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llvm-project/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp

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//===- MemoryDependenceAnalysis.cpp - Mem Deps Implementation -------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements an analysis that determines, for a given memory
// operation, what preceding memory operations it depends on. It builds on
// alias analysis information, and tries to provide a lazy, caching interface to
// a common kind of alias information query.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/Analysis/OrderedBasicBlock.h"
#include "llvm/Analysis/PHITransAddr.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PredIteratorCache.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Support/AtomicOrdering.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/MathExtras.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <iterator>
#include <utility>
using namespace llvm;
#define DEBUG_TYPE "memdep"
STATISTIC(NumCacheNonLocal, "Number of fully cached non-local responses");
STATISTIC(NumCacheDirtyNonLocal, "Number of dirty cached non-local responses");
STATISTIC(NumUncacheNonLocal, "Number of uncached non-local responses");
STATISTIC(NumCacheNonLocalPtr,
"Number of fully cached non-local ptr responses");
STATISTIC(NumCacheDirtyNonLocalPtr,
"Number of cached, but dirty, non-local ptr responses");
STATISTIC(NumUncacheNonLocalPtr, "Number of uncached non-local ptr responses");
STATISTIC(NumCacheCompleteNonLocalPtr,
"Number of block queries that were completely cached");
// Limit for the number of instructions to scan in a block.
static cl::opt<unsigned> BlockScanLimit(
"memdep-block-scan-limit", cl::Hidden, cl::init(100),
cl::desc("The number of instructions to scan in a block in memory "
"dependency analysis (default = 100)"));
static cl::opt<unsigned>
BlockNumberLimit("memdep-block-number-limit", cl::Hidden, cl::init(1000),
cl::desc("The number of blocks to scan during memory "
"dependency analysis (default = 1000)"));
// Limit on the number of memdep results to process.
static const unsigned int NumResultsLimit = 100;
/// This is a helper function that removes Val from 'Inst's set in ReverseMap.
///
/// If the set becomes empty, remove Inst's entry.
template <typename KeyTy>
static void
RemoveFromReverseMap(DenseMap<Instruction *, SmallPtrSet<KeyTy, 4>> &ReverseMap,
Instruction *Inst, KeyTy Val) {
typename DenseMap<Instruction *, SmallPtrSet<KeyTy, 4>>::iterator InstIt =
ReverseMap.find(Inst);
assert(InstIt != ReverseMap.end() && "Reverse map out of sync?");
bool Found = InstIt->second.erase(Val);
assert(Found && "Invalid reverse map!");
(void)Found;
if (InstIt->second.empty())
ReverseMap.erase(InstIt);
}
/// If the given instruction references a specific memory location, fill in Loc
/// with the details, otherwise set Loc.Ptr to null.
///
/// Returns a ModRefInfo value describing the general behavior of the
/// instruction.
static ModRefInfo GetLocation(const Instruction *Inst, MemoryLocation &Loc,
const TargetLibraryInfo &TLI) {
if (const LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
if (LI->isUnordered()) {
Loc = MemoryLocation::get(LI);
return ModRefInfo::Ref;
}
if (LI->getOrdering() == AtomicOrdering::Monotonic) {
Loc = MemoryLocation::get(LI);
return ModRefInfo::ModRef;
}
Loc = MemoryLocation();
return ModRefInfo::ModRef;
}
if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
if (SI->isUnordered()) {
Loc = MemoryLocation::get(SI);
return ModRefInfo::Mod;
}
if (SI->getOrdering() == AtomicOrdering::Monotonic) {
Loc = MemoryLocation::get(SI);
return ModRefInfo::ModRef;
}
Loc = MemoryLocation();
return ModRefInfo::ModRef;
}
if (const VAArgInst *V = dyn_cast<VAArgInst>(Inst)) {
Loc = MemoryLocation::get(V);
return ModRefInfo::ModRef;
}
if (const CallInst *CI = isFreeCall(Inst, &TLI)) {
// calls to free() deallocate the entire structure
Loc = MemoryLocation(CI->getArgOperand(0));
return ModRefInfo::Mod;
}
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
switch (II->getIntrinsicID()) {
case Intrinsic::lifetime_start:
case Intrinsic::lifetime_end:
case Intrinsic::invariant_start:
Loc = MemoryLocation::getForArgument(II, 1, TLI);
// These intrinsics don't really modify the memory, but returning Mod
// will allow them to be handled conservatively.
return ModRefInfo::Mod;
case Intrinsic::invariant_end:
Loc = MemoryLocation::getForArgument(II, 2, TLI);
// These intrinsics don't really modify the memory, but returning Mod
// will allow them to be handled conservatively.
return ModRefInfo::Mod;
default:
break;
}
}
// Otherwise, just do the coarse-grained thing that always works.
if (Inst->mayWriteToMemory())
return ModRefInfo::ModRef;
if (Inst->mayReadFromMemory())
return ModRefInfo::Ref;
return ModRefInfo::NoModRef;
}
/// Private helper for finding the local dependencies of a call site.
MemDepResult MemoryDependenceResults::getCallSiteDependencyFrom(
CallSite CS, bool isReadOnlyCall, BasicBlock::iterator ScanIt,
BasicBlock *BB) {
unsigned Limit = BlockScanLimit;
// Walk backwards through the block, looking for dependencies.
while (ScanIt != BB->begin()) {
Instruction *Inst = &*--ScanIt;
// Debug intrinsics don't cause dependences and should not affect Limit
if (isa<DbgInfoIntrinsic>(Inst))
continue;
// Limit the amount of scanning we do so we don't end up with quadratic
// running time on extreme testcases.
--Limit;
if (!Limit)
return MemDepResult::getUnknown();
// If this inst is a memory op, get the pointer it accessed
MemoryLocation Loc;
ModRefInfo MR = GetLocation(Inst, Loc, TLI);
if (Loc.Ptr) {
// A simple instruction.
if (isModOrRefSet(AA.getModRefInfo(CS, Loc)))
return MemDepResult::getClobber(Inst);
continue;
}
if (auto InstCS = CallSite(Inst)) {
// If these two calls do not interfere, look past it.
if (isNoModRef(AA.getModRefInfo(CS, InstCS))) {
// If the two calls are the same, return InstCS as a Def, so that
// CS can be found redundant and eliminated.
if (isReadOnlyCall && !isModSet(MR) &&
CS.getInstruction()->isIdenticalToWhenDefined(Inst))
return MemDepResult::getDef(Inst);
// Otherwise if the two calls don't interact (e.g. InstCS is readnone)
// keep scanning.
continue;
} else
return MemDepResult::getClobber(Inst);
}
// If we could not obtain a pointer for the instruction and the instruction
// touches memory then assume that this is a dependency.
if (isModOrRefSet(MR))
return MemDepResult::getClobber(Inst);
}
// No dependence found. If this is the entry block of the function, it is
// unknown, otherwise it is non-local.
if (BB != &BB->getParent()->getEntryBlock())
return MemDepResult::getNonLocal();
return MemDepResult::getNonFuncLocal();
}
unsigned MemoryDependenceResults::getLoadLoadClobberFullWidthSize(
const Value *MemLocBase, int64_t MemLocOffs, unsigned MemLocSize,
const LoadInst *LI) {
// We can only extend simple integer loads.
if (!isa<IntegerType>(LI->getType()) || !LI->isSimple())
return 0;
// Load widening is hostile to ThreadSanitizer: it may cause false positives
// or make the reports more cryptic (access sizes are wrong).
if (LI->getParent()->getParent()->hasFnAttribute(Attribute::SanitizeThread))
return 0;
const DataLayout &DL = LI->getModule()->getDataLayout();
// Get the base of this load.
int64_t LIOffs = 0;
const Value *LIBase =
GetPointerBaseWithConstantOffset(LI->getPointerOperand(), LIOffs, DL);
// If the two pointers are not based on the same pointer, we can't tell that
// they are related.
if (LIBase != MemLocBase)
return 0;
// Okay, the two values are based on the same pointer, but returned as
// no-alias. This happens when we have things like two byte loads at "P+1"
// and "P+3". Check to see if increasing the size of the "LI" load up to its
// alignment (or the largest native integer type) will allow us to load all
// the bits required by MemLoc.
