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llvm-project/llvm/lib/Transforms/IPO/LowerBitSets.cpp

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//===-- LowerBitSets.cpp - Bitset lowering pass ---------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass lowers bitset metadata and calls to the llvm.bitset.test intrinsic.
// See http://llvm.org/docs/LangRef.html#bitsets for more information.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/IPO/LowerBitSets.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/ADT/EquivalenceClasses.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Operator.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
using namespace llvm;
#define DEBUG_TYPE "lowerbitsets"
STATISTIC(NumBitSetsCreated, "Number of bitsets created");
STATISTIC(NumBitSetCallsLowered, "Number of bitset calls lowered");
STATISTIC(NumBitSetDisjointSets, "Number of disjoint sets of bitsets");
bool BitSetInfo::containsGlobalOffset(uint64_t Offset) const {
if (Offset < ByteOffset)
return false;
if ((Offset - ByteOffset) % (uint64_t(1) << AlignLog2) != 0)
return false;
uint64_t BitOffset = (Offset - ByteOffset) >> AlignLog2;
if (BitOffset >= BitSize)
return false;
return (Bits[BitOffset / 8] >> (BitOffset % 8)) & 1;
}
bool BitSetInfo::containsValue(
const DataLayout *DL,
const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout, Value *V,
uint64_t COffset) const {
if (auto GV = dyn_cast<GlobalVariable>(V)) {
auto I = GlobalLayout.find(GV);
if (I == GlobalLayout.end())
return false;
return containsGlobalOffset(I->second + COffset);
}
if (auto GEP = dyn_cast<GEPOperator>(V)) {
APInt APOffset(DL->getPointerSizeInBits(0), 0);
bool Result = GEP->accumulateConstantOffset(*DL, APOffset);
if (!Result)
return false;
COffset += APOffset.getZExtValue();
return containsValue(DL, GlobalLayout, GEP->getPointerOperand(),
COffset);
}
if (auto Op = dyn_cast<Operator>(V)) {
if (Op->getOpcode() == Instruction::BitCast)
return containsValue(DL, GlobalLayout, Op->getOperand(0), COffset);
if (Op->getOpcode() == Instruction::Select)
return containsValue(DL, GlobalLayout, Op->getOperand(1), COffset) &&
containsValue(DL, GlobalLayout, Op->getOperand(2), COffset);
}
return false;
}
BitSetInfo BitSetBuilder::build() {
if (Min > Max)
Min = 0;
// Normalize each offset against the minimum observed offset, and compute
// the bitwise OR of each of the offsets. The number of trailing zeros
// in the mask gives us the log2 of the alignment of all offsets, which
// allows us to compress the bitset by only storing one bit per aligned
// address.
uint64_t Mask = 0;
for (uint64_t &Offset : Offsets) {
Offset -= Min;
Mask |= Offset;
}
BitSetInfo BSI;
BSI.ByteOffset = Min;
BSI.AlignLog2 = 0;
// FIXME: Can probably do something smarter if all offsets are 0.
if (Mask != 0)
BSI.AlignLog2 = countTrailingZeros(Mask, ZB_Undefined);
// Build the compressed bitset while normalizing the offsets against the
// computed alignment.
BSI.BitSize = ((Max - Min) >> BSI.AlignLog2) + 1;
uint64_t ByteSize = (BSI.BitSize + 7) / 8;
BSI.Bits.resize(ByteSize);
for (uint64_t Offset : Offsets) {
Offset >>= BSI.AlignLog2;
BSI.Bits[Offset / 8] |= 1 << (Offset % 8);
}
return BSI;
}
namespace {
struct LowerBitSets : public ModulePass {
static char ID;
LowerBitSets() : ModulePass(ID) {
initializeLowerBitSetsPass(*PassRegistry::getPassRegistry());
}
const DataLayout *DL;
IntegerType *Int1Ty;
IntegerType *Int32Ty;
Type *Int32PtrTy;
IntegerType *Int64Ty;
Type *IntPtrTy;
// The llvm.bitsets named metadata.
