Improve support of PDB as an external layout source

Summary:
This patch improves support of PDB as an external layout source
in the next cases:

- Multiple non-virtual inheritance from packed base classes. When using
  external layout, there's no need to align `NonVirtualSize` of a base class.
  It may cause an overlapping when the next base classes will be layouted
  (but there is a slightly different case in the test because I can't find
  a way to specify a base offset);
- Support of nameless structs and unions. There is no info about nameless child
  structs and unions in Microsoft cl-emitted PDBs. Instead all its fields
  are just treated as outer structure's (union's) fields. This also causes
  a fields overlapping, and makes it possible for unions to have fields located
  at a non-zero offset.

Reviewers: rsmith, zturner, rnk, mstorsjo, majnemer

Reviewed By: rnk

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D49871

llvm-svn: 338353

1 files changed, 16 insertions, 0 deletions

diff --git a/clang/test/CodeGenCXX/Inputs/override-layout-nameless-struct-union.layout b/clang/test/CodeGenCXX/Inputs/override-layout-nameless-struct-union.layout
new file mode 100644
index 00000000000..9eb4d244bd7
--- /dev/null
+++ b/clang/test/CodeGenCXX/Inputs/override-layout-nameless-struct-union.layout
@@ -0,0 +1,16 @@
+
+*** Dumping AST Record Layout
+Type: struct S
+
+Layout: <ASTRecordLayout
+  Size:64
+  Alignment:32
+  FieldOffsets: [0, 32, 32]>
+
+*** Dumping AST Record Layout
+Type: union U
+
+Layout: <ASTRecordLayout
+  Size:96
+  Alignment:32
+  FieldOffsets: [0, 0, 32, 64, 68, 73]>