C++ PATCH to prevent bogus -Wint-in-bool-context warning (PR c++/79184)

[Marek Polacek]

This PR complains about -Wint-in-bool-context warning where it shouldn't.
Here, in "f<1 * 1>()" the MULT_EXPR isn't really in a boolean context, but we
warn anyway during overload resolution, when adding various template
candidates.  I believe the way to prevent this is to honor complain &
tf_warning which is what this patch does.  Does that seem reasonable or
is there a better way?

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2017-02-10  Marek Polacek  <pola...@redhat.com>

        PR c++/79184
        * cvt.c (ocp_convert): Add a sentinel against -Wint-in-bool-context
        if warnings shouldn't be given.

        * g++.dg/warn/Wint-in-bool-context-1.C: New.

diff --git gcc/cp/cvt.c gcc/cp/cvt.c
index ae9991a..5f4b5e3 100644
--- gcc/cp/cvt.c
+++ gcc/cp/cvt.c
@@ -798,7 +798,15 @@ ocp_convert (tree type, tree expr, int convtype, int flags,
             to the underlying type first.  */
          if (SCOPED_ENUM_P (intype) && (convtype & CONV_STATIC))
            e = build_nop (ENUM_UNDERLYING_TYPE (intype), e);
-         return cp_truthvalue_conversion (e);
+         if (complain & tf_warning)
+           return cp_truthvalue_conversion (e);
+         else
+           {
+             /* Prevent bogus -Wint-in-bool-context warnings coming
+                from c_common_truthvalue_conversion down the line.  */
+             warning_sentinel w (warn_int_in_bool_context);
+             return cp_truthvalue_conversion (e);
+           }
        }
 
       converted = convert_to_integer_maybe_fold (type, e, dofold);
diff --git gcc/testsuite/g++.dg/warn/Wint-in-bool-context-1.C 
gcc/testsuite/g++.dg/warn/Wint-in-bool-context-1.C
index e69de29..117eca4 100644
--- gcc/testsuite/g++.dg/warn/Wint-in-bool-context-1.C
+++ gcc/testsuite/g++.dg/warn/Wint-in-bool-context-1.C
@@ -0,0 +1,16 @@
+// PR c++/79184
+// { dg-do compile }
+// { dg-options "-Wint-in-bool-context" }
+
+enum { E = 2 };
+template <bool> void f(int) { }
+template <int> void f() {}
+
+int
+main ()
+{
+  f<1 * 1>(); // { dg-bogus "in boolean context" }
+  f<1 << 1>(); // { dg-bogus "in boolean context" }
+  f<1 ? 3 : 2>(); // { dg-bogus "in boolean context" }
+  f<E>(); // { dg-bogus "in boolean context" }
+}

        Marek