compiler: More volatiles to work around -O3 issues

devito/ir/iet/utils.py

@@ -3,7 +3,8 @@
 from devito.tools import filter_ordered
 from devito.types import Global
 
-__all__ = ['filter_iterations', 'retrieve_iteration_tree', 'derive_parameters']
+__all__ = ['filter_iterations', 'retrieve_iteration_tree', 'derive_parameters',
+           'maybe_alias']
 
 
 class IterationTree(tuple):
@@ -122,3 +123,34 @@ def derive_parameters(iet, drop_locals=False):
         parameters = [p for p in parameters if not (p.is_ArrayBasic or p.is_LocalObject)]
 
     return parameters
+
+
+def maybe_alias(obj, candidate):
+    """
+    True if `candidate` can act as an alias for `obj`, False otherwise.
+    """
+    if obj is candidate:
+        return True
+
+    # Names are unique throughout compilation, so this is another case we can handle
+    # straightforwardly. It might happen that we have an alias used in a subroutine
+    # with different type qualifiers (e.g., const vs not const, volatile vs not
+    # volatile), but if the names match, they definitely represent the same
+    # logical object
+    if obj.name == candidate.name:
+        return True
+
+    if obj.is_AbstractFunction:
+        if not candidate.is_AbstractFunction:
+            # Obv
+            return False
+
+        # E.g. TimeFunction vs SparseFunction -> False
+        if type(obj).__base__ is not type(candidate).__base__:
+            return False
+
+        # TODO: At some point we may need to introduce some logic here, but we'll
+        # also need to introduce something like __eq_weak__ that compares most of
+        # the __rkwargs__ except for e.g. the name
+
+    return False

devito/passes/iet/asynchrony.py

@@ -1,16 +1,18 @@
 from collections import OrderedDict
+from ctypes import c_int
 
 import cgen as c
 
 from devito.ir import (AsyncCall, AsyncCallable, BlankLine, Call, Callable,
                        Conditional, Dereference, DummyExpr, FindNodes, FindSymbols,
                        Iteration, List, PointerCast, Return, ThreadCallable,
-                       Transformer, While)
+                       Transformer, While, maybe_alias)
 from devito.passes.iet.engine import iet_pass
 from devito.symbolics import (CondEq, CondNe, FieldFromComposite, FieldFromPointer,
                               Null)
 from devito.tools import DefaultOrderedDict, Bunch, split
-from devito.types import Lock, Pointer, PThreadArray, QueueID, SharedData, Symbol
+from devito.types import (Lock, Pointer, PThreadArray, QueueID, SharedData, Symbol,
+                          VolatileInt)
 
 __all__ = ['pthreadify']
 
@@ -48,6 +50,9 @@ def lower_async_callables(iet, track=None, root=None, sregistry=None):
     defines = FindSymbols('defines').visit(root.body)
     ncfields, cfields = split(fields, lambda i: i in defines)
 
+    # Postprocess `ncfields`
+    ncfields = sanitize_ncfields(ncfields)
+
     # SharedData -- that is the data structure that will be used by the
     # main thread to pass information down to the child thread(s)
     sdata = track[iet.name].sdata = SharedData(name='sdata',
@@ -135,7 +140,7 @@ def lower_async_calls(iet, track=None, sregistry=None):
         d = threads.index
         arguments = []
         for a in n.arguments:
-            if a in sdata.ncfields:
+            if any(maybe_alias(a, i) for i in sdata.ncfields):
                 continue
             elif isinstance(a, QueueID):
                 # Different pthreads use different queues
@@ -208,3 +213,20 @@ def lower_async_calls(iet, track=None, sregistry=None):
         assert not finalization
 
     return iet, {'efuncs': tuple(efuncs.values())}
+
+
+# *** Utils
+
+def sanitize_ncfields(ncfields):
+    # Due to a bug in the NVC compiler (v<=22.7 and potentially later),
+    # we have to use C's `volatile` more extensively than strictly necessary
+    # to avoid flaky optimizations that would cause fauly behaviour in rare,
+    # non-deterministic scenarios
+    sanitized = []
+    for i in ncfields:
+        if i._C_ctype is c_int:
+            sanitized.append(VolatileInt(name=i.name))
+        else:
+            sanitized.append(i)
+
+    return sanitized

tests/test_gpu_common.py

@@ -182,7 +182,7 @@ def test_tasking_fused(self):
         exprs = FindNodes(Expression).visit(op._func_table['copy_to_host0'].root)
         b = 13 if configuration['language'] == 'openacc' else 12  # No `qid` w/ OMP
         assert str(exprs[b]) == 'const int deviceid = sdata->deviceid;'
-        assert str(exprs[b+1]) == 'int time = sdata->time;'
+        assert str(exprs[b+1]) == 'volatile int time = sdata->time;'
         assert str(exprs[b+2]) == 'lock0[0] = 1;'
         assert exprs[b+3].write is u
         assert exprs[b+4].write is v