//===----------------------------------------------------------------------===//
//
// 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.
+// that do not have their address taken, and keeps track of whether functions
+// read or write memory (are "pure"). For this simple (but very common) case,
+// we can provide pretty accurate and useful information.
//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "globalsmodref"
+#define DEBUG_TYPE "globalsmodref-aa"
#include "llvm/Analysis/Passes.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Constants.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/CallGraph.h"
+#include "llvm/Support/InstIterator.h"
+#include "Support/CommandLine.h"
#include "Support/Debug.h"
#include "Support/Statistic.h"
#include "Support/SCCIterator.h"
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");
+
+ /// 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 {
+ /// GlobalInfo - Maintain mod/ref info for all of the globals without
+ /// addresses taken that are read or written (transitively) by this
+ /// function.
+ std::map<GlobalValue*, unsigned> GlobalInfo;
+
+ unsigned getInfoForGlobal(GlobalValue *GV) const {
+ std::map<GlobalValue*, unsigned>::const_iterator I = GlobalInfo.find(GV);
+ if (I != GlobalInfo.end())
+ return I->second;
+ return 0;
+ }
+
+ /// FunctionEffect - Capture whether or not this function reads or writes to
+ /// ANY memory. If not, we can do a lot of aggressive analysis on it.
+ unsigned FunctionEffect;
+ };
+ /// GlobalsModRef - The actual analysis pass.
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;
+ /// NonAddressTakenGlobals - The globals that do not have their addresses
+ /// taken.
+ std::set<GlobalValue*> NonAddressTakenGlobals;
/// FunctionInfo - For each function, keep track of what globals are
/// modified or read.
- std::map<std::pair<Function*, GlobalValue*>, unsigned> FunctionInfo;
+ std::map<Function*, FunctionRecord> FunctionInfo;
public:
bool run(Module &M) {
ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
bool hasNoModRefInfoForCalls() const { return false; }
+ bool doesNotAccessMemory(Function *F) {
+ if (FunctionRecord *FR = getFunctionInfo(F))
+ if (FR->FunctionEffect == 0)
+ return true;
+ return AliasAnalysis::doesNotAccessMemory(F);
+ }
+ bool onlyReadsMemory(Function *F) {
+ if (FunctionRecord *FR = getFunctionInfo(F))
+ if ((FR->FunctionEffect & Mod) == 0)
+ return true;
+ return AliasAnalysis::onlyReadsMemory(F);
+ }
+
+
virtual void deleteValue(Value *V);
virtual void copyValue(Value *From, Value *To);
private:
+ /// getFunctionInfo - Return the function info for the function, or null if
+ /// the function calls an external function (in which case we don't have
+ /// anything useful to say about it).
+ FunctionRecord *getFunctionInfo(Function *F) {
+ std::map<Function*, FunctionRecord>::iterator I = FunctionInfo.find(F);
+ if (I != FunctionInfo.end())
+ return &I->second;
+ return 0;
+ }
+
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);
};
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());
+ // Remember that we are tracking this global.
+ NonAddressTakenGlobals.insert(I);
++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());
+ NonAddressTakenGlobals.insert(I);
+ for (unsigned i = 0, e = Readers.size(); i != e; ++i)
+ FunctionInfo[Readers[i]].GlobalInfo[I] |= Ref;
+
+ if (!I->isConstant()) // No need to keep track of writers to constants
+ for (unsigned i = 0, e = Writers.size(); i != e; ++i)
+ FunctionInfo[Writers[i]].GlobalInfo[I] |= Mod;
++NumNonAddrTakenGlobalVars;
}
Readers.clear(); Writers.clear();
bool GlobalsModRef::AnalyzeUsesOfGlobal(Value *V,
std::vector<Function*> &Readers,
std::vector<Function*> &Writers) {
-
//if (!isa<PointerType>(V->getType())) return true;
+ 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)) {
/// 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.