NamedMDNode *BitSetNM;
// Mapping from bitset mdstrings to the call sites that test them.
DenseMap<MDString *, std::vector<CallInst *>> BitSetTestCallSites;
BitSetInfo
buildBitSet(MDString *BitSet,
const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout);
Value *createBitSetTest(IRBuilder<> &B, const BitSetInfo &BSI,
GlobalVariable *BitSetGlobal, Value *BitOffset);
void
lowerBitSetCall(CallInst *CI, const BitSetInfo &BSI,
GlobalVariable *BitSetGlobal, GlobalVariable *CombinedGlobal,
const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout);
void buildBitSetsFromGlobals(Module &M,
const std::vector<MDString *> &BitSets,
const std::vector<GlobalVariable *> &Globals);
bool buildBitSets(Module &M);
bool eraseBitSetMetadata(Module &M);
bool doInitialization(Module &M) override;
bool runOnModule(Module &M) override;
};
} // namespace
INITIALIZE_PASS_BEGIN(LowerBitSets, "lowerbitsets",
"Lower bitset metadata", false, false)
INITIALIZE_PASS_END(LowerBitSets, "lowerbitsets",
"Lower bitset metadata", false, false)
char LowerBitSets::ID = 0;
ModulePass *llvm::createLowerBitSetsPass() { return new LowerBitSets; }
bool LowerBitSets::doInitialization(Module &M) {
DL = M.getDataLayout();
if (!DL)
report_fatal_error("Data layout required");
Int1Ty = Type::getInt1Ty(M.getContext());
Int32Ty = Type::getInt32Ty(M.getContext());
Int32PtrTy = PointerType::getUnqual(Int32Ty);
Int64Ty = Type::getInt64Ty(M.getContext());
IntPtrTy = DL->getIntPtrType(M.getContext(), 0);
BitSetNM = M.getNamedMetadata("llvm.bitsets");
BitSetTestCallSites.clear();
return false;
}
/// Build a bit set for BitSet using the object layouts in
/// GlobalLayout.
BitSetInfo LowerBitSets::buildBitSet(
MDString *BitSet,
const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout) {
BitSetBuilder BSB;
// Compute the byte offset of each element of this bitset.
if (BitSetNM) {
for (MDNode *Op : BitSetNM->operands()) {
if (Op->getOperand(0) != BitSet || !Op->getOperand(1))
continue;
auto OpGlobal = cast<GlobalVariable>(
cast<ConstantAsMetadata>(Op->getOperand(1))->getValue());
uint64_t Offset =
cast<ConstantInt>(cast<ConstantAsMetadata>(Op->getOperand(2))
->getValue())->getZExtValue();
Offset += GlobalLayout.find(OpGlobal)->second;
BSB.addOffset(Offset);
}
}
return BSB.build();
}
/// Build a test that bit BitOffset mod sizeof(Bits)*8 is set in
/// Bits. This pattern matches to the bt instruction on x86.
static Value *createMaskedBitTest(IRBuilder<> &B, Value *Bits,
Value *BitOffset) {
auto BitsType = cast<IntegerType>(Bits->getType());
unsigned BitWidth = BitsType->getBitWidth();
BitOffset = B.CreateZExtOrTrunc(BitOffset, BitsType);
Value *BitIndex =
B.CreateAnd(BitOffset, ConstantInt::get(BitsType, BitWidth - 1));
Value *BitMask = B.CreateShl(ConstantInt::get(BitsType, 1), BitIndex);
Value *MaskedBits = B.CreateAnd(Bits, BitMask);
return B.CreateICmpNE(MaskedBits, ConstantInt::get(BitsType, 0));
}
/// Build a test that bit BitOffset is set in BSI, where
/// BitSetGlobal is a global containing the bits in BSI.
Value *LowerBitSets::createBitSetTest(IRBuilder<> &B, const BitSetInfo &BSI,
GlobalVariable *BitSetGlobal,
Value *BitOffset) {
if (BSI.Bits.size() <= 8) {
// If the bit set is sufficiently small, we can avoid a load by bit testing
// a constant.
