[Sema] Fix bug in TypeLocBuilder::pushImpl

The code in TypeLocBuilder::pushImpl wasn't correctly handling the case
where an element that has an 8-byte alignment was being pushed.

I plan to follow up with a patch to remove redundancies and simplify the
function.

rdar://problem/23838912

Differential Revision: http://reviews.llvm.org/D16843

llvm-svn: 261260

clang/lib/Sema/TypeLocBuilder.cpp

@@ -115,11 +115,39 @@ TypeLoc TypeLocBuilder::pushImpl(QualType T, size_t LocalSize, unsigned LocalAli
       NumBytesAtAlign4 += LocalSize;
     }
   } else if (LocalAlignment == 8) {
-    if (!NumBytesAtAlign8 && NumBytesAtAlign4 % 8 != 0) {
-      // No existing padding and misaligned members; add in 4 bytes padding
-      memmove(&Buffer[Index - 4], &Buffer[Index], NumBytesAtAlign4);
-      Index -= 4;
+    if (NumBytesAtAlign8 == 0) {
+      // We have not seen any 8-byte aligned element yet. We insert a padding
+      // only if the new Index is not 8-byte-aligned.
+      if ((Index - LocalSize) % 8 != 0) {
+        memmove(&Buffer[Index - 4], &Buffer[Index], NumBytesAtAlign4);
+        Index -= 4;
+      }
+    } else {
+      unsigned Padding = NumBytesAtAlign4 % 8;
+      if (Padding == 0) {
+        if (LocalSize % 8 == 0) {
+          // Everything is set: there's no padding and we don't need to add
+          // any.
+        } else {
+          assert(LocalSize % 8 == 4);
+          // No existing padding; add in 4 bytes padding
+          memmove(&Buffer[Index - 4], &Buffer[Index], NumBytesAtAlign4);
+          Index -= 4;
+        }
+      } else {
+        assert(Padding == 4);
+        if (LocalSize % 8 == 0) {
+          // Everything is set: there's 4 bytes padding and we don't need
+          // to add any.
+        } else {
+          assert(LocalSize % 8 == 4);
+          // There are 4 bytes padding, but we don't need any; remove it.
+          memmove(&Buffer[Index + 4], &Buffer[Index], NumBytesAtAlign4);
+          Index += 4;
+        }
+      }
     }
+
     // Forget about any padding.
     NumBytesAtAlign4 = 0;
     NumBytesAtAlign8 += LocalSize;

clang/test/SemaObjCXX/typeloc-data-alignment.mm

@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+// expected-no-diagnostics
+
+// Make sure this doesn't crash.
+
+@protocol P
+@end
+template <class T>
+id<P> foo(T) {
+  int i;
+  foo(i);
+}