[CodeGen] Require use of Address::invalid() for invalid address (NFC)

This no longer allows creating an invalid Address through the regular
constructor. There were only two places that did this (AggValueSlot
and EHCleanupScope) which did this by converting a potential nullptr
into an Address. I've fixed both of these by directly storing an
Address instead.

This is intended as a bit of preliminary cleanup for D103465.

Differential Revision: https://reviews.llvm.org/D115630

clang/lib/CodeGen/Address.h

@@ -24,14 +24,18 @@ namespace CodeGen {
 class Address {
   llvm::Value *Pointer;
   CharUnits Alignment;
+
+protected:
+  Address(nullptr_t) : Pointer(nullptr) {}
+
 public:
   Address(llvm::Value *pointer, CharUnits alignment)
       : Pointer(pointer), Alignment(alignment) {
-    assert((!alignment.isZero() || pointer == nullptr) &&
-           "creating valid address with invalid alignment");
+    assert(pointer != nullptr && "Pointer cannot be null");
+    assert(!alignment.isZero() && "Alignment cannot be zero");
   }
 
-  static Address invalid() { return Address(nullptr, CharUnits()); }
+  static Address invalid() { return Address(nullptr); }
   bool isValid() const { return Pointer != nullptr; }
 
   llvm::Value *getPointer() const {
@@ -72,12 +76,14 @@ public:
 /// A specialization of Address that requires the address to be an
 /// LLVM Constant.
 class ConstantAddress : public Address {
+  ConstantAddress(nullptr_t) : Address(nullptr) {}
+
 public:
   ConstantAddress(llvm::Constant *pointer, CharUnits alignment)
     : Address(pointer, alignment) {}
 
   static ConstantAddress invalid() {
-    return ConstantAddress(nullptr, CharUnits());
+    return ConstantAddress(nullptr);
   }
 
   llvm::Constant *getPointer() const {

clang/lib/CodeGen/CGCall.cpp

@@ -4308,11 +4308,8 @@ void CodeGenFunction::EmitCallArg(CallArgList &args, const Expr *E,
       type->castAs<RecordType>()->getDecl()->isParamDestroyedInCallee()) {
     // If we're using inalloca, use the argument memory.  Otherwise, use a
     // temporary.
-    AggValueSlot Slot;
-    if (args.isUsingInAlloca())
-      Slot = createPlaceholderSlot(*this, type);
-    else
-      Slot = CreateAggTemp(type, "agg.tmp");
+    AggValueSlot Slot = args.isUsingInAlloca()
+        ? createPlaceholderSlot(*this, type) : CreateAggTemp(type, "agg.tmp");
 
     bool DestroyedInCallee = true, NeedsEHCleanup = true;
     if (const auto *RD = type->getAsCXXRecordDecl())

clang/lib/CodeGen/CGCleanup.h

@@ -242,7 +242,7 @@ class alignas(8) EHCleanupScope : public EHScope {
 
   /// An optional i1 variable indicating whether this cleanup has been
   /// activated yet.
-  llvm::AllocaInst *ActiveFlag;
+  Address ActiveFlag;
 
   /// Extra information required for cleanups that have resolved
   /// branches through them.  This has to be allocated on the side
@@ -290,7 +290,8 @@ public:
                  EHScopeStack::stable_iterator enclosingEH)
       : EHScope(EHScope::Cleanup, enclosingEH),
         EnclosingNormal(enclosingNormal), NormalBlock(nullptr),
-        ActiveFlag(nullptr), ExtInfo(nullptr), FixupDepth(fixupDepth) {
+        ActiveFlag(Address::invalid()), ExtInfo(nullptr),
+        FixupDepth(fixupDepth) {
     CleanupBits.IsNormalCleanup = isNormal;
     CleanupBits.IsEHCleanup = isEH;
     CleanupBits.IsActive = true;
@@ -320,13 +321,13 @@ public:
   bool isLifetimeMarker() const { return CleanupBits.IsLifetimeMarker; }
   void setLifetimeMarker() { CleanupBits.IsLifetimeMarker = true; }
 
