[-Wunreachable-code] Treat constant globals as configuration values in unreachable code heuristics.

This one could possibly be refined even further; e.g. looking
at the initializer and see if it is truly a configuration value.

llvm-svn: 203283

1 files changed, 14 insertions, 2 deletions

diff --git a/clang/lib/Analysis/ReachableCode.cpp b/clang/lib/Analysis/ReachableCode.cpp
index f563cbdc593..47f8f2b90cd 100644
--- a/clang/lib/Analysis/ReachableCode.cpp
+++ b/clang/lib/Analysis/ReachableCode.cpp
@@ -194,8 +194,20 @@ static bool isConfigurationValue(const Stmt *S) {
   switch (S->getStmtClass()) {
     case Stmt::DeclRefExprClass: {
       const DeclRefExpr *DR = cast<DeclRefExpr>(S);
-      const EnumConstantDecl *ED = dyn_cast<EnumConstantDecl>(DR->getDecl());
-      return ED ? isConfigurationValue(ED->getInitExpr()) : false;
+      const ValueDecl *D = DR->getDecl();
+      if (const EnumConstantDecl *ED = dyn_cast<EnumConstantDecl>(D))
+        return ED ? isConfigurationValue(ED->getInitExpr()) : false;
+      if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
+        // As a heuristic, treat globals as configuration values.  Note
+        // that we only will get here if Sema evaluated this
+        // condition to a constant expression, which means the global
+        // had to be declared in a way to be a truly constant value.
+        // We could generalize this to local variables, but it isn't
+        // clear if those truly represent configuration values that
+        // gate unreachable code.
+        return !VD->hasLocalStorage();
+      }
+      return false;
     }
     case Stmt::IntegerLiteralClass:
       return isExpandedFromConfigurationMacro(S);