def _dump_storage(self, iet, storage):
mapper = {}
for k, v in storage.items():
# Expr -> LocalExpr ?
if k.is_Expression:
mapper[k] = v
continue
# allocs/pallocs
allocs = flatten(v.allocs)
for tid, body in as_mapper(v.pallocs, itemgetter(0), itemgetter(1)).items():
header = self.lang.Region._make_header(tid.symbolic_size)
init = c.Initializer(c.Value(tid._C_typedata, tid.name),
self.lang['thread-num'])
allocs.append(c.Module((header, c.Block([init] + body))))
if allocs:
allocs.append(c.Line())
# frees/pfrees
frees = []
for tid, body in as_mapper(v.pfrees, itemgetter(0), itemgetter(1)).items():
header = self.lang.Region._make_header(tid.symbolic_size)
init = c.Initializer(c.Value(tid._C_typedata, tid.name),
self.lang['thread-num'])
frees.append(c.Module((header, c.Block([init] + body))))
frees.extend(flatten(v.frees))
if frees:
frees.insert(0, c.Line())
mapper[k] = k._rebuild(body=List(header=allocs, body=k.body, footer=frees),
**k.args_frozen)
processed = Transformer(mapper, nested=True).visit(iet)
return processed
def _inject_definitions(self, iet, storage):
mapper = {}
for k, v in storage.items():
# Expr -> LocalExpr ?
if k.is_Expression:
mapper[k] = v
continue
# objects
objs = flatten(v.objs)
# allocs/pallocs
allocs = flatten(v.allocs)
for tid, body in as_mapper(v.pallocs, itemgetter(0),
itemgetter(1)).items():
header = self.lang.Region._make_header(tid.symbolic_size)
init = self.lang['thread-num'](retobj=tid)
allocs.append(Block(header=header, body=[init] + body))
# frees/pfrees
frees = []
for tid, body in as_mapper(v.pfrees, itemgetter(0),
itemgetter(1)).items():
header = self.lang.Region._make_header(tid.symbolic_size)
init = self.lang['thread-num'](retobj=tid)
frees.append(Block(header=header, body=[init] + body))
frees.extend(flatten(v.frees))
mapper[k.body] = k.body._rebuild(allocs=allocs,
objs=objs,
frees=frees)
processed = Transformer(mapper, nested=True).visit(iet)
return processed
def _lower_stepping_dims(iet):
"""
Lower SteppingDimensions: index functions involving SteppingDimensions are
turned into ModuloDimensions.
Examples
--------
u[t+1, x] = u[t, x] + 1
becomes
u[t1, x] = u[t0, x] + 1
"""
for i in FindNodes(Iteration).visit(iet):
if not i.uindices:
# Be quick: avoid uselessy reconstructing nodes
continue
# In an expression, there could be `u[t+1, ...]` and `v[t+1, ...]`, where
# `u` and `v` are TimeFunction with circular time buffers (save=None) *but*
# different modulo extent. The `t+1` indices above are therefore conceptually
# different, so they will be replaced with the proper ModuloDimension through
# two different calls to `xreplace`
mindices = [d for d in i.uindices if d.is_Modulo]
groups = as_mapper(mindices, lambda d: d.modulo)
for k, v in groups.items():
mapper = {d.origin: d for d in v}
rule = lambda i: i.function.is_TimeFunction and i.function._time_size == k
replacer = lambda i: xreplace_indices(i, mapper, rule)
iet = XSubs(replacer=replacer).visit(iet)
return iet
def _(expr, terms):
derivs, others = split(terms, lambda i: i.deriv is not None)
if not derivs:
return expr, Term(expr)
# Map by type of derivative
mapper = as_mapper(derivs, lambda i: key(i.deriv))
if len(mapper) == len(derivs):
return expr, Term(expr)
processed = []
for v in mapper.values():
fact, nonfact = split(v, lambda i: _is_const_coeff(i.other, i.deriv))
if fact:
# Finally factorize derivative arguments
func = fact[0].deriv._new_from_self
exprs = []
for i in fact:
if i.func:
exprs.append(i.func(i.other, i.deriv.expr))
else:
assert i.other == 1
exprs.append(i.deriv.expr)
fact = [Term(func(expr=expr.func(*exprs)))]
for i in fact + nonfact:
if i.func:
processed.append(i.func(i.other, i.deriv))
else:
processed.append(i.other)
others = [i.other for i in others]
expr = expr.func(*(processed + others))
return expr, Term(expr)
def callback(self, clusters, prefix, xtracted=None):
if not prefix:
return clusters
d = prefix[-1].dim
# Rule out extractions that would break data dependencies
exclude = set().union(*[c.scope.writes for c in clusters])
# Rule out extractions that depend on the Dimension currently investigated,
# as they clearly wouldn't be invariants
exclude.add(d)
key = lambda c: self._lookup_key(c, d)
processed = list(clusters)
for ak, group in as_mapper(clusters, key=key).items():
g = [c for c in group if c.is_dense and c not in xtracted]
if not g:
