From: Fariborz Jahanian <fjahanian@apple.com>
Date: Wed, 2 Feb 2011 19:36:18 +0000 (+0000)
Subject: For gcc compatibility, size of a class which is zero
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=adf082e829eb71871b6043009888df3b79055dba;p=clang

For gcc compatibility, size of a class which is zero
but has non-empty data fields, such as array of zero length,
remains zero.
// rdar://8945175


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@124741 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/AST/RecordLayoutBuilder.cpp b/lib/AST/RecordLayoutBuilder.cpp
index 730ec21358..a871c3d176 100644
--- a/lib/AST/RecordLayoutBuilder.cpp
+++ b/lib/AST/RecordLayoutBuilder.cpp
@@ -1469,8 +1469,17 @@ void RecordLayoutBuilder::LayoutField(const FieldDecl *D) {
 
 void RecordLayoutBuilder::FinishLayout(const NamedDecl *D) {
   // In C++, records cannot be of size 0.
-  if (Context.getLangOptions().CPlusPlus && Size == 0)
-    Size = 8;
+  if (Context.getLangOptions().CPlusPlus && Size == 0) {
+    if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D)) {
+      // Compatibility with gcc requires a class (pod or non-pod)
+      // which is not empty but of size 0; such as having fields of
+      // array of zero-length, remains of Size 0
+      if (RD->isEmpty())
+        Size = 8;
+    }
+    else
+      Size = 8;
+  }
   // Finally, round the size of the record up to the alignment of the
   // record itself.
   uint64_t UnpaddedSize = Size - UnfilledBitsInLastByte;
diff --git a/test/CodeGenCXX/non-empty-class-size-zero.cpp b/test/CodeGenCXX/non-empty-class-size-zero.cpp
new file mode 100644
index 0000000000..810717bb50
--- /dev/null
+++ b/test/CodeGenCXX/non-empty-class-size-zero.cpp
@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -emit-llvm -o - %s | FileCheck %s
+// rdar://8945175
+
+struct X { 
+  int array[0]; 
+  int array1[0]; 
+  int array2[0]; 
+  X();
+  ~X();
+};
+
+struct Y {
+  int first;
+  X padding;
+  int second;
+};
+
+int main() {
+// CHECK: store i32 0, i32* [[RETVAL:%.*]]
+  return sizeof(Y) -8 ;
+}