Compute and preserve alignment more faithfully in IR-generation.

Introduce an Address type to bundle a pointer value with an
alignment.  Introduce APIs on CGBuilderTy to work with Address
values.  Change core APIs on CGF/CGM to traffic in Address where
appropriate.  Require alignments to be non-zero.  Update a ton
of code to compute and propagate alignment information.

As part of this, I've promoted CGBuiltin's EmitPointerWithAlignment
helper function to CGF and made use of it in a number of places in
the expression emitter.

The end result is that we should now be significantly more correct
when performing operations on objects that are locally known to
be under-aligned.  Since alignment is not reliably tracked in the
type system, there are inherent limits to this, but at least we
are no longer confused by standard operations like derived-to-base
conversions and array-to-pointer decay.  I've also fixed a large
number of bugs where we were applying the complete-object alignment
to a pointer instead of the non-virtual alignment, although most of
these were hidden by the very conservative approach we took with
member alignment.

Also, because IRGen now reliably asserts on zero alignments, we
should no longer be subject to an absurd but frustrating recurring
bug where an incomplete type would report a zero alignment and then
we'd naively do a alignmentAtOffset on it and emit code using an
alignment equal to the largest power-of-two factor of the offset.

We should also now be emitting much more aggressive alignment
attributes in the presence of over-alignment.  In particular,
field access now uses alignmentAtOffset instead of min.

Several times in this patch, I had to change the existing
code-generation pattern in order to more effectively use
the Address APIs.  For the most part, this seems to be a strict
improvement, like doing pointer arithmetic with GEPs instead of
ptrtoint.  That said, I've tried very hard to not change semantics,
but it is likely that I've failed in a few places, for which I
apologize.

ABIArgInfo now always carries the assumed alignment of indirect and
indirect byval arguments.  In order to cut down on what was already
a dauntingly large patch, I changed the code to never set align
attributes in the IR on non-byval indirect arguments.  That is,
we still generate code which assumes that indirect arguments have
the given alignment, but we don't express this information to the
backend except where it's semantically required (i.e. on byvals).
This is likely a minor regression for those targets that did provide
this information, but it'll be trivial to add it back in a later
patch.

I partially punted on applying this work to CGBuiltin.  Please
do not add more uses of the CreateDefaultAligned{Load,Store}
APIs; they will be going away eventually.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@246985 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 34 insertions, 26 deletions

diff --git a/lib/CodeGen/CGCXXABI.h b/lib/CodeGen/CGCXXABI.h
index 5ef409ecde..828c9ecfc6 100644
--- a/lib/CodeGen/CGCXXABI.h
+++ b/lib/CodeGen/CGCXXABI.h
@@ -48,12 +48,15 @@ protected:
     : CGM(CGM), MangleCtx(CGM.getContext().createMangleContext()) {}
 
 protected:
-  ImplicitParamDecl *&getThisDecl(CodeGenFunction &CGF) {
+  ImplicitParamDecl *getThisDecl(CodeGenFunction &CGF) {
     return CGF.CXXABIThisDecl;
   }
-  llvm::Value *&getThisValue(CodeGenFunction &CGF) {
+  llvm::Value *getThisValue(CodeGenFunction &CGF) {
     return CGF.CXXABIThisValue;
   }
+  Address getThisAddress(CodeGenFunction &CGF) {
+    return Address(CGF.CXXABIThisValue, CGF.CXXABIThisAlignment);
+  }
 
   /// Issue a diagnostic about unsupported features in the ABI.
   void ErrorUnsupportedABI(CodeGenFunction &CGF, StringRef S);
@@ -77,6 +80,12 @@ protected:
   virtual bool requiresArrayCookie(const CXXDeleteExpr *E, QualType eltType);
   virtual bool requiresArrayCookie(const CXXNewExpr *E);
 
+  /// Determine whether there's something special about the rules of
+  /// the ABI tell us that 'this' is a complete object within the
+  /// given function.  Obvious common logic like being defined on a
+  /// final class will have been taken care of by the caller.
+  virtual bool isThisCompleteObject(GlobalDecl GD) const = 0;
+
 public:
 
   virtual ~CGCXXABI();
@@ -135,13 +144,14 @@ public:
   /// pointer.  Apply the this-adjustment and set 'This' to the
   /// adjusted value.
   virtual llvm::Value *EmitLoadOfMemberFunctionPointer(
-      CodeGenFunction &CGF, const Expr *E, llvm::Value *&This,
-      llvm::Value *MemPtr, const MemberPointerType *MPT);
+      CodeGenFunction &CGF, const Expr *E, Address This,
+      llvm::Value *&ThisPtrForCall, llvm::Value *MemPtr,
+      const MemberPointerType *MPT);
 
   /// Calculate an l-value from an object and a data member pointer.
   virtual llvm::Value *
   EmitMemberDataPointerAddress(CodeGenFunction &CGF, const Expr *E,
-                               llvm::Value *Base, llvm::Value *MemPtr,
+                               Address Base, llvm::Value *MemPtr,
                                const MemberPointerType *MPT);
 