continue
made = self._aliases_from_clusters(g, exclude, ak)
if made:
for n, c in enumerate(g, -len(g)):
processed[processed.index(c)] = made.pop(n)
processed = made + processed
xtracted.extend(made)
return processed
def _drop_halospots(iet):
"""
Remove HaloSpots that:
* Embed SEQUENTIAL Iterations
* Would be used to compute Increments (in which case, a halo exchange
is actually unnecessary)
"""
mapper = defaultdict(set)
# If a HaloSpot Dimension turns out to be SEQUENTIAL, then the HaloSpot is useless
for hs, iterations in MapNodes(HaloSpot, Iteration).visit(iet).items():
dmapper = as_mapper(iterations, lambda i: i.dim.root)
for d, v in dmapper.items():
if d in hs.dimensions and all(i.is_Sequential for i in v):
mapper[hs].update(set(hs.functions))
break
# If all HaloSpot reads pertain to increments, then the HaloSpot is useless
for hs, expressions in MapNodes(HaloSpot, Expression).visit(iet).items():
for f in hs.fmapper:
scope = Scope([i.expr for i in expressions])
if all(i.is_increment for i in scope.reads.get(f, [])):
mapper[hs].add(f)
# Transform the IET introducing the "reduced" HaloSpots
subs = {
hs: hs._rebuild(halo_scheme=hs.halo_scheme.drop(mapper[hs]))
for hs in FindNodes(HaloSpot).visit(iet)
}
iet = Transformer(subs, nested=True).visit(iet)
return iet
def iet_lower_dimensions(iet):
"""
Replace all DerivedDimensions within the ``iet``'s expressions with
lower-level symbolic objects (other Dimensions or Symbols).
* Array indices involving SteppingDimensions are turned into ModuloDimensions.
Example: ``u[t+1, x] = u[t, x] + 1 >>> u[t1, x] = u[t0, x] + 1``
* Array indices involving ConditionalDimensions used are turned into
integer-division expressions.
Example: ``u[t_sub, x] = u[time, x] >>> u[time / 4, x] = u[time, x]``
"""
# Lower SteppingDimensions
for i in FindNodes(Iteration).visit(iet):
if not i.uindices:
# Be quick: avoid uselessy reconstructing nodes
continue
# In an expression, there could be `u[t+1, ...]` and `v[t+1, ...]`, where
# `u` and `v` are TimeFunction with circular time buffers (save=None) *but*
# different modulo extent. The `t+1` indices above are therefore conceptually
# different, so they will be replaced with the proper ModuloDimension through
# two different calls to `xreplace`
groups = as_mapper(i.uindices, lambda d: d.modulo)
for k, v in groups.items():
mapper = {d.origin: d for d in v}
rule = lambda i: i.function.is_TimeFunction and i.function._time_size == k
replacer = lambda i: xreplace_indices(i, mapper, rule)
iet = XSubs(replacer=replacer).visit(iet)
# Lower ConditionalDimensions
cdims = [d for d in FindSymbols('free-symbols').visit(iet)
if isinstance(d, ConditionalDimension)]
mapper = {d: IntDiv(d.index, d.factor) for d in cdims}
iet = XSubs(mapper).visit(iet)
return iet
def _eval_at(self, func):
"""
Evaluates the derivative at the location of `func`. It is necessary for staggered
setup where one could have Eq(u(x + h_x/2), v(x).dx)) in which case v(x).dx
has to be computed at x=x + h_x/2.
"""
# If an x0 already exists do not overwrite it
x0 = self.x0 or dict(func.indices_ref._getters)
if self.expr.is_Add:
# If `expr` has both staggered and non-staggered terms such as
# `(u(x + h_x/2) + v(x)).dx` then we exploit linearity of FD to split
# it into `u(x + h_x/2).dx` and `v(x).dx`, since they require
# different FD indices
mapper = as_mapper(self.expr._args_diff, lambda i: i.staggered)
args = [self.expr.func(*v) for v in mapper.values()]
args.extend(
[a for a in self.expr.args if a not in self.expr._args_diff])
args = [self._new_from_self(expr=a, x0=x0) for a in args]
return self.expr.func(*args)
elif self.expr.is_Mul:
# For Mul, We treat the basic case `u(x + h_x/2) * v(x) which is what appear
# in most equation with div(a * u) for example. The expression is re-centered
# at the highest priority index (see _gather_for_diff) to compute the
# derivative at x0.
return self._new_from_self(x0=x0, expr=self.expr._gather_for_diff)
else:
# For every other cases, that has more functions or more complexe arithmetic,
# there is not actual way to decide what to do so it’s as safe to use
# the expression as is.
return self._new_from_self(x0=x0)
def hs_comp_locindices(f, dims, ispace, scope):
"""
Map the Dimensions in ``dims`` to the local indices necessary
to perform a halo exchange, as described in HaloScheme.__doc__.
