From 21761d2b2b01f6cef4287c646845f6b3006546aa Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Mon, 21 Jun 2021 07:54:29 -0400 Subject: [PATCH] c++: REF_PARENTHESIZED_P wrapper inhibiting NRVO [PR67302] Here, in C++14 or later, we remember the parentheses around 'a' in the return statement by using a REF_PARENTHESIZED_P wrapper, which ends up inhibiting NRVO because we don't look through this wrapper before checking the conditions for NRVO. This patch fixes this by calling maybe_undo_parenthesized_ref sooner in check_return_expr. PR c++/67302 gcc/cp/ChangeLog: * typeck.c (check_return_expr): Call maybe_undo_parenthesized_ref sooner, before the NRVO handling. gcc/testsuite/ChangeLog: * g++.dg/opt/nrv21.C: New test. --- gcc/cp/typeck.c | 9 ++++----- gcc/testsuite/g++.dg/opt/nrv21.C | 14 ++++++++++++++ 2 files changed, 18 insertions(+), 5 deletions(-) create mode 100644 gcc/testsuite/g++.dg/opt/nrv21.C diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c index 5a9331b..937581a 100644 --- a/gcc/cp/typeck.c +++ b/gcc/cp/typeck.c @@ -10311,7 +10311,10 @@ check_return_expr (tree retval, bool *no_warning) See finish_function and finalize_nrv for the rest of this optimization. */ if (retval) - STRIP_ANY_LOCATION_WRAPPER (retval); + { + retval = maybe_undo_parenthesized_ref (retval); + STRIP_ANY_LOCATION_WRAPPER (retval); + } bool named_return_value_okay_p = can_do_nrvo_p (retval, functype); if (fn_returns_value_p && flag_elide_constructors) @@ -10345,10 +10348,6 @@ check_return_expr (tree retval, bool *no_warning) if (VOID_TYPE_P (functype)) return error_mark_node; - /* If we had an id-expression obfuscated by force_paren_expr, we need - to undo it so we can try to treat it as an rvalue below. */ - retval = maybe_undo_parenthesized_ref (retval); - if (processing_template_decl) retval = build_non_dependent_expr (retval); diff --git a/gcc/testsuite/g++.dg/opt/nrv21.C b/gcc/testsuite/g++.dg/opt/nrv21.C new file mode 100644 index 0000000..ff33852 --- /dev/null +++ b/gcc/testsuite/g++.dg/opt/nrv21.C @@ -0,0 +1,14 @@ +// PR c++/67302 +// { dg-additional-options -fdump-tree-gimple } +// { dg-final { scan-tree-dump-not " = a" "gimple" } } + +struct A +{ + int ar[42]; + A(); +}; + +A f() { + A a; + return (a); // The parens should not inhibit NRVO. +} -- 2.7.4