//
// The LLVM Compiler Infrastructure
//
-// This file was developed by the LLVM research group and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "globalsmodref-aa"
#include "llvm/Analysis/Passes.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Instructions.h"
#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/CallGraph.h"
-#include "llvm/Support/InstIterator.h"
+#include "llvm/Support/Compiler.h"
#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/InstIterator.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/SCCIterator.h"
#include <set>
using namespace llvm;
-namespace {
- Statistic<>
- NumNonAddrTakenGlobalVars("globalsmodref-aa",
- "Number of global vars without address taken");
- Statistic<>
- NumNonAddrTakenFunctions("globalsmodref-aa",
- "Number of functions without address taken");
- Statistic<>
- NumNoMemFunctions("globalsmodref-aa",
- "Number of functions that do not access memory");
- Statistic<>
- NumReadMemFunctions("globalsmodref-aa",
- "Number of functions that only read memory");
+STATISTIC(NumNonAddrTakenGlobalVars,
+ "Number of global vars without address taken");
+STATISTIC(NumNonAddrTakenFunctions,"Number of functions without address taken");
+STATISTIC(NumNoMemFunctions, "Number of functions that do not access memory");
+STATISTIC(NumReadMemFunctions, "Number of functions that only read memory");
+STATISTIC(NumIndirectGlobalVars, "Number of indirect global objects");
+namespace {
/// FunctionRecord - One instance of this structure is stored for every
/// function in the program. Later, the entries for these functions are
/// removed if the function is found to call an external function (in which
/// case we know nothing about it.
- struct FunctionRecord {
+ struct VISIBILITY_HIDDEN FunctionRecord {
/// GlobalInfo - Maintain mod/ref info for all of the globals without
/// addresses taken that are read or written (transitively) by this
/// function.
};
/// GlobalsModRef - The actual analysis pass.
- class GlobalsModRef : public ModulePass, public AliasAnalysis {
+ class VISIBILITY_HIDDEN GlobalsModRef
+ : public ModulePass, public AliasAnalysis {
/// NonAddressTakenGlobals - The globals that do not have their addresses
/// taken.
std::set<GlobalValue*> NonAddressTakenGlobals;
+ /// IndirectGlobals - The memory pointed to by this global is known to be
+ /// 'owned' by the global.
+ std::set<GlobalValue*> IndirectGlobals;
+
+ /// AllocsForIndirectGlobals - If an instruction allocates memory for an
+ /// indirect global, this map indicates which one.
+ std::map<Value*, GlobalValue*> AllocsForIndirectGlobals;
+
/// FunctionInfo - For each function, keep track of what globals are
/// modified or read.
std::map<Function*, FunctionRecord> FunctionInfo;
public:
+ static char ID;
+ GlobalsModRef() : ModulePass((intptr_t)&ID) {}
+
bool runOnModule(Module &M) {
InitializeAliasAnalysis(this); // set up super class
AnalyzeGlobals(M); // find non-addr taken globals
void AnalyzeGlobals(Module &M);
void AnalyzeCallGraph(CallGraph &CG, Module &M);
void AnalyzeSCC(std::vector<CallGraphNode *> &SCC);
- bool AnalyzeUsesOfGlobal(Value *V, std::vector<Function*> &Readers,
- std::vector<Function*> &Writers);
+ bool AnalyzeUsesOfPointer(Value *V, std::vector<Function*> &Readers,
+ std::vector<Function*> &Writers,
+ GlobalValue *OkayStoreDest = 0);
+ bool AnalyzeIndirectGlobalMemory(GlobalValue *GV);
};
+ char GlobalsModRef::ID = 0;
RegisterPass<GlobalsModRef> X("globalsmodref-aa",
"Simple mod/ref analysis for globals");
- RegisterAnalysisGroup<AliasAnalysis, GlobalsModRef> Y;
+ RegisterAnalysisGroup<AliasAnalysis> Y(X);
}
Pass *llvm::createGlobalsModRefPass() { return new GlobalsModRef(); }
+/// getUnderlyingObject - This traverses the use chain to figure out what object
+/// the specified value points to. If the value points to, or is derived from,
+/// a global object, return it.
+static Value *getUnderlyingObject(Value *V) {
+ if (!isa<PointerType>(V->getType())) return V;
+
+ // If we are at some type of object... return it.
+ if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) return GV;
+
+ // Traverse through different addressing mechanisms.
+ if (Instruction *I = dyn_cast<Instruction>(V)) {
+ if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I))
+ return getUnderlyingObject(I->getOperand(0));
+ } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
+ if (CE->getOpcode() == Instruction::BitCast ||
+ CE->getOpcode() == Instruction::GetElementPtr)
+ return getUnderlyingObject(CE->getOperand(0));
+ }
+
+ // Othewise, we don't know what this is, return it as the base pointer.
