What say we document some of these AggValueSlot flags a bit
better.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@138628 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGValue.h b/lib/CodeGen/CGValue.h
index 36b318f..489e600 100644
--- a/lib/CodeGen/CGValue.h
+++ b/lib/CodeGen/CGValue.h
@@ -338,17 +338,33 @@
// Qualifiers
Qualifiers Quals;
- // Associated flags.
- bool LifetimeFlag : 1;
- bool RequiresGCollection : 1;
+ /// DestructedFlag - This is set to true if some external code is
+ /// responsible for setting up a destructor for the slot. Otherwise
+ /// the code which constructs it should push the appropriate cleanup.
+ bool DestructedFlag : 1;
+
+ /// ObjCGCFlag - This is set to true if writing to the memory in the
+ /// slot might require calling an appropriate Objective-C GC
+ /// barrier. The exact interaction here is unnecessarily mysterious.
+ bool ObjCGCFlag : 1;
- /// ZeroedFlag - This is set to true if the destination is known to be zero
- /// before the assignment into it. This means that zero fields don't need to
- /// be set.
+ /// ZeroedFlag - This is set to true if the memory in the slot is
+ /// known to be zero before the assignment into it. This means that
+ /// zero fields don't need to be set.
bool ZeroedFlag : 1;
- /// AliasedFlag - This generally defaults to false, but can be true
- /// if the memory is known not to be aliased.
+ /// AliasedFlag - This is set to true if the slot might be aliased
+ /// and it's not undefined behavior to access it through such an
+ /// alias. Note that it's always undefined behavior to access a C++
+ /// object that's under construction through an alias derived from
+ /// outside the construction process.
+ ///
+ /// This flag controls whether calls that produce the aggregate
+ /// value may be evaluated directly into the slot, or whether they
+ /// must be evaluated into an unaliased temporary and then memcpy'ed
+ /// over. Since it's invalid in general to memcpy a non-POD C++
+ /// object, it's important that this flag never be set when
+ /// evaluating an expression which constructs such an object.
bool AliasedFlag : 1;
public:
@@ -363,10 +379,7 @@
AggValueSlot AV;
AV.Addr = 0;
AV.Quals = Qualifiers();
- AV.LifetimeFlag = AV.RequiresGCollection = AV.ZeroedFlag = false;
-
- // If there's ever an address here, it will be a temporary.
- AV.AliasedFlag = false;
+ AV.DestructedFlag = AV.ObjCGCFlag = AV.ZeroedFlag = AV.AliasedFlag = false;
return AV;
}
@@ -388,8 +401,8 @@
AggValueSlot AV;
AV.Addr = addr;
AV.Quals = quals;
- AV.LifetimeFlag = isDestructed;
- AV.RequiresGCollection = needsGC;
+ AV.DestructedFlag = isDestructed;
+ AV.ObjCGCFlag = needsGC;
AV.ZeroedFlag = isZeroed;
AV.AliasedFlag = isAliased;
return AV;
@@ -403,11 +416,11 @@
isDestructed, needsGC, isAliased, isZeroed);
}
- IsDestructed_t isLifetimeExternallyManaged() const {
- return IsDestructed_t(LifetimeFlag);
+ IsDestructed_t isExternallyDestructed() const {
+ return IsDestructed_t(DestructedFlag);
}
- void setLifetimeExternallyManaged(bool Managed = true) {
- LifetimeFlag = Managed;
+ void setExternallyDestructed(bool destructed = true) {
+ DestructedFlag = destructed;
}
Qualifiers getQualifiers() const { return Quals; }
@@ -421,7 +434,7 @@
}
NeedsGCBarriers_t requiresGCollection() const {
- return NeedsGCBarriers_t(RequiresGCollection);
+ return NeedsGCBarriers_t(ObjCGCFlag);
}
llvm::Value *getAddr() const {