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Add a basic intra-procedural escape analysis. This hasn't be extensively tested yet, but feedback is welcome.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57342 91177308-0d34-0410-b5e6-96231b3b80d8
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include/llvm/Analysis/EscapeAnalysis.h
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include/llvm/Analysis/EscapeAnalysis.h
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//===------------- EscapeAnalysis.h - Pointer escape analysis -------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the interface for the pointer escape analysis.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_LOOPVR_H
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#define LLVM_ANALYSIS_LOOPVR_H
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#include "llvm/Pass.h"
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#include "llvm/Instructions.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Target/TargetData.h"
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#include <set>
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#include <vector>
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namespace llvm {
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/// EscapeAnalysis - This class determines whether an allocation (a MallocInst
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/// or an AllocaInst) can escape from the current function. It performs some
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/// precomputation, with the rest of the work happening on-demand.
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class EscapeAnalysis : public FunctionPass {
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private:
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std::set<Instruction*> EscapePoints;
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public:
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static char ID; // Class identification, replacement for typeinfo
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EscapeAnalysis() : FunctionPass(intptr_t(&ID)) {}
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bool runOnFunction(Function &F);
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void releaseMemory() {
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EscapePoints.clear();
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}
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void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequiredTransitive<TargetData>();
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AU.addRequiredTransitive<AliasAnalysis>();
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AU.setPreservesAll();
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}
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//===---------------------------------------------------------------------
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// Client API
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/// escapes - returns true if the AllocationInst can escape.
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bool escapes(AllocationInst* A);
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};
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} // end llvm namespace
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#endif
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131
lib/Analysis/EscapeAnalysis.cpp
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lib/Analysis/EscapeAnalysis.cpp
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//===------------- EscapeAnalysis.h - Pointer escape analysis -------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file provides the implementation of the pointer escape analysis.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "escape-analysis"
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#include "llvm/Analysis/EscapeAnalysis.h"
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#include "llvm/Module.h"
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#include "llvm/Support/InstIterator.h"
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#include "llvm/ADT/SmallPtrSet.h"
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using namespace llvm;
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char EscapeAnalysis::ID = 0;
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static RegisterPass<EscapeAnalysis> X("escape-analysis",
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"Pointer Escape Analysis", true, true);
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/// runOnFunction - Precomputation for escape analysis. This collects all know
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/// "escape points" in the def-use graph of the function. These are
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/// instructions which allow their inputs to escape from the current function.
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bool EscapeAnalysis::runOnFunction(Function& F) {
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EscapePoints.clear();
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TargetData& TD = getAnalysis<TargetData>();
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AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
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Module* M = F.getParent();
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// Walk through all instructions in the function, identifying those that
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// may allow their inputs to escape.
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for(inst_iterator II = inst_begin(F), IE = inst_end(F); II != IE; ++II) {
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Instruction* I = &*II;
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// The most obvious case is stores. Any store that may write to global
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// memory or to a function argument potentially allows its input to escape.
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if (StoreInst* S = dyn_cast<StoreInst>(I)) {
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const Type* StoreType = S->getOperand(0)->getType();
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unsigned StoreSize = TD.getTypeStoreSize(StoreType);
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Value* Pointer = S->getPointerOperand();
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bool inserted = false;
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for (Function::arg_iterator AI = F.arg_begin(), AE = F.arg_end();
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AI != AE; ++AI) {
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AliasAnalysis::AliasResult R = AA.alias(Pointer, StoreSize, AI, ~0UL);
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if (R != AliasAnalysis::NoAlias) {
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EscapePoints.insert(S);
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inserted = true;
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break;
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}
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}
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if (inserted)
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continue;
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for (Module::global_iterator GI = M->global_begin(), GE = M->global_end();
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GI != GE; ++GI) {
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AliasAnalysis::AliasResult R = AA.alias(Pointer, StoreSize, GI, ~0UL);
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if (R != AliasAnalysis::NoAlias) {
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EscapePoints.insert(S);
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break;
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}
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}
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// Calls and invokes potentially allow their parameters to escape.
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// FIXME: This can and should be refined. Intrinsics have known escape
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// behavior, and alias analysis may be able to tell us more about callees.
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} else if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
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EscapePoints.insert(I);
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// Returns allow the return value to escape. This is mostly important
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// for malloc to alloca promotion.
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} else if (isa<ReturnInst>(I)) {
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EscapePoints.insert(I);
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}
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// FIXME: Are there any other possible escape points?
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}
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return false;
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}
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/// escapes - Determines whether the passed allocation can escape from the
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/// current function. It does this by using a simple worklist algorithm to
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/// search for a path in the def-use graph from the allocation to an
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/// escape point.
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/// FIXME: Once we've discovered a path, it would be a good idea to memoize it,
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/// and all of its subpaths, to amortize the cost of future queries.
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bool EscapeAnalysis::escapes(AllocationInst* A) {
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std::vector<Value*> worklist;
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worklist.push_back(A);
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SmallPtrSet<Value*, 8> visited;
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while (!worklist.empty()) {
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Value* curr = worklist.back();
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worklist.pop_back();
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visited.insert(curr);
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if (Instruction* CurrInst = dyn_cast<Instruction>(curr))
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if (EscapePoints.count(CurrInst))
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return true;
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for (Instruction::use_iterator UI = curr->use_begin(), UE = curr->use_end();
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UI != UE; ++UI)
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if (Instruction* U = dyn_cast<Instruction>(UI))
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if (!visited.count(U))
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if (StoreInst* S = dyn_cast<StoreInst>(U)) {
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// We know this must be an instruction, because constant gep's would
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// have been found to alias a global, so stores to them would have
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// been in EscapePoints.
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worklist.push_back(cast<Instruction>(S->getPointerOperand()));
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} else if (isa<BranchInst>(U) || isa<SwitchInst>(U)) {
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// Because branches on the pointer value can hide data dependencies,
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// we need to track values that were generated by branching on the
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// pointer (or some derived value). To do that, we push the block,
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// whose uses will be the PHINodes that generate information based
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// one it.
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worklist.push_back(U->getParent());
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} else
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worklist.push_back(U);
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}
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return false;
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}
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