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-rw-r--r--llvm/lib/Analysis/TypeMetadataUtils.cpp32
-rw-r--r--llvm/lib/IR/Metadata.cpp18
-rw-r--r--llvm/lib/LTO/LTO.cpp2
-rw-r--r--llvm/lib/LTO/LTOCodeGenerator.cpp2
-rw-r--r--llvm/lib/Transforms/IPO/GlobalDCE.cpp156
-rw-r--r--llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp41
6 files changed, 215 insertions, 36 deletions
diff --git a/llvm/lib/Analysis/TypeMetadataUtils.cpp b/llvm/lib/Analysis/TypeMetadataUtils.cpp
index 9311dfbc6eb..072d291f3f9 100644
--- a/llvm/lib/Analysis/TypeMetadataUtils.cpp
+++ b/llvm/lib/Analysis/TypeMetadataUtils.cpp
@@ -127,3 +127,35 @@ void llvm::findDevirtualizableCallsForTypeCheckedLoad(
findCallsAtConstantOffset(DevirtCalls, &HasNonCallUses, LoadedPtr,
Offset->getZExtValue(), CI, DT);
}
+
+Constant *llvm::getPointerAtOffset(Constant *I, uint64_t Offset, Module &M) {
+ if (I->getType()->isPointerTy()) {
+ if (Offset == 0)
+ return I;
+ return nullptr;
+ }
+
+ const DataLayout &DL = M.getDataLayout();
+
+ if (auto *C = dyn_cast<ConstantStruct>(I)) {
+ const StructLayout *SL = DL.getStructLayout(C->getType());
+ if (Offset >= SL->getSizeInBytes())
+ return nullptr;
+
+ unsigned Op = SL->getElementContainingOffset(Offset);
+ return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
+ Offset - SL->getElementOffset(Op), M);
+ }
+ if (auto *C = dyn_cast<ConstantArray>(I)) {
+ ArrayType *VTableTy = C->getType();
+ uint64_t ElemSize = DL.getTypeAllocSize(VTableTy->getElementType());
+
+ unsigned Op = Offset / ElemSize;
+ if (Op >= C->getNumOperands())
+ return nullptr;
+
+ return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
+ Offset % ElemSize, M);
+ }
+ return nullptr;
+}
diff --git a/llvm/lib/IR/Metadata.cpp b/llvm/lib/IR/Metadata.cpp
index 748a2238e64..62c2aa86f3b 100644
--- a/llvm/lib/IR/Metadata.cpp
+++ b/llvm/lib/IR/Metadata.cpp
@@ -1497,6 +1497,24 @@ void GlobalObject::addTypeMetadata(unsigned Offset, Metadata *TypeID) {
TypeID}));
}
+void GlobalObject::addVCallVisibilityMetadata(VCallVisibility Visibility) {
+ addMetadata(LLVMContext::MD_vcall_visibility,
+ *MDNode::get(getContext(),
+ {ConstantAsMetadata::get(ConstantInt::get(
+ Type::getInt64Ty(getContext()), Visibility))}));
+}
+
+GlobalObject::VCallVisibility GlobalObject::getVCallVisibility() const {
+ if (MDNode *MD = getMetadata(LLVMContext::MD_vcall_visibility)) {
+ uint64_t Val = cast<ConstantInt>(
+ cast<ConstantAsMetadata>(MD->getOperand(0))->getValue())
+ ->getZExtValue();
+ assert(Val <= 2 && "unknown vcall visibility!");
+ return (VCallVisibility)Val;
+ }
+ return VCallVisibility::VCallVisibilityPublic;
+}
+
void Function::setSubprogram(DISubprogram *SP) {
setMetadata(LLVMContext::MD_dbg, SP);
}
diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 71076084006..1e345e7dd89 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -1004,6 +1004,8 @@ Error LTO::runRegularLTO(AddStreamFn AddStream) {
GV->setLinkage(GlobalValue::InternalLinkage);
}
+ RegularLTO.CombinedModule->addModuleFlag(Module::Error, "LTOPostLink", 1);
+
if (Conf.PostInternalizeModuleHook &&
!Conf.PostInternalizeModuleHook(0, *RegularLTO.CombinedModule))
return Error::success();