Examples
--------
1) u[t+1, x] = f(u[t, x]) => shift == 1
2) u[t-1, x] = f(u[t, x]) => shift == 1
3) u[t+1, x] = f(u[t+1, x]) => shift == 0
In the first and second cases, the x-halo should be inserted at `t`,
while in the last case it should be inserted at `t+1`.
"""
loc_indices = {}
for d in dims:
func = max if ispace.is_forward(d.root) else min
loc_index = func([i[d] for i in scope.getreads(f)],
key=lambda i: i - d)
if d.is_Stepping:
subiters = ispace.sub_iterators.get(d.root, [])
submap = as_mapper(subiters, lambda md: md.modulo)
submap = {i.origin: i for i in submap[f._time_size]}
try:
loc_indices[d] = submap[loc_index]
except KeyError:
raise HaloSchemeException(
"Don't know how to build a HaloScheme as the "
"stepping index `%s` is undefined" % loc_index)
else:
loc_indices[d] = loc_index
return loc_indices
def cross_cluster_cse(clusters):
"""
Perform common sub-expressions elimination across an iterable of Clusters.
"""
clusters = clusters.unfreeze()
# Detect redundancies
mapper = {}
for c in clusters:
candidates = [i for i in c.trace.values() if i.is_unbound_temporary]
for v in as_mapper(candidates, lambda i: i.rhs).values():
for i in v[:-1]:
mapper[i.lhs.base] = v[-1].lhs.base
if not mapper:
# Do not waste time reconstructing identical expressions
return clusters
# Apply substitutions
for c in clusters:
c.exprs = [
i.xreplace(mapper) for i in c.trace.values()
if i.lhs.base not in mapper
]
return clusters
def iet_lower_dimensions(iet):
"""
Replace all DerivedDimensions within the ``iet``'s expressions with
lower-level symbolic objects (other Dimensions or Symbols).
* Array indices involving SteppingDimensions are turned into ModuloDimensions.
Example: ``u[t+1, x] = u[t, x] + 1 >>> u[t1, x] = u[t0, x] + 1``
* Array indices involving ConditionalDimensions used are turned into
integer-division expressions.
Example: ``u[t_sub, x] = u[time, x] >>> u[time / 4, x] = u[time, x]``
"""
# Lower SteppingDimensions
for i in FindNodes(Iteration).visit(iet):
if not i.uindices:
# Be quick: avoid uselessy reconstructing nodes
continue
# In an expression, there could be `u[t+1, ...]` and `v[t+1, ...]`, where
# `u` and `v` are TimeFunction with circular time buffers (save=None) *but*
# different modulo extent. The `t+1` indices above are therefore conceptually
# different, so they will be replaced with the proper ModuloDimension through
# two different calls to `xreplace`
groups = as_mapper(i.uindices, lambda d: d.modulo)
for k, v in groups.items():
mapper = {d.origin: d for d in v}
rule = lambda i: i.function.is_TimeFunction and i.function._time_size == k
replacer = lambda i: xreplace_indices(i, mapper, rule)
iet = XSubs(replacer=replacer).visit(iet)
# Lower ConditionalDimensions
cdims = [d for d in FindSymbols('free-symbols').visit(iet)
if isinstance(d, ConditionalDimension)]
mapper = {d: IntDiv(d.index, d.factor) for d in cdims}
iet = XSubs(mapper).visit(iet)
return iet
def _apply_substitutions(self, expressions, subs):
"""
Transform ``expressions`` by: ::
* Applying any user-provided symbolic substitution;
* Replacing :class:`Dimension`s with :class:`SubDimension`s based
on the expression :class:`Region`.
