llvm-6502/lib/Analysis/IPA/GlobalsModRef.cpp
Reid Spencer e840434755 bug 122:
- Replace ConstantPointerRef usage with GlobalValue usage
- Minimize redundant isa<GlobalValue> usage
- Correct isa<Constant> for GlobalValue subclass


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@14942 91177308-0d34-0410-b5e6-96231b3b80d8
2004-07-18 00:18:30 +00:00

326 lines
14 KiB
C++

//===- GlobalsModRef.cpp - Simple Mod/Ref Analysis for Globals ------------===//
//
// 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 simple pass provides alias and mod/ref information for global values
// that do not have their address taken. For this simple (but very common)
// case, we can provide pretty accurate and useful information.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "globalsmodref"
#include "llvm/Analysis/Passes.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Instructions.h"
#include "llvm/Constants.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/CallGraph.h"
#include "Support/Debug.h"
#include "Support/Statistic.h"
#include "Support/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");
class GlobalsModRef : public Pass, public AliasAnalysis {
/// ModRefFns - One instance of this record is kept for each global without
/// its address taken.
struct ModRefFns {
/// RefFns/ModFns - Sets of functions that and write globals.
std::set<Function*> RefFns, ModFns;
};
/// NonAddressTakenGlobals - A map of globals that do not have their
/// addresses taken to their record.
std::map<GlobalValue*, ModRefFns> NonAddressTakenGlobals;
/// FunctionInfo - For each function, keep track of what globals are
/// modified or read.
std::map<std::pair<Function*, GlobalValue*>, unsigned> FunctionInfo;
public:
bool run(Module &M) {
InitializeAliasAnalysis(this); // set up super class
AnalyzeGlobals(M); // find non-addr taken globals
AnalyzeCallGraph(getAnalysis<CallGraph>(), M); // Propagate on CG
return false;
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AliasAnalysis::getAnalysisUsage(AU);
AU.addRequired<CallGraph>();
AU.setPreservesAll(); // Does not transform code
}
//------------------------------------------------
// Implement the AliasAnalysis API
//
AliasResult alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size);
ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
bool hasNoModRefInfoForCalls() const { return false; }
virtual void deleteValue(Value *V);
virtual void copyValue(Value *From, Value *To);
private:
void AnalyzeGlobals(Module &M);
void AnalyzeCallGraph(CallGraph &CG, Module &M);
bool AnalyzeUsesOfGlobal(Value *V, std::vector<Function*> &Readers,
std::vector<Function*> &Writers);
};
RegisterOpt<GlobalsModRef> X("globalsmodref-aa",
"Simple mod/ref analysis for globals");
RegisterAnalysisGroup<AliasAnalysis, GlobalsModRef> Y;
}
Pass *llvm::createGlobalsModRefPass() { return new GlobalsModRef(); }
/// AnalyzeGlobalUses - 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.
void GlobalsModRef::AnalyzeGlobals(Module &M) {
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)) {
// Remember that we are tracking this global, and the mod/ref fns
ModRefFns &E = NonAddressTakenGlobals[I];
E.RefFns.insert(Readers.begin(), Readers.end());
E.ModFns.insert(Writers.begin(), Writers.end());
++NumNonAddrTakenFunctions;
}
Readers.clear(); Writers.clear();
}
for (Module::giterator I = M.gbegin(), E = M.gend(); I != E; ++I)
// FIXME: it is kinda dumb to track aliasing properties for constant
// globals, it will never be particularly useful anyways, 'cause they can
// never be modified (and the optimizer knows this already)!
if (I->hasInternalLinkage()) {
if (!AnalyzeUsesOfGlobal(I, Readers, Writers)) {
// Remember that we are tracking this global, and the mod/ref fns
ModRefFns &E = NonAddressTakenGlobals[I];
E.RefFns.insert(Readers.begin(), Readers.end());
E.ModFns.insert(Writers.begin(), Writers.end());
++NumNonAddrTakenGlobalVars;
}
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) {
//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());
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) {
if (AnalyzeUsesOfGlobal(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 = 1, e = CI->getNumOperands(); i != e; ++i)
if (CI->getOperand(i) == V) 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 = 1, e = CI->getNumOperands(); i != e; ++i)
if (CI->getOperand(i) == V) return true;