// If MemLoc is before LI, then no widening of LI will help us out.
if (MemLocOffs < LIOffs)
return 0;
// Get the alignment of the load in bytes. We assume that it is safe to load
// any legal integer up to this size without a problem. For example, if we're
// looking at an i8 load on x86-32 that is known 1024 byte aligned, we can
// widen it up to an i32 load. If it is known 2-byte aligned, we can widen it
// to i16.
unsigned LoadAlign = LI->getAlignment();
int64_t MemLocEnd = MemLocOffs + MemLocSize;
// If no amount of rounding up will let MemLoc fit into LI, then bail out.
if (LIOffs + LoadAlign < MemLocEnd)
return 0;
// This is the size of the load to try. Start with the next larger power of
// two.
unsigned NewLoadByteSize = LI->getType()->getPrimitiveSizeInBits() / 8U;
NewLoadByteSize = NextPowerOf2(NewLoadByteSize);
while (true) {
// If this load size is bigger than our known alignment or would not fit
// into a native integer register, then we fail.
if (NewLoadByteSize > LoadAlign ||
!DL.fitsInLegalInteger(NewLoadByteSize * 8))
return 0;
if (LIOffs + NewLoadByteSize > MemLocEnd &&
(LI->getParent()->getParent()->hasFnAttribute(
Attribute::SanitizeAddress) ||
LI->getParent()->getParent()->hasFnAttribute(
Attribute::SanitizeHWAddress)))
// We will be reading past the location accessed by the original program.
// While this is safe in a regular build, Address Safety analysis tools
// may start reporting false warnings. So, don't do widening.
return 0;
// If a load of this width would include all of MemLoc, then we succeed.
if (LIOffs + NewLoadByteSize >= MemLocEnd)
return NewLoadByteSize;
NewLoadByteSize <<= 1;
}
}
static bool isVolatile(Instruction *Inst) {
if (auto *LI = dyn_cast<LoadInst>(Inst))
return LI->isVolatile();
if (auto *SI = dyn_cast<StoreInst>(Inst))
return SI->isVolatile();
if (auto *AI = dyn_cast<AtomicCmpXchgInst>(Inst))
return AI->isVolatile();
return false;
}
MemDepResult MemoryDependenceResults::getPointerDependencyFrom(
const MemoryLocation &MemLoc, bool isLoad, BasicBlock::iterator ScanIt,
BasicBlock *BB, Instruction *QueryInst, unsigned *Limit) {
MemDepResult InvariantGroupDependency = MemDepResult::getUnknown();
if (QueryInst != nullptr) {
if (auto *LI = dyn_cast<LoadInst>(QueryInst)) {
InvariantGroupDependency = getInvariantGroupPointerDependency(LI, BB);
if (InvariantGroupDependency.isDef())
return InvariantGroupDependency;
}
}
MemDepResult SimpleDep = getSimplePointerDependencyFrom(
MemLoc, isLoad, ScanIt, BB, QueryInst, Limit);
if (SimpleDep.isDef())
return SimpleDep;
// Non-local invariant group dependency indicates there is non local Def
// (it only returns nonLocal if it finds nonLocal def), which is better than
// local clobber and everything else.
if (InvariantGroupDependency.isNonLocal())
return InvariantGroupDependency;
assert(InvariantGroupDependency.isUnknown() &&
"InvariantGroupDependency should be only unknown at this point");
return SimpleDep;
}
MemDepResult
MemoryDependenceResults::getInvariantGroupPointerDependency(LoadInst *LI,
BasicBlock *BB) {
auto *InvariantGroupMD = LI->getMetadata(LLVMContext::MD_invariant_group);
if (!InvariantGroupMD)
return MemDepResult::getUnknown();
// Take the ptr operand after all casts and geps 0. This way we can search
// cast graph down only.
Value *LoadOperand = LI->getPointerOperand()->stripPointerCasts();
// It's is not safe to walk the use list of global value, because function
// passes aren't allowed to look outside their functions.
// FIXME: this could be fixed by filtering instructions from outside
// of current function.
if (isa<GlobalValue>(LoadOperand))
return MemDepResult::getUnknown();
// Queue to process all pointers that are equivalent to load operand.
SmallVector<const Value *, 8> LoadOperandsQueue;
LoadOperandsQueue.push_back(LoadOperand);
Instruction *ClosestDependency = nullptr;
// Order of instructions in uses list is unpredictible. In order to always
// get the same result, we will look for the closest dominance.
auto GetClosestDependency = [this](Instruction *Best, Instruction *Other) {
assert(Other && "Must call it with not null instruction");
if (Best == nullptr || DT.dominates(Best, Other))
return Other;
return Best;
};
// FIXME: This loop is O(N^2) because dominates can be O(n) and in worst case
// we will see all the instructions. This should be fixed in MSSA.
while (!LoadOperandsQueue.empty()) {
const Value *Ptr = LoadOperandsQueue.pop_back_val();
assert(Ptr && !isa<GlobalValue>(Ptr) &&
"Null or GlobalValue should not be inserted");
for (const Use &Us : Ptr->uses()) {
auto *U = dyn_cast<Instruction>(Us.getUser());
if (!U || U == LI || !DT.dominates(U, LI))
continue;
// Bitcast or gep with zeros are using Ptr. Add to queue to check it's
// users. U = bitcast Ptr
if (isa<BitCastInst>(U)) {
LoadOperandsQueue.push_back(U);
continue;
}
// Gep with zeros is equivalent to bitcast.
// FIXME: we are not sure if some bitcast should be canonicalized to gep 0
// or gep 0 to bitcast because of SROA, so there are 2 forms. When
// typeless pointers will be ready then both cases will be gone
// (and this BFS also won't be needed).
if (auto *GEP = dyn_cast<GetElementPtrInst>(U))
if (GEP->hasAllZeroIndices()) {
LoadOperandsQueue.push_back(U);
continue;
}
// If we hit load/store with the same invariant.group metadata (and the
// same pointer operand) we can assume that value pointed by pointer
// operand didn't change.
if ((isa<LoadInst>(U) || isa<StoreInst>(U)) &&
U->getMetadata(LLVMContext::MD_invariant_group) == InvariantGroupMD)
ClosestDependency = GetClosestDependency(ClosestDependency, U);
}
}
if (!ClosestDependency)
return MemDepResult::getUnknown();
if (ClosestDependency->getParent() == BB)
return MemDepResult::getDef(ClosestDependency);
// Def(U) can't be returned here because it is non-local. If local
// dependency won't be found then return nonLocal counting that the
// user will call getNonLocalPointerDependency, which will return cached
// result.
NonLocalDefsCache.try_emplace(
LI, NonLocalDepResult(ClosestDependency->getParent(),
MemDepResult::getDef(ClosestDependency), nullptr));
return MemDepResult::getNonLocal();
}
MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom(
const MemoryLocation &MemLoc, bool isLoad, BasicBlock::iterator ScanIt,
BasicBlock *BB, Instruction *QueryInst, unsigned *Limit) {
bool isInvariantLoad = false;
if (!Limit) {
unsigned DefaultLimit = BlockScanLimit;
return getSimplePointerDependencyFrom(MemLoc, isLoad, ScanIt, BB, QueryInst,
&DefaultLimit);
}
// We must be careful with atomic accesses, as they may allow another thread
// to touch this location, clobbering it. We are conservative: if the
// QueryInst is not a simple (non-atomic) memory access, we automatically
// return getClobber.
// If it is simple, we know based on the results of
// "Compiler testing via a theory of sound optimisations in the C11/C++11
// memory model" in PLDI 2013, that a non-atomic location can only be
// clobbered between a pair of a release and an acquire action, with no
// access to the location in between.
// Here is an example for giving the general intuition behind this rule.
// In the following code:
// store x 0;
// release action; [1]
// acquire action; [4]
// %val = load x;
// It is unsafe to replace %val by 0 because another thread may be running:
// acquire action; [2]
// store x 42;
// release action; [3]
// with synchronization from 1 to 2 and from 3 to 4, resulting in %val
// being 42. A key property of this program however is that if either
// 1 or 4 were missing, there would be a race between the store of 42
// either the store of 0 or the load (making the whole program racy).
// The paper mentioned above shows that the same property is respected
// by every program that can detect any optimization of that kind: either
// it is racy (undefined) or there is a release followed by an acquire
// between the pair of accesses under consideration.
// If the load is invariant, we "know" that it doesn't alias *any* write. We
// do want to respect mustalias results since defs are useful for value
// forwarding, but any mayalias write can be assumed to be noalias.
