[OpenMP] Fix use_device_… with absent optional arg
diff mbox series

Message ID 749d496b-3807-6438-2ed9-c44efe455bd9@mentor.com
State New
Headers show
Series
  • [OpenMP] Fix use_device_… with absent optional arg
Related show

Commit Message

Tobias Burnus Nov. 21, 2019, 4:46 p.m. UTC
This fixes two issues with the recently added absent-optional patch for 
use_device_…

(a) For nonallocatable, nonpointer arrays the data component of the 
array descriptor is replaced by a local variable – if the argument is 
absent, this variable is not initialized and, unless it is NULL, a 
pointer to undefined memory attempted to be mapped.

(b) For per-value arguments, the dummy argument itself always exists and 
as it is not a pointer, there is nothing to dereference. Hence, 
'use_device_addr(val_arg)' can be run unconditionally. However, doing so 
will fail if 'val_arg' has never been mapped to the device. – I think 
the most sensible is to update the test case. (One could add a 
condition, to use a NULL pointer if absent, but as I cannot come up with 
a valid program, leaving the condition out in the generated code makes 
more sense.)

OK?

Tobias

PS: I wonder why I didn't see it when initially submitting the patch. I 
think it must be after I did a small change and did a quick regtesting. 
I assume for some reasons the device became unavailable – turning all 
checks into unsupported and I only looked for FAIL and didn't check 
whether some new unsupported popped up. – Namely, 
use_device_addr-{3,4}.f90 failed without (a) – but only with -O1 (and 
with 1 of 11 (hardware, cuda version) combos with -Os). 
use_device_ptr-optional-2.f90 failed with '-O' (which is the only option 
which was actually run) due to (a) and (b).

Comments

Tobias Burnus Nov. 29, 2019, 12:03 p.m. UTC | #1
Revised patch after some re-considerations (and finding tons of issues 
with VALUE + OPTIONAL in gfortran itself). – What the patch does [all 
related to use_device_{addr,ptr} and 'optional' arguments]:

For assumed-shape arrays, the compiler generates code like "if (arg) 
arg.0 = arg->data;". Hence, arg.0 was always available – but possibly 
pointing to uninitialized memory. – Likewise, per-value-passed 
arguments, 'arg' (i.e. &arg) is always available. — But, in the absent 
case, if 'arg->data is not NULL or the per-value decl is not mapped (cf. 
test case), that's not the best idea.

I thought that I don't need a condition in thoses case – but it turns 
out that the offloading plugin might (rightly!) complain that the 
address is not mapped. – Hence, I add the is-present condition now also 
in for those case; as none remain, the do_optional_check is now gone.

However, after the library call, amp_arr.arg is known to be initialized. 
In this case, I keep the do_optional_check check. – This avoids code 
which boils down to  "x0 = arg ? omp_arr.arg : NULL". – and keeps 
generating condtions only for complex code such as:  if (present) { 
tmp.data = omp_arr.arg; arg = &tmp; } else {arg = NULL;}.

Finally, while testing/exploring value+optional bugs, I stumbled over 
'type(c_ptr),value' which is 'void *'. In particular, it is pointer but 
still the is-present status is passed as hidden argument. This patch 
fixes both mapping and the is-present check.

Build on x86-64-gnu-linux + tested once on a system without offloading 
support and with nvptx offloading.
OK?

Tobias

PS: Regarding the issues with OPTIONAL and VALUE, see PR fortran/92703 
and PR fortran/92702. Found issues: const-len character strings are 
passed as value w/o hidden is-present arg but func call passes them; 
those and derived types/the outer class container are passed by value - 
but the 'present()' check assumes pointers (hence: ICE); if basent 
null_ptr_node is passed, I fear that this will give stack issues, at 
least on some platforms. — Additionally, deferred-length character 
strings and arrays are permitted since F2008 but not yet supported.
Jakub Jelinek Dec. 5, 2019, 11:46 a.m. UTC | #2
On Fri, Nov 29, 2019 at 01:03:13PM +0100, Tobias Burnus wrote:
> --- a/gcc/fortran/trans-openmp.c
> +++ b/gcc/fortran/trans-openmp.c
> @@ -60,7 +60,8 @@ gfc_omp_is_allocatable_or_ptr (const_tree decl)
>  
>  /* True if the argument is an optional argument; except that false is also
>     returned for arguments with the value attribute (nonpointers) and for
> -   assumed-shape variables (decl is a local variable containing arg->data).  */
> +   assumed-shape variables (decl is a local variable containing arg->data).
> +   Note that pvoid_type_node is for 'type(c_ptr), value.  */
>  
>  static bool
>  gfc_omp_is_optional_argument (const_tree decl)
> @@ -68,6 +69,7 @@ gfc_omp_is_optional_argument (const_tree decl)
>    return (TREE_CODE (decl) == PARM_DECL
>  	  && DECL_LANG_SPECIFIC (decl)
>  	  && TREE_CODE (TREE_TYPE (decl)) == POINTER_TYPE
> +	  && TREE_TYPE (decl) != pvoid_type_node

