Automatic Reference Counting.

Language-design credit goes to a lot of people, but I particularly want
to single out Blaine Garst and Patrick Beard for their contributions.

Compiler implementation credit goes to Argyrios, Doug, Fariborz, and myself,
in no particular order.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@133103 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 264 insertions, 10 deletions

diff --git a/lib/CodeGen/CGCall.cpp b/lib/CodeGen/CGCall.cpp
index 05c11ceac6..712ec62bd4 100644
--- a/lib/CodeGen/CGCall.cpp
+++ b/lib/CodeGen/CGCall.cpp
@@ -25,6 +25,7 @@
 #include "llvm/Attributes.h"
 #include "llvm/Support/CallSite.h"
 #include "llvm/Target/TargetData.h"
+#include "llvm/InlineAsm.h"
 #include "llvm/Transforms/Utils/Local.h"
 using namespace clang;
 using namespace CodeGen;
@@ -190,13 +191,15 @@ const CGFunctionInfo &CodeGenTypes::getFunctionInfo(const ObjCMethodDecl *MD) {
          e = MD->param_end(); i != e; ++i) {
     ArgTys.push_back(Context.getCanonicalParamType((*i)->getType()));
   }
-  return getFunctionInfo(GetReturnType(MD->getResultType()),
-                         ArgTys,
-                         FunctionType::ExtInfo(
-                             /*NoReturn*/ false,
-                             /*HasRegParm*/ false,
-                             /*RegParm*/ 0,
-                             getCallingConventionForDecl(MD)));
+
+  FunctionType::ExtInfo einfo;
+  einfo = einfo.withCallingConv(getCallingConventionForDecl(MD));
+
+  if (getContext().getLangOptions().ObjCAutoRefCount &&
+      MD->hasAttr<NSReturnsRetainedAttr>())
+    einfo = einfo.withProducesResult(true);
+
+  return getFunctionInfo(GetReturnType(MD->getResultType()), ArgTys, einfo);
 }
 
 const CGFunctionInfo &CodeGenTypes::getFunctionInfo(GlobalDecl GD) {
@@ -262,7 +265,8 @@ const CGFunctionInfo &CodeGenTypes::getFunctionInfo(CanQualType ResTy,
     return *FI;
 
   // Construct the function info.
-  FI = new CGFunctionInfo(CC, Info.getNoReturn(), Info.getHasRegParm(), Info.getRegParm(), ResTy,
+  FI = new CGFunctionInfo(CC, Info.getNoReturn(), Info.getProducesResult(),
+                          Info.getHasRegParm(), Info.getRegParm(), ResTy,
                           ArgTys.data(), ArgTys.size());
   FunctionInfos.InsertNode(FI, InsertPos);
 
@@ -291,13 +295,15 @@ const CGFunctionInfo &CodeGenTypes::getFunctionInfo(CanQualType ResTy,
 }
 
 CGFunctionInfo::CGFunctionInfo(unsigned _CallingConvention,
-                               bool _NoReturn, bool _HasRegParm, unsigned _RegParm,
+                               bool _NoReturn, bool returnsRetained,
+                               bool _HasRegParm, unsigned _RegParm,
                                CanQualType ResTy,
                                const CanQualType *ArgTys,
                                unsigned NumArgTys)
   : CallingConvention(_CallingConvention),
     EffectiveCallingConvention(_CallingConvention),
-    NoReturn(_NoReturn), HasRegParm(_HasRegParm), RegParm(_RegParm)
+    NoReturn(_NoReturn), ReturnsRetained(returnsRetained),
+    HasRegParm(_HasRegParm), RegParm(_RegParm)
 {
   NumArgs = NumArgTys;
 
@@ -1068,6 +1074,95 @@ void CodeGenFunction::EmitFunctionProlog(const CGFunctionInfo &FI,
   assert(AI == Fn->arg_end() && "Argument mismatch!");
 }
 