// Arguably, this logic should be pushed inside AliasAnalysis itself.
if (isLoad && QueryInst) {
LoadInst *LI = dyn_cast<LoadInst>(QueryInst);
if (LI && LI->getMetadata(LLVMContext::MD_invariant_load) != nullptr)
isInvariantLoad = true;
}
const DataLayout &DL = BB->getModule()->getDataLayout();
// Create a numbered basic block to lazily compute and cache instruction
// positions inside a BB. This is used to provide fast queries for relative
// position between two instructions in a BB and can be used by
// AliasAnalysis::callCapturesBefore.
OrderedBasicBlock OBB(BB);
// Return "true" if and only if the instruction I is either a non-simple
// load or a non-simple store.
auto isNonSimpleLoadOrStore = [](Instruction *I) -> bool {
if (auto *LI = dyn_cast<LoadInst>(I))
return !LI->isSimple();
if (auto *SI = dyn_cast<StoreInst>(I))
return !SI->isSimple();
return false;
};
// Return "true" if I is not a load and not a store, but it does access
// memory.
auto isOtherMemAccess = [](Instruction *I) -> bool {
return !isa<LoadInst>(I) && !isa<StoreInst>(I) && I->mayReadOrWriteMemory();
};
// Walk backwards through the basic block, looking for dependencies.
while (ScanIt != BB->begin()) {
Instruction *Inst = &*--ScanIt;
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst))
// Debug intrinsics don't (and can't) cause dependencies.
if (isa<DbgInfoIntrinsic>(II))
continue;
// Limit the amount of scanning we do so we don't end up with quadratic
// running time on extreme testcases.
--*Limit;
if (!*Limit)
return MemDepResult::getUnknown();
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
// If we reach a lifetime begin or end marker, then the query ends here
// because the value is undefined.
if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
// FIXME: This only considers queries directly on the invariant-tagged
// pointer, not on query pointers that are indexed off of them. It'd
// be nice to handle that at some point (the right approach is to use
// GetPointerBaseWithConstantOffset).
if (AA.isMustAlias(MemoryLocation(II->getArgOperand(1)), MemLoc))
return MemDepResult::getDef(II);
continue;
}
}
// Values depend on loads if the pointers are must aliased. This means
// that a load depends on another must aliased load from the same value.
// One exception is atomic loads: a value can depend on an atomic load that
// it does not alias with when this atomic load indicates that another
// thread may be accessing the location.
if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
// While volatile access cannot be eliminated, they do not have to clobber
// non-aliasing locations, as normal accesses, for example, can be safely
// reordered with volatile accesses.
if (LI->isVolatile()) {
if (!QueryInst)
// Original QueryInst *may* be volatile
return MemDepResult::getClobber(LI);
if (isVolatile(QueryInst))
// Ordering required if QueryInst is itself volatile
return MemDepResult::getClobber(LI);
// Otherwise, volatile doesn't imply any special ordering
}
// Atomic loads have complications involved.
// A Monotonic (or higher) load is OK if the query inst is itself not
// atomic.
// FIXME: This is overly conservative.
if (LI->isAtomic() && isStrongerThanUnordered(LI->getOrdering())) {
if (!QueryInst || isNonSimpleLoadOrStore(QueryInst) ||
isOtherMemAccess(QueryInst))
return MemDepResult::getClobber(LI);
if (LI->getOrdering() != AtomicOrdering::Monotonic)
return MemDepResult::getClobber(LI);
}
MemoryLocation LoadLoc = MemoryLocation::get(LI);
// If we found a pointer, check if it could be the same as our pointer.
AliasResult R = AA.alias(LoadLoc, MemLoc);
if (isLoad) {
if (R == NoAlias)
continue;
// Must aliased loads are defs of each other.
if (R == MustAlias)
return MemDepResult::getDef(Inst);
#if 0 // FIXME: Temporarily disabled. GVN is cleverly rewriting loads
// in terms of clobbering loads, but since it does this by looking
// at the clobbering load directly, it doesn't know about any
// phi translation that may have happened along the way.
// If we have a partial alias, then return this as a clobber for the
// client to handle.
if (R == PartialAlias)
return MemDepResult::getClobber(Inst);
#endif
// Random may-alias loads don't depend on each other without a
// dependence.
continue;
}
// Stores don't depend on other no-aliased accesses.
if (R == NoAlias)
continue;
// Stores don't alias loads from read-only memory.
if (AA.pointsToConstantMemory(LoadLoc))
continue;
// Stores depend on may/must aliased loads.
return MemDepResult::getDef(Inst);
}
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
// Atomic stores have complications involved.
// A Monotonic store is OK if the query inst is itself not atomic.
// FIXME: This is overly conservative.
if (!SI->isUnordered() && SI->isAtomic()) {
if (!QueryInst || isNonSimpleLoadOrStore(QueryInst) ||
isOtherMemAccess(QueryInst))
return MemDepResult::getClobber(SI);
if (SI->getOrdering() != AtomicOrdering::Monotonic)
return MemDepResult::getClobber(SI);
}
// FIXME: this is overly conservative.
// While volatile access cannot be eliminated, they do not have to clobber
// non-aliasing locations, as normal accesses can for example be reordered
// with volatile accesses.
if (SI->isVolatile())
if (!QueryInst || isNonSimpleLoadOrStore(QueryInst) ||
isOtherMemAccess(QueryInst))
return MemDepResult::getClobber(SI);
// If alias analysis can tell that this store is guaranteed to not modify
// the query pointer, ignore it. Use getModRefInfo to handle cases where
// the query pointer points to constant memory etc.
if (!isModOrRefSet(AA.getModRefInfo(SI, MemLoc)))
continue;
// Ok, this store might clobber the query pointer. Check to see if it is
// a must alias: in this case, we want to return this as a def.
// FIXME: Use ModRefInfo::Must bit from getModRefInfo call above.
MemoryLocation StoreLoc = MemoryLocation::get(SI);
// If we found a pointer, check if it could be the same as our pointer.
AliasResult R = AA.alias(StoreLoc, MemLoc);
if (R == NoAlias)
continue;
if (R == MustAlias)
return MemDepResult::getDef(Inst);
if (isInvariantLoad)
continue;
return MemDepResult::getClobber(Inst);
}
// If this is an allocation, and if we know that the accessed pointer is to
// the allocation, return Def. This means that there is no dependence and
// the access can be optimized based on that. For example, a load could
// turn into undef. Note that we can bypass the allocation itself when
// looking for a clobber in many cases; that's an alias property and is
// handled by BasicAA.
if (isa<AllocaInst>(Inst) || isNoAliasFn(Inst, &TLI)) {
const Value *AccessPtr = GetUnderlyingObject(MemLoc.Ptr, DL);
if (AccessPtr == Inst || AA.isMustAlias(Inst, AccessPtr))
return MemDepResult::getDef(Inst);
}
if (isInvariantLoad)
continue;
// A release fence requires that all stores complete before it, but does
// not prevent the reordering of following loads or stores 'before' the
// fence. As a result, we look past it when finding a dependency for
// loads. DSE uses this to find preceeding stores to delete and thus we
// can't bypass the fence if the query instruction is a store.
if (FenceInst *FI = dyn_cast<FenceInst>(Inst))
if (isLoad && FI->getOrdering() == AtomicOrdering::Release)
continue;
// See if this instruction (e.g. a call or vaarg) mod/ref's the pointer.