Is it always pvoid_type_node, or could it be say const qualified version
thereof etc. (C void const *) etc.?  If the latter, then
	  && !VOID_TYPE_P (TREE_TYPE (TREE_TYPE (decl)))
might be better check.  If it is always just pvoid_type_node, the above is
fine sure.

>  	  && GFC_DECL_OPTIONAL_ARGUMENT (decl));
>  }
>  
> @@ -99,9 +101,12 @@ gfc_omp_check_optional_argument (tree decl, bool for_present_check)
>        || !GFC_DECL_OPTIONAL_ARGUMENT (decl))
>      return NULL_TREE;
>  
> -  /* For VALUE, the scalar variable is passed as is but a hidden argument
> -     denotes the value.  Cf. trans-expr.c.  */
> -  if (TREE_CODE (TREE_TYPE (decl)) != POINTER_TYPE)
> +   /* Scalars with VALUE attribute which are passed by value use a hidden
> +      argument to denote the present status.  They are passed as nonpointer type
> +      with one exception: 'type(c_ptr), value' as '*void'.  */

void* or void * instead of *void?

> +   /* Cf. trans-expr.c's gfc_conv_expr_present.  */
> +   if (TREE_CODE (TREE_TYPE (decl)) != POINTER_TYPE
> +       || TREE_TYPE (decl) == pvoid_type_node)

And similar question to the above one.

> @@ -12027,14 +12022,12 @@ lower_omp_target (gimple_stmt_iterator *gsi_p, omp_context *ctx)
>  			       && omp_is_allocatable_or_ptr (ovar))))
>  		      {
>  			var = build_simple_mem_ref (var);
> -			do_optional_check = true;
>  		      }

The above then becomes { single_stmt } and so should be changed to
single_stmt without {}s around it.

> @@ -1,33 +1,47 @@
>  ! Check whether absent optional arguments are properly
>  ! handled with use_device_{addr,ptr}.
>  program main
> + use iso_c_binding, only: c_ptr, c_loc
>   implicit none (type, external)
>   call foo()
>  contains
> -  subroutine foo(v, w, x, y, z)
> +  subroutine foo(v, w, x, y, z, cptr)
>      integer, target, optional, value :: v
>      integer, target, optional :: w
>      integer, target, optional :: x(:)
>      integer, target, optional, allocatable :: y
>      integer, target, optional, allocatable :: z(:)
> +    type(c_ptr), target, optional, value :: cptr
>      integer :: d
>  
> -    !$omp target data map(d) use_device_addr(v, w, x, y, z)
> -      if(present(v)) stop 1
> -      if(present(w)) stop 2
> -      if(present(x)) stop 3
> -      if(present(y)) stop 4
> -      if(present(z)) stop 5
> +    ! Need to map per-VALUE arguments, if present
> +    if (present(v)) then
> +      !$omp target enter data map(to:v)
> +      stop 1  ! – but it shall not be present in this test case.
> +    end if
> +    if (present(cptr)) then
> +      !$omp target enter data map(to:cptr)
> +      stop 2  ! – but it shall not be present in this test case.
> +    end if

Shouln't the stop arguments differ from anything else already in the
testcase?

