Compatibility macro detection for the -Wimplicit-fallthrough diagnostic.

Summary:
When issuing a diagnostic message for the -Wimplicit-fallthrough diagnostics, always try to find the latest macro, defined at the point of fallthrough, which is immediately expanded to "[[clang::fallthrough]]", and use it's name instead of the actual sequence.

Known issues: 
  * uses PP.getSpelling() to compare macro definition with a string (anyone can suggest a convenient way to fill a token array, or maybe lex it in runtime?);
  * this can be generalized and used in other similar cases, any ideas where it should reside then?

Reviewers: doug.gregor, rsmith

Reviewed By: rsmith

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D50

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@164858 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 12 insertions, 0 deletions

diff --git a/lib/Lex/MacroInfo.cpp b/lib/Lex/MacroInfo.cpp
index 7a4964f7d2..ffe31f24d3 100644
--- a/lib/Lex/MacroInfo.cpp
+++ b/lib/Lex/MacroInfo.cpp
@@ -58,6 +58,18 @@ MacroInfo::MacroInfo(const MacroInfo &MI, llvm::BumpPtrAllocator &PPAllocator)
   setArgumentList(MI.ArgumentList, MI.NumArguments, PPAllocator);
 }
 
+const MacroInfo *MacroInfo::findDefinitionAtLoc(SourceLocation L,
+                                                SourceManager &SM) const {
+  assert(L.isValid() && "SourceLocation is invalid.");
+  for (const MacroInfo *MI = this; MI; MI = MI->PreviousDefinition) {
+    if (MI->Location.isInvalid() ||  // For macros defined on the command line.
+        SM.isBeforeInTranslationUnit(MI->Location, L))
+      return (MI->UndefLocation.isInvalid() ||
+              SM.isBeforeInTranslationUnit(L, MI->UndefLocation)) ? MI : NULL;
+  }
+  return NULL;
+}
+
 unsigned MacroInfo::getDefinitionLengthSlow(SourceManager &SM) const {
   assert(!IsDefinitionLengthCached);
   IsDefinitionLengthCached = true;