[gcc/devel/omp/gcc-13] Fortran changes for 'requires unified_shared_memory', insert USM allocators into libgfortran

[gcc/devel/omp/gcc-13] Fortran changes for 'requires unified_shared_memory', insert USM allocators into libgfortran

[Chung-Lin Tang]

https://gcc.gnu.org/g:e802f253ffdbc7d7ede16953b753172bb68e951f

commit e802f253ffdbc7d7ede16953b753172bb68e951f
Author: Chung-Lin Tang <cltang@codesourcery.com>
Date:   Thu Jun 15 23:50:35 2023 -0700

    Fortran changes for 'requires unified_shared_memory', insert USM allocators into libgfortran
    
    (this is a merge of:
     https://gcc.gnu.org/pipermail/gcc-patches/2022-August/599704.html)
    
    After the prior libgfortran memory allocator preparation patch, this is the
    actual patch that organizes unified_shared_memory allocation into libgfortran.
    
    In the current OpenMP requires implementation, the requires_mask is collected
    through offload LTO processing, and presented to libgomp when registering
    offload images through GOMP_offload_register_ver() (called by the mkoffload
    generated constructor linked into the program binary)
    
    This means that the only reliable place to access omp_requires_mask is in
    GOMP_offload_register_ver, however since it is called through an ELF
    constructor in the *main program*, this runs later than
    libgfortran/runtime/main.c:init() constructor, and because some libgfortran
    init actions there start allocating memory, this can cause more deallocation
    errors later.
    
    Another issue is that CUDA appears to be registering some cleanup actions using
    atexit(), which forces libgomp to register gomp_target_fini() using atexit as
    well (to properly run before the underlying CUDA stuff disappears).
    This happens to us here as well.
    
    So to summarize we need to: (1) order libgfortran init actions after
    omp_requires_mask processing is done, and (2) order libgfortran cleanup actions
    before gomp_target_fini, to properly deallocate stuff without crashing.
    
    The above explanation is for why there's a little new set of definitions,
    as well as callback registering functions exported from libgomp to libgfortran,
    basically to register libgfortran init/fini actions into libgomp to run.
    
    Inside GOMP_offload_register_ver, after omp_requires_mask processing is done,
    we call into libgfortran through a new _gfortran_mem_allocators_init function
    to insert the omp_free/alloc/etc. based allocators into the Fortran runtime,
    when GOMP_REQUIRES_UNIFIED_SHARED_MEMORY is set.
    
    All symbol references between libgfortran/libgomp are defined with weak
    symbols. Test of the weak symbols are also used to determine if the other
    library exists in this program.
    
    A final issue is: the case where we have an OpenMP program that does NOT have
    offloading. We cannot passively determine in libgomp/libgfortran whether
    offloading exists or not, only the main program itself can, by seeing if the
    hidden __OFFLOAD_TABLE__ exists.
    
    When we do init/fini libgomp callback registering for OpenMP programs, those
    with no offloading will not have those callback properly run (because of no
    offload image loading) Therefore the solution here is a constructor added into
    the crtoffloadend.o fragment that does a "null" call of
    GOMP_offload_register_ver, solely for triggering the post-offload_register
    callbacks when __OFFLOAD_TABLE__ is NULL. (and because of this, the
    crtoffloadend.o Makefile rule is adjusted to compile with PIC)
    
    libgcc/ChangeLog:
    
            * Makefile.in (crtoffloadend$(objext)): Add $(PICFLAG) to compile rule.
            * offloadstuff.c (GOMP_offload_register_ver): Add declaration of weak
            symbol.
            (__OFFLOAD_TABLE__): Likewise.
            (init_non_offload): New function.
    
    libgfortran/ChangeLog:
    
