introduce overridable clear_cache emitter

This patch introduces maybe_emit_call_builtin___clear_cache for the
builtin expander machinery and the trampoline initializers to use to
clear the instruction cache, removing a source of inconsistencies and
subtle errors in low-level machinery.

I've adjusted all trampoline_init implementations that used to issue
explicit calls to __clear_cache or similar to use this new primitive.


Specifically on vxworks targets, we needed to drop the __clear_cache
symbol in libgcc, for reasons related with linking that I didn't need
to understand, and we wanted to call cacheTextUpdate directly, despite
the different calling conventions: the second argument is a length
rather than the end address.

So I introduced a target hook to enable target OS-level overriding of
builtin __clear_cache call emission, retaining nearly (*) the same
logic to govern the decision on whether to emit a call (or nothing, or
a machine-dependent insn) but enabling a call to a target
system-defined function with different calling conventions to be
issued, without having to modify .md files of the various
architectures supported by the target system to introduce or modify
clear_cache insns.

(*) I write "nearly" mainly because, when not optimizing, we'd issue a
call regardless, but since the call may now be overridden, I added it
to the set of builtins that are not directly turned into calls when
not optimizing, following the normal expansion path instead.  It
wouldn't be hard to skip the emission of cache-clearing insns when not
optimizing, but it didn't seem very important, especially for the new
uses from trampoline init.

    Another difference that might be relevant is that now we expand
the begin and end arguments unconditionally.  This might make a
difference if they have side effects.  That's prettty much impossible
at expand time, but I thought I'd mention it.


I have NOT modified targets that did not issue cache-clearing calls in
trampoline init to use the new clear_cache-calling infrastructure even
if it would expand to nothing.  I have considered doing so, to have
__builtin___clear_cache and trampoline init call cacheTextUpdate on
all vxworks targets, but decided not to, since on targets that don't
do any cache clearing, cacheTextUpdate ought to be a no-op, even
though rs6000 seems to use icbi and dcbf instructions in the function
called to initialize a trampoline, but AFAICT not in the __clear_cache
builtin.  Hopefully target maintainers will have a look and take
advantage of this new piece of infrastructure to remove such
(apparent?) inconsistencies.  Not rs6000 and other that call asm-coded
trampoline setup instructions, for sure, but they might wish to
introduce a CLEAR_INSN_CACHE macro or a clear_cache expander if they
don't have one.


for  gcc/ChangeLog

	* builtins.c (default_emit_call_builtin___clear_cache): New.
	(maybe_emit_call_builtin___clear_cache): New.
	(expand_builtin___clear_cache): Split into the above.
	(expand_builtin): Do not issue clear_cache call any more.
	* builtins.h (maybe_emit_call_builtin___clear_cache): Declare.
	* config/aarch64/aarch64.c (aarch64_trampoline_init): Use
	maybe_emit_call_builtin___clear_cache.
	* config/arc/arc.c (arc_trampoline_init): Likewise.
	* config/arm/arm.c (arm_trampoline_init): Likewise.
	* config/c6x/c6x.c (c6x_initialize_trampoline): Likewise.
	* config/csky/csky.c (csky_trampoline_init): Likewise.
	* config/m68k/linux.h (FInALIZE_TRAMPOLINE): Likewise.
	* config/tilegx/tilegx.c (tilegx_trampoline_init): Likewise.
	* config/tilepro/tilepro.c (tilepro_trampoline_init): Ditto.
	* config/vxworks.c: Include rtl.h, memmodel.h, and optabs.h.
	(vxworks_emit_call_builtin___clear_cache): New.
	* config/vxworks.h (CLEAR_INSN_CACHE): Drop.
	(TARGET_EMIT_CALL_BUILTIN___CLEAR_CACHE): Define.
	* target.def (trampoline_init): In the documentation, refer to
	maybe_emit_call_builtin___clear_cache.
	(emit_call_builtin___clear_cache): New.
	* doc/tm.texi.in: Add new hook point.
	(CLEAR_CACHE_INSN): Remove duplicate 'both'.
	* doc/tm.texi: Rebuilt.
	* targhooks.h (default_meit_call_builtin___clear_cache):
	Declare.
	* tree.h (BUILTIN_ASM_NAME_PTR): New.

for  libgcc/ChangeLog

	* config/t-vxworks (LIB2ADD): Drop.
	* config/t-vxworks7 (LIB2ADD): Likewise.
	* config/vxcache.c: Remove.

3 files changed, 0 insertions, 37 deletions

diff --git a/libgcc/config/t-vxworks b/libgcc/config/t-vxworks
index 02e2efa..b4bb85b 100644
--- a/libgcc/config/t-vxworks
+++ b/libgcc/config/t-vxworks
@@ -4,7 +4,6 @@ LIBGCC2_DEBUG_CFLAGS =
 # We provide our own implementation for __clear_cache, using a
 # VxWorks specific entry point.
 LIB2FUNCS_EXCLUDE += _clear_cache
-LIB2ADD += $(srcdir)/config/vxcache.c
 
 # This ensures that the correct target headers are used; some VxWorks
 # system headers have names that collide with GCC's internal (host)
diff --git a/libgcc/config/t-vxworks7 b/libgcc/config/t-vxworks7
index 20c72f4..6ddd3e8 100644
--- a/libgcc/config/t-vxworks7
+++ b/libgcc/config/t-vxworks7
@@ -4,7 +4,6 @@ LIBGCC2_DEBUG_CFLAGS =
 # We provide our own implementation for __clear_cache, using a
 # VxWorks specific entry point.
 LIB2FUNCS_EXCLUDE += _clear_cache
-LIB2ADD += $(srcdir)/config/vxcache.c
 
 # This ensures that the correct target headers are used; some VxWorks
 # system headers have names that collide with GCC's internal (host)
diff --git a/libgcc/config/vxcache.c b/libgcc/config/vxcache.c
deleted file mode 100644
index e25e0cc..0000000
--- a/libgcc/config/vxcache.c
+++ /dev/null
@@ -1,35 +0,0 @@
-/* Copyright (C) 2018-2020 Free Software Foundation, Inc.
-   Contributed by Alexandre Oliva <oliva@adacore.com>
-
-This file is part of GCC.
-
-GCC is free software; you can redistribute it and/or modify it under
-the terms of the GNU General Public License as published by the Free
-Software Foundation; either version 3, or (at your option) any later
-version.
-
-GCC is distributed in the hope that it will be useful, but WITHOUT ANY
-WARRANTY; without even the implied warranty of MERCHANTABILITY or
-FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
-for more details.
-
-Under Section 7 of GPL version 3, you are granted additional
-permissions described in the GCC Runtime Library Exception, version
-3.1, as published by the Free Software Foundation.
-
-You should have received a copy of the GNU General Public License and
-a copy of the GCC Runtime Library Exception along with this program;
-see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
-<http://www.gnu.org/licenses/>.  */
-
-/* Instruction cache invalidation routine using VxWorks' cacheLib.  */
-
-#include <vxWorks.h>
-#include <cacheLib.h>
-
-void
-__clear_cache (char *beg __attribute__((__unused__)),
-	       char *end __attribute__((__unused__)))
-{
-  cacheTextUpdate (beg, end - beg);
-}