diff --git a/llvm/lib/LTO/LTOCodeGenerator.cpp b/llvm/lib/LTO/LTOCodeGenerator.cpp
index 4d1d07aec3c..88219289286 100644
--- a/llvm/lib/LTO/LTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/LTOCodeGenerator.cpp
@@ -463,6 +463,8 @@ void LTOCodeGenerator::applyScopeRestrictions() {
internalizeModule(*MergedModule, mustPreserveGV);
+ MergedModule->addModuleFlag(Module::Error, "LTOPostLink", 1);
+
ScopeRestrictionsDone = true;
}
diff --git a/llvm/lib/Transforms/IPO/GlobalDCE.cpp b/llvm/lib/Transforms/IPO/GlobalDCE.cpp
index 86b7f3e49ee..f010f7b703a 100644
--- a/llvm/lib/Transforms/IPO/GlobalDCE.cpp
+++ b/llvm/lib/Transforms/IPO/GlobalDCE.cpp
@@ -17,9 +17,11 @@
#include "llvm/Transforms/IPO/GlobalDCE.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/TypeMetadataUtils.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
+#include "llvm/IR/Operator.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Transforms/Utils/CtorUtils.h"
@@ -29,10 +31,15 @@ using namespace llvm;
#define DEBUG_TYPE "globaldce"
+static cl::opt<bool>
+ ClEnableVFE("enable-vfe", cl::Hidden, cl::init(true), cl::ZeroOrMore,
+ cl::desc("Enable virtual function elimination"));
+
STATISTIC(NumAliases , "Number of global aliases removed");
STATISTIC(NumFunctions, "Number of functions removed");
STATISTIC(NumIFuncs, "Number of indirect functions removed");
STATISTIC(NumVariables, "Number of global variables removed");
+STATISTIC(NumVFuncs, "Number of virtual functions removed");
namespace {
class GlobalDCELegacyPass : public ModulePass {
@@ -118,6 +125,15 @@ void GlobalDCEPass::UpdateGVDependencies(GlobalValue &GV) {
ComputeDependencies(User, Deps);
Deps.erase(&GV); // Remove self-reference.
for (GlobalValue *GVU : Deps) {
+ // If this is a dep from a vtable to a virtual function, and we have
+ // complete information about all virtual call sites which could call
+ // though this vtable, then skip it, because the call site information will
+ // be more precise.
+ if (VFESafeVTables.count(GVU) && isa<Function>(&GV)) {
+ LLVM_DEBUG(dbgs() << "Ignoring dep " << GVU->getName() << " -> "
+ << GV.getName() << "\n");
+ continue;
+ }
GVDependencies[GVU].insert(&GV);
}
}
@@ -132,12 +148,133 @@ void GlobalDCEPass::MarkLive(GlobalValue &GV,
if (Updates)
Updates->push_back(&GV);
if (Comdat *C = GV.getComdat()) {
- for (auto &&CM : make_range(ComdatMembers.equal_range(C)))
+ for (auto &&CM : make_range(ComdatMembers.equal_range(C))) {
MarkLive(*CM.second, Updates); // Recursion depth is only two because only
// globals in the same comdat are visited.
+ }
+ }
+}
+
+void GlobalDCEPass::ScanVTables(Module &M) {
+ SmallVector<MDNode *, 2> Types;
+ LLVM_DEBUG(dbgs() << "Building type info -> vtable map\n");
+
+ auto *LTOPostLinkMD =
+ cast_or_null<ConstantAsMetadata>(M.getModuleFlag("LTOPostLink"));
+ bool LTOPostLink =
+ LTOPostLinkMD &&
+ (cast<ConstantInt>(LTOPostLinkMD->getValue())->getZExtValue() != 0);
+
+ for (GlobalVariable &GV : M.globals()) {
+ Types.clear();
+ GV.getMetadata(LLVMContext::MD_type, Types);
+ if (GV.isDeclaration() || Types.empty())
+ continue;
+
+ // Use the typeid metadata on the vtable to build a mapping from typeids to
+ // the list of (GV, offset) pairs which are the possible vtables for that
+ // typeid.
