C++ PATCH for c++/89612 - ICE with member friend template with noexcept

[Jason Merrill]

On 3/28/19 2:59 PM, Marek Polacek wrote:
> On Thu, Mar 21, 2019 at 04:00:41PM -0400, Jason Merrill wrote:
>> On 3/19/19 11:45 AM, Marek Polacek wrote:
>>> On Thu, Mar 14, 2019 at 04:22:41PM -0400, Jason Merrill wrote:
>>>> On 3/7/19 4:52 PM, Marek Polacek wrote:
>>>>> This was one of those PRs where the more you poke, the more ICEs turn up.
>>>>> This patch fixes the ones I could find.  The original problem was that
>>>>> maybe_instantiate_noexcept got a TEMPLATE_DECL created for the member
>>>>> friend template in do_friend.  Its noexcept-specification was deferred,
>>>>> so we went to the block with push_access_scope, but that crashes on a
>>>>> TEMPLATE_DECL.  One approach could be to somehow not defer noexcept-specs
>>>>> for friend templates, I guess, but I didn't want to do that.
>>
>>>> How does it make sense to instantiate the noexcept-specifier of a template?
>>>> We should only get there for fully-instantiated function decls.
>>>
>>> Hmm, but duplicate_decls calls check_redeclaration_exception_specification even
>>> for DECL_FUNCTION_TEMPLATE_Ps.
>>> ...
>>> Note the crash happens in tsubst_friend_function.  I wouldn't know when to
>>> check the noexcept-specifier of such a TEMPLATE_DECL for a template friend
>>> if not there.
>>
>> Hmm, true, I guess we do need to do a partial instantiation of the
>> noexcept-specifier in order to compare it.
> 
> *nod*
> 
>>> That broke in register_parameter_specializations but we don't need this
>>> code anyway, so let's do away with it -- the current_class_{ref,ptr}
>>> code is enough to fix the PR that register_parameter_specializations was
>>> introduced for.
>>
>> What about uses of non-'this' parameters in the noexcept-specification?
>>
>> template <typename T>
>> struct C {
>>    template <int N>
>>    friend void foo(T t) noexcept(sizeof(decltype(t)) > 1);
>> };
>>
>> template <int N>
>> void foo(int i) noexcept { }
>>
>> C<int> c;
> 
> Still works.  I extended the test to see if we detect the scenario when the
> noexcept-specifiers don't match, and we do.  It's noexcept39.C.
> 
>>>>> Lastly, I found an invalid testcase that was breaking because a template code
>>>>> leaked to constexpr functions.  This I fixed similarly to the recent explicit
>>>>> PR fix (r269131).
>>>>
>>>> This spot should probably also use build_converted_constant_expr.
>>>
>>> Ok, I'll address this.
>>
>> I'm finding this repeated pattern awkward.  Earlier you changed
>> check_narrowing to use maybe_constant_value instead of
>> fold_non_dependent_expr, but perhaps whatever that fixed should have been
>> fixed instead with a processing_template_decl_sentinel in the enclosing code
>> that already instantiated the expression.  That ought to avoid any need to
>> change this spot or r269131.
> 
> So this also came up in the other patch.  Why don't I drop this part (and the
> noexcept1.C test) and open a new PR for this issue, so that we don't conflate
> two problems?  The following patch fixes the original issue.
> 
> Bootstrapped/regtested on x86_64-linux, ok for trunk?

OK.