ModRefInfo MR = AA.getModRefInfo(Inst, MemLoc);
// If necessary, perform additional analysis.
if (isModAndRefSet(MR))
MR = AA.callCapturesBefore(Inst, MemLoc, &DT, &OBB);
switch (clearMust(MR)) {
case ModRefInfo::NoModRef:
// If the call has no effect on the queried pointer, just ignore it.
continue;
case ModRefInfo::Mod:
return MemDepResult::getClobber(Inst);
case ModRefInfo::Ref:
// If the call is known to never store to the pointer, and if this is a
// load query, we can safely ignore it (scan past it).
if (isLoad)
continue;
LLVM_FALLTHROUGH;
default:
// Otherwise, there is a potential dependence. Return a clobber.
return MemDepResult::getClobber(Inst);
}
}
// No dependence found. If this is the entry block of the function, it is
// unknown, otherwise it is non-local.
if (BB != &BB->getParent()->getEntryBlock())
return MemDepResult::getNonLocal();
return MemDepResult::getNonFuncLocal();
}
MemDepResult MemoryDependenceResults::getDependency(Instruction *QueryInst) {
Instruction *ScanPos = QueryInst;
// Check for a cached result
MemDepResult &LocalCache = LocalDeps[QueryInst];
// If the cached entry is non-dirty, just return it. Note that this depends
// on MemDepResult's default constructing to 'dirty'.
if (!LocalCache.isDirty())
return LocalCache;
// Otherwise, if we have a dirty entry, we know we can start the scan at that
// instruction, which may save us some work.
if (Instruction *Inst = LocalCache.getInst()) {
ScanPos = Inst;
RemoveFromReverseMap(ReverseLocalDeps, Inst, QueryInst);
}
BasicBlock *QueryParent = QueryInst->getParent();
// Do the scan.
if (BasicBlock::iterator(QueryInst) == QueryParent->begin()) {
// No dependence found. If this is the entry block of the function, it is
// unknown, otherwise it is non-local.
if (QueryParent != &QueryParent->getParent()->getEntryBlock())
LocalCache = MemDepResult::getNonLocal();
else
LocalCache = MemDepResult::getNonFuncLocal();
} else {
MemoryLocation MemLoc;
ModRefInfo MR = GetLocation(QueryInst, MemLoc, TLI);
if (MemLoc.Ptr) {
// If we can do a pointer scan, make it happen.
bool isLoad = !isModSet(MR);
if (auto *II = dyn_cast<IntrinsicInst>(QueryInst))
isLoad |= II->getIntrinsicID() == Intrinsic::lifetime_start;
LocalCache = getPointerDependencyFrom(
MemLoc, isLoad, ScanPos->getIterator(), QueryParent, QueryInst);
} else if (isa<CallInst>(QueryInst) || isa<InvokeInst>(QueryInst)) {
CallSite QueryCS(QueryInst);
bool isReadOnly = AA.onlyReadsMemory(QueryCS);
LocalCache = getCallSiteDependencyFrom(
QueryCS, isReadOnly, ScanPos->getIterator(), QueryParent);
} else
// Non-memory instruction.
LocalCache = MemDepResult::getUnknown();
}
// Remember the result!
if (Instruction *I = LocalCache.getInst())
ReverseLocalDeps[I].insert(QueryInst);
return LocalCache;
}
#ifndef NDEBUG
/// This method is used when -debug is specified to verify that cache arrays
/// are properly kept sorted.
static void AssertSorted(MemoryDependenceResults::NonLocalDepInfo &Cache,
int Count = -1) {
if (Count == -1)
Count = Cache.size();
assert(std::is_sorted(Cache.begin(), Cache.begin() + Count) &&
"Cache isn't sorted!");
}
#endif
const MemoryDependenceResults::NonLocalDepInfo &
MemoryDependenceResults::getNonLocalCallDependency(CallSite QueryCS) {
assert(getDependency(QueryCS.getInstruction()).isNonLocal() &&
"getNonLocalCallDependency should only be used on calls with "
"non-local deps!");
PerInstNLInfo &CacheP = NonLocalDeps[QueryCS.getInstruction()];
NonLocalDepInfo &Cache = CacheP.first;
// This is the set of blocks that need to be recomputed. In the cached case,
// this can happen due to instructions being deleted etc. In the uncached
// case, this starts out as the set of predecessors we care about.
SmallVector<BasicBlock *, 32> DirtyBlocks;
if (!Cache.empty()) {
// Okay, we have a cache entry. If we know it is not dirty, just return it
// with no computation.
if (!CacheP.second) {
++NumCacheNonLocal;
return Cache;
}
// If we already have a partially computed set of results, scan them to
// determine what is dirty, seeding our initial DirtyBlocks worklist.
for (auto &Entry : Cache)
if (Entry.getResult().isDirty())
DirtyBlocks.push_back(Entry.getBB());
// Sort the cache so that we can do fast binary search lookups below.
std::sort(Cache.begin(), Cache.end());
++NumCacheDirtyNonLocal;
// cerr << "CACHED CASE: " << DirtyBlocks.size() << " dirty: "
// << Cache.size() << " cached: " << *QueryInst;
} else {
// Seed DirtyBlocks with each of the preds of QueryInst's block.
BasicBlock *QueryBB = QueryCS.getInstruction()->getParent();
for (BasicBlock *Pred : PredCache.get(QueryBB))
DirtyBlocks.push_back(Pred);
++NumUncacheNonLocal;
}
// isReadonlyCall - If this is a read-only call, we can be more aggressive.
bool isReadonlyCall = AA.onlyReadsMemory(QueryCS);
SmallPtrSet<BasicBlock *, 32> Visited;
unsigned NumSortedEntries = Cache.size();
DEBUG(AssertSorted(Cache));
// Iterate while we still have blocks to update.
while (!DirtyBlocks.empty()) {
BasicBlock *DirtyBB = DirtyBlocks.back();
DirtyBlocks.pop_back();
// Already processed this block?
if (!Visited.insert(DirtyBB).second)
continue;
// Do a binary search to see if we already have an entry for this block in
// the cache set. If so, find it.
DEBUG(AssertSorted(Cache, NumSortedEntries));
NonLocalDepInfo::iterator Entry =
std::upper_bound(Cache.begin(), Cache.begin() + NumSortedEntries,
NonLocalDepEntry(DirtyBB));
if (Entry != Cache.begin() && std::prev(Entry)->getBB() == DirtyBB)
--Entry;
NonLocalDepEntry *ExistingResult = nullptr;
if (Entry != Cache.begin() + NumSortedEntries &&
Entry->getBB() == DirtyBB) {
// If we already have an entry, and if it isn't already dirty, the block
// is done.
if (!Entry->getResult().isDirty())
continue;
// Otherwise, remember this slot so we can update the value.
ExistingResult = &*Entry;
}
// If the dirty entry has a pointer, start scanning from it so we don't have
// to rescan the entire block.
BasicBlock::iterator ScanPos = DirtyBB->end();
if (ExistingResult) {
if (Instruction *Inst = ExistingResult->getResult().getInst()) {
ScanPos = Inst->getIterator();
// We're removing QueryInst's use of Inst.
RemoveFromReverseMap(ReverseNonLocalDeps, Inst,
QueryCS.getInstruction());
}
}
// Find out if this block has a local dependency for QueryInst.
MemDepResult Dep;
if (ScanPos != DirtyBB->begin()) {
Dep =
getCallSiteDependencyFrom(QueryCS, isReadonlyCall, ScanPos, DirtyBB);
} else if (DirtyBB != &DirtyBB->getParent()->getEntryBlock()) {
// No dependence found. If this is the entry block of the function, it is
// a clobber, otherwise it is unknown.
Dep = MemDepResult::getNonLocal();
} else {
Dep = MemDepResult::getNonFuncLocal();
}
// If we had a dirty entry for the block, update it. Otherwise, just add
// a new entry.
if (ExistingResult)
ExistingResult->setResult(Dep);
else
Cache.push_back(NonLocalDepEntry(DirtyBB, Dep));
// If the block has a dependency (i.e. it isn't completely transparent to
// the value), remember the association!
if (!Dep.isNonLocal()) {
// Keep the ReverseNonLocalDeps map up to date so we can efficiently
// update this when we remove instructions.
if (Instruction *Inst = Dep.getInst())
ReverseNonLocalDeps[Inst].insert(QueryCS.getInstruction());
} else {
// If the block *is* completely transparent to the load, we need to check
// the predecessors of this block. Add them to our worklist.
for (BasicBlock *Pred : PredCache.get(DirtyBB))
DirtyBlocks.push_back(Pred);
}
}
return Cache;
}
void MemoryDependenceResults::getNonLocalPointerDependency(
Instruction *QueryInst, SmallVectorImpl<NonLocalDepResult> &Result) {
const MemoryLocation Loc = MemoryLocation::get(QueryInst);
bool isLoad = isa<LoadInst>(QueryInst);
BasicBlock *FromBB = QueryInst->getParent();
assert(FromBB);
assert(Loc.Ptr->getType()->isPointerTy() &&
"Can't get pointer deps of a non-pointer!");
Result.clear();
{
// Check if there is cached Def with invariant.group. FIXME: cache might be
// invalid if cached instruction would be removed between call to
// getPointerDependencyFrom and this function.
auto NonLocalDefIt = NonLocalDefsCache.find(QueryInst);
if (NonLocalDefIt != NonLocalDefsCache.end()) {
Result.push_back(std::move(NonLocalDefIt->second));
NonLocalDefsCache.erase(NonLocalDefIt);
return;
}
}
// This routine does not expect to deal with volatile instructions.