+/// Try to emit a fused autorelease of a return result.
+static llvm::Value *tryEmitFusedAutoreleaseOfResult(CodeGenFunction &CGF,
+                                                    llvm::Value *result) {
+  // We must be immediately followed the cast.
+  llvm::BasicBlock *BB = CGF.Builder.GetInsertBlock();
+  if (BB->empty()) return 0;
+  if (&BB->back() != result) return 0;
+
+  const llvm::Type *resultType = result->getType();
+
+  // result is in a BasicBlock and is therefore an Instruction.
+  llvm::Instruction *generator = cast<llvm::Instruction>(result);
+
+  llvm::SmallVector<llvm::Instruction*,4> insnsToKill;
+
+  // Look for:
+  //  %generator = bitcast %type1* %generator2 to %type2*
+  while (llvm::BitCastInst *bitcast = dyn_cast<llvm::BitCastInst>(generator)) {
+    // We would have emitted this as a constant if the operand weren't
+    // an Instruction.
+    generator = cast<llvm::Instruction>(bitcast->getOperand(0));
+
+    // Require the generator to be immediately followed by the cast.
+    if (generator->getNextNode() != bitcast)
+      return 0;
+
+    insnsToKill.push_back(bitcast);
+  }
+
+  // Look for:
+  //   %generator = call i8* @objc_retain(i8* %originalResult)
+  // or
+  //   %generator = call i8* @objc_retainAutoreleasedReturnValue(i8* %originalResult)
+  llvm::CallInst *call = dyn_cast<llvm::CallInst>(generator);
+  if (!call) return 0;
+
+  bool doRetainAutorelease;
+
+  if (call->getCalledValue() == CGF.CGM.getARCEntrypoints().objc_retain) {
+    doRetainAutorelease = true;
+  } else if (call->getCalledValue() == CGF.CGM.getARCEntrypoints()
+                                          .objc_retainAutoreleasedReturnValue) {
+    doRetainAutorelease = false;
+
+    // Look for an inline asm immediately preceding the call and kill it, too.
+    llvm::Instruction *prev = call->getPrevNode();
+    if (llvm::CallInst *asmCall = dyn_cast_or_null<llvm::CallInst>(prev))
+      if (asmCall->getCalledValue()
+            == CGF.CGM.getARCEntrypoints().retainAutoreleasedReturnValueMarker)
+        insnsToKill.push_back(prev);
+  } else {
+    return 0;
+  }
+
+  result = call->getArgOperand(0);
+  insnsToKill.push_back(call);
+
+  // Keep killing bitcasts, for sanity.  Note that we no longer care
+  // about precise ordering as long as there's exactly one use.
+  while (llvm::BitCastInst *bitcast = dyn_cast<llvm::BitCastInst>(result)) {
+    if (!bitcast->hasOneUse()) break;
+    insnsToKill.push_back(bitcast);
+    result = bitcast->getOperand(0);
+  }
+
+  // Delete all the unnecessary instructions, from latest to earliest.
+  for (llvm::SmallVectorImpl<llvm::Instruction*>::iterator
+         i = insnsToKill.begin(), e = insnsToKill.end(); i != e; ++i)
+    (*i)->eraseFromParent();
+
+  // Do the fused retain/autorelease if we were asked to.
+  if (doRetainAutorelease)
+    result = CGF.EmitARCRetainAutoreleaseReturnValue(result);
+
+  // Cast back to the result type.
+  return CGF.Builder.CreateBitCast(result, resultType);
+}
+
+/// Emit an ARC autorelease of the result of a function.
+static llvm::Value *emitAutoreleaseOfResult(CodeGenFunction &CGF,
+                                            llvm::Value *result) {
+  // At -O0, try to emit a fused retain/autorelease.
+  if (CGF.shouldUseFusedARCCalls())
+    if (llvm::Value *fused = tryEmitFusedAutoreleaseOfResult(CGF, result))
+      return fused;
+
+  return CGF.EmitARCAutoreleaseReturnValue(result);
+}
+
 void CodeGenFunction::EmitFunctionEpilog(const CGFunctionInfo &FI) {
   // Functions with no result always return void.
   if (ReturnValue == 0) {
@@ -1135,6 +1230,16 @@ void CodeGenFunction::EmitFunctionEpilog(const CGFunctionInfo &FI) {
 