            * gfortran.map (GFORTRAN_14): New namespace.
            (_gfortran_mem_allocators_init): New name inside GFORTRAN_13.
            * libgfortran.h (mem_allocators_init): New exported declaration.
            * runtime/main.c (do_init): Rename from init, add run-once guard code.
            (cleanup): Add run-once guard code.
            (GOMP_post_offload_register_callback): Declare weak symbol.
            (GOMP_pre_gomp_target_fini_callback): Likewise.
            (init): New constructor to register offload callbacks, or call do_init
            when not OpenMP.
            * runtime/memory.c (gfortran_malloc): New pointer variable.
            (gfortran_calloc): Likewise.
            (gfortran_realloc): Likewise.
            (gfortran_free): Likewise.
            (mem_allocators_init): New function.
            (xmalloc): Use gfortran_malloc.
            (xmallocarray): Use gfortran_malloc.
            (xcalloc): Use gfortran_calloc.
            (xrealloc): Use gfortran_realloc.
            (xfree): Use gfortran_free.
    
    libgomp/ChangeLog:
    
            * libgomp.map (GOMP_5.1.2): New version namespace.
            (GOMP_post_offload_register_callback): New name inside GOMP_5.1.2.
            (GOMP_pre_gomp_target_fini_callback): Likewise.
            (GOMP_DEFINE_CALLBACK_SET): Macro to define callback set.
            (post_offload_register): Define callback set for after offload image
            register.
            (pre_gomp_target_fini): Define callback set for before gomp_target_fini
            is called.
            (libgfortran_malloc_usm): New function.
            (libgfortran_calloc_usm): Likewise
            (libgfortran_realloc_usm): Likewise
            (libgfortran_free_usm): Likewise.
            (_gfortran_mem_allocators_init): Declare weak symbol.
            (gomp_libgfortran_omp_allocators_init): New function.
            (GOMP_offload_register_ver): Add handling of host_table == NULL,
            calling into libgfortran to set unified_shared_memory allocators,
            and execution of post_offload_register callbacks.
            (gomp_target_init): Register all pre_gomp_target_fini callbacks to run
            at end of main using atexit().
    
            * libgomp.fortran/target-unified_shared_memory-1.f90: New testcase.

Diff:
---
 libgcc/Makefile.in                                 |  3 +-
 libgcc/offloadstuff.c                              | 13 ++++
 libgfortran/gfortran.map                           |  5 ++
 libgfortran/libgfortran.h                          |  5 ++
 libgfortran/runtime/main.c                         | 43 ++++++++++-
 libgfortran/runtime/memory.c                       | 32 +++++++--
 libgomp/libgomp.map                                |  6 ++
 libgomp/target.c                                   | 84 +++++++++++++++++++++-
 .../target-unified_shared_memory-1.f90             | 13 ++++
 9 files changed, 195 insertions(+), 9 deletions(-)

diff --git a/libgcc/Makefile.in b/libgcc/Makefile.in
index 6c4dc79ab71..5ef94380ec0 100644
--- a/libgcc/Makefile.in
+++ b/libgcc/Makefile.in
@@ -1048,8 +1048,9 @@ crtbeginT$(objext): $(srcdir)/crtstuff.c
 crtoffloadbegin$(objext): $(srcdir)/offloadstuff.c
 	$(crt_compile) $(CRTSTUFF_T_CFLAGS) -c $< -DCRT_BEGIN
 
+# crtoffloadend contains a constructor with calls to libgomp, so build as PIC.
 crtoffloadend$(objext): $(srcdir)/offloadstuff.c
-	$(crt_compile) $(CRTSTUFF_T_CFLAGS) -c $< -DCRT_END
+	$(crt_compile) $(CRTSTUFF_T_CFLAGS) $(PICFLAG) -c $< -DCRT_END
 
 crtoffloadtable$(objext): $(srcdir)/offloadstuff.c
 	$(crt_compile) $(CRTSTUFF_T_CFLAGS) -c $< -DCRT_TABLE
diff --git a/libgcc/offloadstuff.c b/libgcc/offloadstuff.c
index 4e1c4d41dd5..6796aa2a83c 100644
--- a/libgcc/offloadstuff.c
+++ b/libgcc/offloadstuff.c
@@ -63,6 +63,19 @@ const void *const __offload_vars_end[0]
   __attribute__ ((__used__, visibility ("hidden"),
 		  section (OFFLOAD_VAR_TABLE_SECTION_NAME))) = { };
 