+ return V;
+}
-/// AnalyzeGlobalUses - Scan through the users of all of the internal
+/// AnalyzeGlobals - Scan through the users of all of the internal
/// GlobalValue's in the program. If none of them have their "Address taken"
/// (really, their address passed to something nontrivial), record this fact,
/// and record the functions that they are used directly in.
std::vector<Function*> Readers, Writers;
for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
if (I->hasInternalLinkage()) {
- if (!AnalyzeUsesOfGlobal(I, Readers, Writers)) {
+ if (!AnalyzeUsesOfPointer(I, Readers, Writers)) {
// Remember that we are tracking this global.
NonAddressTakenGlobals.insert(I);
++NumNonAddrTakenFunctions;
for (Module::global_iterator I = M.global_begin(), E = M.global_end();
I != E; ++I)
if (I->hasInternalLinkage()) {
- if (!AnalyzeUsesOfGlobal(I, Readers, Writers)) {
+ if (!AnalyzeUsesOfPointer(I, Readers, Writers)) {
// Remember that we are tracking this global, and the mod/ref fns
NonAddressTakenGlobals.insert(I);
for (unsigned i = 0, e = Readers.size(); i != e; ++i)
for (unsigned i = 0, e = Writers.size(); i != e; ++i)
FunctionInfo[Writers[i]].GlobalInfo[I] |= Mod;
++NumNonAddrTakenGlobalVars;
+
+ // If this global holds a pointer type, see if it is an indirect global.
+ if (isa<PointerType>(I->getType()->getElementType()) &&
+ AnalyzeIndirectGlobalMemory(I))
+ ++NumIndirectGlobalVars;
}
Readers.clear(); Writers.clear();
}
}
-/// AnalyzeUsesOfGlobal - Look at all of the users of the specified global value
-/// derived pointer. If this is used by anything complex (i.e., the address
-/// escapes), return true. Also, while we are at it, keep track of those
-/// functions that read and write to the value.
-bool GlobalsModRef::AnalyzeUsesOfGlobal(Value *V,
- std::vector<Function*> &Readers,
- std::vector<Function*> &Writers) {
+/// AnalyzeUsesOfPointer - Look at all of the users of the specified pointer.
+/// If this is used by anything complex (i.e., the address escapes), return
+/// true. Also, while we are at it, keep track of those functions that read and
+/// write to the value.
+///
+/// If OkayStoreDest is non-null, stores into this global are allowed.
+bool GlobalsModRef::AnalyzeUsesOfPointer(Value *V,
+ std::vector<Function*> &Readers,
+ std::vector<Function*> &Writers,
+ GlobalValue *OkayStoreDest) {
if (!isa<PointerType>(V->getType())) return true;
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
Readers.push_back(LI->getParent()->getParent());
} else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
- if (V == SI->getOperand(0)) return true; // Storing the pointer
- Writers.push_back(SI->getParent()->getParent());
+ if (V == SI->getOperand(1)) {
+ Writers.push_back(SI->getParent()->getParent());
+ } else if (SI->getOperand(1) != OkayStoreDest) {
+ return true; // Storing the pointer
+ }
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) {
- if (AnalyzeUsesOfGlobal(GEP, Readers, Writers)) return true;
+ if (AnalyzeUsesOfPointer(GEP, Readers, Writers)) return true;
} else if (CallInst *CI = dyn_cast<CallInst>(*UI)) {
// Make sure that this is just the function being called, not that it is
// passing into the function.
for (unsigned i = 3, e = II->getNumOperands(); i != e; ++i)
if (II->getOperand(i) == V) return true;
} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) {
- if (CE->getOpcode() == Instruction::GetElementPtr ||
- CE->getOpcode() == Instruction::Cast) {
- if (AnalyzeUsesOfGlobal(CE, Readers, Writers))
+ if (CE->getOpcode() == Instruction::GetElementPtr ||
+ CE->getOpcode() == Instruction::BitCast) {
+ if (AnalyzeUsesOfPointer(CE, Readers, Writers))
return true;
} else {
return true;
}
- } else if (GlobalValue *GV = dyn_cast<GlobalValue>(*UI)) {
- if (AnalyzeUsesOfGlobal(GV, Readers, Writers)) return true;
+ } else if (ICmpInst *ICI = dyn_cast<ICmpInst>(*UI)) {
+ if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
+ return true; // Allow comparison against null.
+ } else if (FreeInst *F = dyn_cast<FreeInst>(*UI)) {
+ Writers.push_back(F->getParent()->getParent());
} else {
return true;
}
return false;
}
+/// AnalyzeIndirectGlobalMemory - We found an non-address-taken global variable
+/// which holds a pointer type. See if the global always points to non-aliased
+/// heap memory: that is, all initializers of the globals are allocations, and
+/// those allocations have no use other than initialization of the global.
