Fixed a bug where we were tail calling objc_autorelease causing an object to not be placed into an autorelease pool.
The reason that this occurs is that tail calling objc_autorelease eventually
tail calls -[NSObject autorelease] which supports fast autorelease. This can
cause us to violate the semantic gaurantees of __autoreleasing variables that
assignment to an __autoreleasing variables always yields an object that is
placed into the innermost autorelease pool.
The fix included in this patch works by:
1. In the peephole optimization function OptimizeIndividualFunctions, always
remove tail call from objc_autorelease.
2. Whenever we convert to/from an objc_autorelease, set/unset the tail call
keyword as appropriate.
*NOTE* I also handled the case where objc_autorelease is converted in
OptimizeReturns to an autoreleaseRV which still violates the ARC semantics. I
will be removing that in a later patch and I wanted to make sure that the tree
is in a consistent state vis-a-vis ARC always.
Additionally some test cases are provided and all tests that have tail call marked
objc_autorelease keywords have been modified so that tail call has been removed.
*NOTE* One test fails due to a separate bug that I am going to commit soon. Thus
I marked the check line TMP: instead of CHECK: so make check does not fail.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172287 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/ObjCARC.cpp b/lib/Transforms/Scalar/ObjCARC.cpp
index 34700eb..1607e8e 100644
--- a/lib/Transforms/Scalar/ObjCARC.cpp
+++ b/lib/Transforms/Scalar/ObjCARC.cpp
@@ -426,10 +426,20 @@
// IC_RetainBlock may be given a stack argument.
return Class == IC_Retain ||
Class == IC_RetainRV ||
- Class == IC_Autorelease ||
Class == IC_AutoreleaseRV;
}
+/// \brief Test if the given class represents instructions which are never safe
+/// to mark with the "tail" keyword.
+static bool IsNeverTail(InstructionClass Class) {
+ /// It is never safe to tail call objc_autorelease since by tail calling
+ /// objc_autorelease, we also tail call -[NSObject autorelease] which supports
+ /// fast autoreleasing causing our object to be potentially reclaimed from the
+ /// autorelease pool which violates the semantics of __autoreleasing types in
+ /// ARC.
+ return Class == IC_Autorelease;
+}
+
/// IsNoThrow - Test if the given class represents instructions which are always
/// safe to mark with the nounwind attribute..
static bool IsNoThrow(InstructionClass Class) {
@@ -2306,8 +2316,10 @@
" Old: "
<< *AutoreleaseRV << "\n");
- cast<CallInst>(AutoreleaseRV)->
+ CallInst *AutoreleaseRVCI = cast<CallInst>(AutoreleaseRV);
+ AutoreleaseRVCI->
setCalledFunction(getAutoreleaseCallee(F.getParent()));
+ AutoreleaseRVCI->setTailCall(false); // Never tail call objc_autorelease.
DEBUG(dbgs() << " New: "
<< *AutoreleaseRV << "\n");
@@ -2449,6 +2461,16 @@
cast<CallInst>(Inst)->setTailCall();
}
+ // Ensure that functions that can never have a "tail" keyword due to the
+ // semantics of ARC truly do not do so.
+ if (IsNeverTail(Class)) {
+ Changed = true;
+ DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Removing tail keyword"
+ " from function: " << *Inst <<
+ "\n");
+ cast<CallInst>(Inst)->setTailCall(false);
+ }
+
// Set nounwind as needed.
if (IsNoThrow(Class)) {
Changed = true;
@@ -3756,6 +3778,7 @@
Autorelease->setCalledFunction(getAutoreleaseRVCallee(F.getParent()));
DEBUG(dbgs() << " Out: " << *Autorelease
<< "\n");
+ Autorelease->setTailCall(); // Always tail call autoreleaseRV.
AutoreleaseClass = IC_AutoreleaseRV;
}