} else if (InvokeInst *II = dyn_cast<InvokeInst>(*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))
return true;
} else {
return true;
}
} else if (GlobalValue *GV = dyn_cast<GlobalValue>(*UI)) {
if (AnalyzeUsesOfGlobal(GV, Readers, Writers)) return true;
} else {
return true;
}
return false;
}
/// 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.
void GlobalsModRef::AnalyzeCallGraph(CallGraph &CG, Module &M) {
if (NonAddressTakenGlobals.empty()) return; // Don't bother, nothing to do.
// Invert the NonAddressTakenGlobals map into the FunctionInfo map.
for (std::map<GlobalValue*, ModRefFns>::iterator I =
NonAddressTakenGlobals.begin(), E = NonAddressTakenGlobals.end();
I != E; ++I) {
GlobalValue *GV = I->first;
ModRefFns &MRInfo = I->second;
for (std::set<Function*>::iterator I = MRInfo.RefFns.begin(),
E = MRInfo.RefFns.begin(); I != E; ++I)
FunctionInfo[std::make_pair(*I, GV)] |= Ref;
MRInfo.RefFns.clear();
for (std::set<Function*>::iterator I = MRInfo.ModFns.begin(),
E = MRInfo.ModFns.begin(); I != E; ++I)
FunctionInfo[std::make_pair(*I, GV)] |= Mod;
MRInfo.ModFns.clear();
}
// We do a bottom-up SCC traversal of the call graph. In other words, we
// visit all callees before callers (leaf-first).
for (scc_iterator<CallGraph*> I = scc_begin(&CG), E = scc_end(&CG);
I != E; ++I) {
std::map<GlobalValue*, unsigned> ModRefProperties;
const std::vector<CallGraphNode *> &SCC = *I;
// Collect the mod/ref properties due to called functions.
for (unsigned i = 0, e = SCC.size(); i != e; ++i)
for (CallGraphNode::iterator CI = SCC[i]->begin(), E = SCC[i]->end();
CI != E; ++CI) {
if (Function *Callee = (*CI)->getFunction()) {
// Otherwise, combine the callee properties into our accumulated set.
std::map<std::pair<Function*, GlobalValue*>, unsigned>::iterator
CI = FunctionInfo.lower_bound(std::make_pair(Callee,
(GlobalValue*)0));
for (;CI != FunctionInfo.end() && CI->first.first == Callee; ++CI)
ModRefProperties[CI->first.second] |= CI->second;
} else {
// For now assume that external functions could mod/ref anything,
// since they could call into an escaping function that mod/refs an
// internal. FIXME: We need better tracking!
for (std::map<GlobalValue*, ModRefFns>::iterator GI =
NonAddressTakenGlobals.begin(),
E = NonAddressTakenGlobals.end(); GI != E; ++GI)
ModRefProperties[GI->first] = ModRef;
goto Out;
}
}
Out:
// Set all functions in the CFG to have these properties. FIXME: it would
// be better to use union find to only store these properties once,
// PARTICULARLY if it's the universal set.
for (unsigned i = 0, e = SCC.size(); i != e; ++i)
if (Function *F = SCC[i]->getFunction()) {
for (std::map<GlobalValue*, unsigned>::iterator I =
ModRefProperties.begin(), E = ModRefProperties.end();
I != E; ++I)
FunctionInfo[std::make_pair(F, I->first)] = I->second;
}
}
}
/// 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;
if ((GV1 || GV2) && GV1 != GV2)
return NoAlias;
return AliasAnalysis::alias(V1, V1Size, V2, V2Size);
}
AliasAnalysis::ModRefResult
GlobalsModRef::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
unsigned Known = ModRef;
// If we are asking for mod/ref info of a direct call with a pointer to a
// global, return information if we have it.
if (GlobalValue *GV = const_cast<GlobalValue*>(getUnderlyingObject(P)))
if (GV->hasInternalLinkage())
if (Function *F = CS.getCalledFunction()) {
std::map<std::pair<Function*, GlobalValue*>, unsigned>::iterator
it = FunctionInfo.find(std::make_pair(F, GV));
if (it != FunctionInfo.end())
Known = it->second;
}
if (Known == NoModRef)
return NoModRef; // No need to query other mod/ref analyses
return ModRefResult(Known & AliasAnalysis::getModRefInfo(CS, P, Size));
}
//===----------------------------------------------------------------------===//
// Methods to update the analysis as a result of the client transformation.
//
void GlobalsModRef::deleteValue(Value *V) {
if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
std::map<GlobalValue*, ModRefFns>::iterator I =
NonAddressTakenGlobals.find(GV);
if (I != NonAddressTakenGlobals.end())
NonAddressTakenGlobals.erase(I);
}
}
void GlobalsModRef::copyValue(Value *From, Value *To) {
if (GlobalValue *FromGV = dyn_cast<GlobalValue>(From))
if (GlobalValue *ToGV = dyn_cast<GlobalValue>(To)) {
std::map<GlobalValue*, ModRefFns>::iterator I =
NonAddressTakenGlobals.find(FromGV);
if (I != NonAddressTakenGlobals.end())
NonAddressTakenGlobals[ToGV] = I->second;
}
}