diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt index 9cfd2a6bc4e..9a4828ebe37 100644 --- a/gcc/c-family/c.opt +++ b/gcc/c-family/c.opt @@ -1731,6 +1731,10 @@ Support dynamic initialization of thread-local variables in a different translat fexternal-templates C++ ObjC++ WarnRemoved +ffold-simple-inlines +C++ ObjC++ Optimization Var(flag_fold_simple_inlines) +Fold calls to simple inline functions. + ffor-scope C++ ObjC++ WarnRemoved diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc index d7323fb5c09..e4c2644af15 100644 --- a/gcc/cp/cp-gimplify.cc +++ b/gcc/cp/cp-gimplify.cc @@ -41,6 +41,7 @@ along with GCC; see the file COPYING3. If not see #include "file-prefix-map.h" #include "cgraph.h" #include "omp-general.h" +#include "opts.h" /* Forward declarations. */ @@ -2756,9 +2757,44 @@ cp_fold (tree x) case CALL_EXPR: { - int sv = optimize, nw = sv; tree callee = get_callee_fndecl (x); + /* "Inline" calls to std::move/forward and other cast-like functions + by simply folding them into a corresponding cast to their return + type. This is cheaper than relying on the middle end to do so, and + also means we avoid generating useless debug info for them at all. + + At this point the argument has already been converted into a + reference, so it suffices to use a NOP_EXPR to express the + cast. */ + if ((OPTION_SET_P (flag_fold_simple_inlines) + ? flag_fold_simple_inlines + : !flag_no_inline) + && call_expr_nargs (x) == 1 + && decl_in_std_namespace_p (callee) + && DECL_NAME (callee) != NULL_TREE + && (id_equal (DECL_NAME (callee), "move") + || id_equal (DECL_NAME (callee), "forward") + || id_equal (DECL_NAME (callee), "addressof") + /* This addressof equivalent is used heavily in libstdc++. */ + || id_equal (DECL_NAME (callee), "__addressof") + || id_equal (DECL_NAME (callee), "as_const"))) + { + r = CALL_EXPR_ARG (x, 0); + /* Check that the return and argument types are sane before + folding. */ + if (INDIRECT_TYPE_P (TREE_TYPE (x)) + && INDIRECT_TYPE_P (TREE_TYPE (r))) + { + if (!same_type_p (TREE_TYPE (x), TREE_TYPE (r))) + r = build_nop (TREE_TYPE (x), r); + x = cp_fold (r); + break; + } + } + + int sv = optimize, nw = sv; + /* Some built-in function calls will be evaluated at compile-time in fold (). Set optimize to 1 when folding __builtin_constant_p inside a constexpr function so that fold_builtin_1 doesn't fold it to 0. */ diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 2a14e1a9472..d65979bba3f 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -3124,6 +3124,16 @@ On targets that support symbol aliases, the default is @option{-fextern-tls-init}. On targets that do not support symbol aliases, the default is @option{-fno-extern-tls-init}. +@item -ffold-simple-inlines +@itemx -fno-fold-simple-inlines +@opindex ffold-simple-inlines +@opindex fno-fold-simple-inlines +Permit the C++ frontend to fold calls to @code{std::move}, @code{std::forward}, +@code{std::addressof} and @code{std::as_const}. In contrast to inlining, this +means no debug information will be generated for such calls. Since these +functions are rarely interesting to debug, this flag is enabled by default +unless @option{-fno-inline} is active. + @item -fno-gnu-keywords @opindex fno-gnu-keywords @opindex fgnu-keywords diff --git a/gcc/testsuite/g++.dg/opt/pr96780.C b/gcc/testsuite/g++.dg/opt/pr96780.C new file mode 100644 index 00000000000..61e11855eeb --- /dev/null +++ b/gcc/testsuite/g++.dg/opt/pr96780.C @@ -0,0 +1,38 @@ +// PR c++/96780 +// Verify calls to std::move/forward are folded away by the frontend. +// { dg-do compile { target c++11 } } +// { dg-additional-options "-ffold-simple-inlines -fdump-tree-gimple" } + +#include + +struct A; + +extern A& a; +extern const A& ca; + +void f() { + auto&& x1 = std::move(a); + auto&& x2 = std::forward(a); + auto&& x3 = std::forward(a); + + auto&& x4 = std::move(ca); + auto&& x5 = std::forward(ca); + auto&& x6 = std::forward(ca); + + auto x7 = std::addressof(a); + auto x8 = std::addressof(ca); +#if __GLIBCXX__ + auto x9 = std::__addressof(a); + auto x10 = std::__addressof(ca); +#endif +#if __cpp_lib_as_const + auto&& x11 = std::as_const(a); + auto&& x12 = std::as_const(ca); +#endif +} + +// { dg-final { scan-tree-dump-not "= std::move" "gimple" } } +// { dg-final { scan-tree-dump-not "= std::forward" "gimple" } } +// { dg-final { scan-tree-dump-not "= std::addressof" "gimple" } } +// { dg-final { scan-tree-dump-not "= std::__addressof" "gimple" } } +// { dg-final { scan-tree-dump-not "= std::as_const" "gimple" } }