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[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
This commit is contained in:
Akira Hatanaka 2018-01-27 00:34:09 +00:00
parent 1edb905e82
commit e5dbb64652
2 changed files with 42 additions and 1 deletions
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9
clang/lib/CodeGen/CGClass.cpp
View File

@ -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);

34
clang/test/CodeGenCXX/virtual-bases.cpp
View File

@ -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; }
}