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Fix alignment of class derived from empty class.

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The record layout code didn't properly take into account that
an empty class at offset 0 can have an alignment greater than 1.

Patch by Andrea Di Biagio.

llvm-svn: 186370
This commit is contained in:
Eli Friedman 2013-07-16 00:21:28 +00:00
parent 5bd5affe2d
commit 69d27d2d05
2 changed files with 45 additions and 3 deletions
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7
clang/lib/AST/RecordLayoutBuilder.cpp
View File

@ -1532,18 +1532,19 @@ CharUnits RecordLayoutBuilder::LayoutBase(const BaseSubobjectInfo *Base) {
}
}
CharUnits UnpackedBaseAlign = Layout.getNonVirtualAlign();
CharUnits BaseAlign = (Packed) ? CharUnits::One() : UnpackedBaseAlign;
// If we have an empty base class, try to place it at offset 0.
if (Base->Class->isEmpty() &&
(!HasExternalLayout || Offset == CharUnits::Zero()) &&
EmptySubobjects->CanPlaceBaseAtOffset(Base, CharUnits::Zero())) {
setSize(std::max(getSize(), Layout.getSize()));
UpdateAlignment(BaseAlign, UnpackedBaseAlign);
return CharUnits::Zero();
}
CharUnits UnpackedBaseAlign = Layout.getNonVirtualAlign();
CharUnits BaseAlign = (Packed) ? CharUnits::One() : UnpackedBaseAlign;
// The maximum field alignment overrides base align.
if (!MaxFieldAlignment.isZero()) {
BaseAlign = std::min(BaseAlign, MaxFieldAlignment);

41
clang/test/SemaCXX/alignment-of-derived-class.cpp Normal file
View File

@ -0,0 +1,41 @@
// RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++11
// expected-no-diagnostics
// Test that the alignment of a empty direct base class is correctly
// inherited by the derived class.
struct A {
} __attribute__ ((aligned(16)));
static_assert(__alignof(A) == 16, "A should be aligned to 16 bytes");
struct B1 : public A {
};
static_assert(__alignof(B1) == 16, "B1 should be aligned to 16 bytes");
struct B2 : public A {
} __attribute__ ((aligned(2)));
static_assert(__alignof(B2) == 16, "B2 should be aligned to 16 bytes");
struct B3 : public A {
} __attribute__ ((aligned(4)));
static_assert(__alignof(B3) == 16, "B3 should be aligned to 16 bytes");
struct B4 : public A {
} __attribute__ ((aligned(8)));
static_assert(__alignof(B4) == 16, "B4 should be aligned to 16 bytes");
struct B5 : public A {
} __attribute__ ((aligned(16)));
static_assert(__alignof(B5) == 16, "B5 should be aligned to 16 bytes");
struct B6 : public A {
} __attribute__ ((aligned(32)));
static_assert(__alignof(B6) == 32, "B6 should be aligned to 32 bytes");