[analyzer] Allow padding checker to traverse simple class hierarchies

The existing padding checker skips classes that have any base classes. 
This patch allows the checker to traverse very simple cases: 
classes that have no fields and have exactly one base class. 
This is important mostly in the case of array declarations.

Patch by Max Bernstein!

Test plan: make check-all

Differential revision: https://reviews.llvm.org/D53206

llvm-svn: 345558

1 files changed, 28 insertions, 0 deletions

diff --git a/clang/test/Analysis/padding_inherit.cpp b/clang/test/Analysis/padding_inherit.cpp
new file mode 100644
index 00000000000..2222c990a1d
--- /dev/null
+++ b/clang/test/Analysis/padding_inherit.cpp
@@ -0,0 +1,28 @@
+// RUN: %clang_analyze_cc1 -std=c++14 -analyzer-checker=optin.performance -analyzer-config optin.performance.Padding:AllowedPad=20 -verify %s
+
+// A class that has no fields and one base class should visit that base class
+// instead. Note that despite having excess padding of 2, this is flagged
+// because of its usage in an array of 100 elements below (`ais').
+// TODO: Add a note to the bug report with BugReport::addNote() to mention the
+// variable using the class and also mention what class is inherting from what.
+// expected-warning@+1{{Excessive padding in 'struct FakeIntSandwich'}}
+struct FakeIntSandwich {
+  char c1;
+  int i;
+  char c2;
+};
+
+struct AnotherIntSandwich : FakeIntSandwich { // no-warning
+};
+
+// But we don't yet support multiple base classes.
+struct IntSandwich {};
+struct TooManyBaseClasses : FakeIntSandwich, IntSandwich { // no-warning
+};
+
+AnotherIntSandwich ais[100];
+
+struct Empty {};
+struct DoubleEmpty : Empty { // no-warning
+    Empty e;
+};