// Doing so would require piping through the QueryInst all the way through.
// TODO: volatiles can't be elided, but they can be reordered with other
// non-volatile accesses.
// We currently give up on any instruction which is ordered, but we do handle
// atomic instructions which are unordered.
// TODO: Handle ordered instructions
auto isOrdered = [](Instruction *Inst) {
if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
return !LI->isUnordered();
} else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
return !SI->isUnordered();
}
return false;
};
if (isVolatile(QueryInst) || isOrdered(QueryInst)) {
Result.push_back(NonLocalDepResult(FromBB, MemDepResult::getUnknown(),
const_cast<Value *>(Loc.Ptr)));
return;
}
const DataLayout &DL = FromBB->getModule()->getDataLayout();
PHITransAddr Address(const_cast<Value *>(Loc.Ptr), DL, &AC);
// This is the set of blocks we've inspected, and the pointer we consider in
// each block. Because of critical edges, we currently bail out if querying
// a block with multiple different pointers. This can happen during PHI
// translation.
DenseMap<BasicBlock *, Value *> Visited;
if (getNonLocalPointerDepFromBB(QueryInst, Address, Loc, isLoad, FromBB,
Result, Visited, true))
return;
Result.clear();
Result.push_back(NonLocalDepResult(FromBB, MemDepResult::getUnknown(),
const_cast<Value *>(Loc.Ptr)));
}
/// Compute the memdep value for BB with Pointer/PointeeSize using either
/// cached information in Cache or by doing a lookup (which may use dirty cache
/// info if available).
///
/// If we do a lookup, add the result to the cache.
MemDepResult MemoryDependenceResults::GetNonLocalInfoForBlock(
Instruction *QueryInst, const MemoryLocation &Loc, bool isLoad,
BasicBlock *BB, NonLocalDepInfo *Cache, unsigned NumSortedEntries) {
// Do a binary search to see if we already have an entry for this block in
// the cache set. If so, find it.
NonLocalDepInfo::iterator Entry = std::upper_bound(
Cache->begin(), Cache->begin() + NumSortedEntries, NonLocalDepEntry(BB));
if (Entry != Cache->begin() && (Entry - 1)->getBB() == BB)
--Entry;
NonLocalDepEntry *ExistingResult = nullptr;
if (Entry != Cache->begin() + NumSortedEntries && Entry->getBB() == BB)
ExistingResult = &*Entry;
// If we have a cached entry, and it is non-dirty, use it as the value for
// this dependency.
if (ExistingResult && !ExistingResult->getResult().isDirty()) {
++NumCacheNonLocalPtr;
return ExistingResult->getResult();
}
// Otherwise, we have to scan for the value. If we have a dirty cache
// entry, start scanning from its position, otherwise we scan from the end
// of the block.
BasicBlock::iterator ScanPos = BB->end();
if (ExistingResult && ExistingResult->getResult().getInst()) {
assert(ExistingResult->getResult().getInst()->getParent() == BB &&
"Instruction invalidated?");
++NumCacheDirtyNonLocalPtr;
ScanPos = ExistingResult->getResult().getInst()->getIterator();
// Eliminating the dirty entry from 'Cache', so update the reverse info.
ValueIsLoadPair CacheKey(Loc.Ptr, isLoad);
RemoveFromReverseMap(ReverseNonLocalPtrDeps, &*ScanPos, CacheKey);
} else {
++NumUncacheNonLocalPtr;
}
// Scan the block for the dependency.
MemDepResult Dep =
getPointerDependencyFrom(Loc, isLoad, ScanPos, BB, QueryInst);
// If we had a dirty entry for the block, update it. Otherwise, just add
// a new entry.
if (ExistingResult)
ExistingResult->setResult(Dep);
else
Cache->push_back(NonLocalDepEntry(BB, Dep));
// If the block has a dependency (i.e. it isn't completely transparent to
// the value), remember the reverse association because we just added it
// to Cache!
if (!Dep.isDef() && !Dep.isClobber())
return Dep;
// Keep the ReverseNonLocalPtrDeps map up to date so we can efficiently
// update MemDep when we remove instructions.
Instruction *Inst = Dep.getInst();
assert(Inst && "Didn't depend on anything?");
ValueIsLoadPair CacheKey(Loc.Ptr, isLoad);
ReverseNonLocalPtrDeps[Inst].insert(CacheKey);
return Dep;
}
/// Sort the NonLocalDepInfo cache, given a certain number of elements in the
/// array that are already properly ordered.
///
/// This is optimized for the case when only a few entries are added.
static void
SortNonLocalDepInfoCache(MemoryDependenceResults::NonLocalDepInfo &Cache,
unsigned NumSortedEntries) {
switch (Cache.size() - NumSortedEntries) {
case 0:
// done, no new entries.
break;
case 2: {
// Two new entries, insert the last one into place.
NonLocalDepEntry Val = Cache.back();
Cache.pop_back();
MemoryDependenceResults::NonLocalDepInfo::iterator Entry =
std::upper_bound(Cache.begin(), Cache.end() - 1, Val);
Cache.insert(Entry, Val);
LLVM_FALLTHROUGH;
}
case 1:
// One new entry, Just insert the new value at the appropriate position.
if (Cache.size() != 1) {
NonLocalDepEntry Val = Cache.back();
Cache.pop_back();
MemoryDependenceResults::NonLocalDepInfo::iterator Entry =
std::upper_bound(Cache.begin(), Cache.end(), Val);
Cache.insert(Entry, Val);
}
break;
default:
// Added many values, do a full scale sort.
std::sort(Cache.begin(), Cache.end());
break;
}
}
/// Perform a dependency query based on pointer/pointeesize starting at the end
/// of StartBB.
///
/// Add any clobber/def results to the results vector and keep track of which
/// blocks are visited in 'Visited'.
///
/// This has special behavior for the first block queries (when SkipFirstBlock
/// is true). In this special case, it ignores the contents of the specified
/// block and starts returning dependence info for its predecessors.
///
/// This function returns true on success, or false to indicate that it could
/// not compute dependence information for some reason. This should be treated
/// as a clobber dependence on the first instruction in the predecessor block.
bool MemoryDependenceResults::getNonLocalPointerDepFromBB(
Instruction *QueryInst, const PHITransAddr &Pointer,
const MemoryLocation &Loc, bool isLoad, BasicBlock *StartBB,
SmallVectorImpl<NonLocalDepResult> &Result,
DenseMap<BasicBlock *, Value *> &Visited, bool SkipFirstBlock) {
// Look up the cached info for Pointer.
ValueIsLoadPair CacheKey(Pointer.getAddr(), isLoad);
// Set up a temporary NLPI value. If the map doesn't yet have an entry for
// CacheKey, this value will be inserted as the associated value. Otherwise,
// it'll be ignored, and we'll have to check to see if the cached size and
// aa tags are consistent with the current query.
NonLocalPointerInfo InitialNLPI;
InitialNLPI.Size = Loc.Size;
InitialNLPI.AATags = Loc.AATags;
// Get the NLPI for CacheKey, inserting one into the map if it doesn't
// already have one.
std::pair<CachedNonLocalPointerInfo::iterator, bool> Pair =
NonLocalPointerDeps.insert(std::make_pair(CacheKey, InitialNLPI));
NonLocalPointerInfo *CacheInfo = &Pair.first->second;
// If we already have a cache entry for this CacheKey, we may need to do some
// work to reconcile the cache entry and the current query.
if (!Pair.second) {
if (CacheInfo->Size < Loc.Size) {
// The query's Size is greater than the cached one. Throw out the
// cached data and proceed with the query at the greater size.
