[ARC] Pull the ObjC ARC components that really serve the role of

analyses into LLVM's Analysis library rather than having them in
a Transforms library.

This is motivated by the need to have the core AliasAnalysis
infrastructure be aware of the ObjCARCAliasAnalysis. However, it also
seems like a nice and clean separation. Everything was very easy to move
and this doesn't create much clutter in the analysis library IMO.

Differential Revision: http://reviews.llvm.org/D12133

llvm-svn: 245541

1 files changed, 162 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ObjCARCAliasAnalysis.cpp b/llvm/lib/Analysis/ObjCARCAliasAnalysis.cpp
new file mode 100644
index 0000000..29b7411
--- /dev/null
+++ b/llvm/lib/Analysis/ObjCARCAliasAnalysis.cpp
@@ -0,0 +1,162 @@
+//===- ObjCARCAliasAnalysis.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 simple ARC-aware AliasAnalysis using special knowledge
+/// of Objective C to enhance other optimization passes which rely on the Alias
+/// Analysis infrastructure.
+///
+/// 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 "llvm/Analysis/ObjCARCAliasAnalysis.h"
+#include "llvm/Analysis/ObjCARCAnalysisUtils.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Value.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/PassAnalysisSupport.h"
+#include "llvm/PassSupport.h"
+
+#define DEBUG_TYPE "objc-arc-aa"
+
+using namespace llvm;
+using namespace llvm::objcarc;
+
+// Register this pass...
+char ObjCARCAliasAnalysis::ID = 0;
+INITIALIZE_AG_PASS(ObjCARCAliasAnalysis, AliasAnalysis, "objc-arc-aa",
+                   "ObjC-ARC-Based Alias Analysis", false, true, false)
+
+ImmutablePass *llvm::createObjCARCAliasAnalysisPass() {
+  return new ObjCARCAliasAnalysis();
+}
+
+bool ObjCARCAliasAnalysis::doInitialization(Module &M) {
+  InitializeAliasAnalysis(this, &M.getDataLayout());
+  return true;
+}
+
+void ObjCARCAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.setPreservesAll();
+  AliasAnalysis::getAnalysisUsage(AU);
+}
+
+AliasResult ObjCARCAliasAnalysis::alias(const MemoryLocation &LocA,
+                                        const MemoryLocation &LocB) {
+  if (!EnableARCOpts)
+    return AliasAnalysis::alias(LocA, LocB);
+
+  // First, strip off no-ops, including ObjC-specific no-ops, and try making a
+  // precise alias query.
+  const Value *SA = GetRCIdentityRoot(LocA.Ptr);
+  const Value *SB = GetRCIdentityRoot(LocB.Ptr);
+  AliasResult Result =
+      AliasAnalysis::alias(MemoryLocation(SA, LocA.Size, LocA.AATags),
+                           MemoryLocation(SB, LocB.Size, LocB.AATags));
+  if (Result != MayAlias)
+    return Result;
+
+  // If that failed, climb to the underlying object, including climbing through
+  // ObjC-specific no-ops, and try making an imprecise alias query.
+  const Value *UA = GetUnderlyingObjCPtr(SA, *DL);
+  const Value *UB = GetUnderlyingObjCPtr(SB, *DL);
+  if (UA != SA || UB != SB) {
+    Result = AliasAnalysis::alias(MemoryLocation(UA), MemoryLocation(UB));
+    // We can't use MustAlias or PartialAlias results here because
+    // GetUnderlyingObjCPtr may return an offsetted pointer value.
+    if (Result == NoAlias)
+      return NoAlias;
+  }
+
+  // If that failed, fail. We don't need to chain here, since that's covered
+  // by the earlier precise query.
+  return MayAlias;
+}
+
+bool ObjCARCAliasAnalysis::pointsToConstantMemory(const MemoryLocation &Loc,
+                                                  bool OrLocal) {
+  if (!EnableARCOpts)
+    return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
+
+  // First, strip off no-ops, including ObjC-specific no-ops, and try making
+  // a precise alias query.
+  const Value *S = GetRCIdentityRoot(Loc.Ptr);
+  if (AliasAnalysis::pointsToConstantMemory(
+          MemoryLocation(S, Loc.Size, Loc.AATags), OrLocal))
+    return true;
+
+  // If that failed, climb to the underlying object, including climbing through
+  // ObjC-specific no-ops, and try making an imprecise alias query.
+  const Value *U = GetUnderlyingObjCPtr(S, *DL);
+  if (U != S)
+    return AliasAnalysis::pointsToConstantMemory(MemoryLocation(U), OrLocal);
+
+  // If that failed, fail. We don't need to chain here, since that's covered
+  // by the earlier precise query.
+  return false;
+}
+
+FunctionModRefBehavior
+ObjCARCAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
+  // We have nothing to do. Just chain to the next AliasAnalysis.
+  return AliasAnalysis::getModRefBehavior(CS);
+}
+
+FunctionModRefBehavior
+ObjCARCAliasAnalysis::getModRefBehavior(const Function *F) {
+  if (!EnableARCOpts)
+    return AliasAnalysis::getModRefBehavior(F);
+
+  switch (GetFunctionClass(F)) {
+  case ARCInstKind::NoopCast:
+    return FMRB_DoesNotAccessMemory;
+  default:
+    break;
+  }
+
+  return AliasAnalysis::getModRefBehavior(F);
+}
+
+ModRefInfo ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
+                                               const MemoryLocation &Loc) {
+  if (!EnableARCOpts)
+    return AliasAnalysis::getModRefInfo(CS, Loc);
+
+  switch (GetBasicARCInstKind(CS.getInstruction())) {
+  case ARCInstKind::Retain:
+  case ARCInstKind::RetainRV:
+  case ARCInstKind::Autorelease:
+  case ARCInstKind::AutoreleaseRV:
+  case ARCInstKind::NoopCast:
+  case ARCInstKind::AutoreleasepoolPush:
+  case ARCInstKind::FusedRetainAutorelease:
+  case ARCInstKind::FusedRetainAutoreleaseRV:
+    // These functions don't access any memory visible to the compiler.
+    // Note that this doesn't include objc_retainBlock, because it updates
+    // pointers when it copies block data.
+    return MRI_NoModRef;
+  default:
+    break;
+  }
+
+  return AliasAnalysis::getModRefInfo(CS, Loc);
+}
+
+ModRefInfo ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS1,
+                                               ImmutableCallSite CS2) {
+  // TODO: Theoretically we could check for dependencies between objc_* calls
+  // and FMRB_OnlyAccessesArgumentPointees calls or other well-behaved calls.
+  return AliasAnalysis::getModRefInfo(CS1, CS2);
+}