+/// Further, all loads out of GV must directly use the memory, not store the
+/// pointer somewhere. If this is true, we consider the memory pointed to by
+/// GV to be owned by GV and can disambiguate other pointers from it.
+bool GlobalsModRef::AnalyzeIndirectGlobalMemory(GlobalValue *GV) {
+ // Keep track of values related to the allocation of the memory, f.e. the
+ // value produced by the malloc call and any casts.
+ std::vector<Value*> AllocRelatedValues;
+
+ // Walk the user list of the global. If we find anything other than a direct
+ // load or store, bail out.
+ for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I){
+ if (LoadInst *LI = dyn_cast<LoadInst>(*I)) {
+ // The pointer loaded from the global can only be used in simple ways:
+ // we allow addressing of it and loading storing to it. We do *not* allow
+ // storing the loaded pointer somewhere else or passing to a function.
+ std::vector<Function*> ReadersWriters;
+ if (AnalyzeUsesOfPointer(LI, ReadersWriters, ReadersWriters))
+ return false; // Loaded pointer escapes.
+ // TODO: Could try some IP mod/ref of the loaded pointer.
+ } else if (StoreInst *SI = dyn_cast<StoreInst>(*I)) {
+ // Storing the global itself.
+ if (SI->getOperand(0) == GV) return false;
+
+ // If storing the null pointer, ignore it.
+ if (isa<ConstantPointerNull>(SI->getOperand(0)))
+ continue;
+
+ // Check the value being stored.
+ Value *Ptr = getUnderlyingObject(SI->getOperand(0));
+
+ if (isa<MallocInst>(Ptr)) {
+ // Okay, easy case.
+ } else if (CallInst *CI = dyn_cast<CallInst>(Ptr)) {
+ Function *F = CI->getCalledFunction();
+ if (!F || !F->isDeclaration()) return false; // Too hard to analyze.
+ if (F->getName() != "calloc") return false; // Not calloc.
+ } else {
+ return false; // Too hard to analyze.
+ }
+
+ // Analyze all uses of the allocation. If any of them are used in a
+ // non-simple way (e.g. stored to another global) bail out.
+ std::vector<Function*> ReadersWriters;
+ if (AnalyzeUsesOfPointer(Ptr, ReadersWriters, ReadersWriters, GV))
+ return false; // Loaded pointer escapes.
+
+ // Remember that this allocation is related to the indirect global.
+ AllocRelatedValues.push_back(Ptr);
+ } else {
+ // Something complex, bail out.
+ return false;
+ }
+ }
+
+ // Okay, this is an indirect global. Remember all of the allocations for
+ // this global in AllocsForIndirectGlobals.
+ while (!AllocRelatedValues.empty()) {
+ AllocsForIndirectGlobals[AllocRelatedValues.back()] = GV;
+ AllocRelatedValues.pop_back();
+ }
+ IndirectGlobals.insert(GV);
+ return true;
+}
+
/// AnalyzeCallGraph - At this point, we know the functions where globals are
/// immediately stored to and read from. Propagate this information up the call
/// graph to all callers and compute the mod/ref info for all memory for each
if ((*I).size() != 1) {
AnalyzeSCC(*I);
} else if (Function *F = (*I)[0]->getFunction()) {
- if (!F->isExternal()) {
+ if (!F->isDeclaration()) {
// Nonexternal function.
AnalyzeSCC(*I);
} else {
// Okay, if we can't say anything about it, maybe some other alias
// analysis can.
ModRefBehavior MRB =
- AliasAnalysis::getModRefBehavior(Callee, CallSite());
+ AliasAnalysis::getModRefBehavior(Callee);
if (MRB != DoesNotAccessMemory) {
// FIXME: could make this more aggressive for functions that just
// read memory. We should just say they read all globals.
-/// getUnderlyingObject - This traverses the use chain to figure out what object
-/// the specified value points to. If the value points to, or is derived from,
-/// a global object, return it.
-static const GlobalValue *getUnderlyingObject(const Value *V) {
- if (!isa<PointerType>(V->getType())) return 0;
-
- // If we are at some type of object... return it.
- if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) return GV;
-
- // Traverse through different addressing mechanisms...
- if (const Instruction *I = dyn_cast<Instruction>(V)) {
- if (isa<CastInst>(I) || isa<GetElementPtrInst>(I))
- return getUnderlyingObject(I->getOperand(0));
- } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
- if (CE->getOpcode() == Instruction::Cast ||
- CE->getOpcode() == Instruction::GetElementPtr)
- return getUnderlyingObject(CE->getOperand(0));
- }
- return 0;
-}
-
/// alias - If one of the pointers is to a global that we are tracking, and the
/// other is some random pointer, we know there cannot be an alias, because the
/// address of the global isn't taken.
