[gcc r13-3337] c++ modules: streaming constexpr_fundef [PR101449]

[gcc r13-3337] c++ modules: streaming constexpr_fundef [PR101449]

[Patrick Palka]

https://gcc.gnu.org/g:3bd5d9a28e1ce4d1615902397b5ad50909839d6d

commit r13-3337-g3bd5d9a28e1ce4d1615902397b5ad50909839d6d
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon Oct 17 11:14:36 2022 -0400

    c++ modules: streaming constexpr_fundef [PR101449]
    
    It looks like we currently avoid streaming the RESULT_DECL and PARM_DECLs
    of a constexpr_fundef entry under the assumption that they're just copies
    of the DECL_RESULT and DECL_ARGUMENTS of the FUNCTION_DECL.  Thus we can
    just make new copies of DECL_RESULT and DECL_ARGUMENTS on stream in rather
    than separately streaming them.
    
    But the FUNCTION_DECL's DECL_RESULT and DECL_ARGUMENTS eventually get
    genericized, whereas the constexpr_fundef entry consists of a copy of the
    FUNCTION_DECL's pre-GENERIC trees.  And notably during genericization we
    lower invisref parms (which entails changing their TREE_TYPE and setting
    DECL_BY_REFERENCE), the lowered form of which the constexpr evaluator
    doesn't expect to see, and so this copying approach causes us to ICE for
    the below testcase.
    
    This patch fixes this by faithfully streaming the RESULT_DECL and
    PARM_DECLs of a constexpr_fundef entry, which seems to just work.
    
    Nathan says[1]: Hm, the reason for the complexity was that I wanted to
    recreate the tree graph where the fndecl came from one TU and the defn
    came from another one -- we need the definition to refer to argument
    decls from the already-read decl.  However, it seems that for constexpr
    fns here, that is not needed, resulting in a significant simplification.
    
    [1]: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/603662.html
    
            PR c++/101449
    
    gcc/cp/ChangeLog:
    
            * module.cc (trees_out::write_function_def): Stream the
            parms and result of the constexpr_fundef entry.
            (trees_in::read_function_def): Likewise.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/modules/cexpr-3_a.C: New test.
            * g++.dg/modules/cexpr-3_b.C: New test.

Diff:
---
 gcc/cp/module.cc                         | 59 +++++---------------------------
 gcc/testsuite/g++.dg/modules/cexpr-3_a.C | 14 ++++++++
 gcc/testsuite/g++.dg/modules/cexpr-3_b.C |  7 ++++
 3 files changed, 29 insertions(+), 51 deletions(-)

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 7ffeefa7c1f..999ff3faafc 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -11553,34 +11553,13 @@ trees_out::write_function_def (tree decl)
   tree_node (DECL_FRIEND_CONTEXT (decl));
 
   constexpr_fundef *cexpr = retrieve_constexpr_fundef (decl);
-  int tag = 0;
-  if (cexpr)
-    {
-      if (cexpr->result == error_mark_node)
-	/* We'll stream the RESULT_DECL naturally during the
-	   serialization.  We never need to fish it back again, so
-	   that's ok.  */
-	tag = 0;
-      else
-	tag = insert (cexpr->result);
-    }
+
   if (streaming_p ())
+    u (cexpr != nullptr);
+  if (cexpr)
     {
-      i (tag);
-      if (tag)
-	dump (dumper::TREE)
-	  && dump ("Constexpr:%d result %N", tag, cexpr->result);
-    }
-  if (tag)
-    {
-      unsigned ix = 0;
-      for (tree parm = cexpr->parms; parm; parm = DECL_CHAIN (parm), ix++)
-	{
-	  tag = insert (parm);
-	  if (streaming_p ())
-	    dump (dumper::TREE)
-	      && dump ("Constexpr:%d parm:%u %N", tag, ix, parm);
-	}
+      chained_decls (cexpr->parms);
+      tree_node (cexpr->result);
       tree_node (cexpr->body);
     }
 
@@ -11613,32 +11592,10 @@ trees_in::read_function_def (tree decl, tree maybe_template)
   tree maybe_dup = odr_duplicate (maybe_template, DECL_SAVED_TREE (decl));
   bool installing = maybe_dup && !DECL_SAVED_TREE (decl);
 
-  if (int wtag = i ())
+  if (u ())
     {
-      int tag = 1;
-      cexpr.result = error_mark_node;
-
-      cexpr.result = copy_decl (result);
-      tag = insert (cexpr.result);
-
-      if (wtag != tag)
-	set_overrun ();
-      dump (dumper::TREE)
-	&& dump ("Constexpr:%d result %N", tag, cexpr.result);
-
-      cexpr.parms = NULL_TREE;
-      tree *chain = &cexpr.parms;
-      unsigned ix = 0;
-      for (tree parm = DECL_ARGUMENTS (maybe_dup ? maybe_dup : decl);
-	   parm; parm = DECL_CHAIN (parm), ix++)
-	{
-	  tree p = copy_decl (parm);
-	  tag = insert (p);
-	  dump (dumper::TREE)
-	    && dump ("Constexpr:%d parm:%u %N", tag, ix, p);
-	  *chain = p;
-	  chain = &DECL_CHAIN (p);
-	}
+      cexpr.parms = chained_decls ();
+      cexpr.result = tree_node ();
       cexpr.body = tree_node ();
       cexpr.decl = decl;
     }
diff --git a/gcc/testsuite/g++.dg/modules/cexpr-3_a.C b/gcc/testsuite/g++.dg/modules/cexpr-3_a.C
new file mode 100644
index 00000000000..be24bb43a7b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/cexpr-3_a.C
@@ -0,0 +1,14 @@
+// PR c++/101449
+// { dg-additional-options -fmodules-ts }
+// { dg-module-cmi pr101449 }
+
+export module pr101449;
+
+struct X {
+  bool b = true;
+  constexpr X() { }
+  constexpr X(const X&) { }
+};
+
+export constexpr X f() { return {}; }
+export constexpr bool g(X x) { return x.b; }
diff --git a/gcc/testsuite/g++.dg/modules/cexpr-3_b.C b/gcc/testsuite/g++.dg/modules/cexpr-3_b.C
new file mode 100644
index 00000000000..cbf3be4fcab
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/cexpr-3_b.C
@@ -0,0 +1,7 @@
+// PR c++/101449
+// { dg-additional-options -fmodules-ts }
+
+import pr101449;
+
+static_assert(f().b);
+static_assert(g(f()));