C++ PATCH for c++/86201, diagnostic routines re-entered crash

[Marek Polacek]

This is an ICE of kind "Error reporting routines re-entered".  From the PR:

The problem here is that we report the missing return value:
 9224         permerror (input_location, "return-statement with no value, in "
 9225                    "function returning %qT", valtype);
but permerror will end up calling print_instantiation_full_context, which ends
up calling dump_template_bindings and then tsubst -> tsubst_copy_and_build ->
build_functional_cast -> ... -> ocp_convert which has (complain is tf_none)
 829           if (complain & tf_warning)
 830             return cp_truthvalue_conversion (e);
 831           else
 832             {
 833               /* Prevent bogus -Wint-in-bool-context warnings coming
 834                  from c_common_truthvalue_conversion down the line.  */
 835               warning_sentinel w (warn_int_in_bool_context);
 836               return cp_truthvalue_conversion (e);
 837             }
So we call cp_truthvalue_conversion -> c_common_truthvalue_conversion ->
build_binary_op which only calls cp_build_binary_op but with
tf_warning_or_error.  So even though the warning
 4736       if ((complain & tf_warning)
 4737           && (FLOAT_TYPE_P (type0) || FLOAT_TYPE_P (type1)))
 4738         warning (OPT_Wfloat_equal,
 4739                  "comparing floating point with == or != is unsafe");
is properly guarded, we still re-enter the diagnostic routines.

But since we're parsing decltype we can check c_inhibit_evaluation_warnings
which means we won't call warning().

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

2018-07-03  Marek Polacek  <pola...@redhat.com>

        PR c++/86201
        * typeck.c (cp_build_binary_op): Check c_inhibit_evaluation_warnings.

        * g++.dg/diagnostic/pr86201.C: New test.

diff --git gcc/cp/typeck.c gcc/cp/typeck.c
index 3a4f1cdf479..ea4ce9649cd 100644
--- gcc/cp/typeck.c
+++ gcc/cp/typeck.c
@@ -4734,6 +4734,7 @@ cp_build_binary_op (location_t location,
       if (code0 == VECTOR_TYPE && code1 == VECTOR_TYPE)
        goto vector_compare;
       if ((complain & tf_warning)
+         && c_inhibit_evaluation_warnings == 0
          && (FLOAT_TYPE_P (type0) || FLOAT_TYPE_P (type1)))
        warning (OPT_Wfloat_equal,
                 "comparing floating point with == or != is unsafe");
diff --git gcc/testsuite/g++.dg/diagnostic/pr86201.C 
gcc/testsuite/g++.dg/diagnostic/pr86201.C
index e69de29bb2d..e7019c22d95 100644
--- gcc/testsuite/g++.dg/diagnostic/pr86201.C
+++ gcc/testsuite/g++.dg/diagnostic/pr86201.C
@@ -0,0 +1,12 @@
+// PR c++/86201
+// { dg-do compile { target c++11 } }
+
+template <class U, class V>
+auto fn1 (V&& v) -> decltype(U(v))
+{
+  return; // { dg-error "return-statement with no value" }
+}
+void fn2 ()
+{
+  fn1<bool>(1.0);
+}