r323578 - [CodeGen] Use the non-virtual alignment when emitting the base

[Akira Hatanaka via cfe-commits]

Author: ahatanak
Date: Fri Jan 26 16:34:09 2018
New Revision: 323578

URL: http://llvm.org/viewvc/llvm-project?rev=323578&view=rev
Log:
[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

Modified:
    cfe/trunk/lib/CodeGen/CGClass.cpp
    cfe/trunk/test/CodeGenCXX/virtual-bases.cpp

Modified: cfe/trunk/lib/CodeGen/CGClass.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGClass.cpp?rev=323578&r1=323577&r2=323578&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CGClass.cpp (original)
+++ cfe/trunk/lib/CodeGen/CGClass.cpp Fri Jan 26 16:34:09 2018
@@ -615,7 +615,14 @@ static void EmitMemberInitializer(CodeGe
 
   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);
 

Modified: cfe/trunk/test/CodeGenCXX/virtual-bases.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/virtual-bases.cpp?rev=323578&r1=323577&r2=323578&view=diff
==============================================================================
--- cfe/trunk/test/CodeGenCXX/virtual-bases.cpp (original)
+++ cfe/trunk/test/CodeGenCXX/virtual-bases.cpp Fri Jan 26 16:34:09 2018
@@ -46,3 +46,37 @@ struct D : B, C  {
 D::D() { }
 
 }
+
+namespace virtualBaseAlignment {
+
+// Check that the store to B::x in the base constructor has an 8-byte alignment.
+
+// CHECK: define linkonce_odr void @_ZN20virtualBaseAlignment1BC1Ev(%[[STRUCT_B:.*]]* %[[THIS:.*]])
+// CHECK: %[[THIS_ADDR:.*]] = alloca %[[STRUCT_B]]*, align 8
+// CHECK: store %[[STRUCT_B]]* %[[THIS]], %[[STRUCT_B]]** %[[THIS_ADDR]], align 8
+// CHECK: %[[THIS1:.*]] = load %[[STRUCT_B]]*, %[[STRUCT_B]]** %[[THIS_ADDR]], align 8
+// CHECK: %[[X:.*]] = getelementptr inbounds %[[STRUCT_B]], %[[STRUCT_B]]* %[[THIS1]], i32 0, i32 2
+// CHECK: store i32 123, i32* %[[X]], align 16
+
+// CHECK: define linkonce_odr void @_ZN20virtualBaseAlignment1BC2Ev(%[[STRUCT_B]]* %[[THIS:.*]], i8** %{{.*}})
+// CHECK: %[[THIS_ADDR:.*]] = alloca %[[STRUCT_B]]*, align 8
+// CHECK: store %[[STRUCT_B]]* %[[THIS]], %[[STRUCT_B]]** %[[THIS_ADDR]], align 8
+// CHECK: %[[THIS1:.*]] = load %[[STRUCT_B]]*, %[[STRUCT_B]]** %[[THIS_ADDR]], align 8
+// CHECK: %[[X:.*]] = getelementptr inbounds %[[STRUCT_B]], %[[STRUCT_B]]* %[[THIS1]], i32 0, i32 2
+// CHECK: store i32 123, i32* %[[X]], align 8
+
+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; }
+
+}