+extern void GOMP_offload_register_ver (unsigned, const void *, int,
+				       const void *);
+extern const void *const __OFFLOAD_TABLE__[0] __attribute__ ((weak));
+static void __attribute__((constructor))
+init_non_offload (void)
+{
+  /* If an OpenMP program has no offloading, post-offload_register callbacks
+     that need to run will require a call to GOMP_offload_register_ver, in
+     order to properly trigger those callbacks during init.  */
+  if (__OFFLOAD_TABLE__ == NULL)
+    GOMP_offload_register_ver (0, NULL, 0, NULL);
+}
+
 #elif defined CRT_TABLE
 
 extern const void *const __offload_func_table[];
diff --git a/libgfortran/gfortran.map b/libgfortran/gfortran.map
index db9b86cb183..abb4def5b80 100644
--- a/libgfortran/gfortran.map
+++ b/libgfortran/gfortran.map
@@ -1765,3 +1765,8 @@ GFORTRAN_13 {
     __ieee_exceptions_MOD_ieee_get_modes;
     __ieee_exceptions_MOD_ieee_set_modes;
 } GFORTRAN_12;
+
+GFORTRAN_14 {
+  global:
+  _gfortran_mem_allocators_init;
+} GFORTRAN_13;
diff --git a/libgfortran/libgfortran.h b/libgfortran/libgfortran.h
index b972b0aa0cd..65d30c18661 100644
--- a/libgfortran/libgfortran.h
+++ b/libgfortran/libgfortran.h
@@ -878,6 +878,11 @@ internal_proto(xrealloc);
 extern void xfree (void *);
 internal_proto(xfree);
 
+#ifndef LIBGFOR_MINIMAL
+extern void mem_allocators_init (void *, void *, void *, void *);
+export_proto(mem_allocators_init);
+#endif
+
 /* environ.c */
 
 extern void init_variables (void);
diff --git a/libgfortran/runtime/main.c b/libgfortran/runtime/main.c
index bcdcb20a123..7891af9ed94 100644
--- a/libgfortran/runtime/main.c
+++ b/libgfortran/runtime/main.c
@@ -61,9 +61,16 @@ get_args (int *argc, char ***argv)
 
 /* Initialize the runtime library.  */
 
-static void __attribute__((constructor))
-init (void)
+static void
+do_init (void)
 {
+#ifndef LIBGFOR_MINIMAL
+  static bool do_init_ran = false;
+  if (do_init_ran)
+    return;
+  do_init_ran = true;
+#endif
+
   /* Must be first */
   init_variables ();
 
@@ -82,5 +89,37 @@ init (void)
 static void __attribute__((destructor))
 cleanup (void)
 {
+#ifndef LIBGFOR_MINIMAL
+  static bool cleanup_ran = false;
+  if (cleanup_ran)
+    return;
+  cleanup_ran = true;
+#endif
+
   close_units ();
 }
+
+#ifndef LIBGFOR_MINIMAL
+extern void __attribute__((weak))
+GOMP_post_offload_register_callback (void (*func)(void));
+
+extern void __attribute__((weak))
+GOMP_pre_gomp_target_fini_callback (void (*func)(void));
+#endif
+
+static void __attribute__((constructor))
+init (void)
+{
+#ifndef LIBGFOR_MINIMAL
+  if (GOMP_post_offload_register_callback)
+    {
+      GOMP_post_offload_register_callback (do_init);
+      GOMP_pre_gomp_target_fini_callback (cleanup);
+      return;
+    }
+#endif
+
+  /* If libgomp is not present, then we can go ahead and call do_init
+     directly.  */
+  do_init ();
+}
diff --git a/libgfortran/runtime/memory.c b/libgfortran/runtime/memory.c
index a1539836c9c..5eb4540ad6f 100644
--- a/libgfortran/runtime/memory.c
+++ b/libgfortran/runtime/memory.c
@@ -26,6 +26,28 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #include "libgfortran.h"
 #include <errno.h>
 