Jason

> 
> 2019-03-28  Marek Polacek  <polacek@redhat.com>
> 
> 	PR c++/89612 - ICE with member friend template with noexcept.
> 	* pt.c (maybe_instantiate_noexcept): For function templates, use their
> 	template result (function decl).  Don't set up local specializations.
> 	Temporarily turn on processing_template_decl.  Update the template type
> 	too.
> 
> 	* g++.dg/cpp0x/noexcept38.C: New test.
> 	* g++.dg/cpp0x/noexcept39.C: New test.
> 	* g++.dg/cpp1z/noexcept-type21.C: New test.
> 
> diff --git gcc/cp/pt.c gcc/cp/pt.c
> index 05d5371d8a6..fa30a7f00c8 100644
> --- gcc/cp/pt.c
> +++ gcc/cp/pt.c
> @@ -24192,6 +24192,17 @@ maybe_instantiate_noexcept (tree fn, tsubst_flags_t complain)
>   
>     if (DECL_CLONED_FUNCTION_P (fn))
>       fn = DECL_CLONED_FUNCTION (fn);
> +
> +  tree orig_fn = NULL_TREE;
> +  /* For a member friend template we can get a TEMPLATE_DECL.  Let's use
> +     its FUNCTION_DECL for the rest of this function -- push_access_scope
> +     doesn't accept TEMPLATE_DECLs.  */
> +  if (DECL_FUNCTION_TEMPLATE_P (fn))
> +    {
> +      orig_fn = fn;
> +      fn = DECL_TEMPLATE_RESULT (fn);
> +    }
> +
>     fntype = TREE_TYPE (fn);
>     spec = TYPE_RAISES_EXCEPTIONS (fntype);
>   
> @@ -24228,37 +24239,41 @@ maybe_instantiate_noexcept (tree fn, tsubst_flags_t complain)
>   	  push_deferring_access_checks (dk_no_deferred);
>   	  input_location = DECL_SOURCE_LOCATION (fn);
>   
> -	  /* A new stack interferes with pop_access_scope.  */
> -	  {
> -	    /* Set up the list of local specializations.  */
> -	    local_specialization_stack lss (lss_copy);
> -
> -	    tree save_ccp = current_class_ptr;
> -	    tree save_ccr = current_class_ref;
> -	    /* If needed, set current_class_ptr for the benefit of
> -	       tsubst_copy/PARM_DECL.  */
> -	    tree tdecl = DECL_TEMPLATE_RESULT (DECL_TI_TEMPLATE (fn));
> -	    if (DECL_NONSTATIC_MEMBER_FUNCTION_P (tdecl))
> -	      {
> -		tree this_parm = DECL_ARGUMENTS (tdecl);
> -		current_class_ptr = NULL_TREE;
> -		current_class_ref = cp_build_fold_indirect_ref (this_parm);
> -		current_class_ptr = this_parm;
> -	      }
> +	  tree save_ccp = current_class_ptr;
> +	  tree save_ccr = current_class_ref;
> +	  /* If needed, set current_class_ptr for the benefit of
> +	     tsubst_copy/PARM_DECL.  */
> +	  tree tdecl = DECL_TEMPLATE_RESULT (DECL_TI_TEMPLATE (fn));
> +	  if (DECL_NONSTATIC_MEMBER_FUNCTION_P (tdecl))
> +	    {
> +	      tree this_parm = DECL_ARGUMENTS (tdecl);
> +	      current_class_ptr = NULL_TREE;
> +	      current_class_ref = cp_build_fold_indirect_ref (this_parm);
> +	      current_class_ptr = this_parm;
> +	    }
>   
> -	    /* Create substitution entries for the parameters.  */
> -	    register_parameter_specializations (tdecl, fn);
> +	  /* If this function is represented by a TEMPLATE_DECL, then
> +	     the deferred noexcept-specification might still contain
> +	     dependent types, even after substitution.  And we need the
> +	     dependency check functions to work in build_noexcept_spec.  */
> +	  if (orig_fn)
> +	    ++processing_template_decl;
>   
> -	    /* Do deferred instantiation of the noexcept-specifier.  */
> -	    noex = tsubst_copy_and_build (DEFERRED_NOEXCEPT_PATTERN (noex),
> -					  DEFERRED_NOEXCEPT_ARGS (noex),
