c++: Set loc on call even if result is discarded

This patch fixes a divergence in line numbers in diagnostics and,
presumably, debug information, between targets whose cdtors return
this and those that don't.

The problem was visible in g++.dg/cpp2a/constexpr-dtor3.C: while the
dtor call in the cleanup for f4 was expected at the closing brace, on
returning-this targets it came up at the assignment.

The reason is convoluted: statements in cleanups have their location
information removed, to avoid bumpy debugger behavior, and then set to
the location of the end of the scope.

The cleanup dtor call has its locus cleared in both kinds of targets,
but the end-of-scope locus doesn't make it on returning-this targets.
The calls are wrapped with a cast-to-void to discard the unused return
value, and the existing logic only attached the locus to the
conversion NOP_EXPR.

The call thus remains locus-less.  When constexpr logic copies and
evals the body, it sets unset locations; while copying cleanups, the
locus is taken from the cleanup expression, rather than matching the
end-of-scope locus set by the parser.  So we end up with different
locations.

This patch sets the locus of the call even when it's wrapped by a
convert-to-void NOP_EXPR, so it won't diverge any more.

for  gcc/cp/ChangeLog

	* semantics.cc (set_cleanup_locs): Propagate locus to call
	wrapped in cast-to-void.

diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index a7f6449dafd2e0451a53e4117b8e65888d56c4b7..43627ed30afcb2bcab2e5a8094738f9124aacd1f 100644 (file)
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -609,7 +609,17 @@ set_cleanup_locs (tree stmts, location_t loc)
 {
   if (TREE_CODE (stmts) == CLEANUP_STMT)
     {
-      protected_set_expr_location (CLEANUP_EXPR (stmts), loc);
+      tree t = CLEANUP_EXPR (stmts);
+      protected_set_expr_location (t, loc);
+      /* Avoid locus differences for C++ cdtor calls depending on whether
+        cdtor_returns_this: a conversion to void is added to discard the return
+        value, and this conversion ends up carrying the location, and when it
+        gets discarded, the location is lost.  So hold it in the call as
+        well.  */
+      if (TREE_CODE (t) == NOP_EXPR
+         && TREE_TYPE (t) == void_type_node
+         && TREE_CODE (TREE_OPERAND (t, 0)) == CALL_EXPR)
+       protected_set_expr_location (TREE_OPERAND (t, 0), loc);
       set_cleanup_locs (CLEANUP_BODY (stmts), loc);
     }
   else if (TREE_CODE (stmts) == STATEMENT_LIST)