IntegerType *BitsTy;
if (BSI.Bits.size() <= 4)
BitsTy = Int32Ty;
else
BitsTy = Int64Ty;
uint64_t Bits = 0;
for (auto I = BSI.Bits.rbegin(), E = BSI.Bits.rend(); I != E; ++I) {
Bits <<= 8;
Bits |= *I;
}
Constant *BitsConst = ConstantInt::get(BitsTy, Bits);
return createMaskedBitTest(B, BitsConst, BitOffset);
} else {
// TODO: We might want to use the memory variant of the bt instruction
// with the previously computed bit offset at -Os. This instruction does
// exactly what we want but has been benchmarked as being slower than open
// coding the load+bt.
Value *BitSetGlobalOffset =
B.CreateLShr(BitOffset, ConstantInt::get(IntPtrTy, 5));
Value *BitSetEntryAddr = B.CreateGEP(
ConstantExpr::getBitCast(BitSetGlobal, Int32PtrTy), BitSetGlobalOffset);
Value *BitSetEntry = B.CreateLoad(BitSetEntryAddr);
return createMaskedBitTest(B, BitSetEntry, BitOffset);
}
}
/// Lower a llvm.bitset.test call to its implementation.
void LowerBitSets::lowerBitSetCall(
CallInst *CI, const BitSetInfo &BSI, GlobalVariable *BitSetGlobal,
GlobalVariable *CombinedGlobal,
const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout) {
Value *Ptr = CI->getArgOperand(0);
if (BSI.containsValue(DL, GlobalLayout, Ptr)) {
CI->replaceAllUsesWith(
ConstantInt::getTrue(BitSetGlobal->getParent()->getContext()));
CI->eraseFromParent();
return;
}
Constant *GlobalAsInt = ConstantExpr::getPtrToInt(CombinedGlobal, IntPtrTy);
Constant *OffsetedGlobalAsInt = ConstantExpr::getAdd(
GlobalAsInt, ConstantInt::get(IntPtrTy, BSI.ByteOffset));
BasicBlock *InitialBB = CI->getParent();
IRBuilder<> B(CI);
Value *PtrAsInt = B.CreatePtrToInt(Ptr, IntPtrTy);
if (BSI.isSingleOffset()) {
Value *Eq = B.CreateICmpEQ(PtrAsInt, OffsetedGlobalAsInt);
CI->replaceAllUsesWith(Eq);
CI->eraseFromParent();
return;
}
Value *PtrOffset = B.CreateSub(PtrAsInt, OffsetedGlobalAsInt);
Value *BitOffset;
if (BSI.AlignLog2 == 0) {
BitOffset = PtrOffset;
} else {
// We need to check that the offset both falls within our range and is
// suitably aligned. We can check both properties at the same time by
// performing a right rotate by log2(alignment) followed by an integer
// comparison against the bitset size. The rotate will move the lower
// order bits that need to be zero into the higher order bits of the
// result, causing the comparison to fail if they are nonzero. The rotate
// also conveniently gives us a bit offset to use during the load from
// the bitset.
Value *OffsetSHR =
B.CreateLShr(PtrOffset, ConstantInt::get(IntPtrTy, BSI.AlignLog2));
Value *OffsetSHL = B.CreateShl(
PtrOffset, ConstantInt::get(IntPtrTy, DL->getPointerSizeInBits(0) -
BSI.AlignLog2));
BitOffset = B.CreateOr(OffsetSHR, OffsetSHL);
}
Constant *BitSizeConst = ConstantInt::get(IntPtrTy, BSI.BitSize);
Value *OffsetInRange = B.CreateICmpULT(BitOffset, BitSizeConst);
TerminatorInst *Term = SplitBlockAndInsertIfThen(OffsetInRange, CI, false);
IRBuilder<> ThenB(Term);
// Now that we know that the offset is in range and aligned, load the
// appropriate bit from the bitset.