       RV = CreateCoercedLoad(V, RetAI.getCoerceToType(), *this);
     }
+
+    // In ARC, end functions that return a retainable type with a call
+    // to objc_autoreleaseReturnValue.
+    if (AutoreleaseResult) {
+      assert(getLangOptions().ObjCAutoRefCount &&
+             !FI.isReturnsRetained() &&
+             RetTy->isObjCRetainableType());
+      RV = emitAutoreleaseOfResult(*this, RV);
+    }
+
     break;
 
   case ABIArgInfo::Ignore:
@@ -1184,8 +1289,152 @@ void CodeGenFunction::EmitDelegateCallArg(CallArgList &args,
   return args.add(RValue::get(value), type);
 }
 
+static bool isProvablyNull(llvm::Value *addr) {
+  return isa<llvm::ConstantPointerNull>(addr);
+}
+
+static bool isProvablyNonNull(llvm::Value *addr) {
+  return isa<llvm::AllocaInst>(addr);
+}
+
+/// Emit the actual writing-back of a writeback.
+static void emitWriteback(CodeGenFunction &CGF,
+                          const CallArgList::Writeback &writeback) {
+  llvm::Value *srcAddr = writeback.Address;
+  assert(!isProvablyNull(srcAddr) &&
+         "shouldn't have writeback for provably null argument");
+
+  llvm::BasicBlock *contBB = 0;
+
+  // If the argument wasn't provably non-null, we need to null check
+  // before doing the store.
+  bool provablyNonNull = isProvablyNonNull(srcAddr);
+  if (!provablyNonNull) {
+    llvm::BasicBlock *writebackBB = CGF.createBasicBlock("icr.writeback");
+    contBB = CGF.createBasicBlock("icr.done");
+
+    llvm::Value *isNull = CGF.Builder.CreateIsNull(srcAddr, "icr.isnull");
+    CGF.Builder.CreateCondBr(isNull, contBB, writebackBB);
+    CGF.EmitBlock(writebackBB);
+  }
+
+  // Load the value to writeback.
+  llvm::Value *value = CGF.Builder.CreateLoad(writeback.Temporary);
+
+  // Cast it back, in case we're writing an id to a Foo* or something.
+  value = CGF.Builder.CreateBitCast(value,
+               cast<llvm::PointerType>(srcAddr->getType())->getElementType(),
+                            "icr.writeback-cast");
+  
+  // Perform the writeback.
+  QualType srcAddrType = writeback.AddressType;
+  CGF.EmitStoreThroughLValue(RValue::get(value),
+                             CGF.MakeAddrLValue(srcAddr, srcAddrType),
+                             srcAddrType);
+
+  // Jump to the continuation block.
+  if (!provablyNonNull)
+    CGF.EmitBlock(contBB);
+}
+
+static void emitWritebacks(CodeGenFunction &CGF,
+                           const CallArgList &args) {
+  for (CallArgList::writeback_iterator
+         i = args.writeback_begin(), e = args.writeback_end(); i != e; ++i)
+    emitWriteback(CGF, *i);
+}
+
+/// Emit an argument that's being passed call-by-writeback.  That is,
+/// we are passing the address of 
+static void emitWritebackArg(CodeGenFunction &CGF, CallArgList &args,
+                             const ObjCIndirectCopyRestoreExpr *CRE) {
+  llvm::Value *srcAddr = CGF.EmitScalarExpr(CRE->getSubExpr());
+
+  // The dest and src types don't necessarily match in LLVM terms
+  // because of the crazy ObjC compatibility rules.
+
+  const llvm::PointerType *destType =
+    cast<llvm::PointerType>(CGF.ConvertType(CRE->getType()));
+
+  // If the address is a constant null, just pass the appropriate null.
+  if (isProvablyNull(srcAddr)) {
+    args.add(RValue::get(llvm::ConstantPointerNull::get(destType)),
