From 9a036b945c67aeb44093c6c515e4b85e21094335 Mon Sep 17 00:00:00 2001 From: Duncan Sands Date: Wed, 3 Sep 2008 12:55:42 +0000 Subject: [PATCH] Cleanup GlobalsModRef a bit. When analysing the callgraph, when one member of a SCC calls another then the analysis would drop to mod-ref because there is (usually) no function info for the callee yet; fix this. Teach the analysis about function attributes, in particular the readonly attribute (which requires being careful about globals). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@55696 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Analysis/IPA/GlobalsModRef.cpp | 212 +++++++++--------- .../GlobalsModRef/2008-09-03-Mutual.ll | 11 + .../GlobalsModRef/2008-09-03-ReadGlobals.ll | 18 ++ .../GlobalsModRef/2008-09-03-ReadOnly.ll | 9 + 4 files changed, 146 insertions(+), 104 deletions(-) create mode 100644 test/Analysis/GlobalsModRef/2008-09-03-Mutual.ll create mode 100644 test/Analysis/GlobalsModRef/2008-09-03-ReadGlobals.ll create mode 100644 test/Analysis/GlobalsModRef/2008-09-03-ReadOnly.ll diff --git a/lib/Analysis/IPA/GlobalsModRef.cpp b/lib/Analysis/IPA/GlobalsModRef.cpp index 6d6282029ae..c8347c23fdb 100644 --- a/lib/Analysis/IPA/GlobalsModRef.cpp +++ b/lib/Analysis/IPA/GlobalsModRef.cpp @@ -64,20 +64,24 @@ namespace { }; /// GlobalsModRef - The actual analysis pass. - class VISIBILITY_HIDDEN GlobalsModRef + class VISIBILITY_HIDDEN GlobalsModRef : public ModulePass, public AliasAnalysis { /// NonAddressTakenGlobals - The globals that do not have their addresses /// taken. std::set NonAddressTakenGlobals; + /// ReadGlobals - The globals without addresses taken that are read by + /// some function. + std::set ReadGlobals; + /// IndirectGlobals - The memory pointed to by this global is known to be /// 'owned' by the global. std::set IndirectGlobals; - + /// AllocsForIndirectGlobals - If an instruction allocates memory for an /// indirect global, this map indicates which one. std::map AllocsForIndirectGlobals; - + /// FunctionInfo - For each function, keep track of what globals are /// modified or read. std::map FunctionInfo; @@ -129,8 +133,7 @@ namespace { 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). + /// we don't have anything useful to say about it. FunctionRecord *getFunctionInfo(Function *F) { std::map::iterator I = FunctionInfo.find(F); if (I != FunctionInfo.end()) @@ -140,7 +143,6 @@ namespace { void AnalyzeGlobals(Module &M); void AnalyzeCallGraph(CallGraph &CG, Module &M); - void AnalyzeSCC(std::vector &SCC); bool AnalyzeUsesOfPointer(Value *V, std::vector &Readers, std::vector &Writers, GlobalValue *OkayStoreDest = 0); @@ -160,26 +162,26 @@ Pass *llvm::createGlobalsModRefPass() { return new GlobalsModRef(); } /// a global object, return it. static Value *getUnderlyingObject(Value *V) { if (!isa(V->getType())) return V; - + // If we are at some type of object... return it. if (GlobalValue *GV = dyn_cast(V)) return GV; - + // Traverse through different addressing mechanisms. if (Instruction *I = dyn_cast(V)) { if (isa(I) || isa(I)) return getUnderlyingObject(I->getOperand(0)); } else if (ConstantExpr *CE = dyn_cast(V)) { - if (CE->getOpcode() == Instruction::BitCast || + 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. + + // Otherwise, we don't know what this is, return it as the base pointer. return V; } /// AnalyzeGlobals - Scan through the users of all of the internal -/// GlobalValue's in the program. If none of them have their "Address taken" +/// 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) { @@ -200,6 +202,11 @@ void GlobalsModRef::AnalyzeGlobals(Module &M) { if (!AnalyzeUsesOfPointer(I, Readers, Writers)) { // Remember that we are tracking this global, and the mod/ref fns NonAddressTakenGlobals.insert(I); + + if (!Readers.empty()) + // Some function read this global - remember that. + ReadGlobals.insert(I); + for (unsigned i = 0, e = Readers.size(); i != e; ++i) FunctionInfo[Readers[i]].GlobalInfo[I] |= Ref; @@ -207,7 +214,7 @@ void GlobalsModRef::AnalyzeGlobals(Module &M) { 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(I->getType()->getElementType()) && AnalyzeIndirectGlobalMemory(I)) @@ -251,7 +258,7 @@ bool GlobalsModRef::AnalyzeUsesOfPointer(Value *V, for (unsigned i = 3, e = II->getNumOperands(); i != e; ++i) if (II->getOperand(i) == V) return true; } else if (ConstantExpr *CE = dyn_cast(*UI)) { - if (CE->getOpcode() == Instruction::GetElementPtr || + if (CE->getOpcode() == Instruction::GetElementPtr || CE->getOpcode() == Instruction::BitCast) { if (AnalyzeUsesOfPointer(CE, Readers, Writers)) return true; @@ -280,7 +287,7 @@ 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 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){ @@ -295,11 +302,11 @@ bool GlobalsModRef::AnalyzeIndirectGlobalMemory(GlobalValue *GV) { } else if (StoreInst *SI = dyn_cast(*I)) { // Storing the global itself. if (SI->getOperand(0) == GV) return false; - + // If storing the null pointer, ignore it. if (isa(SI->getOperand(0))) continue; - + // Check the value being stored. Value *Ptr = getUnderlyingObject(SI->getOperand(0)); @@ -312,7 +319,7 @@ bool GlobalsModRef::AnalyzeIndirectGlobalMemory(GlobalValue *GV) { } 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 ReadersWriters; @@ -326,7 +333,7 @@ bool GlobalsModRef::AnalyzeIndirectGlobalMemory(GlobalValue *GV) { return false; } } - + // Okay, this is an indirect global. Remember all of the allocations for // this global in AllocsForIndirectGlobals. while (!AllocRelatedValues.empty()) { @@ -344,81 +351,78 @@ bool GlobalsModRef::AnalyzeIndirectGlobalMemory(GlobalValue *GV) { void GlobalsModRef::AnalyzeCallGraph(CallGraph &CG, Module &M) { // 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 I = scc_begin(&CG), E = scc_end(&CG); I!=E; ++I) - if ((*I).size() != 1) { - AnalyzeSCC(*I); - } else if (Function *F = (*I)[0]->getFunction()) { - if (!F->isDeclaration()) { - // Nonexternal function. - AnalyzeSCC(*I); - } else { - // Otherwise external function. Handle intrinsics and other special - // cases here. - if (getAnalysis().doesNotAccessMemory(F)) - // If it does not access memory, process the function, causing us to - // realize it doesn't do anything (the body is empty). - AnalyzeSCC(*I); - else { - // Otherwise, don't process it. This will cause us to conservatively - // assume the worst. - } - } - } else { + for (scc_iterator I = scc_begin(&CG), E = scc_end(&CG); I != E; + ++I) { + std::vector &SCC = *I; + assert(!SCC.empty() && "SCC with no functions?"); + + if (!SCC[0]->getFunction()) // Do not process the external node, assume the worst. - } -} + continue; -void GlobalsModRef::AnalyzeSCC(std::vector &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->second->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::iterator GI = - CalleeFR->GlobalInfo.begin(), E = CalleeFR->GlobalInfo.end(); - GI != E; ++GI) - FR.GlobalInfo[GI->first] |= GI->second; + FunctionRecord &FR = FunctionInfo[SCC[0]->getFunction()]; - } else { - // Okay, if we can't say anything about it, maybe some other alias - // analysis can. - ModRefBehavior MRB = - 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. - CallsExternal = true; - break; - } - } - } else { - CallsExternal = true; + bool KnowNothing = 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 && !KnowNothing; ++i) { + Function *F = SCC[i]->getFunction(); + if (!F) { + KnowNothing = true; break; } - // 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) - FunctionInfo.erase(SCC[i]->getFunction()); - return; - } + if (F->isDeclaration()) { + // Try to get mod/ref behaviour from function attributes. + if (F->onlyReadsMemory()) { + FunctionEffect |= Ref; + // This function might call back into the module and read a global, so + // mark all globals read somewhere as being read by this function. + for (std::set::iterator GI = ReadGlobals.begin(), + E = ReadGlobals.end(); GI != E; ++GI) + FR.GlobalInfo[*GI] |= Ref; + } else if (!F->doesNotAccessMemory()) { + // Can't say anything useful. + KnowNothing = true; + } + continue; + } + + for (CallGraphNode::iterator CI = SCC[i]->begin(), E = SCC[i]->end(); + CI != E; ++CI) + if (Function *Callee = CI->second->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::iterator GI = + CalleeFR->GlobalInfo.begin(), E = CalleeFR->GlobalInfo.end(); + GI != E; ++GI) + FR.GlobalInfo[GI->first] |= GI->second; + } else { + // Can't say anything about it. However, if it is inside our SCC, + // then nothing needs to be done. + CallGraphNode *CalleeNode = CG[Callee]; + if (std::find(SCC.begin(), SCC.end(), CalleeNode) == SCC.end()) + KnowNothing = true; + } + } else { + KnowNothing = true; + } + } + + // If we can't say anything useful about this SCC, remove all SCC functions + // from the FunctionInfo map. + if (KnowNothing) { + for (unsigned i = 0, e = SCC.size(); i != e; ++i) + 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) { + // Scan the function bodies for explicit loads or stores. 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()); @@ -429,18 +433,18 @@ void GlobalsModRef::AnalyzeSCC(std::vector &SCC) { FunctionEffect |= Mod; else if (isa(*II) || isa(*II)) FunctionEffect |= ModRef; - } - if ((FunctionEffect & Mod) == 0) - ++NumReadMemFunctions; - if (FunctionEffect == 0) - ++NumNoMemFunctions; - FR.FunctionEffect = FunctionEffect; + 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; + // 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; + } } @@ -454,7 +458,7 @@ GlobalsModRef::alias(const Value *V1, unsigned V1Size, // Get the base object these pointers point to. Value *UV1 = getUnderlyingObject(const_cast(V1)); Value *UV2 = getUnderlyingObject(const_cast(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(UV1); @@ -473,7 +477,7 @@ GlobalsModRef::alias(const Value *V1, unsigned V1Size, // 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. @@ -486,21 +490,21 @@ GlobalsModRef::alias(const Value *V1, unsigned V1Size, if (GlobalVariable *GV = dyn_cast(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); } @@ -545,11 +549,11 @@ void GlobalsModRef::deleteValue(Value *V) { } } } - + // Otherwise, if this is an allocation related to an indirect global, remove // it. AllocsForIndirectGlobals.erase(V); - + AliasAnalysis::deleteValue(V); } diff --git a/test/Analysis/GlobalsModRef/2008-09-03-Mutual.ll b/test/Analysis/GlobalsModRef/2008-09-03-Mutual.ll new file mode 100644 index 00000000000..f6f47f94727 --- /dev/null +++ b/test/Analysis/GlobalsModRef/2008-09-03-Mutual.ll @@ -0,0 +1,11 @@ +; RUN: llvm-as < %s | opt -globalsmodref-aa -markmodref | llvm-dis | grep readnone + +define i32 @a() { + %tmp = call i32 @b( ) ; [#uses=1] + ret i32 %tmp +} + +define i32 @b() { + %tmp = call i32 @a( ) ; [#uses=1] + ret i32 %tmp +} diff --git a/test/Analysis/GlobalsModRef/2008-09-03-ReadGlobals.ll b/test/Analysis/GlobalsModRef/2008-09-03-ReadGlobals.ll new file mode 100644 index 00000000000..aba6082c62e --- /dev/null +++ b/test/Analysis/GlobalsModRef/2008-09-03-ReadGlobals.ll @@ -0,0 +1,18 @@ +; RUN: llvm-as < %s | opt -globalsmodref-aa -gvn | llvm-dis | grep call | count 2 + +@g = internal global i32 0 ; [#uses=2] + +define i32 @r() { + %tmp = load i32* @g ; [#uses=1] + ret i32 %tmp +} + +define i32 @f() { +entry: + %tmp = call i32 @e( ) ; [#uses=1] + store i32 %tmp, i32* @g + %tmp2 = call i32 @e( ) ; [#uses=1] + ret i32 %tmp2 +} + +declare i32 @e() readonly ; might call @r diff --git a/test/Analysis/GlobalsModRef/2008-09-03-ReadOnly.ll b/test/Analysis/GlobalsModRef/2008-09-03-ReadOnly.ll new file mode 100644 index 00000000000..de1666f5152 --- /dev/null +++ b/test/Analysis/GlobalsModRef/2008-09-03-ReadOnly.ll @@ -0,0 +1,9 @@ +; RUN: llvm-as < %s | opt -globalsmodref-aa -markmodref | llvm-dis | grep readonly | count 2 + +define i32 @f() { +entry: + %tmp = call i32 @e( ) ; [#uses=1] + ret i32 %tmp +} + +declare i32 @e() readonly -- 2.34.1