Value *Bit = createBitSetTest(ThenB, BSI, BitSetGlobal, BitOffset);
// The value we want is 0 if we came directly from the initial block
// (having failed the range or alignment checks), or the loaded bit if
// we came from the block in which we loaded it.
B.SetInsertPoint(CI);
PHINode *P = B.CreatePHI(Int1Ty, 2);
P->addIncoming(ConstantInt::get(Int1Ty, 0), InitialBB);
P->addIncoming(Bit, ThenB.GetInsertBlock());
CI->replaceAllUsesWith(P);
CI->eraseFromParent();
}
/// Given a disjoint set of bitsets and globals, layout the globals, build the
/// bit sets and lower the llvm.bitset.test calls.
void LowerBitSets::buildBitSetsFromGlobals(
Module &M,
const std::vector<MDString *> &BitSets,
const std::vector<GlobalVariable *> &Globals) {
// Build a new global with the combined contents of the referenced globals.
std::vector<Constant *> GlobalInits;
for (GlobalVariable *G : Globals)
GlobalInits.push_back(G->getInitializer());
Constant *NewInit = ConstantStruct::getAnon(M.getContext(), GlobalInits);
auto CombinedGlobal =
new GlobalVariable(M, NewInit->getType(), /*isConstant=*/true,
GlobalValue::PrivateLinkage, NewInit);
const StructLayout *CombinedGlobalLayout =
DL->getStructLayout(cast<StructType>(NewInit->getType()));
// Compute the offsets of the original globals within the new global.
DenseMap<GlobalVariable *, uint64_t> GlobalLayout;
for (unsigned I = 0; I != Globals.size(); ++I)
GlobalLayout[Globals[I]] = CombinedGlobalLayout->getElementOffset(I);
// For each bitset in this disjoint set...
for (MDString *BS : BitSets) {
// Build the bitset.
BitSetInfo BSI = buildBitSet(BS, GlobalLayout);
// Create a global in which to store it.
++NumBitSetsCreated;
Constant *BitsConst = ConstantDataArray::get(M.getContext(), BSI.Bits);
auto BitSetGlobal = new GlobalVariable(
M, BitsConst->getType(), /*isConstant=*/true,
GlobalValue::PrivateLinkage, BitsConst, BS->getString() + ".bits");
// Lower each call to llvm.bitset.test for this bitset.
for (CallInst *CI : BitSetTestCallSites[BS]) {
++NumBitSetCallsLowered;
lowerBitSetCall(CI, BSI, BitSetGlobal, CombinedGlobal, GlobalLayout);
}
}
// Build aliases pointing to offsets into the combined global for each
// global from which we built the combined global, and replace references
// to the original globals with references to the aliases.
for (unsigned I = 0; I != Globals.size(); ++I) {
Constant *CombinedGlobalIdxs[] = {ConstantInt::get(Int32Ty, 0),
ConstantInt::get(Int32Ty, I)};
Constant *CombinedGlobalElemPtr =
ConstantExpr::getGetElementPtr(CombinedGlobal, CombinedGlobalIdxs);
GlobalAlias *GAlias = GlobalAlias::create(
Globals[I]->getType()->getElementType(),
Globals[I]->getType()->getAddressSpace(), Globals[I]->getLinkage(),
"", CombinedGlobalElemPtr, &M);
GAlias->takeName(Globals[I]);
Globals[I]->replaceAllUsesWith(GAlias);
Globals[I]->eraseFromParent();
}
}
/// Lower all bit sets in this module.
bool LowerBitSets::buildBitSets(Module &M) {
Function *BitSetTestFunc =
M.getFunction(Intrinsic::getName(Intrinsic::bitset_test));
if (!BitSetTestFunc)
return false;
// Equivalence class set containing bitsets and the globals they reference.