+/// graph to all callers and compute the mod/ref info for all memory for each
+/// function.
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();
- }
+ DEBUG(std::cerr << "GlobalsModRef: Analyze Call Graph\n");
// 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;
+ for (scc_iterator<CallGraph*> I = scc_begin(&CG), E = scc_end(&CG); I!=E; ++I)
+ // Do not call AnalyzeSCC on the external function node.
+ if ((*I).size() != 1 || (*I)[0]->getFunction())
+ AnalyzeSCC(*I);
+}
+
+void GlobalsModRef::AnalyzeSCC(std::vector<CallGraphNode *> &SCC) {
+ assert(!SCC.empty() && "SCC with no functions?");
+ FunctionRecord &FR = FunctionInfo[SCC[0]->getFunction()];
+
+ bool CallsExternal = false;
+ unsigned FunctionEffect = 0;
+
+ // Collect the mod/ref properties due to called functions. We only compute
+ // one mod-ref set
+ for (unsigned i = 0, e = SCC.size(); i != e && !CallsExternal; ++i)
+ for (CallGraphNode::iterator CI = SCC[i]->begin(), E = SCC[i]->end();
+ CI != E; ++CI)
+ if (Function *Callee = (*CI)->getFunction()) {
+ if (FunctionRecord *CalleeFR = getFunctionInfo(Callee)) {
+ // Propagate function effect up.
+ FunctionEffect |= CalleeFR->FunctionEffect;
+
+ // Incorporate callee's effects on globals into our info.
+ for (std::map<GlobalValue*, unsigned>::iterator GI =
+ CalleeFR->GlobalInfo.begin(), E = CalleeFR->GlobalInfo.end();
+ GI != E; ++GI)
+ FR.GlobalInfo[GI->first] |= GI->second;
- // 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;
+ CallsExternal = true;
+ break;
}
+ } else {
+ CallsExternal = true;
+ break;
}
- 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.
+
+ // If this SCC calls an external function, we can't say anything about it, so
+ // remove all SCC functions from the FunctionInfo map.
+ if (CallsExternal) {
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;
- }
+ FunctionInfo.erase(SCC[i]->getFunction());
+ return;
}
+
+ // Otherwise, unless we already know that this function mod/refs memory, scan
+ // the function bodies to see if there are any explicit loads or stores.
+ if (FunctionEffect != ModRef) {
+ for (unsigned i = 0, e = SCC.size(); i != e && FunctionEffect != ModRef;++i)
+ for (inst_iterator II = inst_begin(SCC[i]->getFunction()),
+ E = inst_end(SCC[i]->getFunction());
+ II != E && FunctionEffect != ModRef; ++II)
+ if (isa<LoadInst>(*II))
+ FunctionEffect |= Ref;
+ else if (isa<StoreInst>(*II))
+ FunctionEffect |= Mod;
+ }
+
+ if ((FunctionEffect & Mod) == 0)
+ ++NumReadMemFunctions;
+ if (FunctionEffect == 0)
+ ++NumNoMemFunctions;
+ FR.FunctionEffect = FunctionEffect;
+
+ // Finally, now that we know the full effect on this SCC, clone the
+ // information to each function in the SCC.
+ for (unsigned i = 1, e = SCC.size(); i != e; ++i)
+ FunctionInfo[SCC[i]->getFunction()] = FR;
}
/// 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 (!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;
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.
+ // global we are tracking, 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 (Function *F = CS.getCalledFunction())
+ if (NonAddressTakenGlobals.count(GV))
+ if (FunctionRecord *FR = getFunctionInfo(F))
+ Known = FR->getInfoForGlobal(GV);
if (Known == NoModRef)
return NoModRef; // No need to query other mod/ref analyses
// 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);
- }
+ if (GlobalValue *GV = dyn_cast<GlobalValue>(V))
+ NonAddressTakenGlobals.erase(GV);
}
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;
- }
}
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