CacheInfo->Pair = BBSkipFirstBlockPair();
CacheInfo->Size = Loc.Size;
for (auto &Entry : CacheInfo->NonLocalDeps)
if (Instruction *Inst = Entry.getResult().getInst())
RemoveFromReverseMap(ReverseNonLocalPtrDeps, Inst, CacheKey);
CacheInfo->NonLocalDeps.clear();
} else if (CacheInfo->Size > Loc.Size) {
// This query's Size is less than the cached one. Conservatively restart
// the query using the greater size.
return getNonLocalPointerDepFromBB(
QueryInst, Pointer, Loc.getWithNewSize(CacheInfo->Size), isLoad,
StartBB, Result, Visited, SkipFirstBlock);
}
// If the query's AATags are inconsistent with the cached one,
// conservatively throw out the cached data and restart the query with
// no tag if needed.
if (CacheInfo->AATags != Loc.AATags) {
if (CacheInfo->AATags) {
CacheInfo->Pair = BBSkipFirstBlockPair();
CacheInfo->AATags = AAMDNodes();
for (auto &Entry : CacheInfo->NonLocalDeps)
if (Instruction *Inst = Entry.getResult().getInst())
RemoveFromReverseMap(ReverseNonLocalPtrDeps, Inst, CacheKey);
CacheInfo->NonLocalDeps.clear();
}
if (Loc.AATags)
return getNonLocalPointerDepFromBB(
QueryInst, Pointer, Loc.getWithoutAATags(), isLoad, StartBB, Result,
Visited, SkipFirstBlock);
}
}
NonLocalDepInfo *Cache = &CacheInfo->NonLocalDeps;
// If we have valid cached information for exactly the block we are
// investigating, just return it with no recomputation.
if (CacheInfo->Pair == BBSkipFirstBlockPair(StartBB, SkipFirstBlock)) {
// We have a fully cached result for this query then we can just return the
// cached results and populate the visited set. However, we have to verify
// that we don't already have conflicting results for these blocks. Check
// to ensure that if a block in the results set is in the visited set that
// it was for the same pointer query.
if (!Visited.empty()) {
for (auto &Entry : *Cache) {
DenseMap<BasicBlock *, Value *>::iterator VI =
Visited.find(Entry.getBB());
if (VI == Visited.end() || VI->second == Pointer.getAddr())
continue;
// We have a pointer mismatch in a block. Just return false, saying
// that something was clobbered in this result. We could also do a
// non-fully cached query, but there is little point in doing this.
return false;
}
}
Value *Addr = Pointer.getAddr();
for (auto &Entry : *Cache) {
Visited.insert(std::make_pair(Entry.getBB(), Addr));
if (Entry.getResult().isNonLocal()) {
continue;
}
if (DT.isReachableFromEntry(Entry.getBB())) {
Result.push_back(
NonLocalDepResult(Entry.getBB(), Entry.getResult(), Addr));
}
}
++NumCacheCompleteNonLocalPtr;
return true;
}
// Otherwise, either this is a new block, a block with an invalid cache
// pointer or one that we're about to invalidate by putting more info into it
// than its valid cache info. If empty, the result will be valid cache info,
// otherwise it isn't.
if (Cache->empty())
CacheInfo->Pair = BBSkipFirstBlockPair(StartBB, SkipFirstBlock);
else
CacheInfo->Pair = BBSkipFirstBlockPair();
SmallVector<BasicBlock *, 32> Worklist;
Worklist.push_back(StartBB);
// PredList used inside loop.
SmallVector<std::pair<BasicBlock *, PHITransAddr>, 16> PredList;
// Keep track of the entries that we know are sorted. Previously cached
// entries will all be sorted. The entries we add we only sort on demand (we
// don't insert every element into its sorted position). We know that we
// won't get any reuse from currently inserted values, because we don't
// revisit blocks after we insert info for them.
unsigned NumSortedEntries = Cache->size();
unsigned WorklistEntries = BlockNumberLimit;
bool GotWorklistLimit = false;
DEBUG(AssertSorted(*Cache));
while (!Worklist.empty()) {
BasicBlock *BB = Worklist.pop_back_val();
// If we do process a large number of blocks it becomes very expensive and
// likely it isn't worth worrying about
if (Result.size() > NumResultsLimit) {
Worklist.clear();
// Sort it now (if needed) so that recursive invocations of
// getNonLocalPointerDepFromBB and other routines that could reuse the
// cache value will only see properly sorted cache arrays.
if (Cache && NumSortedEntries != Cache->size()) {
SortNonLocalDepInfoCache(*Cache, NumSortedEntries);
}
// Since we bail out, the "Cache" set won't contain all of the
// results for the query. This is ok (we can still use it to accelerate
// specific block queries) but we can't do the fastpath "return all
// results from the set". Clear out the indicator for this.
CacheInfo->Pair = BBSkipFirstBlockPair();
return false;
}
// Skip the first block if we have it.
if (!SkipFirstBlock) {
// Analyze the dependency of *Pointer in FromBB. See if we already have
// been here.
assert(Visited.count(BB) && "Should check 'visited' before adding to WL");
// Get the dependency info for Pointer in BB. If we have cached
// information, we will use it, otherwise we compute it.
DEBUG(AssertSorted(*Cache, NumSortedEntries));
MemDepResult Dep = GetNonLocalInfoForBlock(QueryInst, Loc, isLoad, BB,
Cache, NumSortedEntries);
// If we got a Def or Clobber, add this to the list of results.
if (!Dep.isNonLocal()) {
if (DT.isReachableFromEntry(BB)) {
Result.push_back(NonLocalDepResult(BB, Dep, Pointer.getAddr()));
continue;
}
}
}
// If 'Pointer' is an instruction defined in this block, then we need to do
// phi translation to change it into a value live in the predecessor block.
// If not, we just add the predecessors to the worklist and scan them with
// the same Pointer.
if (!Pointer.NeedsPHITranslationFromBlock(BB)) {
SkipFirstBlock = false;
SmallVector<BasicBlock *, 16> NewBlocks;
for (BasicBlock *Pred : PredCache.get(BB)) {
// Verify that we haven't looked at this block yet.
std::pair<DenseMap<BasicBlock *, Value *>::iterator, bool> InsertRes =
Visited.insert(std::make_pair(Pred, Pointer.getAddr()));
if (InsertRes.second) {
// First time we've looked at *PI.
NewBlocks.push_back(Pred);
continue;
}
// If we have seen this block before, but it was with a different
// pointer then we have a phi translation failure and we have to treat
// this as a clobber.
if (InsertRes.first->second != Pointer.getAddr()) {
// Make sure to clean up the Visited map before continuing on to
// PredTranslationFailure.
for (unsigned i = 0; i < NewBlocks.size(); i++)
Visited.erase(NewBlocks[i]);
goto PredTranslationFailure;
}
}
if (NewBlocks.size() > WorklistEntries) {
// Make sure to clean up the Visited map before continuing on to
// PredTranslationFailure.
for (unsigned i = 0; i < NewBlocks.size(); i++)
Visited.erase(NewBlocks[i]);
GotWorklistLimit = true;
goto PredTranslationFailure;
}
WorklistEntries -= NewBlocks.size();
Worklist.append(NewBlocks.begin(), NewBlocks.end());
continue;
}
// We do need to do phi translation, if we know ahead of time we can't phi
// translate this value, don't even try.
if (!Pointer.IsPotentiallyPHITranslatable())
goto PredTranslationFailure;
// We may have added values to the cache list before this PHI translation.
// If so, we haven't done anything to ensure that the cache remains sorted.
// Sort it now (if needed) so that recursive invocations of
// getNonLocalPointerDepFromBB and other routines that could reuse the cache
// value will only see properly sorted cache arrays.
if (Cache && NumSortedEntries != Cache->size()) {
SortNonLocalDepInfoCache(*Cache, NumSortedEntries);
NumSortedEntries = Cache->size();
}
Cache = nullptr;
PredList.clear();
for (BasicBlock *Pred : PredCache.get(BB)) {
PredList.push_back(std::make_pair(Pred, Pointer));
// Get the PHI translated pointer in this predecessor. This can fail if
// not translatable, in which case the getAddr() returns null.
PHITransAddr &PredPointer = PredList.back().second;
PredPointer.PHITranslateValue(BB, Pred, &DT, /*MustDominate=*/false);
Value *PredPtrVal = PredPointer.getAddr();
// Check to see if we have already visited this pred block with another
// pointer. If so, we can't do this lookup. This failure can occur
// with PHI translation when a critical edge exists and the PHI node in
// the successor translates to a pointer value different than the
// pointer the block was first analyzed with.
std::pair<DenseMap<BasicBlock *, Value *>::iterator, bool> InsertRes =
Visited.insert(std::make_pair(Pred, PredPtrVal));
if (!InsertRes.second) {
// We found the pred; take it off the list of preds to visit.