// This is used to partition the set of bitsets in the module into disjoint
// sets.
typedef EquivalenceClasses<PointerUnion<GlobalVariable *, MDString *>>
GlobalClassesTy;
GlobalClassesTy GlobalClasses;
for (const Use &U : BitSetTestFunc->uses()) {
auto CI = cast<CallInst>(U.getUser());
auto BitSetMDVal = dyn_cast<MetadataAsValue>(CI->getArgOperand(1));
if (!BitSetMDVal || !isa<MDString>(BitSetMDVal->getMetadata()))
report_fatal_error(
"Second argument of llvm.bitset.test must be metadata string");
auto BitSet = cast<MDString>(BitSetMDVal->getMetadata());
// Add the call site to the list of call sites for this bit set. We also use
// BitSetTestCallSites to keep track of whether we have seen this bit set
// before. If we have, we don't need to re-add the referenced globals to the
// equivalence class.
std::pair<DenseMap<MDString *, std::vector<CallInst *>>::iterator,
bool> Ins =
BitSetTestCallSites.insert(
std::make_pair(BitSet, std::vector<CallInst *>()));
Ins.first->second.push_back(CI);
if (!Ins.second)
continue;
// Add the bitset to the equivalence class.
GlobalClassesTy::iterator GCI = GlobalClasses.insert(BitSet);
GlobalClassesTy::member_iterator CurSet = GlobalClasses.findLeader(GCI);
if (!BitSetNM)
continue;
// Verify the bitset metadata and add the referenced globals to the bitset's
// equivalence class.
for (MDNode *Op : BitSetNM->operands()) {
if (Op->getNumOperands() != 3)
report_fatal_error(
"All operands of llvm.bitsets metadata must have 3 elements");
if (Op->getOperand(0) != BitSet || !Op->getOperand(1))
continue;
auto OpConstMD = dyn_cast<ConstantAsMetadata>(Op->getOperand(1));
if (!OpConstMD)
report_fatal_error("Bit set element must be a constant");
auto OpGlobal = dyn_cast<GlobalVariable>(OpConstMD->getValue());
if (!OpGlobal)
report_fatal_error("Bit set element must refer to global");
auto OffsetConstMD = dyn_cast<ConstantAsMetadata>(Op->getOperand(2));
if (!OffsetConstMD)
report_fatal_error("Bit set element offset must be a constant");
auto OffsetInt = dyn_cast<ConstantInt>(OffsetConstMD->getValue());
if (!OffsetInt)
report_fatal_error(
"Bit set element offset must be an integer constant");
CurSet = GlobalClasses.unionSets(
CurSet, GlobalClasses.findLeader(GlobalClasses.insert(OpGlobal)));
}
}
if (GlobalClasses.empty())
return false;
// For each disjoint set we found...
for (GlobalClassesTy::iterator I = GlobalClasses.begin(),
E = GlobalClasses.end();
I != E; ++I) {
if (!I->isLeader()) continue;
++NumBitSetDisjointSets;
// Build the list of bitsets and referenced globals in this disjoint set.
std::vector<MDString *> BitSets;
std::vector<GlobalVariable *> Globals;
for (GlobalClassesTy::member_iterator MI = GlobalClasses.member_begin(I);
MI != GlobalClasses.member_end(); ++MI) {
if ((*MI).is<MDString *>())
BitSets.push_back(MI->get<MDString *>());
else
Globals.push_back(MI->get<GlobalVariable *>());
}
// Order bitsets and globals by name for determinism. TODO: We may later
// want to use a more sophisticated ordering that lays out globals so as to
// minimize the sizes of the bitsets.
std::sort(BitSets.begin(), BitSets.end(), [](MDString *S1, MDString *S2) {
return S1->getString() < S2->getString();
});
std::sort(Globals.begin(), Globals.end(),
[](GlobalVariable *GV1, GlobalVariable *GV2) {
return GV1->getName() < GV2->getName();
});
// Build the bitsets from this disjoint set.
buildBitSetsFromGlobals(M, BitSets, Globals);
}
return true;
}
bool LowerBitSets::eraseBitSetMetadata(Module &M) {
if (!BitSetNM)
return false;
M.eraseNamedMetadata(BitSetNM);
return true;
}
bool LowerBitSets::runOnModule(Module &M) {
bool Changed = buildBitSets(M);
Changed |= eraseBitSetMetadata(M);
return Changed;
}
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