> -					  tf_warning_or_error, fn,
> -					  /*function_p=*/false,
> -					  /*i_c_e_p=*/true);
> -	    current_class_ptr = save_ccp;
> -	    current_class_ref = save_ccr;
> -	    spec = build_noexcept_spec (noex, tf_warning_or_error);
> -	  }
> +	  /* Do deferred instantiation of the noexcept-specifier.  */
> +	  noex = tsubst_copy_and_build (DEFERRED_NOEXCEPT_PATTERN (noex),
> +					DEFERRED_NOEXCEPT_ARGS (noex),
> +					tf_warning_or_error, fn,
> +					/*function_p=*/false,
> +					/*i_c_e_p=*/true);
> +
> +	  current_class_ptr = save_ccp;
> +	  current_class_ref = save_ccr;
> +
> +	  /* Build up the noexcept-specification.  */
> +	  spec = build_noexcept_spec (noex, tf_warning_or_error);
> +
> +	  if (orig_fn)
> +	    --processing_template_decl;
>   
>   	  pop_deferring_access_checks ();
>   	  pop_access_scope (fn);
> @@ -24278,6 +24293,8 @@ maybe_instantiate_noexcept (tree fn, tsubst_flags_t complain)
>   	}
>   
>         TREE_TYPE (fn) = build_exception_variant (fntype, spec);
> +      if (orig_fn)
> +	TREE_TYPE (orig_fn) = TREE_TYPE (fn);
>       }
>   
>     FOR_EACH_CLONE (clone, fn)
> diff --git gcc/testsuite/g++.dg/cpp0x/noexcept38.C gcc/testsuite/g++.dg/cpp0x/noexcept38.C
> new file mode 100644
> index 00000000000..ecab59df694
> --- /dev/null
> +++ gcc/testsuite/g++.dg/cpp0x/noexcept38.C
> @@ -0,0 +1,19 @@
> +// PR c++/89612
> +// { dg-do compile { target c++11 } }
> +
> +template <typename>
> +struct C {
> +  template <int N>
> +  friend int foo() noexcept(N);
> +
> +  template <int N>
> +  friend int foo2() noexcept(N); // { dg-error "different exception" }
> +};
> +
> +template <int N>
> +int foo() noexcept(N);
> +
> +template <int N>
> +int foo2() noexcept(N + 1);
> +
> +C<int> c;
> diff --git gcc/testsuite/g++.dg/cpp0x/noexcept39.C gcc/testsuite/g++.dg/cpp0x/noexcept39.C
> new file mode 100644
> index 00000000000..fbebbed5e4c
> --- /dev/null
> +++ gcc/testsuite/g++.dg/cpp0x/noexcept39.C
> @@ -0,0 +1,19 @@
> +// PR c++/89612
> +// { dg-do compile { target c++11 } }
> +
> +template <typename T>
> +struct C {
> +  template <int N>
> +  friend void foo(T t) noexcept(sizeof(decltype(t)) > 1);
> +
> +  template <int N>
> +  friend void foo2(T t) noexcept(sizeof(decltype(t)) < 1); // { dg-error "different exception" }
> +};
> +
> +template <int N>
> +void foo(int i) noexcept { }
> +
> +template <int N>
> +void foo2(int i) noexcept { }
> +
> +C<int> c;
> diff --git gcc/testsuite/g++.dg/cpp1z/noexcept-type21.C gcc/testsuite/g++.dg/cpp1z/noexcept-type21.C
> new file mode 100644
> index 00000000000..d0a61d95e87
> --- /dev/null
> +++ gcc/testsuite/g++.dg/cpp1z/noexcept-type21.C
> @@ -0,0 +1,16 @@
> +// PR c++/89612
> +// { dg-do compile { target c++17 } }
> +
> +template <typename a> using b = typename a ::c;
> +template <typename> bool d;
> +template <typename, typename> struct e {
> +  template <typename f, typename g> e(f, g) {}
> +  template <typename h, typename i, typename j>
> +  friend auto k(h &&, const j &, i &&) noexcept(d<b<h>, h> &&d<b<i>, i>);
> +};
> +template <typename l, typename m> e(l, m)->e<l, m>;
> +template <typename l, typename m, typename j>
> +auto k(l &&, const j &, m &&) noexcept(d<b<l>, l> &&d<b<m>, m>);
> +int main() {
> +  e(0, [] {});
> +}
>