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

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  <polacek@redhat.com>

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

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

OK.

On Tue, Jul 3, 2018 at 12:08 PM, Marek Polacek <polacek@redhat.com> wrote:
> 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  <polacek@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);
> +}