Imported Upstream version 5.18.0.205

Former-commit-id: 7f59f7e792705db773f1caecdaa823092f4e2927

external/llvm/lib/Transforms/ObjCARC/ProvenanceAnalysis.cpp

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+//===- ProvenanceAnalysis.cpp - ObjC ARC Optimization ---------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file
+///
+/// This file defines a special form of Alias Analysis called ``Provenance
+/// Analysis''. The word ``provenance'' refers to the history of the ownership
+/// of an object. Thus ``Provenance Analysis'' is an analysis which attempts to
+/// use various techniques to determine if locally
+///
+/// WARNING: This file knows about certain library functions. It recognizes them
+/// by name, and hardwires knowledge of their semantics.
+///
+/// WARNING: This file knows about how certain Objective-C library functions are
+/// used. Naive LLVM IR transformations which would otherwise be
+/// behavior-preserving may break these assumptions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ProvenanceAnalysis.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/ObjCARCAnalysisUtils.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Use.h"
+#include "llvm/IR/User.h"
+#include "llvm/IR/Value.h"
+#include "llvm/Support/Casting.h"
+#include <utility>
+
+using namespace llvm;
+using namespace llvm::objcarc;
+
+bool ProvenanceAnalysis::relatedSelect(const SelectInst *A,
+                                       const Value *B) {
+  const DataLayout &DL = A->getModule()->getDataLayout();
+  // If the values are Selects with the same condition, we can do a more precise
+  // check: just check for relations between the values on corresponding arms.
+  if (const SelectInst *SB = dyn_cast<SelectInst>(B))
+    if (A->getCondition() == SB->getCondition())
+      return related(A->getTrueValue(), SB->getTrueValue(), DL) ||
+             related(A->getFalseValue(), SB->getFalseValue(), DL);
+
+  // Check both arms of the Select node individually.
+  return related(A->getTrueValue(), B, DL) ||
+         related(A->getFalseValue(), B, DL);
+}
+
+bool ProvenanceAnalysis::relatedPHI(const PHINode *A,
+                                    const Value *B) {
+  const DataLayout &DL = A->getModule()->getDataLayout();
+  // If the values are PHIs in the same block, we can do a more precise as well
+  // as efficient check: just check for relations between the values on
+  // corresponding edges.
+  if (const PHINode *PNB = dyn_cast<PHINode>(B))
+    if (PNB->getParent() == A->getParent()) {
+      for (unsigned i = 0, e = A->getNumIncomingValues(); i != e; ++i)
+        if (related(A->getIncomingValue(i),
+                    PNB->getIncomingValueForBlock(A->getIncomingBlock(i)), DL))
+          return true;
+      return false;
+    }
+
+  // Check each unique source of the PHI node against B.
+  SmallPtrSet<const Value *, 4> UniqueSrc;
+  for (Value *PV1 : A->incoming_values()) {
+    if (UniqueSrc.insert(PV1).second && related(PV1, B, DL))
+      return true;
+  }
+
+  // All of the arms checked out.
+  return false;
+}
+
+/// Test if the value of P, or any value covered by its provenance, is ever
+/// stored within the function (not counting callees).
+static bool IsStoredObjCPointer(const Value *P) {
+  SmallPtrSet<const Value *, 8> Visited;
+  SmallVector<const Value *, 8> Worklist;
+  Worklist.push_back(P);
+  Visited.insert(P);
+  do {
+    P = Worklist.pop_back_val();
+    for (const Use &U : P->uses()) {
+      const User *Ur = U.getUser();
+      if (isa<StoreInst>(Ur)) {
+        if (U.getOperandNo() == 0)
+          // The pointer is stored.
+          return true;
+        // The pointed is stored through.
+        continue;
+      }
+      if (isa<CallInst>(Ur))
+        // The pointer is passed as an argument, ignore this.
+        continue;
+      if (isa<PtrToIntInst>(P))
+        // Assume the worst.
+        return true;
+      if (Visited.insert(Ur).second)
+        Worklist.push_back(Ur);
+    }
+  } while (!Worklist.empty());
+
+  // Everything checked out.
+  return false;
+}
+
+bool ProvenanceAnalysis::relatedCheck(const Value *A, const Value *B,
+                                      const DataLayout &DL) {
+  // Skip past provenance pass-throughs.
+  A = GetUnderlyingObjCPtr(A, DL);
+  B = GetUnderlyingObjCPtr(B, DL);
+
+  // Quick check.
+  if (A == B)
+    return true;
+
+  // Ask regular AliasAnalysis, for a first approximation.
+  switch (AA->alias(A, B)) {
+  case NoAlias:
+    return false;
+  case MustAlias:
+  case PartialAlias:
+    return true;
+  case MayAlias:
+    break;
+  }
+
+  bool AIsIdentified = IsObjCIdentifiedObject(A);
+  bool BIsIdentified = IsObjCIdentifiedObject(B);
+
+  // An ObjC-Identified object can't alias a load if it is never locally stored.
+  if (AIsIdentified) {
+    // Check for an obvious escape.
+    if (isa<LoadInst>(B))
+      return IsStoredObjCPointer(A);
+    if (BIsIdentified) {
+      // Check for an obvious escape.
+      if (isa<LoadInst>(A))
+        return IsStoredObjCPointer(B);
+      // Both pointers are identified and escapes aren't an evident problem.
+      return false;
+    }
+  } else if (BIsIdentified) {
+    // Check for an obvious escape.
+    if (isa<LoadInst>(A))
+      return IsStoredObjCPointer(B);
+  }
+
+   // Special handling for PHI and Select.
+  if (const PHINode *PN = dyn_cast<PHINode>(A))
+    return relatedPHI(PN, B);
+  if (const PHINode *PN = dyn_cast<PHINode>(B))
+    return relatedPHI(PN, A);
+  if (const SelectInst *S = dyn_cast<SelectInst>(A))
+    return relatedSelect(S, B);
+  if (const SelectInst *S = dyn_cast<SelectInst>(B))
+    return relatedSelect(S, A);
+
+  // Conservative.
+  return true;
+}
+
+bool ProvenanceAnalysis::related(const Value *A, const Value *B,
+                                 const DataLayout &DL) {
+  // Begin by inserting a conservative value into the map. If the insertion
+  // fails, we have the answer already. If it succeeds, leave it there until we
+  // compute the real answer to guard against recursive queries.
+  if (A > B) std::swap(A, B);
+  std::pair<CachedResultsTy::iterator, bool> Pair =
+    CachedResults.insert(std::make_pair(ValuePairTy(A, B), true));
+  if (!Pair.second)
+    return Pair.first->second;
+
+  bool Result = relatedCheck(A, B, DL);
+  CachedResults[ValuePairTy(A, B)] = Result;
+  return Result;
+}