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[objc-arc] Added ImpreciseAutoreleaseSet to track autorelease calls that were once autoreleaseRV instructions.

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Due to the semantics of ARC, we must be extremely conservative with autorelease
calls inserted by the frontend since ARC gaurantees that said object will be in
the autorelease pool after that point, an optimization invariant that the
optimizer must respect.

On the other hand, we are allowed significantly more flexibility with
autoreleaseRV instructions.

Often times though this flexibility is disrupted by early transformations which
transform objc_autoreleaseRV => objc_autorelease if said instruction is no
longer being used as part of an RV pair (generally due to inlining). Since we
can not tell the difference in between an autorelease put into place by the
frontend and one created through said ``strength reduction'' we can not perform
these optimizations.

The addition of this set gets around said issues by allowing us to differentiate
in between said two cases.

rdar://problem/13697741.

llvm-svn: 180222
This commit is contained in:
Michael Gottesman 2013-04-24 22:18:18 +00:00
parent 6edf0d6d80
commit 0c2ffd01ef
1 changed files with 38 additions and 0 deletions
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38
lib/Transforms/ObjCARC/ObjCARCOpts.cpp
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@ -30,6 +30,7 @@
#include "ObjCARCAliasAnalysis.h"
#include "ProvenanceAnalysis.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
@ -985,6 +986,13 @@ namespace {
/// A flag indicating whether this optimization pass should run.
bool Run;
/// This set contains references to objc_autorelease calls that at one point
/// in time were objc_autoreleaseRV calls. Thus we can disambiguate
/// in between objc_autorelease that were inserted from the frontend (which
/// we must be very conservative with) and those as a result of strength
/// reducing objc_autoreleaseRV calls (which are more flexible).
DenseSet<Instruction *> ImpreciseAutoreleaseSet;
/// Declarations for ObjC runtime functions, for use in creating calls to
/// them. These are initialized lazily to avoid cluttering up the Module
/// with unused declarations.
@ -1034,6 +1042,27 @@ namespace {
bool IsRetainBlockOptimizable(const Instruction *Inst);
/// Erase an instruction.
///
/// This is included separately from the EraseInstruction in ObjCARC.h
/// (which this uses internally) in order to make sure that state is cleaned
/// up. Currently this just means attempting to remove said instruction from
/// ImpreciseAutoreleaseSet if it is an autorelease instruction. This will
/// prevent bugs of the sort where we erase an instruction and forget to
/// remove any associated state.
///
/// TODO: Maybe remove this, the ImpreciseAutoreleaseSet, the
/// MetadataKind/Callee variables into a separate class.
void EraseInstruction(Instruction *Inst) {
// If Inst is an autorelease instruction, erase it from
// ImpreciseAutoreleaseSet if it is contained there in.
if (GetBasicInstructionClass(Inst) == IC_Autorelease) {
ImpreciseAutoreleaseSet.erase(Inst);
}
// Invoke the normal EraseInstruction.
llvm::objcarc::EraseInstruction(Inst);
}
void OptimizeRetainCall(Function &F, Instruction *Retain);
bool OptimizeRetainRVCall(Function &F, Instruction *RetainRV);
void OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
@ -1359,6 +1388,12 @@ ObjCARCOpt::OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
AutoreleaseRVCI->setTailCall(false); // Never tail call objc_autorelease.
Class = IC_Autorelease;
// Stash the given instruction in the ImpreciseAutoreleaseSet so we can check
// later on that this instruction was an autoreleaseRV instruction that was
// converted to an autorelease instead of an autorelease inserted by the
// frontend (which we can not touch).
ImpreciseAutoreleaseSet.insert(AutoreleaseRVCI);
DEBUG(dbgs() << "New: " << *AutoreleaseRV << "\n");
}
@ -3094,11 +3129,14 @@ bool ObjCARCOpt::runOnFunction(Function &F) {
DEBUG(dbgs() << "\n");
ImpreciseAutoreleaseSet.clear();
return Changed;
}
void ObjCARCOpt::releaseMemory() {
PA.clear();
ImpreciseAutoreleaseSet.clear();
}
/// @}