> +
> +    !$omp target data map(d) use_device_addr(v, w, x, y, z, cptr)
> +      if (present(v)) then; v    = 5; stop 1; endif
> +      if (present(w)) then; w    = 5; stop 2; endif
> +      if (present(x)) then; x(1) = 5; stop 3; endif
> +      if (present(y)) then; y    = 5; stop 4; endif
> +      if (present(z)) then; z(1) = 5; stop 5; endif
> +      if (present(cptr)) then; cptr = c_loc(v); stop 6; endif
>      !$omp end target data
>  
>  ! Using 'v' in use_device_ptr gives an ICE
>  ! TODO: Find out what the OpenMP spec permits for use_device_ptr
>  
> -    !$omp target data map(d) use_device_ptr(w, x, y, z)
> -      if(present(w)) stop 6
> -      if(present(x)) stop 7
> -      if(present(y)) stop 8
> -      if(present(z)) stop 9
> +    !$omp target data map(d) use_device_ptr(w, x, y, z, cptr)
> +      if(present(w)) then; w    = 5; stop 11; endif
> +      if(present(x)) then; x(1) = 5; stop 12; endif
> +      if(present(y)) then; y    = 5; stop 13; endif
> +      if(present(z)) then; z(1) = 5; stop 14; endif
> +      if(present(cptr)) then; cptr = c_loc(x); stop 15; endif
>      !$omp end target data
>    end subroutine foo
>  end program main

Otherwise LGTM.

	Jakub
Tobias Burnus Dec. 5, 2019, 3:19 p.m. UTC | #3
Hi Jakub,

thanks for the review – committed as Rev. 279004.

On 12/5/19 12:46 PM, Jakub Jelinek wrote:
> On Fri, Nov 29, 2019 at 01:03:13PM +0100, Tobias Burnus wrote:
>> --- a/gcc/fortran/trans-openmp.c
>> +	  && TREE_TYPE (decl) != pvoid_type_node
> Is it always pvoid_type_node, or could it be say const qualified version
> thereof etc. (C void const *) etc.? If the latter, then
> 	  && !VOID_TYPE_P (TREE_TYPE (TREE_TYPE (decl)))
> might be better check.  If it is always just pvoid_type_node, the above is
> fine sure.

I will use your version (twice) just to be sure. — Currently, I think it 
will always be pvoid_type_node but I don't want to rule out some const 
qualifier might be possible. (volatile is not permitted with value, 
restricted and atomic qualifiers are unlikely.)

[…]

> Shouln't the stop arguments differ from anything else already in the 
> testcase? 
Yes – it makes failure debugging easier. I thought, I had re-enumerated, 
but I missed the two.

Tobias

Patch
diff mbox series

	gcc/
	* omp-low.c (lower_omp_target): Also add is-present condition for
	nonallocatable, nonpointer, optional arguments.

	libgomp/
	* testsuite/libgomp.fortran/use_device_ptr-optional-2.f90: Map
	per-value optional arg before using it in use_device_addr.


diff --git a/gcc/omp-low.c b/gcc/omp-low.c
index 19132f76da2..94f830c644b 100644
--- a/gcc/omp-low.c
+++ b/gcc/omp-low.c
@@ -12029,6 +12029,8 @@  lower_omp_target (gimple_stmt_iterator *gsi_p, omp_context *ctx)
 			var = build_simple_mem_ref (var);
 			do_optional_check = true;
 		      }
+		    else if (TREE_CODE (type) == ARRAY_TYPE)
+		      do_optional_check = true;
 		    var = fold_convert (TREE_TYPE (x), var);
 		  }
 	      }
diff --git a/libgomp/testsuite/libgomp.fortran/use_device_ptr-optional-2.f90 b/libgomp/testsuite/libgomp.fortran/use_device_ptr-optional-2.f90
index 41abf17eede..bad0e00a23a 100644
--- a/libgomp/testsuite/libgomp.fortran/use_device_ptr-optional-2.f90
+++ b/libgomp/testsuite/libgomp.fortran/use_device_ptr-optional-2.f90
@@ -1,3 +1,5 @@ 
+! {dg-do run }
+!
 ! Check whether absent optional arguments are properly
 ! handled with use_device_{addr,ptr}.
 program main
@@ -12,6 +14,10 @@  contains
     integer, target, optional, allocatable :: z(:)
     integer :: d
 
+    !$omp target data map(to:v)
+    ! If 'v' should be usable as device pointer, it has to be mapped at some
+    ! point. As it is declared with the VALUE attribute, it needs to be done
+    ! within 'foo'
     !$omp target data map(d) use_device_addr(v, w, x, y, z)
       if(present(v)) stop 1
       if(present(w)) stop 2
@@ -19,6 +25,7 @@  contains
       if(present(y)) stop 4
       if(present(z)) stop 5
     !$omp end target data
+    !$omp end target data
 
 ! Using 'v' in use_device_ptr gives an ICE
 ! TODO: Find out what the OpenMP spec permits for use_device_ptr