[CodeGen] Use the non-virtual alignment when emitting the base

constructor.

Previously, clang would emit an over-aligned (16-byte) store to
initialize B::x in B's base constructor when compiling the following
code:

struct A {
  __attribute__((aligned(16))) double data1;
};

struct B : public virtual A {
  B() : x(123) {}
  double a;
  int x;
};

struct C : public virtual B {};

void test() { B b; C c; }

This was happening because the code in IRGen that does member
initialization was using the alignment of a complete object instead of
the non-virtual alignment.

This commit fixes the bug.

rdar://problem/36382481

Differential Revision: https://reviews.llvm.org/D42521

llvm-svn: 323578

1 files changed, 8 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
index b1496a8..56bd250 100644
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -615,7 +615,14 @@ static void EmitMemberInitializer(CodeGenFunction &CGF,
 
   llvm::Value *ThisPtr = CGF.LoadCXXThis();
   QualType RecordTy = CGF.getContext().getTypeDeclType(ClassDecl);
-  LValue LHS = CGF.MakeNaturalAlignAddrLValue(ThisPtr, RecordTy);
+  LValue LHS;
+
+  // If a base constructor is being emitted, create an LValue that has the
+  // non-virtual alignment.
+  if (CGF.CurGD.getCtorType() == Ctor_Base)
+    LHS = CGF.MakeNaturalAlignPointeeAddrLValue(ThisPtr, RecordTy);
+  else
+    LHS = CGF.MakeNaturalAlignAddrLValue(ThisPtr, RecordTy);
 
   EmitLValueForAnyFieldInitialization(CGF, MemberInit, LHS);