PredList.pop_back();
// If the predecessor was visited with PredPtr, then we already did
// the analysis and can ignore it.
if (InsertRes.first->second == PredPtrVal)
continue;
// Otherwise, the block was previously analyzed with a different
// pointer. We can't represent the result of this case, so we just
// treat this as a phi translation failure.
// Make sure to clean up the Visited map before continuing on to
// PredTranslationFailure.
for (unsigned i = 0, n = PredList.size(); i < n; ++i)
Visited.erase(PredList[i].first);
goto PredTranslationFailure;
}
}
// Actually process results here; this need to be a separate loop to avoid
// calling getNonLocalPointerDepFromBB for blocks we don't want to return
// any results for. (getNonLocalPointerDepFromBB will modify our
// datastructures in ways the code after the PredTranslationFailure label
// doesn't expect.)
for (unsigned i = 0, n = PredList.size(); i < n; ++i) {
BasicBlock *Pred = PredList[i].first;
PHITransAddr &PredPointer = PredList[i].second;
Value *PredPtrVal = PredPointer.getAddr();
bool CanTranslate = true;
// If PHI translation was unable to find an available pointer in this
// predecessor, then we have to assume that the pointer is clobbered in
// that predecessor. We can still do PRE of the load, which would insert
// a computation of the pointer in this predecessor.
if (!PredPtrVal)
CanTranslate = false;
// FIXME: it is entirely possible that PHI translating will end up with
// the same value. Consider PHI translating something like:
// X = phi [x, bb1], [y, bb2]. PHI translating for bb1 doesn't *need*
// to recurse here, pedantically speaking.
// If getNonLocalPointerDepFromBB fails here, that means the cached
// result conflicted with the Visited list; we have to conservatively
// assume it is unknown, but this also does not block PRE of the load.
if (!CanTranslate ||
!getNonLocalPointerDepFromBB(QueryInst, PredPointer,
Loc.getWithNewPtr(PredPtrVal), isLoad,
Pred, Result, Visited)) {
// Add the entry to the Result list.
NonLocalDepResult Entry(Pred, MemDepResult::getUnknown(), PredPtrVal);
Result.push_back(Entry);
// Since we had a phi translation failure, the cache for CacheKey won't
// include all of the entries that we need to immediately satisfy future
// queries. Mark this in NonLocalPointerDeps by setting the
// BBSkipFirstBlockPair pointer to null. This requires reuse of the
// cached value to do more work but not miss the phi trans failure.
NonLocalPointerInfo &NLPI = NonLocalPointerDeps[CacheKey];
NLPI.Pair = BBSkipFirstBlockPair();
continue;
}
}
// Refresh the CacheInfo/Cache pointer so that it isn't invalidated.
CacheInfo = &NonLocalPointerDeps[CacheKey];
Cache = &CacheInfo->NonLocalDeps;
NumSortedEntries = Cache->size();
// Since we did phi translation, the "Cache" set won't contain all of the
// results for the query. This is ok (we can still use it to accelerate
// specific block queries) but we can't do the fastpath "return all
// results from the set" Clear out the indicator for this.
CacheInfo->Pair = BBSkipFirstBlockPair();
SkipFirstBlock = false;
continue;
PredTranslationFailure:
// The following code is "failure"; we can't produce a sane translation
// for the given block. It assumes that we haven't modified any of
// our datastructures while processing the current block.
if (!Cache) {
// Refresh the CacheInfo/Cache pointer if it got invalidated.
CacheInfo = &NonLocalPointerDeps[CacheKey];
Cache = &CacheInfo->NonLocalDeps;
NumSortedEntries = Cache->size();
}
// Since we failed phi translation, the "Cache" set won't contain all of the
// results for the query. This is ok (we can still use it to accelerate
// specific block queries) but we can't do the fastpath "return all
// results from the set". Clear out the indicator for this.
CacheInfo->Pair = BBSkipFirstBlockPair();
// If *nothing* works, mark the pointer as unknown.
//
// If this is the magic first block, return this as a clobber of the whole
// incoming value. Since we can't phi translate to one of the predecessors,
// we have to bail out.
if (SkipFirstBlock)
return false;
bool foundBlock = false;
for (NonLocalDepEntry &I : llvm::reverse(*Cache)) {
if (I.getBB() != BB)
continue;
assert((GotWorklistLimit || I.getResult().isNonLocal() ||
!DT.isReachableFromEntry(BB)) &&
"Should only be here with transparent block");
foundBlock = true;
I.setResult(MemDepResult::getUnknown());
Result.push_back(
NonLocalDepResult(I.getBB(), I.getResult(), Pointer.getAddr()));
break;
}
(void)foundBlock; (void)GotWorklistLimit;
assert((foundBlock || GotWorklistLimit) && "Current block not in cache?");
}
// Okay, we're done now. If we added new values to the cache, re-sort it.
SortNonLocalDepInfoCache(*Cache, NumSortedEntries);
DEBUG(AssertSorted(*Cache));
return true;
}
/// If P exists in CachedNonLocalPointerInfo, remove it.
void MemoryDependenceResults::RemoveCachedNonLocalPointerDependencies(
ValueIsLoadPair P) {
CachedNonLocalPointerInfo::iterator It = NonLocalPointerDeps.find(P);
if (It == NonLocalPointerDeps.end())
return;
// Remove all of the entries in the BB->val map. This involves removing
// instructions from the reverse map.
NonLocalDepInfo &PInfo = It->second.NonLocalDeps;
for (unsigned i = 0, e = PInfo.size(); i != e; ++i) {
Instruction *Target = PInfo[i].getResult().getInst();
if (!Target)
continue; // Ignore non-local dep results.
assert(Target->getParent() == PInfo[i].getBB());
// Eliminating the dirty entry from 'Cache', so update the reverse info.
RemoveFromReverseMap(ReverseNonLocalPtrDeps, Target, P);
}
// Remove P from NonLocalPointerDeps (which deletes NonLocalDepInfo).
NonLocalPointerDeps.erase(It);
}
void MemoryDependenceResults::invalidateCachedPointerInfo(Value *Ptr) {
// If Ptr isn't really a pointer, just ignore it.
if (!Ptr->getType()->isPointerTy())
return;
// Flush store info for the pointer.
RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair(Ptr, false));
// Flush load info for the pointer.
RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair(Ptr, true));
}
void MemoryDependenceResults::invalidateCachedPredecessors() {
PredCache.clear();
}
void MemoryDependenceResults::removeInstruction(Instruction *RemInst) {
// Walk through the Non-local dependencies, removing this one as the value
// for any cached queries.
NonLocalDepMapType::iterator NLDI = NonLocalDeps.find(RemInst);
if (NLDI != NonLocalDeps.end()) {
NonLocalDepInfo &BlockMap = NLDI->second.first;
for (auto &Entry : BlockMap)
if (Instruction *Inst = Entry.getResult().getInst())
RemoveFromReverseMap(ReverseNonLocalDeps, Inst, RemInst);
NonLocalDeps.erase(NLDI);
}
// If we have a cached local dependence query for this instruction, remove it.
LocalDepMapType::iterator LocalDepEntry = LocalDeps.find(RemInst);
if (LocalDepEntry != LocalDeps.end()) {
// Remove us from DepInst's reverse set now that the local dep info is gone.
if (Instruction *Inst = LocalDepEntry->second.getInst())
RemoveFromReverseMap(ReverseLocalDeps, Inst, RemInst);
// Remove this local dependency info.
LocalDeps.erase(LocalDepEntry);
}
// If we have any cached pointer dependencies on this instruction, remove
// them. If the instruction has non-pointer type, then it can't be a pointer
// base.
// Remove it from both the load info and the store info. The instruction
// can't be in either of these maps if it is non-pointer.
if (RemInst->getType()->isPointerTy()) {
RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair(RemInst, false));
RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair(RemInst, true));
}
// Loop over all of the things that depend on the instruction we're removing.
SmallVector<std::pair<Instruction *, Instruction *>, 8> ReverseDepsToAdd;
// If we find RemInst as a clobber or Def in any of the maps for other values,
// we need to replace its entry with a dirty version of the instruction after
// it. If RemInst is a terminator, we use a null dirty value.
//
// Using a dirty version of the instruction after RemInst saves having to scan
// the entire block to get to this point.
MemDepResult NewDirtyVal;
if (!RemInst->isTerminator())
NewDirtyVal = MemDepResult::getDirty(&*++RemInst->getIterator());
ReverseDepMapType::iterator ReverseDepIt = ReverseLocalDeps.find(RemInst);
if (ReverseDepIt != ReverseLocalDeps.end()) {
// RemInst can't be the terminator if it has local stuff depending on it.
assert(!ReverseDepIt->second.empty() && !isa<TerminatorInst>(RemInst) &&
"Nothing can locally depend on a terminator");
for (Instruction *InstDependingOnRemInst : ReverseDepIt->second) {
assert(InstDependingOnRemInst != RemInst &&
"Already removed our local dep info");
LocalDeps[InstDependingOnRemInst] = NewDirtyVal;
// Make sure to remember that new things depend on NewDepInst.
assert(NewDirtyVal.getInst() &&
"There is no way something else can have "
"a local dep on this if it is a terminator!");
ReverseDepsToAdd.push_back(
std::make_pair(NewDirtyVal.getInst(), InstDependingOnRemInst));
}
ReverseLocalDeps.erase(ReverseDepIt);
// Add new reverse deps after scanning the set, to avoid invalidating the
// 'ReverseDeps' reference.
while (!ReverseDepsToAdd.empty()) {
ReverseLocalDeps[ReverseDepsToAdd.back().first].insert(
ReverseDepsToAdd.back().second);
ReverseDepsToAdd.pop_back();
}
}
ReverseDepIt = ReverseNonLocalDeps.find(RemInst);
if (ReverseDepIt != ReverseNonLocalDeps.end()) {
for (Instruction *I : ReverseDepIt->second) {
assert(I != RemInst && "Already removed NonLocalDep info for RemInst");
PerInstNLInfo &INLD = NonLocalDeps[I];
// The information is now dirty!
INLD.second = true;
for (auto &Entry : INLD.first) {
if (Entry.getResult().getInst() != RemInst)
continue;
// Convert to a dirty entry for the subsequent instruction.
Entry.setResult(NewDirtyVal);
if (Instruction *NextI = NewDirtyVal.getInst())
ReverseDepsToAdd.push_back(std::make_pair(NextI, I));
}
}
ReverseNonLocalDeps.erase(ReverseDepIt);
// Add new reverse deps after scanning the set, to avoid invalidating 'Set'
while (!ReverseDepsToAdd.empty()) {
ReverseNonLocalDeps[ReverseDepsToAdd.back().first].insert(
ReverseDepsToAdd.back().second);
ReverseDepsToAdd.pop_back();
}
}
// If the instruction is in ReverseNonLocalPtrDeps then it appears as a
// value in the NonLocalPointerDeps info.
ReverseNonLocalPtrDepTy::iterator ReversePtrDepIt =
ReverseNonLocalPtrDeps.find(RemInst);
if (ReversePtrDepIt != ReverseNonLocalPtrDeps.end()) {
SmallVector<std::pair<Instruction *, ValueIsLoadPair>, 8>
ReversePtrDepsToAdd;
for (ValueIsLoadPair P : ReversePtrDepIt->second) {
assert(P.getPointer() != RemInst &&
"Already removed NonLocalPointerDeps info for RemInst");
NonLocalDepInfo &NLPDI = NonLocalPointerDeps[P].NonLocalDeps;
// The cache is not valid for any specific block anymore.
NonLocalPointerDeps[P].Pair = BBSkipFirstBlockPair();
// Update any entries for RemInst to use the instruction after it.
for (auto &Entry : NLPDI) {
if (Entry.getResult().getInst() != RemInst)
continue;
// Convert to a dirty entry for the subsequent instruction.
Entry.setResult(NewDirtyVal);
if (Instruction *NewDirtyInst = NewDirtyVal.getInst())
ReversePtrDepsToAdd.push_back(std::make_pair(NewDirtyInst, P));
}
// Re-sort the NonLocalDepInfo. Changing the dirty entry to its
// subsequent value may invalidate the sortedness.
std::sort(NLPDI.begin(), NLPDI.end());
}
ReverseNonLocalPtrDeps.erase(ReversePtrDepIt);
while (!ReversePtrDepsToAdd.empty()) {
ReverseNonLocalPtrDeps[ReversePtrDepsToAdd.back().first].insert(
ReversePtrDepsToAdd.back().second);
ReversePtrDepsToAdd.pop_back();
}
}
assert(!NonLocalDeps.count(RemInst) && "RemInst got reinserted?");
DEBUG(verifyRemoved(RemInst));
}
/// Verify that the specified instruction does not occur in our internal data
/// structures.
///
/// This function verifies by asserting in debug builds.
void MemoryDependenceResults::verifyRemoved(Instruction *D) const {
#ifndef NDEBUG
for (const auto &DepKV : LocalDeps) {
assert(DepKV.first != D && "Inst occurs in data structures");
assert(DepKV.second.getInst() != D && "Inst occurs in data structures");
}
for (const auto &DepKV : NonLocalPointerDeps) {
assert(DepKV.first.getPointer() != D && "Inst occurs in NLPD map key");
for (const auto &Entry : DepKV.second.NonLocalDeps)
assert(Entry.getResult().getInst() != D && "Inst occurs as NLPD value");
}
for (const auto &DepKV : NonLocalDeps) {
assert(DepKV.first != D && "Inst occurs in data structures");
const PerInstNLInfo &INLD = DepKV.second;
for (const auto &Entry : INLD.first)
assert(Entry.getResult().getInst() != D &&
"Inst occurs in data structures");
}
for (const auto &DepKV : ReverseLocalDeps) {
assert(DepKV.first != D && "Inst occurs in data structures");
for (Instruction *Inst : DepKV.second)
assert(Inst != D && "Inst occurs in data structures");
}
for (const auto &DepKV : ReverseNonLocalDeps) {
assert(DepKV.first != D && "Inst occurs in data structures");
for (Instruction *Inst : DepKV.second)
assert(Inst != D && "Inst occurs in data structures");
}
for (const auto &DepKV : ReverseNonLocalPtrDeps) {
assert(DepKV.first != D && "Inst occurs in rev NLPD map");
for (ValueIsLoadPair P : DepKV.second)
assert(P != ValueIsLoadPair(D, false) && P != ValueIsLoadPair(D, true) &&
"Inst occurs in ReverseNonLocalPtrDeps map");
}
#endif
}
AnalysisKey MemoryDependenceAnalysis::Key;
MemoryDependenceResults
MemoryDependenceAnalysis::run(Function &F, FunctionAnalysisManager &AM) {
auto &AA = AM.getResult<AAManager>(F);
auto &AC = AM.getResult<AssumptionAnalysis>(F);
auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
return MemoryDependenceResults(AA, AC, TLI, DT);
}
char MemoryDependenceWrapperPass::ID = 0;
INITIALIZE_PASS_BEGIN(MemoryDependenceWrapperPass, "memdep",
"Memory Dependence Analysis", false, true)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(MemoryDependenceWrapperPass, "memdep",
"Memory Dependence Analysis", false, true)
MemoryDependenceWrapperPass::MemoryDependenceWrapperPass() : FunctionPass(ID) {
initializeMemoryDependenceWrapperPassPass(*PassRegistry::getPassRegistry());
}
MemoryDependenceWrapperPass::~MemoryDependenceWrapperPass() = default;
void MemoryDependenceWrapperPass::releaseMemory() {
MemDep.reset();
}
void MemoryDependenceWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequiredTransitive<AAResultsWrapperPass>();
AU.addRequiredTransitive<TargetLibraryInfoWrapperPass>();
}
bool MemoryDependenceResults::invalidate(Function &F, const PreservedAnalyses &PA,
FunctionAnalysisManager::Invalidator &Inv) {
// Check whether our analysis is preserved.
auto PAC = PA.getChecker<MemoryDependenceAnalysis>();
if (!PAC.preserved() && !PAC.preservedSet<AllAnalysesOn<Function>>())
// If not, give up now.
return true;
// Check whether the analyses we depend on became invalid for any reason.
if (Inv.invalidate<AAManager>(F, PA) ||
Inv.invalidate<AssumptionAnalysis>(F, PA) ||
Inv.invalidate<DominatorTreeAnalysis>(F, PA))
return true;
// Otherwise this analysis result remains valid.
return false;
}
unsigned MemoryDependenceResults::getDefaultBlockScanLimit() const {
return BlockScanLimit;
}
bool MemoryDependenceWrapperPass::runOnFunction(Function &F) {
auto &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
MemDep.emplace(AA, AC, TLI, DT);
return false;
}
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