+#ifndef LIBGFOR_MINIMAL
+static void * (*gfortran_malloc)(size_t) = malloc;
+static void * (*gfortran_calloc)(size_t, size_t) = calloc;
+static void * (*gfortran_realloc)(void *, size_t) = realloc;
+static void (*gfortran_free)(void *) = free;
+
+void
+mem_allocators_init (void *malloc_ptr, void *calloc_ptr,
+		     void *realloc_ptr, void *free_ptr)
+{
+  gfortran_malloc = malloc_ptr;
+  gfortran_calloc = calloc_ptr;
+  gfortran_realloc = realloc_ptr;
+  gfortran_free = free_ptr;
+}
+
+#else
+#define gfortran_malloc malloc
+#define gfortran_calloc calloc
+#define gfortran_realloc realloc
+#define gfortran_free free
+#endif
 
 void *
 xmalloc (size_t n)
@@ -35,7 +57,7 @@ xmalloc (size_t n)
   if (n == 0)
     n = 1;
 
-  p = malloc (n);
+  p = gfortran_malloc (n);
 
   if (p == NULL)
     os_error ("Memory allocation failed");
@@ -57,7 +79,7 @@ xmallocarray (size_t nmemb, size_t size)
       os_error ("Integer overflow in xmallocarray");
     }
 
-  p = malloc (prod);
+  p = gfortran_malloc (prod);
 
   if (!p)
     os_error ("Memory allocation failed in xmallocarray");
@@ -73,7 +95,7 @@ xcalloc (size_t nmemb, size_t size)
   if (!nmemb || !size)
     nmemb = size = 1;
 
-  void *p = calloc (nmemb, size);
+  void *p = gfortran_calloc (nmemb, size);
   if (!p)
     os_error ("Allocating cleared memory failed");
 
@@ -86,7 +108,7 @@ xrealloc (void *ptr, size_t size)
   if (size == 0)
     size = 1;
 
-  void *newp = realloc (ptr, size);
+  void *newp = gfortran_realloc (ptr, size);
   if (!newp)
     os_error ("Memory allocation failure in xrealloc");
 
@@ -96,5 +118,5 @@ xrealloc (void *ptr, size_t size)
 void
 xfree (void *ptr)
 {
-  free (ptr);
+  gfortran_free (ptr);
 }
diff --git a/libgomp/libgomp.map b/libgomp/libgomp.map
index a9621c0a68c..694a8f1a359 100644
--- a/libgomp/libgomp.map
+++ b/libgomp/libgomp.map
@@ -423,6 +423,12 @@ GOMP_5.1.1 {
 	GOMP_taskwait_depend_nowait;
 } GOMP_5.1;
 
+GOMP_5.1.2 {
+  global:
+	GOMP_post_offload_register_callback;
+	GOMP_pre_gomp_target_fini_callback;
+} GOMP_5.1.1;
+
 OACC_2.0 {
   global:
 	acc_get_num_devices;
diff --git a/libgomp/target.c b/libgomp/target.c
index f8c992cf609..e62cf6ad8ce 100644
--- a/libgomp/target.c
+++ b/libgomp/target.c
@@ -3033,6 +3033,70 @@ gomp_requires_to_name (char *buf, size_t size, int requires_mask)
 		   (p == buf ? "" : ", "));
 }
 
