c++: non-dependent .* operand folding [PR112427]

Here when building up the non-dependent .* expression, we crash from
fold_convert on 'b.a' due to this (templated) COMPONENT_REF having an
IDENTIFIER_NODE instead of FIELD_DECL operand that middle-end routines
expect.  Like in r14-4899-gd80a26cca02587, this patch fixes this by
replacing the problematic piecemeal folding with a single call to
cp_fully_fold.  Also, don't bother building the POINTER_PLUS_EXPR in a
template context.  This means the returned non-dependent tree might not
have TREE_SIDE_EFFECTS set when it used to, so we need to compensate
by making build_min_non_dep propagate TREE_SIDE_EFFECTS from the original
arguments like buildN and build_min do.

	PR c++/112427

gcc/cp/ChangeLog:

	* tree.cc (build_min_non_dep): Propagate TREE_SIDE_EFFECTS from
	the original arguments.
	(build_min_non_dep_call_vec): Likewise.
	* typeck2.cc (build_m_component_ref): Use cp_convert, build2 and
	cp_fully_fold instead of fold_build_pointer_plus and fold_convert.
	Don't build the POINTER_PLUS_EXPR in a template context.

gcc/testsuite/ChangeLog:

	* g++.dg/template/non-dependent29.C: New test.

1 files changed, 10 insertions, 1 deletions

diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index 417c92b..dc4126f 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -3601,7 +3601,12 @@ build_min_non_dep (enum tree_code code, tree non_dep, ...)
   TREE_SIDE_EFFECTS (t) = TREE_SIDE_EFFECTS (non_dep);
 
   for (i = 0; i < length; i++)
-    TREE_OPERAND (t, i) = va_arg (p, tree);
+    {
+      tree x = va_arg (p, tree);
+      TREE_OPERAND (t, i) = x;
+      if (x && !TYPE_P (x))
+	TREE_SIDE_EFFECTS (t) |= TREE_SIDE_EFFECTS (x);
+    }
 
   va_end (p);
   return convert_from_reference (t);
@@ -3636,6 +3641,10 @@ build_min_non_dep_call_vec (tree non_dep, tree fn, vec<tree, va_gc> *argvec)
     non_dep = TREE_OPERAND (non_dep, 0);
   TREE_TYPE (t) = TREE_TYPE (non_dep);
   TREE_SIDE_EFFECTS (t) = TREE_SIDE_EFFECTS (non_dep);
+  if (argvec)
+    for (tree x : *argvec)
+      if (x && !TYPE_P (x))
+	TREE_SIDE_EFFECTS (t) |= TREE_SIDE_EFFECTS (x);
   return convert_from_reference (t);
 }