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merged 2 commits into from
Apr 17, 2025
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LowerTypeTests: Fix quadratic complexity (try 2). #136053

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[𝘀𝗽𝗿] initial version
pcc Apr 16, 2025
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194 changes: 107 additions & 87 deletions llvm/lib/Transforms/IPO/LowerTypeTests.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -352,6 +352,30 @@ struct ScopedSaveAliaseesAndUsed {
std::vector<std::pair<GlobalAlias *, Function *>> FunctionAliases;
std::vector<std::pair<GlobalIFunc *, Function *>> ResolverIFuncs;

// This function only removes functions from llvm.used and llvm.compiler.used.
// We cannot remove global variables because they need to follow RAUW, as
// they may be deleted by buildBitSetsFromGlobalVariables.
void collectAndEraseUsedFunctions(Module &M,
SmallVectorImpl<GlobalValue *> &Vec,
bool CompilerUsed) {
auto *GV = collectUsedGlobalVariables(M, Vec, CompilerUsed);
if (!GV)
return;
// There's no API to only remove certain array elements from
// llvm.used/llvm.compiler.used, so we remove all of them and add back only
// the non-functions.
GV->eraseFromParent();
auto NonFuncBegin =
std::stable_partition(Vec.begin(), Vec.end(), [](GlobalValue *GV) {
return isa<Function>(GV);
});
if (CompilerUsed)
appendToCompilerUsed(M, {NonFuncBegin, Vec.end()});
else
appendToUsed(M, {NonFuncBegin, Vec.end()});
Vec.resize(NonFuncBegin - Vec.begin());
}

ScopedSaveAliaseesAndUsed(Module &M) : M(M) {
// The users of this class want to replace all function references except
// for aliases and llvm.used/llvm.compiler.used with references to a jump
Expand All @@ -365,10 +389,8 @@ struct ScopedSaveAliaseesAndUsed {
// llvm.used/llvm.compiler.used and aliases, erase the used lists, let RAUW
// replace the aliasees and then set them back to their original values at
// the end.
if (GlobalVariable *GV = collectUsedGlobalVariables(M, Used, false))
GV->eraseFromParent();
if (GlobalVariable *GV = collectUsedGlobalVariables(M, CompilerUsed, true))
GV->eraseFromParent();
collectAndEraseUsedFunctions(M, Used, false);
collectAndEraseUsedFunctions(M, CompilerUsed, true);

for (auto &GA : M.aliases()) {
// FIXME: This should look past all aliases not just interposable ones,
Expand Down Expand Up @@ -1669,61 +1691,55 @@ void LowerTypeTestsModule::buildBitSetsFromFunctionsNative(

lowerTypeTestCalls(TypeIds, JumpTable, GlobalLayout);

{
ScopedSaveAliaseesAndUsed S(M);
// Build aliases pointing to offsets into the jump table, and replace
// references to the original functions with references to the aliases.
for (unsigned I = 0; I != Functions.size(); ++I) {
Function *F = cast<Function>(Functions[I]->getGlobal());
bool IsJumpTableCanonical = Functions[I]->isJumpTableCanonical();

// Build aliases pointing to offsets into the jump table, and replace
// references to the original functions with references to the aliases.
for (unsigned I = 0; I != Functions.size(); ++I) {
Function *F = cast<Function>(Functions[I]->getGlobal());
bool IsJumpTableCanonical = Functions[I]->isJumpTableCanonical();

Constant *CombinedGlobalElemPtr = ConstantExpr::getInBoundsGetElementPtr(
JumpTableType, JumpTable,
ArrayRef<Constant *>{ConstantInt::get(IntPtrTy, 0),
ConstantInt::get(IntPtrTy, I)});

const bool IsExported = Functions[I]->isExported();
if (!IsJumpTableCanonical) {
GlobalValue::LinkageTypes LT = IsExported
? GlobalValue::ExternalLinkage
: GlobalValue::InternalLinkage;
GlobalAlias *JtAlias = GlobalAlias::create(F->getValueType(), 0, LT,
F->getName() + ".cfi_jt",
CombinedGlobalElemPtr, &M);
if (IsExported)
JtAlias->setVisibility(GlobalValue::HiddenVisibility);
else
appendToUsed(M, {JtAlias});
}
Constant *CombinedGlobalElemPtr = ConstantExpr::getInBoundsGetElementPtr(
JumpTableType, JumpTable,
ArrayRef<Constant *>{ConstantInt::get(IntPtrTy, 0),
ConstantInt::get(IntPtrTy, I)});

const bool IsExported = Functions[I]->isExported();
if (!IsJumpTableCanonical) {
GlobalValue::LinkageTypes LT = IsExported ? GlobalValue::ExternalLinkage
: GlobalValue::InternalLinkage;
GlobalAlias *JtAlias = GlobalAlias::create(F->getValueType(), 0, LT,
F->getName() + ".cfi_jt",
CombinedGlobalElemPtr, &M);
if (IsExported)
JtAlias->setVisibility(GlobalValue::HiddenVisibility);
else
appendToUsed(M, {JtAlias});
}

if (IsExported) {
if (IsJumpTableCanonical)
ExportSummary->cfiFunctionDefs().emplace(F->getName());
else
ExportSummary->cfiFunctionDecls().emplace(F->getName());
}
if (IsExported) {
if (IsJumpTableCanonical)
ExportSummary->cfiFunctionDefs().emplace(F->getName());
else
ExportSummary->cfiFunctionDecls().emplace(F->getName());
}

if (!IsJumpTableCanonical) {
if (F->hasExternalWeakLinkage())
replaceWeakDeclarationWithJumpTablePtr(F, CombinedGlobalElemPtr,
IsJumpTableCanonical);
else
replaceCfiUses(F, CombinedGlobalElemPtr, IsJumpTableCanonical);
} else {
assert(F->getType()->getAddressSpace() == 0);

