[AST] Improve support of external layouts in `MicrosoftRecordLayoutBuilder`

Summary:
This patch fixes several small problems with external layouts support in
`MicrosoftRecordLayoutBuilder`:
- aligns properly the size of a struct that ends with a bit field. It was
  aligned on byte before, not on the size of the field, so the struct size was
  smaller than it should be;
- adjusts the struct size when injecting a vbptr in the case when there were no
  bases or fields allocated after the vbptr. Similarly, without the adjustment
  the struct was smaller than it should be;
- the same fix as above for the vfptr.
All these fixes affect the non-virtual size of a struct, so they are tested
through non-virtual inheritance.

Reviewers: rnk, zturner, rsmith

Reviewed By: rnk

Subscribers: jdoerfert, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D58544

llvm-svn: 356047

1 files changed, 21 insertions, 0 deletions

diff --git a/clang/test/CodeGenCXX/override-layout-virtual-base.cpp b/clang/test/CodeGenCXX/override-layout-virtual-base.cpp
new file mode 100644
index 00000000000..d9e7346737d
--- /dev/null
+++ b/clang/test/CodeGenCXX/override-layout-virtual-base.cpp
@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -w -triple=x86_64-pc-win32 -fms-compatibility -fdump-record-layouts-simple -foverride-record-layout=%S/Inputs/override-layout-virtual-base.layout %s | FileCheck %s
+
+struct S1 {
+  int a;
+};
+
+struct S2 : virtual S1 {
+  virtual void foo() {}
+};
+
+// CHECK: Type: struct S3
+// CHECK:   FieldOffsets: [128]
+struct S3 : S2 {
+  char b;
+};
+
+void use_structs() {
+  S1 s1s[sizeof(S1)];
+  S2 s2s[sizeof(S2)];
+  S3 s3s[sizeof(S3)];
+}