-macosx10.11.0"

@v = common global i16 0, align 4

define i16 *@bar() {
ret i16 *@v
}
65 changes: 65 additions & 0 deletions llvm/test/tools/llvm-lto2/common.ll
View file
@@ -0,0 +1,65 @@
; RUN: llvm-as < %s > %t1.bc
; RUN: llvm-as < %p/Inputs/common.ll > %t2.bc

; Test that the common merging (size + alignment) is properly handled

; Client marked the "large with little alignment" one as prevailing
; RUN: llvm-lto2 %t1.bc %t2.bc -o %t.o -save-temps \
; RUN: -r %t1.bc,v,x \
; RUN: -r %t2.bc,v,px \
; RUN: -r %t1.bc,foo,px \
; RUN: -r %t2.bc,bar,px
; RUN: llvm-dis < %t.o.0.0.preopt.bc | FileCheck %s

; Same as before, but reversing the order of the inputs
; RUN: llvm-lto2 %t2.bc %t1.bc -o %t.o -save-temps \
; RUN: -r %t1.bc,v,x \
; RUN: -r %t2.bc,v,px \
; RUN: -r %t1.bc,foo,px \
; RUN: -r %t2.bc,bar,px
; RUN: llvm-dis < %t.o.0.0.preopt.bc | FileCheck %s


; Client marked the "small with large alignment" one as prevailing
; RUN: llvm-lto2 %t1.bc %t2.bc -o %t.o -save-temps \
; RUN: -r %t1.bc,v,px \
; RUN: -r %t2.bc,v,x \
; RUN: -r %t1.bc,foo,px \
; RUN: -r %t2.bc,bar,px
; RUN: llvm-dis < %t.o.0.0.preopt.bc | FileCheck %s

; Same as before, but reversing the order of the inputs
; RUN: llvm-lto2 %t2.bc %t1.bc -o %t.o -save-temps \
; RUN: -r %t1.bc,v,px \
; RUN: -r %t2.bc,v,x \
; RUN: -r %t1.bc,foo,px \
; RUN: -r %t2.bc,bar,px
; RUN: llvm-dis < %t.o.0.0.preopt.bc | FileCheck %s


; Client didn't mark any as prevailing, we keep the first one we see as "external"
; RUN: llvm-lto2 %t1.bc %t2.bc -o %t.o -save-temps \
; RUN: -r %t1.bc,v,x \
; RUN: -r %t2.bc,v,x \
; RUN: -r %t1.bc,foo,px \
; RUN: -r %t2.bc,bar,px
; RUN: llvm-dis < %t.o.0.0.preopt.bc | FileCheck %s

; Same as before, but reversing the order of the inputs
; RUN: llvm-lto2 %t2.bc %t1.bc -o %t.o -save-temps \
; RUN: -r %t1.bc,v,x \
; RUN: -r %t2.bc,v,x \
; RUN: -r %t1.bc,foo,px \
; RUN: -r %t2.bc,bar,px
; RUN: llvm-dis < %t.o.0.0.preopt.bc | FileCheck %s

target triple = "x86_64-apple-macosx10.11.0"

@v = common global i8 0, align 8


; CHECK: @v = common global [2 x i8] zeroinitializer, align 8

define i8 *@foo() {
ret i8 *@v
}
59 changes: 1 addition & 58 deletions llvm/tools/gold/gold-plugin.cpp
View file
Expand Up @@ -89,13 +89,6 @@ struct ResolutionInfo {
bool DefaultVisibility = true;
};

struct CommonResolution {
bool Prevailing = false;
bool VisibleToRegularObj = false;
uint64_t Size = 0;
unsigned Align = 0;
};

}

static ld_plugin_add_symbols add_symbols = nullptr;
Expand All @@ -109,7 +102,6 @@ static std::string output_name = "";
static std::list<claimed_file> Modules;
static DenseMap<int, void *> FDToLeaderHandle;
static StringMap<ResolutionInfo> ResInfo;
static std::map<std::string, CommonResolution> Commons;
static std::vector<std::string> Cleanup;
static llvm::TargetOptions TargetOpts;
static size_t MaxTasks;
Expand Down Expand Up @@ -572,12 +564,10 @@ static void addModule(LTO &Lto, claimed_file &F, const void *View) {
toString(ObjOrErr.takeError()).c_str());

InputFile &Obj = **ObjOrErr;
bool HasThinLTOSummary =
hasGlobalValueSummary(Obj.getMemoryBufferRef(), diagnosticHandler);

unsigned SymNum = 0;
std::vector<SymbolResolution> Resols(F.syms.size());
for (auto &ObjSym : Obj.symbols()) {
for (LLVM_ATTRIBUTE_UNUSED auto &ObjSym : Obj.symbols()) {
ld_plugin_symbol &Sym = F.syms[SymNum];
SymbolResolution &R = Resols[SymNum];
++SymNum;
Expand Down Expand Up @@ -619,21 +609,6 @@ static void addModule(LTO &Lto, claimed_file &F, const void *View) {
(IsExecutable || !Res.DefaultVisibility))
R.FinalDefinitionInLinkageUnit = true;

if ((ObjSym.getFlags() & object::BasicSymbolRef::SF_Common) &&
!HasThinLTOSummary) {
// We ignore gold's resolution for common symbols. A common symbol with
// the correct size and alignment is added to the module by the pre-opt
// module hook if any common symbol prevailed.
CommonResolution &CommonRes = Commons[ObjSym.getIRName()];
if (R.Prevailing) {
CommonRes.Prevailing = true;
CommonRes.VisibleToRegularObj = R.VisibleToRegularObj;
}
CommonRes.Size = std::max(CommonRes.Size, ObjSym.getCommonSize());
CommonRes.Align = std::max(CommonRes.Align, ObjSym.getCommonAlignment());
R.Prevailing = false;
}

freeSymName(Sym);
}

Expand Down Expand Up @@ -668,32 +643,6 @@ static void getOutputFileName(SmallString<128> InFilename, bool TempOutFile,
}
}

/// Add all required common symbols to M, which is expected to be the first
/// combined module.
static void addCommons(Module &M) {
for (auto &I : Commons) {
if (!I.second.Prevailing)
continue;
ArrayType *Ty =
ArrayType::get(Type::getInt8Ty(M.getContext()), I.second.Size);
GlobalVariable *OldGV = M.getNamedGlobal(I.first);
auto *GV = new GlobalVariable(M, Ty, false, GlobalValue::CommonLinkage,
ConstantAggregateZero::get(Ty), "");
GV->setAlignment(I.second.Align);
if (OldGV) {
OldGV->replaceAllUsesWith(ConstantExpr::getBitCast(GV, OldGV->getType()));
GV->takeName(OldGV);
OldGV->eraseFromParent();
} else {
GV->setName(I.first);
}
// We may only internalize commons if there is a single LTO task because
// other native object files may require the common.
if (MaxTasks == 1 && !I.second.VisibleToRegularObj)
GV->setLinkage(GlobalValue::InternalLinkage);
}
}

static CodeGenOpt::Level getCGOptLevel() {
switch (options::OptLevel) {
case 0:
Expand Down Expand Up @@ -773,12 +722,6 @@ static std::unique_ptr<LTO> createLTO() {

Conf.DiagHandler = diagnosticHandler;

Conf.PreOptModuleHook = [](size_t Task, Module &M) {
if (Task == 0)
addCommons(M);
return true;
};

switch (options::TheOutputType) {
case options::OT_NORMAL:
break;
Expand Down

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