+/* Macro to define a callback set with a name, and routine to register
+   a callback function into set.  */
+#define GOMP_DEFINE_CALLBACK_SET(name)				\
+  static unsigned int num_ ## name ## _callbacks = 0;		\
+  static void (*name ## _callbacks[4])(void);			\
+  void GOMP_ ## name ## _callback (void (*fn)(void))		\
+  {								\
+    if (num_ ## name ## _callbacks				\
+	< (sizeof (name ## _callbacks)				\
+	   / sizeof (name ## _callbacks[0])))			\
+      {								\
+	name ## _callbacks[num_ ## name ## _callbacks] = fn;	\
+	num_ ## name ## _callbacks += 1;			\
+      }								\
+  }
+GOMP_DEFINE_CALLBACK_SET(post_offload_register)
+GOMP_DEFINE_CALLBACK_SET(pre_gomp_target_fini)
+#undef GOMP_DEFINE_CALLBACK_SET
+
+/* Routines to insert into libgfortran, under unified_shared_memory.  */
+static void *
+libgfortran_malloc_usm (size_t size)
+{
+  return omp_alloc (size, ompx_unified_shared_mem_alloc);
+}
+
+static void *
+libgfortran_calloc_usm (size_t n, size_t size)
+{
+  return omp_calloc (n, size, ompx_unified_shared_mem_alloc);
+}
+
+static void *
+libgfortran_realloc_usm (void *ptr, size_t size)
+{
+  return omp_realloc (ptr, size, ompx_unified_shared_mem_alloc,
+		      ompx_unified_shared_mem_alloc);
+}
+
+static void
+libgfortran_free_usm (void *ptr)
+{
+  omp_free (ptr, ompx_unified_shared_mem_alloc);
+}
+
+extern void __attribute__((weak))
+_gfortran_mem_allocators_init (void *, void *, void *, void *);
+
+static void
+gomp_libgfortran_omp_allocators_init (int omp_requires_mask)
+{
+  static bool init = false;
+  if (init)
+    return;
+  init = true;
+
+  if ((omp_requires_mask & GOMP_REQUIRES_UNIFIED_SHARED_MEMORY)
+      && _gfortran_mem_allocators_init != NULL)
+    _gfortran_mem_allocators_init (libgfortran_malloc_usm,
+				   libgfortran_calloc_usm,
+				   libgfortran_realloc_usm,
+				   libgfortran_free_usm);
+}
+
 /* This function should be called from every offload image while loading.
    It gets the descriptor of the host func and var tables HOST_TABLE, TYPE of
    the target, and DATA.  */
@@ -3043,6 +3107,9 @@ GOMP_offload_register_ver (unsigned version, const void *host_table,
 {
   int i;
 
+  if (host_table == NULL)
+    goto end;
+
   if (GOMP_VERSION_LIB (version) > GOMP_VERSION)
     gomp_fatal ("Library too old for offload (version %u < %u)",
 		GOMP_VERSION, GOMP_VERSION_LIB (version));
@@ -3109,6 +3176,14 @@ GOMP_offload_register_ver (unsigned version, const void *host_table,
 
   num_offload_images++;
   gomp_mutex_unlock (&register_lock);
+
+  /* Call into libgfortran to initialize OpenMP memory allocators.  */
+  gomp_libgfortran_omp_allocators_init (omp_requires_mask);
+
+ end:
+  for (int i = 0; i < num_post_offload_register_callbacks; i++)
+    post_offload_register_callbacks[i] ();
+  num_post_offload_register_callbacks = 0;
 }
 
 /* Legacy entry point.  */
@@ -3221,7 +3296,7 @@ gomp_unload_device (struct gomp_device_descr *devicep)
   if (devicep->state == GOMP_DEVICE_INITIALIZED)
     {
       unsigned i;
-      
+
       /* Unload from device all images registered at the moment.  */
       for (i = 0; i < num_offload_images; i++)
 	{
@@ -6346,6 +6421,13 @@ gomp_target_init (void)
   devices = devs;
   if (atexit (gomp_target_fini) != 0)
     gomp_fatal ("atexit failed");
+
+  /* Register 'pre_gomp_target_fini' callbacks to run before gomp_target_fini
+     during finalization.  */
+  for (int i = 0; i < num_pre_gomp_target_fini_callbacks; i++)
+    if (atexit (pre_gomp_target_fini_callbacks[i]) != 0)
+      gomp_fatal ("atexit failed");
+  num_pre_gomp_target_fini_callbacks = 0;
 }
 
 #else /* PLUGIN_SUPPORT */
diff --git a/libgomp/testsuite/libgomp.fortran/target-unified_shared_memory-1.f90 b/libgomp/testsuite/libgomp.fortran/target-unified_shared_memory-1.f90
new file mode 100644
index 00000000000..f82b1c7527c
--- /dev/null
+++ b/libgomp/testsuite/libgomp.fortran/target-unified_shared_memory-1.f90
@@ -0,0 +1,13 @@
+! { dg-do run }
+
+program requires_unified_shared_memory
+  character(32) :: str
+  !$omp requires unified_shared_memory
+
+  str = trim (str)
+
+  !$omp target
+  block
+  end block
+
+end program requires_unified_shared_memory