From: Jason Merrill <jason@redhat.com>
Date: Fri, 9 May 2025 23:13:49 +0000 (-0400)
Subject: c++: -fimplicit-constexpr and modules
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9694bb129c0dbf54138d94caa28d692842fdc233;p=thirdparty%2Fgcc.git

c++: -fimplicit-constexpr and modules

Import didn't like differences in DECL_DECLARED_CONSTEXPR_P due to implicit
constexpr, breaking several g++.dg/modules tests; we should handle that
along with DECL_MAYBE_DELETED.  For which we need to stream the bit.

gcc/cp/ChangeLog:

	* module.cc (trees_out::lang_decl_bools): Stream implicit_constexpr.
	(trees_in::lang_decl_bools): Likewise.
	(trees_in::is_matching_decl): Check it.
---

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index e7782627a49..4f9c3788380 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -6024,7 +6024,7 @@ trees_out::lang_decl_bools (tree t, bits_out& bits)
       WB (lang->u.fn.has_dependent_explicit_spec_p);
       WB (lang->u.fn.immediate_fn_p);
       WB (lang->u.fn.maybe_deleted);
-      /* We do not stream lang->u.fn.implicit_constexpr.  */
+      WB (lang->u.fn.implicit_constexpr);
       WB (lang->u.fn.escalated_p);
       WB (lang->u.fn.xobj_func);
       goto lds_min;
@@ -6095,7 +6095,7 @@ trees_in::lang_decl_bools (tree t, bits_in& bits)
       RB (lang->u.fn.has_dependent_explicit_spec_p);
       RB (lang->u.fn.immediate_fn_p);
       RB (lang->u.fn.maybe_deleted);
-      /* We do not stream lang->u.fn.implicit_constexpr.  */
+      RB (lang->u.fn.implicit_constexpr);
       RB (lang->u.fn.escalated_p);
       RB (lang->u.fn.xobj_func);
       goto lds_min;
@@ -12193,13 +12193,23 @@ trees_in::is_matching_decl (tree existing, tree decl, bool is_typedef)
 
       /* Similarly if EXISTING has undeduced constexpr, but DECL's
 	 is already deduced.  */
-      if (DECL_MAYBE_DELETED (e_inner) && !DECL_MAYBE_DELETED (d_inner)
-	  && DECL_DECLARED_CONSTEXPR_P (d_inner))
-	DECL_DECLARED_CONSTEXPR_P (e_inner) = true;
-      else if (!DECL_MAYBE_DELETED (e_inner) && DECL_MAYBE_DELETED (d_inner))
-	/* Nothing to do.  */;
+      if (DECL_DECLARED_CONSTEXPR_P (e_inner)
+	  == DECL_DECLARED_CONSTEXPR_P (d_inner))
+	/* Already matches.  */;
+      else if (DECL_DECLARED_CONSTEXPR_P (d_inner)
+	       && (DECL_MAYBE_DELETED (e_inner)
+		   || decl_implicit_constexpr_p (d_inner)))
+	/* DECL was deduced, copy to EXISTING.  */
+	{
+	  DECL_DECLARED_CONSTEXPR_P (e_inner) = true;
+	  if (decl_implicit_constexpr_p (d_inner))
+	    DECL_LANG_SPECIFIC (e_inner)->u.fn.implicit_constexpr = true;
+	}
       else if (DECL_DECLARED_CONSTEXPR_P (e_inner)
-	       != DECL_DECLARED_CONSTEXPR_P (d_inner))
+	       && (DECL_MAYBE_DELETED (d_inner)
+		   || decl_implicit_constexpr_p (e_inner)))
+	/* EXISTING was deduced, leave it alone.  */;
+      else
 	{
 	  mismatch_msg = G_("conflicting %<constexpr%> for imported "
 			    "declaration %#qD");