   /// Perform a derived-to-base, base-to-derived, or bitcast member
@@ -212,7 +222,7 @@ protected:
 public:
   virtual void emitVirtualObjectDelete(CodeGenFunction &CGF,
                                        const CXXDeleteExpr *DE,
-                                       llvm::Value *Ptr, QualType ElementType,
+                                       Address Ptr, QualType ElementType,
                                        const CXXDestructorDecl *Dtor) = 0;
   virtual void emitRethrow(CodeGenFunction &CGF, bool isNoReturn) = 0;
   virtual void emitThrow(CodeGenFunction &CGF, const CXXThrowExpr *E) = 0;
@@ -235,26 +245,26 @@ public:
                                          QualType SrcRecordTy) = 0;
   virtual void EmitBadTypeidCall(CodeGenFunction &CGF) = 0;
   virtual llvm::Value *EmitTypeid(CodeGenFunction &CGF, QualType SrcRecordTy,
-                                  llvm::Value *ThisPtr,
+                                  Address ThisPtr,
                                   llvm::Type *StdTypeInfoPtrTy) = 0;
 
   virtual bool shouldDynamicCastCallBeNullChecked(bool SrcIsPtr,
                                                   QualType SrcRecordTy) = 0;
 
   virtual llvm::Value *
-  EmitDynamicCastCall(CodeGenFunction &CGF, llvm::Value *Value,
+  EmitDynamicCastCall(CodeGenFunction &CGF, Address Value,
                       QualType SrcRecordTy, QualType DestTy,
                       QualType DestRecordTy, llvm::BasicBlock *CastEnd) = 0;
 
   virtual llvm::Value *EmitDynamicCastToVoid(CodeGenFunction &CGF,
-                                             llvm::Value *Value,
+                                             Address Value,
                                              QualType SrcRecordTy,
                                              QualType DestTy) = 0;
 
   virtual bool EmitBadCastCall(CodeGenFunction &CGF) = 0;
 
   virtual llvm::Value *GetVirtualBaseClassOffset(CodeGenFunction &CGF,
-                                                 llvm::Value *This,
+                                                 Address This,
                                                  const CXXRecordDecl *ClassDecl,
                                         const CXXRecordDecl *BaseClassDecl) = 0;
 
@@ -297,10 +307,9 @@ public:
   /// Perform ABI-specific "this" argument adjustment required prior to
   /// a call of a virtual function.
   /// The "VirtualCall" argument is true iff the call itself is virtual.
-  virtual llvm::Value *
+  virtual Address
   adjustThisArgumentForVirtualFunctionCall(CodeGenFunction &CGF, GlobalDecl GD,
-                                           llvm::Value *This,
-                                           bool VirtualCall) {
+                                           Address This, bool VirtualCall) {
     return This;
   }
 
@@ -340,7 +349,7 @@ public:
   virtual void EmitDestructorCall(CodeGenFunction &CGF,
                                   const CXXDestructorDecl *DD, CXXDtorType Type,
                                   bool ForVirtualBase, bool Delegating,
-                                  llvm::Value *This) = 0;
+                                  Address This) = 0;
 
   /// Emits the VTable definitions required for the given record type.
   virtual void emitVTableDefinitions(CodeGenVTables &CGVT,
@@ -368,14 +377,14 @@ public:
   /// Build a virtual function pointer in the ABI-specific way.
   virtual llvm::Value *getVirtualFunctionPointer(CodeGenFunction &CGF,
                                                  GlobalDecl GD,
-                                                 llvm::Value *This,
+                                                 Address This,
                                                  llvm::Type *Ty,
                                                  SourceLocation Loc) = 0;
 
   /// Emit the ABI-specific virtual destructor call.
   virtual llvm::Value *
   EmitVirtualDestructorCall(CodeGenFunction &CGF, const CXXDestructorDecl *Dtor,
-                            CXXDtorType DtorType, llvm::Value *This,
+                            CXXDtorType DtorType, Address This,
                             const CXXMemberCallExpr *CE) = 0;
 
   virtual void adjustCallArgsForDestructorThunk(CodeGenFunction &CGF,
@@ -391,11 +400,11 @@ public:
                                GlobalDecl GD, bool ReturnAdjustment) = 0;
 
   virtual llvm::Value *performThisAdjustment(CodeGenFunction &CGF,
-                                             llvm::Value *This,
+                                             Address This,
                                              const ThisAdjustment &TA) = 0;
 
   virtual llvm::Value *performReturnAdjustment(CodeGenFunction &CGF,
-                                               llvm::Value *Ret,
+                                               Address Ret,
                                                const ReturnAdjustment &RA) = 0;
 
   virtual void EmitReturnFromThunk(CodeGenFunction &CGF,
@@ -432,11 +441,11 @@ public:
   ///   always a size_t
   /// \param ElementType - the base element allocated type,
   ///   i.e. the allocated type after stripping all array types
-  virtual llvm::Value *InitializeArrayCookie(CodeGenFunction &CGF,
-                                             llvm::Value *NewPtr,
-                                             llvm::Value *NumElements,
-                                             const CXXNewExpr *expr,
-                                             QualType ElementType);
+  virtual Address InitializeArrayCookie(CodeGenFunction &CGF,
+                                        Address NewPtr,
+                                        llvm::Value *NumElements,
+                                        const CXXNewExpr *expr,
+                                        QualType ElementType);
 
   /// Reads the array cookie associated with the given pointer,
   /// if it has one.
@@ -451,7 +460,7 @@ public:
   ///   function
   /// \param CookieSize - an out parameter which will be initialized
   ///   with the size of the cookie, or zero if there is no cookie
-  virtual void ReadArrayCookie(CodeGenFunction &CGF, llvm::Value *Ptr,
+  virtual void ReadArrayCookie(CodeGenFunction &CGF, Address Ptr,
                                const CXXDeleteExpr *expr,
                                QualType ElementType, llvm::Value *&NumElements,
                                llvm::Value *&AllocPtr, CharUnits &CookieSize);
@@ -474,8 +483,7 @@ protected:
   /// Other parameters are as above.
   ///
   /// \return a size_t
-  virtual llvm::Value *readArrayCookieImpl(CodeGenFunction &IGF,
-                                           llvm::Value *ptr,
+  virtual llvm::Value *readArrayCookieImpl(CodeGenFunction &IGF, Address ptr,
                                            CharUnits cookieSize);
 
 public: