[1/2] c++: modules and non-dependent auto deduction

  The modules streaming code seems to rely on the invariant that a
TEMPLATE_DECL and its DECL_TEMPLATE_RESULT have the same TREE_TYPE.
But for a templated VAR_DECL with deduced non-dependent type, the two
TREE_TYPEs end up diverging: cp_finish_decl deduces the type of the
initializer ahead of time and updates the TREE_TYPE of the VAR_DECL, but
neglects to update the corresponding TEMPLATE_DECL as well, which leads
to a "conflicting global module declaration" error for each of the
__phase_alignment decls in the below testcase (and for the xtreme-header
testcases if we try including <barrier>).

This patch makes cp_finish_decl update the TREE_TYPE of the corresponding
TEMPLATE_DECL so that the invariant is maintained.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?

gcc/cp/ChangeLog:

	* decl.cc (cp_finish_decl): After updating the deduced type of a
	VAR_DECL, also update the corresponding TEMPLATE_DECL if there
	is one.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/auto-3.h: New test.
	* g++.dg/modules/auto-3_a.H: New test.
	* g++.dg/modules/auto-3_b.C: New test.
---
 gcc/cp/decl.cc                          |  6 ++++++
 gcc/testsuite/g++.dg/modules/auto-3.h   | 10 ++++++++++
 gcc/testsuite/g++.dg/modules/auto-3_a.H |  4 ++++
 gcc/testsuite/g++.dg/modules/auto-3_b.C |  4 ++++
 4 files changed, 24 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/modules/auto-3.h
 create mode 100644 gcc/testsuite/g++.dg/modules/auto-3_a.H
 create mode 100644 gcc/testsuite/g++.dg/modules/auto-3_b.C
  

On 9/20/22 15:54, Patrick Palka wrote:
> The modules streaming code seems to rely on the invariant that a
> TEMPLATE_DECL and its DECL_TEMPLATE_RESULT have the same TREE_TYPE.

It does indeed.

> But for a templated VAR_DECL with deduced non-dependent type, the two
> TREE_TYPEs end up diverging: cp_finish_decl deduces the type of the
> initializer ahead of time and updates the TREE_TYPE of the VAR_DECL, but
> neglects to update the corresponding TEMPLATE_DECL as well, which leads
> to a "conflicting global module declaration" error for each of the
> __phase_alignment decls in the below testcase (and for the xtreme-header
> testcases if we try including <barrier>).
> 
> This patch makes cp_finish_decl update the TREE_TYPE of the corresponding
> TEMPLATE_DECL so that the invariant is maintained >
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?

Ok, thanks


> 
> gcc/cp/ChangeLog:
> 
> 	* decl.cc (cp_finish_decl): After updating the deduced type of a
> 	VAR_DECL, also update the corresponding TEMPLATE_DECL if there
> 	is one.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/modules/auto-3.h: New test.
> 	* g++.dg/modules/auto-3_a.H: New test.
> 	* g++.dg/modules/auto-3_b.C: New test.
> ---
>   gcc/cp/decl.cc                          |  6 ++++++
>   gcc/testsuite/g++.dg/modules/auto-3.h   | 10 ++++++++++
>   gcc/testsuite/g++.dg/modules/auto-3_a.H |  4 ++++
>   gcc/testsuite/g++.dg/modules/auto-3_b.C |  4 ++++
>   4 files changed, 24 insertions(+)
>   create mode 100644 gcc/testsuite/g++.dg/modules/auto-3.h
>   create mode 100644 gcc/testsuite/g++.dg/modules/auto-3_a.H
>   create mode 100644 gcc/testsuite/g++.dg/modules/auto-3_b.C
> 
> diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> index 070f673c3a2..80467c19254 100644
> --- a/gcc/cp/decl.cc
> +++ b/gcc/cp/decl.cc
> @@ -8180,6 +8180,12 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p,
>   	  return;
>   	}
>         cp_apply_type_quals_to_decl (cp_type_quals (type), decl);
> +
> +      /* Update the type of the corresponding TEMPLATE_DECL to match.  */
> +      if (DECL_LANG_SPECIFIC (decl)
> +	  && DECL_TEMPLATE_INFO (decl)
> +	  && DECL_TEMPLATE_RESULT (DECL_TI_TEMPLATE (decl)) == decl)
> +	TREE_TYPE (DECL_TI_TEMPLATE (decl)) = type;
>       }
>   
>     if (ensure_literal_type_for_constexpr_object (decl) == error_mark_node)
> diff --git a/gcc/testsuite/g++.dg/modules/auto-3.h b/gcc/testsuite/g++.dg/modules/auto-3.h
> new file mode 100644
> index 00000000000..f129433cbcb
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/auto-3.h
> @@ -0,0 +1,10 @@
> +template<class>
> +struct __tree_barrier {
> +  static const auto __phase_alignment_1 = 0;
> +
> +  template<class>
> +  static const auto __phase_alignment_2 = 0;
> +};
> +
> +template<class>
> +inline auto __phase_alignment_3 = 0;
> diff --git a/gcc/testsuite/g++.dg/modules/auto-3_a.H b/gcc/testsuite/g++.dg/modules/auto-3_a.H
> new file mode 100644
> index 00000000000..25a7a73e73e
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/auto-3_a.H
> @@ -0,0 +1,4 @@
> +// { dg-additional-options "-fmodule-header" }
> +// { dg-module-cmi {} }
> +
> +#include "auto-3.h"
> diff --git a/gcc/testsuite/g++.dg/modules/auto-3_b.C b/gcc/testsuite/g++.dg/modules/auto-3_b.C
> new file mode 100644
> index 00000000000..03b6d46f476
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/auto-3_b.C
> @@ -0,0 +1,4 @@
> +// { dg-additional-options "-fmodules-ts -fno-module-lazy" }
> +
> +#include "auto-3.h"
> +import "auto-3_a.H";