Enable control flow pruning of float overflow warnings.

Like other conversion warnings, allow float overflow warnings to be disabled
in known dead paths of template instantiation.  This often occurs when a
template template type is a numeric type and the template will check the
range of the numeric type before performing the conversion.

llvm-svn: 332310

2 files changed, 36 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 74ecf5fef79..f8ab8a6b385 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -9673,7 +9673,8 @@ static void DiagnoseFloatingImpCast(Sema &S, Expr *E, QualType T,
     return DiagnoseImpCast(
         S, E, T, CContext,
         IsLiteral ? diag::warn_impcast_literal_float_to_integer_out_of_range
-                  : diag::warn_impcast_float_to_integer_out_of_range);
+                  : diag::warn_impcast_float_to_integer_out_of_range,
+        PruneWarnings);
 
   unsigned DiagID = 0;
   if (IsLiteral) {
diff --git a/clang/test/SemaCXX/warn-float-conversion.cpp b/clang/test/SemaCXX/warn-float-conversion.cpp
index 2e89acb3d68..a3d178622c7 100644
--- a/clang/test/SemaCXX/warn-float-conversion.cpp
+++ b/clang/test/SemaCXX/warn-float-conversion.cpp
@@ -89,4 +89,38 @@ void TestOverflow() {
 
   char e = 1.0 / 0.0;  // expected-warning{{implicit conversion of out of range value from 'double' to 'char' is undefined}}
 }
+
+
+template <typename T>
+class Check {
+ public:
+  static constexpr bool Safe();
+};
+
+template<>
+constexpr bool Check<char>::Safe() { return false; }
+
+template<>
+constexpr bool Check<float>::Safe() { return true; }
+
+template <typename T>
+T run1(T t) {
+  const float ret = 800;
+  return ret;  // expected-warning {{implicit conversion of out of range value from 'const float' to 'char' is undefined}}
+}
+
+template <typename T>
+T run2(T t) {
+  const float ret = 800;
+  if (Check<T>::Safe())
+    return ret;
+  else
+    return t;
+}
+
+void test() {
+  float a = run1(a) + run2(a);
+  char b = run1(b) + run2(b);  // expected-note {{in instantiation of function template specialization 'run1<char>' requested here}}
+}
+
 #endif  // OVERFLOW