AliasAnalysis::AliasResult
GlobalsModRef::alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size) {
- GlobalValue *GV1 = const_cast<GlobalValue*>(getUnderlyingObject(V1));
- GlobalValue *GV2 = const_cast<GlobalValue*>(getUnderlyingObject(V2));
-
- // If the global's address is taken, pretend we don't know it's a pointer to
- // the global.
- if (GV1 && !NonAddressTakenGlobals.count(GV1)) GV1 = 0;
- if (GV2 && !NonAddressTakenGlobals.count(GV2)) GV2 = 0;
-
+ // Get the base object these pointers point to.
+ Value *UV1 = getUnderlyingObject(const_cast<Value*>(V1));
+ Value *UV2 = getUnderlyingObject(const_cast<Value*>(V2));
+
+ // If either of the underlying values is a global, they may be non-addr-taken
+ // globals, which we can answer queries about.
+ GlobalValue *GV1 = dyn_cast<GlobalValue>(UV1);
+ GlobalValue *GV2 = dyn_cast<GlobalValue>(UV2);
+ if (GV1 || GV2) {
+ // If the global's address is taken, pretend we don't know it's a pointer to
+ // the global.
+ if (GV1 && !NonAddressTakenGlobals.count(GV1)) GV1 = 0;
+ if (GV2 && !NonAddressTakenGlobals.count(GV2)) GV2 = 0;
+
+ // If the the two pointers are derived from two different non-addr-taken
+ // globals, or if one is and the other isn't, we know these can't alias.
+ if ((GV1 || GV2) && GV1 != GV2)
+ return NoAlias;
+
+ // Otherwise if they are both derived from the same addr-taken global, we
+ // can't know the two accesses don't overlap.
+ }
+
+ // These pointers may be based on the memory owned by an indirect global. If
+ // so, we may be able to handle this. First check to see if the base pointer
+ // is a direct load from an indirect global.
+ GV1 = GV2 = 0;
+ if (LoadInst *LI = dyn_cast<LoadInst>(UV1))
+ if (GlobalVariable *GV = dyn_cast<GlobalVariable>(LI->getOperand(0)))
+ if (IndirectGlobals.count(GV))
+ GV1 = GV;
+ if (LoadInst *LI = dyn_cast<LoadInst>(UV2))
+ if (GlobalVariable *GV = dyn_cast<GlobalVariable>(LI->getOperand(0)))
+ if (IndirectGlobals.count(GV))
+ GV2 = GV;
+
+ // These pointers may also be from an allocation for the indirect global. If
+ // so, also handle them.
+ if (AllocsForIndirectGlobals.count(UV1))
+ GV1 = AllocsForIndirectGlobals[UV1];
+ if (AllocsForIndirectGlobals.count(UV2))
+ GV2 = AllocsForIndirectGlobals[UV2];
+
+ // Now that we know whether the two pointers are related to indirect globals,
+ // use this to disambiguate the pointers. If either pointer is based on an
+ // indirect global and if they are not both based on the same indirect global,
+ // they cannot alias.
if ((GV1 || GV2) && GV1 != GV2)
return NoAlias;
-
+
return AliasAnalysis::alias(V1, V1Size, V2, V2Size);
}
// If we are asking for mod/ref info of a direct call with a pointer to a
// global we are tracking, return information if we have it.
- if (GlobalValue *GV = const_cast<GlobalValue*>(getUnderlyingObject(P)))
+ if (GlobalValue *GV = dyn_cast<GlobalValue>(getUnderlyingObject(P)))
if (GV->hasInternalLinkage())
if (Function *F = CS.getCalledFunction())
if (NonAddressTakenGlobals.count(GV))
// Methods to update the analysis as a result of the client transformation.
//
void GlobalsModRef::deleteValue(Value *V) {
- if (GlobalValue *GV = dyn_cast<GlobalValue>(V))
- NonAddressTakenGlobals.erase(GV);
+ if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
+ if (NonAddressTakenGlobals.erase(GV)) {
+ // This global might be an indirect global. If so, remove it and remove
+ // any AllocRelatedValues for it.
+ if (IndirectGlobals.erase(GV)) {
+ // Remove any entries in AllocsForIndirectGlobals for this global.
+ for (std::map<Value*, GlobalValue*>::iterator
+ I = AllocsForIndirectGlobals.begin(),
+ E = AllocsForIndirectGlobals.end(); I != E; ) {
+ if (I->second == GV) {
+ AllocsForIndirectGlobals.erase(I++);
+ } else {
+ ++I;
+ }
+ }
+ }
+ }
+ }
+
+ // Otherwise, if this is an allocation related to an indirect global, remove
+ // it.
+ AllocsForIndirectGlobals.erase(V);
+
+ AliasAnalysis::deleteValue(V);
}
void GlobalsModRef::copyValue(Value *From, Value *To) {
+ AliasAnalysis::copyValue(From, To);
}
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