+ for (MDNode *Type : Types) {
+ Metadata *TypeID = Type->getOperand(1).get();
+
+ uint64_t Offset =
+ cast<ConstantInt>(
+ cast<ConstantAsMetadata>(Type->getOperand(0))->getValue())
+ ->getZExtValue();
+
+ TypeIdMap[TypeID].insert(std::make_pair(&GV, Offset));
+ }
+
+ // If the type corresponding to the vtable is private to this translation
+ // unit, we know that we can see all virtual functions which might use it,
+ // so VFE is safe.
+ if (auto GO = dyn_cast<GlobalObject>(&GV)) {
+ GlobalObject::VCallVisibility TypeVis = GO->getVCallVisibility();
+ if (TypeVis == GlobalObject::VCallVisibilityTranslationUnit ||
+ (LTOPostLink &&
+ TypeVis == GlobalObject::VCallVisibilityLinkageUnit)) {
+ LLVM_DEBUG(dbgs() << GV.getName() << " is safe for VFE\n");
+ VFESafeVTables.insert(&GV);
+ }
+ }
+ }
+}
+
+void GlobalDCEPass::ScanVTableLoad(Function *Caller, Metadata *TypeId,
+ uint64_t CallOffset) {
+ for (auto &VTableInfo : TypeIdMap[TypeId]) {
+ GlobalVariable *VTable = VTableInfo.first;
+ uint64_t VTableOffset = VTableInfo.second;
+
+ Constant *Ptr =
+ getPointerAtOffset(VTable->getInitializer(), VTableOffset + CallOffset,
+ *Caller->getParent());
+ if (!Ptr) {
+ LLVM_DEBUG(dbgs() << "can't find pointer in vtable!\n");
+ VFESafeVTables.erase(VTable);
+ return;
+ }
+
+ auto Callee = dyn_cast<Function>(Ptr->stripPointerCasts());
+ if (!Callee) {
+ LLVM_DEBUG(dbgs() << "vtable entry is not function pointer!\n");
+ VFESafeVTables.erase(VTable);
+ return;
+ }
+
+ LLVM_DEBUG(dbgs() << "vfunc dep " << Caller->getName() << " -> "
+ << Callee->getName() << "\n");
+ GVDependencies[Caller].insert(Callee);
}
}
+void GlobalDCEPass::ScanTypeCheckedLoadIntrinsics(Module &M) {
+ LLVM_DEBUG(dbgs() << "Scanning type.checked.load intrinsics\n");
+ Function *TypeCheckedLoadFunc =
+ M.getFunction(Intrinsic::getName(Intrinsic::type_checked_load));
+
+ if (!TypeCheckedLoadFunc)
+ return;
+
+ for (auto U : TypeCheckedLoadFunc->users()) {
+ auto CI = dyn_cast<CallInst>(U);
+ if (!CI)
+ continue;
+
+ auto *Offset = dyn_cast<ConstantInt>(CI->getArgOperand(1));
+ Value *TypeIdValue = CI->getArgOperand(2);
+ auto *TypeId = cast<MetadataAsValue>(TypeIdValue)->getMetadata();
+
+ if (Offset) {
+ ScanVTableLoad(CI->getFunction(), TypeId, Offset->getZExtValue());
+ } else {
+ // type.checked.load with a non-constant offset, so assume every entry in
+ // every matching vtable is used.
+ for (auto &VTableInfo : TypeIdMap[TypeId]) {
+ VFESafeVTables.erase(VTableInfo.first);
+ }
+ }
+ }
+}
+
+void GlobalDCEPass::AddVirtualFunctionDependencies(Module &M) {
+ if (!ClEnableVFE)
+ return;
+
+ ScanVTables(M);
+
+ if (VFESafeVTables.empty())
+ return;
+
+ ScanTypeCheckedLoadIntrinsics(M);
+
+ LLVM_DEBUG(
+ dbgs() << "VFE safe vtables:\n";
+ for (auto *VTable : VFESafeVTables)
+ dbgs() << " " << VTable->getName() << "\n";
+ );
+}
+
PreservedAnalyses GlobalDCEPass::run(Module &M, ModuleAnalysisManager &MAM) {
bool Changed = false;
@@ -163,6 +300,10 @@ PreservedAnalyses GlobalDCEPass::run(Module &M, ModuleAnalysisManager &MAM) {
if (Comdat *C = GA.getComdat())
ComdatMembers.insert(std::make_pair(C, &GA));
+ // Add dependencies between virtual call sites and the virtual functions they
+ // might call, if we have that information.
