[gcc r12-8196] c++: Fix up CONSTRUCTOR_PLACEHOLDER_BOUNDARY handling [PR105256]

[gcc r12-8196] c++: Fix up CONSTRUCTOR_PLACEHOLDER_BOUNDARY handling [PR105256]

[Jakub Jelinek]

https://gcc.gnu.org/g:eb03e424598d30fed68801af6d6ef6236d32e32e

commit r12-8196-geb03e424598d30fed68801af6d6ef6236d32e32e
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Apr 19 18:27:41 2022 +0200

    c++: Fix up CONSTRUCTOR_PLACEHOLDER_BOUNDARY handling [PR105256]
    
    The CONSTRUCTOR_PLACEHOLDER_BOUNDARY bit is supposed to separate
    PLACEHOLDER_EXPRs that should be replaced by one object or subobjects of it
    (variable, TARGET_EXPR slot, ...) from other PLACEHOLDER_EXPRs that should
    be replaced by different objects or subobjects.
    The bit is set when finding PLACEHOLDER_EXPRs inside of a CONSTRUCTOR, not
    looking into nested CONSTRUCTOR_PLACEHOLDER_BOUNDARY ctors, and we prevent
    elision of TARGET_EXPRs (through TARGET_EXPR_NO_ELIDE) whose initializer
    is a CONSTRUCTOR_PLACEHOLDER_BOUNDARY ctor.  The following testcase ICEs
    though, we don't replace the placeholders in there at all, because
    CONSTRUCTOR_PLACEHOLDER_BOUNDARY isn't set on the TARGET_EXPR_INITIAL
    ctor, but on a ctor nested in such a ctor.  replace_placeholders should be
    run on the whole TARGET_EXPR slot.
    
    So, the following patch fixes it by moving the CONSTRUCTOR_PLACEHOLDER_BOUNDARY
    bit from nested CONSTRUCTORs to the CONSTRUCTOR containing those (but only
    if it is closely nested, if there is some other tree sandwiched in between,
    it doesn't do it).
    
    2022-04-19  Jakub Jelinek  <jakub@redhat.com>
    
            PR c++/105256
            * typeck2.cc (process_init_constructor_array,
            process_init_constructor_record, process_init_constructor_union): Move
            CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag from CONSTRUCTOR elements to the
            containing CONSTRUCTOR.
    
            * g++.dg/cpp0x/pr105256.C: New test.

Diff:
---
 gcc/cp/typeck2.cc                     | 31 +++++++++++++++++++++++++++++++
 gcc/testsuite/g++.dg/cpp0x/pr105256.C | 18 ++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc
index 23ed81ec063..63d95c1529a 100644
--- a/gcc/cp/typeck2.cc
+++ b/gcc/cp/typeck2.cc
@@ -1515,6 +1515,14 @@ process_init_constructor_array (tree type, tree init, int nested, int flags,
 	      strip_array_types (TREE_TYPE (ce->value)))));
 
       picflags |= picflag_from_initializer (ce->value);
+      /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer
+	 CONSTRUCTOR.  */
+      if (TREE_CODE (ce->value) == CONSTRUCTOR
+	  && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value))
+	{
+	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
+	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value) = 0;
+	}
     }
 
   /* No more initializers. If the array is unbounded, we are done. Otherwise,
@@ -1560,6 +1568,14 @@ process_init_constructor_array (tree type, tree init, int nested, int flags,
 	      }
 
 	    picflags |= picflag_from_initializer (next);
+	    /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer
+	       CONSTRUCTOR.  */
+	    if (TREE_CODE (next) == CONSTRUCTOR
+		&& CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next))
+	      {
+		CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
+		CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next) = 0;
+	      }
 	    if (len > i+1)
 	      {
 		tree range = build2 (RANGE_EXPR, size_type_node,
@@ -1754,6 +1770,13 @@ process_init_constructor_record (tree type, tree init, int nested, int flags,
       if (fldtype != TREE_TYPE (field))
 	next = cp_convert_and_check (TREE_TYPE (field), next, complain);
       picflags |= picflag_from_initializer (next);
+      /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer CONSTRUCTOR.  */
+      if (TREE_CODE (next) == CONSTRUCTOR
+	  && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next))
+	{
+	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
+	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next) = 0;
+	}
       CONSTRUCTOR_APPEND_ELT (v, field, next);
     }
 
@@ -1894,6 +1917,14 @@ process_init_constructor_union (tree type, tree init, int nested, int flags,
     ce->value = massage_init_elt (TREE_TYPE (ce->index), ce->value, nested,
 				  flags, complain);
 
+  /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer CONSTRUCTOR.  */
+  if (ce->value
+      && TREE_CODE (ce->value) == CONSTRUCTOR
+      && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value))
+    {
+      CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
+      CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value) = 0;
+    }
   return picflag_from_initializer (ce->value);
 }
 
diff --git a/gcc/testsuite/g++.dg/cpp0x/pr105256.C b/gcc/testsuite/g++.dg/cpp0x/pr105256.C
new file mode 100644
index 00000000000..98ce5e8b7bf
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/pr105256.C
@@ -0,0 +1,18 @@
+// PR c++/105256
+// { dg-do compile { target c++11 } }
+
+int bar (int &);
+
+struct S {
+  struct T {
+    struct U {
+      int i = bar (i);
+    } u;
+  };
+};
+
+void
+foo (S::T *p)
+{
+  *p = {};
+};