Extend loplugin:unusedmember "layout heuristic" to base classes

With clang-cl on Windows, where CPPU_GCC3_ALIGN expands to nothing, there were
warnings about unsued Char1::c1 and Char2::c2 in cppu/source/uno/check.cxx
(which were suppressed on Linux thanks to CPPU_GCC3_ALIGN(T) making the plugin's
"layout heuristic" kick in for T).  But Char1 and Char2 are also (indirect)
bases of Char3, for which the heuristic kicks in thanks to a sizeof(Char3)
expression.  Extending the heuristic to base classes seems like a good
improvement anyway, and happens to make the unwanted warnings on Windows go
away.

Change-Id: I1fac3104aa7a1745ccf2f23972953eaacbd45104
Reviewed-on: https://gerrit.libreoffice.org/84927
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

2 files changed, 41 insertions, 7 deletions

diff --git a/compilerplugins/clang/test/unusedmember.cxx b/compilerplugins/clang/test/unusedmember.cxx
index 84802414f47b..d40d87b2d29b 100644
--- a/compilerplugins/clang/test/unusedmember.cxx
+++ b/compilerplugins/clang/test/unusedmember.cxx
@@ -145,6 +145,25 @@ void f()
 }
 }
 
+namespace Bases
+{
+namespace
+{
+struct S1
+{
+    int i1;
+};
+struct S2 : S1
+{
+    int i2;
+};
+struct S3 : S2
+{
+};
+}
+void f() { (void)sizeof(S3); }
+}
+
 int main()
 {
     (void)&Enum::f;
@@ -153,6 +172,7 @@ int main()
     (void)&UnusedDataMember::f;
     (void)&Alignof::f;
     (void)&Aligned::f;
+    (void)&Bases::f;
 }
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */
diff --git a/compilerplugins/clang/unusedmember.cxx b/compilerplugins/clang/unusedmember.cxx
index c8a536c79f53..ed7096ecbc1e 100644
--- a/compilerplugins/clang/unusedmember.cxx
+++ b/compilerplugins/clang/unusedmember.cxx
@@ -241,11 +241,7 @@ public:
         {
             return true;
         }
-        layout_.insert(expr->getTypeSourceInfo()
-                           ->getType()
-                           ->castAs<RecordType>()
-                           ->getDecl()
-                           ->getCanonicalDecl());
+        recordRecordDeclAndBases(expr->getTypeSourceInfo()->getType()->castAs<RecordType>());
         return true;
     }
 
@@ -281,7 +277,7 @@ public:
         }
         if (auto const t1 = t->getAs<RecordType>())
         {
-            layout_.insert(t1->getDecl()->getCanonicalDecl());
+            recordRecordDeclAndBases(t1);
         }
         return true;
     }
@@ -385,6 +381,24 @@ private:
         return t.isTrivialType(compiler.getASTContext()) || isWarnUnusedType(t);
     }
 
+    void recordRecordDeclAndBases(RecordType const* type)
+    {
+        auto const d1 = type->getDecl();
+        if (!layout_.insert(d1->getCanonicalDecl()).second)
+        {
+            return;
+        }
+        if (auto const d2 = dyn_cast_or_null<CXXRecordDecl>(d1->getDefinition()))
+        {
+            for (auto i = d2->bases_begin(); i != d2->bases_end(); ++i)
+            {
+                recordRecordDeclAndBases(i->getType()->castAs<RecordType>());
+            }
+            //TODO: doesn't iterate vbases, but presence of such would run counter to the layout
+            // heuristic anyway
+        }
+    }
+
     void recordCastedRecordDecl(QualType type)
     {
         for (auto t = type;;)
@@ -396,7 +410,7 @@ private:
             }
             if (auto const t1 = t->getAs<RecordType>())
             {
-                layout_.insert(t1->getDecl()->getCanonicalDecl());
+                recordRecordDeclAndBases(t1);
             }
             break;
         }