Improve -Wunreachable-code to provide a means to indicate code is intentionally marked dead via if((0)).

Taking a hint from -Wparentheses, use an extra '()' as a sigil that
a dead condition is intentionally dead.  For example:

  if ((0)) { dead }

When this sigil is found, do not emit a dead code warning.  When the
analysis sees:

  if (0)

it suggests inserting '()' as a Fix-It.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@205069 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 14 insertions, 1 deletions

diff --git a/lib/Sema/AnalysisBasedWarnings.cpp b/lib/Sema/AnalysisBasedWarnings.cpp
index efaf966562..75d7060e2d 100644
--- a/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/lib/Sema/AnalysisBasedWarnings.cpp
@@ -66,7 +66,9 @@ namespace {
     UnreachableCodeHandler(Sema &s) : S(s) {}
 
     void HandleUnreachable(reachable_code::UnreachableKind UK,
-                           SourceLocation L, SourceRange R1,
+                           SourceLocation L,
+                           SourceRange SilenceableCondVal,
+                           SourceRange R1,
                            SourceRange R2) override {
       unsigned diag = diag::warn_unreachable;
       switch (UK) {
@@ -84,6 +86,17 @@ namespace {
       }
 
       S.Diag(L, diag) << R1 << R2;
+      
+      SourceLocation Open = SilenceableCondVal.getBegin();
+      if (Open.isValid()) {
+        SourceLocation Close = SilenceableCondVal.getEnd();        
+        Close = S.PP.getLocForEndOfToken(Close);
+        if (Close.isValid()) {
+          S.Diag(Open, diag::note_unreachable_silence)
+            << FixItHint::CreateInsertion(Open, "/* DISABLES CODE */ (")
+            << FixItHint::CreateInsertion(Close, ")");
+        }
+      }
     }
   };
 }