nvptx target: Global constructor, destructor support, via nvptx-tools 'ld'

The function attributes 'constructor', 'destructor', and 'init_priority' now
work, as do the C++ features making use of this.  Test cases with effective
target 'global_constructor' and 'init_priority' now generally work, and
'check-gcc-c++' test results greatly improve; no more
"sorry, unimplemented: global constructors not supported on this target".

For proper execution test results, this depends on
<96f8fc59a7>
"ld: Global constructor/destructor support".

	gcc/
	* config/nvptx/nvptx.h: Configure global constructor, destructor
	support.
	gcc/testsuite/
	* gcc.dg/no_profile_instrument_function-attr-1.c: GCC/nvptx is
	'NO_DOT_IN_LABEL' but not 'NO_DOLLAR_IN_LABEL', so '$' may apper
	in identifiers.
	* lib/target-supports.exp
	(check_effective_target_global_constructor): Enable for nvptx.
	libgcc/
	* config/nvptx/crt0.c (__gbl_ctors): New weak function.
	(__main): Invoke it.
	* config/nvptx/gbl-ctors.c: New.
	* config/nvptx/t-nvptx: Configure global constructor, destructor
	support.

gcc/config/nvptx/nvptx.h

@@ -356,7 +356,19 @@ struct GTY(()) machine_function
 #define MOVE_MAX 8
 #define MOVE_RATIO(SPEED) 4
 #define FUNCTION_MODE QImode
-#define HAS_INIT_SECTION 1
+
+/* Implement global constructor, destructor support in a conceptually simpler
+   way than using 'collect2' (the program): implement the respective
+   functionality in the nvptx-tools 'ld'.  This however still requires the
+   compiler-side effects corresponding to 'USE_COLLECT2': the global
+   constructor, destructor support functions need to have external linkage, and
+   therefore names that are "unique across the whole link".  Use
+   '!targetm.have_ctors_dtors' to achieve this (..., and thus don't need to
+   provide 'targetm.asm_out.constructor', 'targetm.asm_out.destructor').  */
+#define TARGET_HAVE_CTORS_DTORS false
+
+/* See 'libgcc/config/nvptx/crt0.c' for wrapping of 'main'.  */
+#define HAS_INIT_SECTION
 
 /* The C++ front end insists to link against libstdc++ -- which we don't build.
    Tell it to instead link against the innocuous libgcc.  */

gcc/testsuite/gcc.dg/no_profile_instrument_function-attr-1.c

@@ -18,7 +18,7 @@ int main ()
   return foo ();
 }
 
-/* { dg-final { scan-tree-dump-times "__gcov0\[._\]main.* = PROF_edge_counter" 1 "optimized"} } */
+/* { dg-final { scan-tree-dump-times "__gcov0\[$._\]main.* = PROF_edge_counter" 1 "optimized"} } */
 /* { dg-final { scan-tree-dump-times "__gcov_indirect_call_profiler_v" 1 "optimized" } } */
 /* { dg-final { scan-tree-dump-times "__gcov_time_profiler_counter = " 1 "optimized" } } */
 /* { dg-final { scan-tree-dump-times "__gcov_init" 1 "optimized" } } */

gcc/testsuite/lib/target-supports.exp

@@ -942,8 +942,7 @@ proc check_effective_target_nonlocal_goto {} {
 # Return 1 if global constructors are supported, 0 otherwise.
 
 proc check_effective_target_global_constructor {} {
-    if { [istarget nvptx-*-*]
-	 || [istarget bpf-*-*] } {
+    if { [istarget bpf-*-*] } {
 	return 0
     }
     return 1

libgcc/config/nvptx/crt0.c

@@ -32,6 +32,16 @@ void *__nvptx_stacks[32] __attribute__((shared,nocommon));
 /* Likewise for -muniform-simt.  */
 unsigned __nvptx_uni[32] __attribute__((shared,nocommon));
 
+/* Global constructor/destructor support.  Dummy; if necessary, overridden via
+   'gbl-ctors.c'.  */
+
+extern void __gbl_ctors (void);
+
+void __attribute__((weak))
+__gbl_ctors (void)
+{
+}
+
 extern void __main (int *, int, void **) __attribute__((kernel));
 
 void
@@ -47,5 +57,7 @@ __main (int *rval_ptr, int argc, void **argv)
   __nvptx_stacks[0] = stack + sizeof stack;
   __nvptx_uni[0] = 0;
 
+  __gbl_ctors ();
+
   exit (main (argc, argv));
 }

libgcc/config/nvptx/gbl-ctors.c

@@ -0,0 +1,74 @@
+/* Global constructor/destructor support
+
+   Copyright (C) 2024 Free Software Foundation, Inc.
+
+   This file 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.
+
+   This file 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/>.  */
+
+#include "auto-target.h"
+
+#ifdef HAVE_STDLIB_H
+# include <stdlib.h>
+#endif
+#include "gbl-ctors.h"
+
+extern int atexit (void (*function) (void));
+
+
+/* Handler functions ('static', in contrast to the 'gbl-ctors.h'
+   prototypes).  */
+
+static void __static_do_global_ctors (void);
+
+static void
+__static_do_global_ctors (void)
+{
+  __SIZE_TYPE__ nptrs = (__SIZE_TYPE__) __CTOR_LIST__[0];
+  for (__SIZE_TYPE__ i = nptrs; i >= 1; --i)
+    __CTOR_LIST__[i] ();
+}
+
+static void __static_do_global_dtors (void);
+
+static void
+__static_do_global_dtors (void)
+{
+  func_ptr *p = __DTOR_LIST__;
+  ++p;
+  for (; *p; ++p)
+    (*p) ();
+}
+
+
+/* For nvptx target configurations, override the 'crt0.c' dummy.  */
+
+extern void __gbl_ctors (void);
+
+void
+__gbl_ctors (void)
+{
+  __static_do_global_ctors ();
+  atexit (__static_do_global_dtors);
+}
+
+
+/* The following symbol just provides a means for the nvptx-tools 'ld' to
+   trigger linking in this file.  */
+
+int __trigger_gbl_ctors;

libgcc/config/nvptx/t-nvptx

@@ -6,8 +6,10 @@ LIB2ADD=$(srcdir)/config/nvptx/reduction.c \
 LIB2ADD += $(srcdir)/c++-minimal/guard.c
 
 LIB2ADDEH=
-LIB2FUNCS_EXCLUDE=__main
+LIB2FUNCS_EXCLUDE=
 
+# Wrapping of 'main'.
+LIB2FUNCS_EXCLUDE += __main
 crt0.o: $(srcdir)/config/nvptx/crt0.c
 	$(crt_compile) -c $<
 
@@ -15,3 +17,8 @@ crt0.o: $(srcdir)/config/nvptx/crt0.c
 # support it, and it may cause the build to fail, because of alloca usage, for
 # example.
 INHIBIT_LIBC_CFLAGS = -Dinhibit_libc
+
+# Support for global constructors/destructors is implemented via the
+# nvptx-tools 'ld' and the following helpers.
+LIB2ADD += $(srcdir)/config/nvptx/gbl-ctors.c
+LIB2FUNCS_EXCLUDE += _ctors