GlobalAlias *FAlias =
GlobalAlias::create(F->getValueType(), 0, F->getLinkage(), "",
CombinedGlobalElemPtr, &M);
FAlias->setVisibility(F->getVisibility());
FAlias->takeName(F);
if (FAlias->hasName())
F->setName(FAlias->getName() + ".cfi");
replaceCfiUses(F, FAlias, IsJumpTableCanonical);
if (!F->hasLocalLinkage())
F->setVisibility(GlobalVariable::HiddenVisibility);
}
if (!IsJumpTableCanonical) {
if (F->hasExternalWeakLinkage())
replaceWeakDeclarationWithJumpTablePtr(F, CombinedGlobalElemPtr,
IsJumpTableCanonical);
else
replaceCfiUses(F, CombinedGlobalElemPtr, IsJumpTableCanonical);
} else {
assert(F->getType()->getAddressSpace() == 0);

GlobalAlias *FAlias = GlobalAlias::create(
F->getValueType(), 0, F->getLinkage(), "", CombinedGlobalElemPtr, &M);
FAlias->setVisibility(F->getVisibility());
FAlias->takeName(F);
if (FAlias->hasName())
F->setName(FAlias->getName() + ".cfi");
replaceCfiUses(F, FAlias, IsJumpTableCanonical);
if (!F->hasLocalLinkage())
F->setVisibility(GlobalVariable::HiddenVisibility);
}
}

Expand Down Expand Up @@ -2339,39 +2355,43 @@ bool LowerTypeTestsModule::lower() {
if (GlobalClasses.empty())
return false;

// For each disjoint set we found...
for (const auto &C : GlobalClasses) {
if (!C->isLeader())
continue;

++NumTypeIdDisjointSets;
// Build the list of type identifiers in this disjoint set.
std::vector<Metadata *> TypeIds;
std::vector<GlobalTypeMember *> Globals;
std::vector<ICallBranchFunnel *> ICallBranchFunnels;
for (auto M : GlobalClasses.members(*C)) {
if (isa<Metadata *>(M))
TypeIds.push_back(cast<Metadata *>(M));
else if (isa<GlobalTypeMember *>(M))
Globals.push_back(cast<GlobalTypeMember *>(M));
else
ICallBranchFunnels.push_back(cast<ICallBranchFunnel *>(M));
}

// Order type identifiers by unique ID for determinism. This ordering is
// stable as there is a one-to-one mapping between metadata and unique IDs.
llvm::sort(TypeIds, [&](Metadata *M1, Metadata *M2) {
return TypeIdInfo[M1].UniqueId < TypeIdInfo[M2].UniqueId;
});
{
ScopedSaveAliaseesAndUsed S(M);
// For each disjoint set we found...
for (const auto &C : GlobalClasses) {
if (!C->isLeader())
continue;

// Same for the branch funnels.
llvm::sort(ICallBranchFunnels,
[&](ICallBranchFunnel *F1, ICallBranchFunnel *F2) {
return F1->UniqueId < F2->UniqueId;
});
++NumTypeIdDisjointSets;
// Build the list of type identifiers in this disjoint set.
std::vector<Metadata *> TypeIds;
std::vector<GlobalTypeMember *> Globals;
std::vector<ICallBranchFunnel *> ICallBranchFunnels;
for (auto M : GlobalClasses.members(*C)) {
if (isa<Metadata *>(M))
TypeIds.push_back(cast<Metadata *>(M));
else if (isa<GlobalTypeMember *>(M))
Globals.push_back(cast<GlobalTypeMember *>(M));
else
ICallBranchFunnels.push_back(cast<ICallBranchFunnel *>(M));
}

// Build bitsets for this disjoint set.
buildBitSetsFromDisjointSet(TypeIds, Globals, ICallBranchFunnels);
// Order type identifiers by unique ID for determinism. This ordering is
// stable as there is a one-to-one mapping between metadata and unique
// IDs.
llvm::sort(TypeIds, [&](Metadata *M1, Metadata *M2) {
return TypeIdInfo[M1].UniqueId < TypeIdInfo[M2].UniqueId;
});

// Same for the branch funnels.
llvm::sort(ICallBranchFunnels,
[&](ICallBranchFunnel *F1, ICallBranchFunnel *F2) {
return F1->UniqueId < F2->UniqueId;
});

// Build bitsets for this disjoint set.
buildBitSetsFromDisjointSet(TypeIds, Globals, ICallBranchFunnels);
}
}

allocateByteArrays();
Expand Down
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