Complete rewrite of this pass to be faster, use less memory, be easier to

understand, and more accurate to boot!  This implements
GlobalModRef/purecse.ll over the previous impl.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@15260 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/IPA/GlobalsModRef.cpp

@@ -8,12 +8,13 @@
 //===----------------------------------------------------------------------===//
 //
 // 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)
+// that do not have their address taken, and keeps track of whether functions
-// case, we can provide pretty accurate and useful information.
+// 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"
@@ -21,6 +22,8 @@
 #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"
@@ -34,22 +37,44 @@ namespace {
   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
+    /// NonAddressTakenGlobals - The globals that do not have their addresses
-    /// its address taken.
+    /// taken.
-    struct ModRefFns {
+    std::set<GlobalValue*> NonAddressTakenGlobals;
-      /// 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;
+    std::map<Function*, FunctionRecord> FunctionInfo;
 
   public:
     bool run(Module &M) {
@@ -73,12 +98,37 @@ namespace {
     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);
   };
@@ -100,25 +150,24 @@ void GlobalsModRef::AnalyzeGlobals(Module &M) {
   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
+        // Remember that we are tracking this global.
-        ModRefFns &E = NonAddressTakenGlobals[I];
+        NonAddressTakenGlobals.insert(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];
+        NonAddressTakenGlobals.insert(I);
-        E.RefFns.insert(Readers.begin(), Readers.end());
+        for (unsigned i = 0, e = Readers.size(); i != e; ++i)
-        E.ModFns.insert(Writers.begin(), Writers.end());
+          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();
@@ -132,7 +181,7 @@ void GlobalsModRef::AnalyzeGlobals(Module &M) {
 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)) {
@@ -175,67 +224,82 @@ bool GlobalsModRef::AnalyzeUsesOfGlobal(Value *V,
 
 /// 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.
+  DEBUG(std::cerr << "GlobalsModRef: Analyze Call Graph\n");
-
-  // 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);
+  for (scc_iterator<CallGraph*> I = scc_begin(&CG), E = scc_end(&CG); I!=E; ++I)
-       I != E; ++I) {
+    // Do not call AnalyzeSCC on the external function node.
-    std::map<GlobalValue*, unsigned> ModRefProperties;
+    if ((*I).size() != 1 || (*I)[0]->getFunction())
-    const std::vector<CallGraphNode *> &SCC = *I;
+      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,
+          CallsExternal = true;
-          // since they could call into an escaping function that mod/refs an
+          break;
-          // 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;
         }
+      } else {
+        CallsExternal = true;
+        break;
       }
-  Out:
+
-    // Set all functions in the CFG to have these properties.  FIXME: it would
+  // If this SCC calls an external function, we can't say anything about it, so
-    // be better to use union find to only store these properties once,
+  // remove all SCC functions from the FunctionInfo map.
-    // PARTICULARLY if it's the universal set.
+  if (CallsExternal) {
     for (unsigned i = 0, e = SCC.size(); i != e; ++i)
-      if (Function *F = SCC[i]->getFunction()) {
+      FunctionInfo.erase(SCC[i]->getFunction());
-        for (std::map<GlobalValue*, unsigned>::iterator I =
+    return;
-               ModRefProperties.begin(), E = ModRefProperties.end();
-             I != E; ++I)
-          FunctionInfo[std::make_pair(F, I->first)] = I->second;
-      }
   }
+  
+  // 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;
 }
 
 
@@ -244,7 +308,7 @@ void GlobalsModRef::AnalyzeCallGraph(CallGraph &CG, Module &M) {
 /// 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;
@@ -286,15 +350,13 @@ 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.
+  // 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()) {
+      if (Function *F = CS.getCalledFunction())
-        std::map<std::pair<Function*, GlobalValue*>, unsigned>::iterator
+        if (NonAddressTakenGlobals.count(GV))
-          it = FunctionInfo.find(std::make_pair(F, GV));
+          if (FunctionRecord *FR = getFunctionInfo(F))
-        if (it != FunctionInfo.end())
+            Known = FR->getInfoForGlobal(GV);
-          Known = it->second;
-      }
 
   if (Known == NoModRef)
     return NoModRef; // No need to query other mod/ref analyses
@@ -306,20 +368,9 @@ GlobalsModRef::getModRefInfo(CallSite CS, Value *P, unsigned 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)) {
+  if (GlobalValue *GV = dyn_cast<GlobalValue>(V))
-    std::map<GlobalValue*, ModRefFns>::iterator I =
+    NonAddressTakenGlobals.erase(GV);
-      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;
-    }
 }