Re: [Patch] libgomp: Fix reverse offload issues

[Tobias Burnus <tobias@codesourcery.com>]

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Now committed as obvious as
r13-5680-g0b1ce70a813b98ef2893779d14ad6c90c5d06a71.

I improved the wording in the commit comment a bit, compared to previous
attachment and I have verified that those features work with AMDGCN* and
without offloading.

Tobias

(* it seems as if there is still another issue with mapping, this time
for array-descriptor variables that do not exist on the host, i.e. that
have to be fully mapped to the host. I will look into this today or Monday.)

On 02.02.23 15:13, Tobias Burnus wrote:
> Found when testing AMD GCN offloading, the second issue came up with
> libgomp.fortran/reverse-offload-5.f90. (But oddly not with nvptx.)
>
> While the first one (new test: libgomp.fortran/reverse-offload-6.f90)
> came up when debugging the issue.
>
> Tobias
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commit 0b1ce70a813b98ef2893779d14ad6c90c5d06a71
Author: Tobias Burnus <tobias@codesourcery.com>
Date:   Fri Feb 3 11:31:53 2023 +0100

    libgomp: Fix reverse offload issues
    
    If there is nothing to map, skip the mapping and avoid attempting to
    copy 0 bytes from addrs, sizes and kinds.
    
    Additionally, it could happen that a non-allocated address was deallocated,
    such as a pointer set, leading to a free for the actual data.
    
    libgomp/
            * target.c (gomp_target_rev): Handle mapnum == 0 and avoid
            freeing not allocated memory.
            * testsuite/libgomp.fortran/reverse-offload-6.f90: New test.
---
 libgomp/target.c                                   |  8 +++---
 .../libgomp.fortran/reverse-offload-6.f90          | 32 ++++++++++++++++++++++
 2 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/libgomp/target.c b/libgomp/target.c
index b16ee761a95..c1682caea13 100644
--- a/libgomp/target.c
+++ b/libgomp/target.c
@@ -3324,7 +3324,7 @@ gomp_target_rev (uint64_t fn_ptr, uint64_t mapnum, uint64_t devaddrs_ptr,
     gomp_fatal ("Cannot find reverse-offload function");
   void (*host_fn)() = (void (*)()) n->k->host_start;
 
-  if (devicep->capabilities & GOMP_OFFLOAD_CAP_SHARED_MEM)
+  if ((devicep->capabilities & GOMP_OFFLOAD_CAP_SHARED_MEM) || mapnum == 0)
     {
       devaddrs = (uint64_t *) (uintptr_t) devaddrs_ptr;
       sizes = (uint64_t *) (uintptr_t) sizes_ptr;
@@ -3402,7 +3402,7 @@ gomp_target_rev (uint64_t fn_ptr, uint64_t mapnum, uint64_t devaddrs_ptr,
 	  }
     }
 
-  if (!(devicep->capabilities & GOMP_OFFLOAD_CAP_SHARED_MEM))
+  if (!(devicep->capabilities & GOMP_OFFLOAD_CAP_SHARED_MEM) && mapnum > 0)
     {
       size_t j, struct_cpy = 0;
       splay_tree_key n2;
@@ -3638,7 +3638,7 @@ gomp_target_rev (uint64_t fn_ptr, uint64_t mapnum, uint64_t devaddrs_ptr,
 
   host_fn (devaddrs);
 
-  if (!(devicep->capabilities & GOMP_OFFLOAD_CAP_SHARED_MEM))
+  if (!(devicep->capabilities & GOMP_OFFLOAD_CAP_SHARED_MEM) && mapnum > 0)
     {
       uint64_t struct_cpy = 0;
       bool clean_struct = false;
@@ -3680,7 +3680,7 @@ gomp_target_rev (uint64_t fn_ptr, uint64_t mapnum, uint64_t devaddrs_ptr,
 	      clean_struct = true;
 	      struct_cpy = sizes[i];
 	    }
-	  else if (cdata[i].aligned)
+	  else if (!cdata[i].present && cdata[i].aligned)
 	    gomp_aligned_free ((void *) (uintptr_t) devaddrs[i]);
 	  else if (!cdata[i].present)
 	    free ((void *) (uintptr_t) devaddrs[i]);
diff --git a/libgomp/testsuite/libgomp.fortran/reverse-offload-6.f90 b/libgomp/testsuite/libgomp.fortran/reverse-offload-6.f90
new file mode 100644
index 00000000000..04866edbba7
--- /dev/null
+++ b/libgomp/testsuite/libgomp.fortran/reverse-offload-6.f90
@@ -0,0 +1,32 @@
+!
+! Ensure that a mapping with no argument works
+!
+
+module m
+  implicit none (type, external)
+  integer :: x = 32
+  integer :: dev_num2 = -1
+contains
+subroutine  foo()
+  use omp_lib, only: omp_get_device_num
+  x = x + 10
+  dev_num2 = omp_get_device_num()
+end
+end module m
+
+use m
+use omp_lib
+!$omp requires reverse_offload
+implicit none (type, external)
+integer :: dev_num = -1
+!$omp target map(from:dev_num)
+  dev_num = omp_get_device_num()
+  ! This calls GOMP_target_ext with number of maps = 0
+  !$omp target device(ancestor:1)
+    call foo
+  !$omp end target
+!$omp end target
+
+if (omp_get_num_devices() > 0 .and.  dev_num2 == dev_num) stop 1
+if (x /= 42) stop 2
+end