[PATCH] D14980: PR18513: make gcc compatible layout for bit-fields with explicit aligned attribute

[Dmitry Polukhin via cfe-commits]

DmitryPolukhin created this revision.
DmitryPolukhin added a reviewer: rjmccall.
DmitryPolukhin added a subscriber: cfe-commits.

Fix binary compatibility issue with GCC.

http://reviews.llvm.org/D14980

Files:
  lib/AST/RecordLayoutBuilder.cpp
  test/Sema/bitfield-layout.c

Index: test/Sema/bitfield-layout.c
===================================================================
--- test/Sema/bitfield-layout.c
+++ test/Sema/bitfield-layout.c
@@ -1,8 +1,13 @@
 // RUN: %clang_cc1 %s -fsyntax-only -verify -triple=i686-apple-darwin9
 // expected-no-diagnostics
+#include <stddef.h>
 
-#define CHECK_SIZE(kind, name, size) extern int name##1[sizeof(kind name) == size ? 1 : -1];
-#define CHECK_ALIGN(kind, name, size) extern int name##2[__alignof(kind name) == size ? 1 : -1];
+#define CHECK_SIZE(kind, name, size) \
+  extern int name##1[sizeof(kind name) == size ? 1 : -1];
+#define CHECK_ALIGN(kind, name, size) \
+  extern int name##2[__alignof(kind name) == size ? 1 : -1];
+#define CHECK_OFFSET(kind, name, member, offset) \
+  extern int name##2[offsetof(kind name, member) == offset ? 1 : -1];
 
 // Zero-width bit-fields
 struct a {char x; int : 0; char y;};
@@ -56,3 +61,35 @@
 CHECK_SIZE(struct, s0, 0x32100008)
 CHECK_ALIGN(struct, s0, 4)
 
+// Bit-field with explicit align bigger than normal.
+struct g0 {
+  char a;
+  __attribute__((aligned(16))) int b : 1;
+  char c;
+};
+
+CHECK_SIZE(struct, g0, 32);
+CHECK_ALIGN(struct, g0, 16);
+CHECK_OFFSET(struct, g0, c, 17);
+
+// Bit-field with explicit align smaller than normal.
+struct g1 {
+  char a;
+  __attribute__((aligned(2))) int b : 1;
+  char c;
+};
+
+CHECK_SIZE(struct, g1, 4);
+CHECK_ALIGN(struct, g1, 4);
+CHECK_OFFSET(struct, g1, c, 3);
+
+// Same as above but without explicit align.
+struct g2 {
+  char a;
+  int b : 1;
+  char c;
+};
+
+CHECK_SIZE(struct, g2, 4);
+CHECK_ALIGN(struct, g2, 4);
+CHECK_OFFSET(struct, g2, c, 2);
Index: lib/AST/RecordLayoutBuilder.cpp
===================================================================
--- lib/AST/RecordLayoutBuilder.cpp
+++ lib/AST/RecordLayoutBuilder.cpp
@@ -1552,7 +1552,8 @@
     FieldAlign = 1;
 
   // But, if there's an 'aligned' attribute on the field, honor that.
-  if (unsigned ExplicitFieldAlign = D->getMaxAlignment()) {
+  unsigned ExplicitFieldAlign = D->getMaxAlignment();
+  if (ExplicitFieldAlign) {
     FieldAlign = std::max(FieldAlign, ExplicitFieldAlign);
     UnpackedFieldAlign = std::max(UnpackedFieldAlign, ExplicitFieldAlign);
   }
@@ -1601,10 +1602,12 @@
         (AllowPadding &&
          (FieldOffset & (FieldAlign-1)) + FieldSize > TypeSize)) {
       FieldOffset = llvm::RoundUpToAlignment(FieldOffset, FieldAlign);
-    }
+    } else if (ExplicitFieldAlign)
+      FieldOffset = llvm::RoundUpToAlignment(FieldOffset, ExplicitFieldAlign);
 
     // Repeat the computation for diagnostic purposes.
     if (FieldSize == 0 ||
+        ExplicitFieldAlign ||
         (AllowPadding &&
          (UnpackedFieldOffset & (UnpackedFieldAlign-1)) + FieldSize > TypeSize))
       UnpackedFieldOffset = llvm::RoundUpToAlignment(UnpackedFieldOffset,


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