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Add some comments, and fix a few places that missed setting Changed.

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llvm-svn: 154687
This commit is contained in:
Dan Gohman 2012-04-13 18:57:48 +00:00
parent 84e97c7df2
commit 0387e6b701
1 changed files with 24 additions and 2 deletions
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26
lib/Transforms/Scalar/ObjCARC.cpp
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@ -898,7 +898,7 @@ bool ObjCARCExpand::runOnFunction(Function &F) {
// These calls return their argument verbatim, as a low-level
// optimization. However, this makes high-level optimizations
// harder. Undo any uses of this optimization that the front-end
// emitted here. We'll redo them in a later pass.
// emitted here. We'll redo them in the contract pass.
Changed = true;
Inst->replaceAllUsesWith(cast<CallInst>(Inst)->getArgOperand(0));
break;
@ -1012,7 +1012,11 @@ bool ObjCARCAPElim::runOnModule(Module &M) {
return false;
// Find the llvm.global_ctors variable, as the first step in
// identifying the global constructors.
// identifying the global constructors. In theory, unnecessary autorelease
// pools could occur anywhere, but in practice it's pretty rare. Global
// ctors are a place where autorelease pools get inserted automatically,
// so it's pretty common for them to be unnecessary, and it's pretty
// profitable to eliminate them.
GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors");
if (!GV)
return false;
@ -2278,6 +2282,7 @@ void ObjCARCOpt::OptimizeIndividualCalls(Function &F) {
case IC_DestroyWeak: {
CallInst *CI = cast<CallInst>(Inst);
if (isNullOrUndef(CI->getArgOperand(0))) {
Changed = true;
Type *Ty = CI->getArgOperand(0)->getType();
new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
Constant::getNullValue(Ty),
@ -2293,6 +2298,7 @@ void ObjCARCOpt::OptimizeIndividualCalls(Function &F) {
CallInst *CI = cast<CallInst>(Inst);
if (isNullOrUndef(CI->getArgOperand(0)) ||
isNullOrUndef(CI->getArgOperand(1))) {
Changed = true;
Type *Ty = CI->getArgOperand(0)->getType();
new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
Constant::getNullValue(Ty),
@ -3180,6 +3186,8 @@ void ObjCARCOpt::MoveCalls(Value *Arg,
}
}
/// PerformCodePlacement - Identify pairings between the retains and releases,
/// and delete and/or move them.
bool
ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
&BBStates,
@ -3193,6 +3201,7 @@ ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
SmallVector<Instruction *, 4> NewReleases;
SmallVector<Instruction *, 8> DeadInsts;
// Visit each retain.
for (MapVector<Value *, RRInfo>::const_iterator I = Retains.begin(),
E = Retains.end(); I != E; ++I) {
Value *V = I->first;
@ -3666,6 +3675,7 @@ bool ObjCARCOpt::doInitialization(Module &M) {
if (!EnableARCOpts)
return false;
// If nothing in the Module uses ARC, don't do anything.
Run = ModuleHasARC(M);
if (!Run)
return false;
@ -4000,6 +4010,7 @@ void ObjCARCContract::ContractRelease(Instruction *Release,
}
bool ObjCARCContract::doInitialization(Module &M) {
// If nothing in the Module uses ARC, don't do anything.
Run = ModuleHasARC(M);
if (!Run)
return false;
@ -4075,6 +4086,7 @@ bool ObjCARCContract::runOnFunction(Function &F) {
--BBI;
while (isNoopInstruction(BBI)) --BBI;
if (&*BBI == GetObjCArg(Inst)) {
Changed = true;
InlineAsm *IA =
InlineAsm::get(FunctionType::get(Type::getVoidTy(Inst->getContext()),
/*isVarArg=*/false),
@ -4124,6 +4136,13 @@ bool ObjCARCContract::runOnFunction(Function &F) {
Use &U = UI.getUse();
unsigned OperandNo = UI.getOperandNo();
++UI; // Increment UI now, because we may unlink its element.
// If the call's return value dominates a use of the call's argument
// value, rewrite the use to use the return value. We check for
// reachability here because an unreachable call is considered to
// trivially dominate itself, which would lead us to rewriting its
// argument in terms of its return value, which would lead to
// infinite loops in GetObjCArg.
if (DT->isReachableFromEntry(U) &&
DT->dominates(Inst, U)) {
Changed = true;
@ -4138,6 +4157,9 @@ bool ObjCARCContract::runOnFunction(Function &F) {
if (Replacement->getType() != UseTy)
Replacement = new BitCastInst(Replacement, UseTy, "",
&BB->back());
// While we're here, rewrite all edges for this PHI, rather
// than just one use at a time, to minimize the number of
// bitcasts we emit.
for (unsigned i = 0, e = PHI->getNumIncomingValues();
i != e; ++i)
if (PHI->getIncomingBlock(i) == BB) {