-  bool hasActiveFlag() const { return ActiveFlag != nullptr; }
+  bool hasActiveFlag() const { return ActiveFlag.isValid(); }
   Address getActiveFlag() const {
-    return Address(ActiveFlag, CharUnits::One());
+    return ActiveFlag;
   }
   void setActiveFlag(Address Var) {
     assert(Var.getAlignment().isOne());
-    ActiveFlag = cast<llvm::AllocaInst>(Var.getPointer());
+    ActiveFlag = Var;
   }
 
   void setTestFlagInNormalCleanup() {

clang/lib/CodeGen/CGExprAgg.cpp

@@ -301,7 +301,7 @@ void AggExprEmitter::withReturnValueSlot(
   if (!UseTemp)
     return;
 
-  assert(Dest.getPointer() != Src.getAggregatePointer());
+  assert(Dest.isIgnored() || Dest.getPointer() != Src.getAggregatePointer());
   EmitFinalDestCopy(E->getType(), Src);
 
   if (!RequiresDestruction && LifetimeStartInst) {

clang/lib/CodeGen/CGValue.h

@@ -470,13 +470,11 @@ public:
 /// An aggregate value slot.
 class AggValueSlot {
   /// The address.
-  llvm::Value *Addr;
+  Address Addr;
 
   // Qualifiers
   Qualifiers Quals;
 
-  unsigned Alignment;
-
   /// 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.
@@ -520,6 +518,14 @@ class AggValueSlot {
   /// them.
   bool SanitizerCheckedFlag : 1;
 
+  AggValueSlot(Address Addr, Qualifiers Quals, bool DestructedFlag,
+               bool ObjCGCFlag, bool ZeroedFlag, bool AliasedFlag,
+               bool OverlapFlag, bool SanitizerCheckedFlag)
+      : Addr(Addr), Quals(Quals), DestructedFlag(DestructedFlag),
+        ObjCGCFlag(ObjCGCFlag), ZeroedFlag(ZeroedFlag),
+        AliasedFlag(AliasedFlag), OverlapFlag(OverlapFlag),
+        SanitizerCheckedFlag(SanitizerCheckedFlag) {}
+
 public:
   enum IsAliased_t { IsNotAliased, IsAliased };
   enum IsDestructed_t { IsNotDestructed, IsDestructed };
@@ -553,22 +559,8 @@ public:
                               Overlap_t mayOverlap,
                               IsZeroed_t isZeroed = IsNotZeroed,
                        IsSanitizerChecked_t isChecked = IsNotSanitizerChecked) {
-    AggValueSlot AV;
-    if (addr.isValid()) {
-      AV.Addr = addr.getPointer();
-      AV.Alignment = addr.getAlignment().getQuantity();
-    } else {
-      AV.Addr = nullptr;
-      AV.Alignment = 0;
-    }
-    AV.Quals = quals;
-    AV.DestructedFlag = isDestructed;
-    AV.ObjCGCFlag = needsGC;
-    AV.ZeroedFlag = isZeroed;
-    AV.AliasedFlag = isAliased;
-    AV.OverlapFlag = mayOverlap;
-    AV.SanitizerCheckedFlag = isChecked;
-    return AV;
+    return AggValueSlot(addr, quals, isDestructed, needsGC, isZeroed, isAliased,
+                        mayOverlap, isChecked);
   }
 
   static AggValueSlot
@@ -609,19 +601,19 @@ public:
   }
 
   llvm::Value *getPointer() const {
-    return Addr;
+    return Addr.getPointer();
   }
 
   Address getAddress() const {
-    return Address(Addr, getAlignment());
+    return Addr;
   }
 
   bool isIgnored() const {
-    return Addr == nullptr;
+    return !Addr.isValid();
   }
 
   CharUnits getAlignment() const {
-    return CharUnits::fromQuantity(Alignment);
+    return Addr.getAlignment();
   }
 
   IsAliased_t isPotentiallyAliased() const {