+             CRE->getType());
+    return;
+  }
+
+  QualType srcAddrType =
+    CRE->getSubExpr()->getType()->castAs<PointerType>()->getPointeeType();
+
+  // Create the temporary.
+  llvm::Value *temp = CGF.CreateTempAlloca(destType->getElementType(),
+                                           "icr.temp");
+
+  // Zero-initialize it if we're not doing a copy-initialization.
+  bool shouldCopy = CRE->shouldCopy();
+  if (!shouldCopy) {
+    llvm::Value *null =
+      llvm::ConstantPointerNull::get(
+        cast<llvm::PointerType>(destType->getElementType()));
+    CGF.Builder.CreateStore(null, temp);
+  }
+
+  llvm::BasicBlock *contBB = 0;
+
+  // If the address is *not* known to be non-null, we need to switch.
+  llvm::Value *finalArgument;
+
+  bool provablyNonNull = isProvablyNonNull(srcAddr);
+  if (provablyNonNull) {
+    finalArgument = temp;
+  } else {
+    llvm::Value *isNull = CGF.Builder.CreateIsNull(srcAddr, "icr.isnull");
+
+    finalArgument = CGF.Builder.CreateSelect(isNull, 
+                                   llvm::ConstantPointerNull::get(destType),
+                                             temp, "icr.argument");
+
+    // If we need to copy, then the load has to be conditional, which
+    // means we need control flow.
+    if (shouldCopy) {
+      contBB = CGF.createBasicBlock("icr.cont");
+      llvm::BasicBlock *copyBB = CGF.createBasicBlock("icr.copy");
+      CGF.Builder.CreateCondBr(isNull, contBB, copyBB);
+      CGF.EmitBlock(copyBB);
+    }
+  }
+
+  // Perform a copy if necessary.
+  if (shouldCopy) {
+    LValue srcLV = CGF.MakeAddrLValue(srcAddr, srcAddrType);
+    RValue srcRV = CGF.EmitLoadOfLValue(srcLV, srcAddrType);
+    assert(srcRV.isScalar());
+
+    llvm::Value *src = srcRV.getScalarVal();
+    src = CGF.Builder.CreateBitCast(src, destType->getElementType(),
+                                    "icr.cast");
+
+    // Use an ordinary store, not a store-to-lvalue.
+    CGF.Builder.CreateStore(src, temp);
+  }
+
+  // Finish the control flow if we needed it.
+  if (shouldCopy && !provablyNonNull)
+    CGF.EmitBlock(contBB);
+
+  args.addWriteback(srcAddr, srcAddrType, temp);
+  args.add(RValue::get(finalArgument), CRE->getType());
+}
+
 void CodeGenFunction::EmitCallArg(CallArgList &args, const Expr *E,
                                   QualType type) {
+  if (const ObjCIndirectCopyRestoreExpr *CRE
+        = dyn_cast<ObjCIndirectCopyRestoreExpr>(E)) {
+    assert(getContext().getLangOptions().ObjCAutoRefCount);
+    assert(getContext().hasSameType(E->getType(), type));
+    return emitWritebackArg(*this, args, CRE);
+  }
+
   if (type->isReferenceType())
     return args.add(EmitReferenceBindingToExpr(E, /*InitializedDecl=*/0),
                     type);
@@ -1435,6 +1684,11 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
   if (Builder.isNamePreserving() && !CI->getType()->isVoidTy())
     CI->setName("call");
 
+  // Emit any writebacks immediately.  Arguably this should happen
+  // after any return-value munging.
+  if (CallArgs.hasWritebacks())
+    emitWritebacks(*this, CallArgs);
+
   switch (RetAI.getKind()) {
   case ABIArgInfo::Indirect: {
     unsigned Alignment = getContext().getTypeAlignInChars(RetTy).getQuantity();