+ AddVirtualFunctionDependencies(M);
+
// Loop over the module, adding globals which are obviously necessary.
for (GlobalObject &GO : M.global_objects()) {
Changed |= RemoveUnusedGlobalValue(GO);
@@ -257,8 +398,17 @@ PreservedAnalyses GlobalDCEPass::run(Module &M, ModuleAnalysisManager &MAM) {
};
NumFunctions += DeadFunctions.size();
- for (Function *F : DeadFunctions)
+ for (Function *F : DeadFunctions) {
+ if (!F->use_empty()) {
+ // Virtual functions might still be referenced by one or more vtables,
+ // but if we've proven them to be unused then it's safe to replace the
+ // virtual function pointers with null, allowing us to remove the
+ // function itself.
+ ++NumVFuncs;
+ F->replaceNonMetadataUsesWith(ConstantPointerNull::get(F->getType()));
+ }
EraseUnusedGlobalValue(F);
+ }
NumVariables += DeadGlobalVars.size();
for (GlobalVariable *GV : DeadGlobalVars)
@@ -277,6 +427,8 @@ PreservedAnalyses GlobalDCEPass::run(Module &M, ModuleAnalysisManager &MAM) {
ConstantDependenciesCache.clear();
GVDependencies.clear();
ComdatMembers.clear();
+ TypeIdMap.clear();
+ VFESafeVTables.clear();
if (Changed)
return PreservedAnalyses::none();
diff --git a/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp b/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
index ec54e529b60..f0cf5581ba8 100644
--- a/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
+++ b/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
@@ -492,7 +492,6 @@ struct DevirtModule {
void buildTypeIdentifierMap(
std::vector<VTableBits> &Bits,
DenseMap<Metadata *, std::set<TypeMemberInfo>> &TypeIdMap);
- Constant *getPointerAtOffset(Constant *I, uint64_t Offset);
bool
tryFindVirtualCallTargets(std::vector<VirtualCallTarget> &TargetsForSlot,
const std::set<TypeMemberInfo> &TypeMemberInfos,
@@ -810,38 +809,6 @@ void DevirtModule::buildTypeIdentifierMap(
}
}
-Constant *DevirtModule::getPointerAtOffset(Constant *I, uint64_t Offset) {
- if (I->getType()->isPointerTy()) {
- if (Offset == 0)
- return I;
- return nullptr;
- }
-
- const DataLayout &DL = M.getDataLayout();
-
- if (auto *C = dyn_cast<ConstantStruct>(I)) {
- const StructLayout *SL = DL.getStructLayout(C->getType());
- if (Offset >= SL->getSizeInBytes())
- return nullptr;
-
- unsigned Op = SL->getElementContainingOffset(Offset);
- return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
- Offset - SL->getElementOffset(Op));
- }
- if (auto *C = dyn_cast<ConstantArray>(I)) {
- ArrayType *VTableTy = C->getType();
- uint64_t ElemSize = DL.getTypeAllocSize(VTableTy->getElementType());
-
- unsigned Op = Offset / ElemSize;
- if (Op >= C->getNumOperands())
- return nullptr;
-
- return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
- Offset % ElemSize);
- }
- return nullptr;
-}
-
bool DevirtModule::tryFindVirtualCallTargets(
std::vector<VirtualCallTarget> &TargetsForSlot,
const std::set<TypeMemberInfo> &TypeMemberInfos, uint64_t ByteOffset) {
@@ -850,7 +817,7 @@ bool DevirtModule::tryFindVirtualCallTargets(
return false;
Constant *Ptr = getPointerAtOffset(TM.Bits->GV->getInitializer(),
- TM.Offset + ByteOffset);
+ TM.Offset + ByteOffset, M);
if (!Ptr)
return false;
@@ -1951,6 +1918,12 @@ bool DevirtModule::run() {
for (VTableBits &B : Bits)
rebuildGlobal(B);
+ // We have lowered or deleted the type checked load intrinsics, so we no
+ // longer have enough information to reason about the liveness of virtual
+ // function pointers in GlobalDCE.
+ for (GlobalVariable &GV : M.globals())
+ GV.eraseMetadata(LLVMContext::MD_vcall_visibility);
+
return true;
}
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