Explicitly permit undefined behavior in constant initializers for global

variables in C, in the cases where we can constant-fold it to a value
regardless (such as floating-point division by zero and signed integer
overflow). Strictly enforcing this rule breaks too much code.

llvm-svn: 254992

1 files changed, 4 insertions, 1 deletions

diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 33ea76ea74a..9996546a176 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -2891,7 +2891,10 @@ bool Expr::isConstantInitializer(ASTContext &Ctx, bool IsForRef,
     return cast<CXXDefaultInitExpr>(this)->getExpr()
       ->isConstantInitializer(Ctx, false, Culprit);
   }
-  if (isEvaluatable(Ctx))
+  // Allow certain forms of UB in constant initializers: signed integer
+  // overflow and floating-point division by zero. We'll give a warning on
+  // these, but they're common enough that we have to accept them.
+  if (isEvaluatable(Ctx, SE_AllowUndefinedBehavior))
     return true;
   if (Culprit)
     *Culprit = this;