r186370 - Fix alignment of class derived from empty class.
Eli Friedman
eli.friedman at gmail.com
Mon Jul 15 17:21:28 PDT 2013
Author: efriedma
Date: Mon Jul 15 19:21:28 2013
New Revision: 186370
URL: http://llvm.org/viewvc/llvm-project?rev=186370&view=rev
Log:
Fix alignment of class derived from empty class.
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.
Added:
cfe/trunk/test/SemaCXX/alignment-of-derived-class.cpp
Modified:
cfe/trunk/lib/AST/RecordLayoutBuilder.cpp
Modified: cfe/trunk/lib/AST/RecordLayoutBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/RecordLayoutBuilder.cpp?rev=186370&r1=186369&r2=186370&view=diff
==============================================================================
--- cfe/trunk/lib/AST/RecordLayoutBuilder.cpp (original)
+++ cfe/trunk/lib/AST/RecordLayoutBuilder.cpp Mon Jul 15 19:21:28 2013
@@ -1532,18 +1532,19 @@ CharUnits RecordLayoutBuilder::LayoutBas
}
}
+ 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);
Added: cfe/trunk/test/SemaCXX/alignment-of-derived-class.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/alignment-of-derived-class.cpp?rev=186370&view=auto
==============================================================================
--- cfe/trunk/test/SemaCXX/alignment-of-derived-class.cpp (added)
+++ cfe/trunk/test/SemaCXX/alignment-of-derived-class.cpp Mon Jul 15 19:21:28 2013
@@ -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");
+
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