Fix clang -Wimplicit-fallthrough warnings across llvm, NFC

This patch should not introduce any behavior changes. It consists of
mostly one of two changes:
1. Replacing fall through comments with the LLVM_FALLTHROUGH macro
2. Inserting 'break' before falling through into a case block consisting
   of only 'break'.

We were already using this warning with GCC, but its warning behaves
slightly differently. In this patch, the following differences are
relevant:
1. GCC recognizes comments that say "fall through" as annotations, clang
   doesn't
2. GCC doesn't warn on "case N: foo(); default: break;", clang does
3. GCC doesn't warn when the case contains a switch, but falls through
   the outer case.

I will enable the warning separately in a follow-up patch so that it can
be cleanly reverted if necessary.

Reviewers: alexfh, rsmith, lattner, rtrieu, EricWF, bollu

Differential Revision: https://reviews.llvm.org/D53950

llvm-svn: 345882

1 files changed, 1 insertions, 1 deletions

diff --git a/clang/lib/Index/USRGeneration.cpp b/clang/lib/Index/USRGeneration.cpp
index f7be0a90b0a..ae1fa1fbc80 100644
--- a/clang/lib/Index/USRGeneration.cpp
+++ b/clang/lib/Index/USRGeneration.cpp
@@ -942,7 +942,7 @@ void USRGenerator::VisitTemplateArgument(const TemplateArgument &Arg) {
 
   case TemplateArgument::TemplateExpansion:
     Out << 'P'; // pack expansion of...
-    // Fall through
+    LLVM_FALLTHROUGH;
   case TemplateArgument::Template:
     VisitTemplateName(Arg.getAsTemplateOrTemplatePattern());
     break;