"""
domain_subs = subs
interior_subs = subs.copy()
processed = []
mapper = as_mapper(expressions, lambda i: i._region)
for k, v in mapper.items():
for e in v:
if k is INTERIOR:
# Introduce SubDimensions to iterate over the INTERIOR region only
candidates = [
i for i in e.free_symbols
if isinstance(i, Dimension) and i.is_Space
]
interior_subs.update({
i: SubDimension.middle("%si" % i, i, 1, 1)
for i in candidates if i not in interior_subs
})
processed.append(e.xreplace(interior_subs))
elif k is DOMAIN:
processed.append(e.xreplace(domain_subs))
else:
raise ValueError("Unsupported Region `%s`" % k)
return processed
def process(self, iet):
sync_spots = FindNodes(SyncSpot).visit(iet)
if not sync_spots:
return iet, {}
def key(s):
# The SyncOps are to be processed in the following order
return [
WaitLock, WithLock, Delete, FetchUpdate, FetchPrefetch,
PrefetchUpdate, WaitPrefetch
].index(s)
callbacks = {
WaitLock: self._make_waitlock,
WithLock: self._make_withlock,
Delete: self._make_delete,
FetchUpdate: self._make_fetchupdate,
FetchPrefetch: self._make_fetchprefetch,
PrefetchUpdate: self._make_prefetchupdate
}
postponed_callbacks = {WaitPrefetch: self._make_waitprefetch}
all_callbacks = [callbacks, postponed_callbacks]
pieces = namedtuple('Pieces', 'init finalize funcs objs')([], [], [],
Objs())
# The processing is a two-step procedure; first, we apply the `callbacks`;
# then, the `postponed_callbacks`, as these depend on objects produced by the
# `callbacks`
subs = {}
for cbks in all_callbacks:
for n in sync_spots:
mapper = as_mapper(n.sync_ops, lambda i: type(i))
for _type in sorted(mapper, key=key):
try:
subs[n] = cbks[_type](subs.get(n, n), mapper[_type],
pieces, iet)
except KeyError:
pass
iet = Transformer(subs).visit(iet)
# Add initialization and finalization code
init = List(body=pieces.init, footer=c.Line())
finalize = List(header=c.Line(), body=pieces.finalize)
body = iet.body._rebuild(body=(init, ) + iet.body.body + (finalize, ))
iet = iet._rebuild(body=body)
return iet, {
'efuncs': pieces.funcs,
'includes': ['pthread.h'],
'args':
[i.size for i in pieces.objs.threads if not is_integer(i.size)]
}
def iet_lower_steppers(iet):
"""
Replace the :class:`SteppingDimension`s within ``iet``'s expressions with
suitable :class:`ModuloDimension`s.
"""
for i in FindNodes(Iteration).visit(iet):
if not i.uindices:
# Be quick: avoid uselessy reconstructing nodes
continue
# In an expression, there could be `u[t+1, ...]` and `v[t+1, ...]`, where
# `u` and `v` are TimeFunction with circular time buffers (save=None) *but*
# different modulo extent. The `t+1` indices above are therefore conceptually
# different, so they will be replaced with the proper ModuloDimension through
# two different calls to `xreplace`
groups = as_mapper(i.uindices, lambda d: d.modulo)
for k, v in groups.items():
mapper = {d.origin: d for d in v}
rule = lambda i: i.function._time_size == k
iet = ReplaceStepIndices(mapper, rule).visit(iet)
return iet
def mark_halospots(analysis):
"""Update the ``analysis`` detecting the ``REDUNDANT`` HaloSpots within
``analysis.iet``."""
properties = OrderedDict()
def analyze(fmapper, scope):
for f, hse in fmapper.items():
if any(dep.cause & set(hse.loc_indices) for dep in scope.d_anti.project(f)):
return False
return True
for i, scope in analysis.scopes.items():
mapper = as_mapper(FindNodes(HaloSpot).visit(i), lambda hs: hs.halo_scheme)
for k, v in mapper.items():
if len(v) == 1:
continue
if analyze(k.fmapper, scope):
properties.update({i: REDUNDANT for i in v[1:]})
analysis.update(properties)
def process(self, iet):
def key(s):
# The SyncOps are to be processed in the following order
return [WaitLock, WithLock, Delete, FetchWait,
FetchWaitPrefetch].index(s)
callbacks = {
WaitLock: self._make_waitlock,
WithLock: self._make_withlock,
FetchWait: self._make_fetchwait,
FetchWaitPrefetch: self._make_fetchwaitprefetch,
Delete: self._make_delete
}
sync_spots = FindNodes(SyncSpot).visit(iet)
if not sync_spots:
return iet, {}
pieces = namedtuple('Pieces', 'init finalize funcs threads')([], [],
[], [])
subs = {}
for n in sync_spots:
mapper = as_mapper(n.sync_ops, lambda i: type(i))
for _type in sorted(mapper, key=key):
subs[n] = callbacks[_type](subs.get(n, n), mapper[_type],
pieces, iet)
iet = Transformer(subs).visit(iet)
# Add initialization and finalization code
init = List(body=pieces.init, footer=c.Line())
finalize = List(header=c.Line(), body=pieces.finalize)
iet = iet._rebuild(body=(init, ) + iet.body + (finalize, ))
return iet, {
'efuncs': pieces.funcs,
'includes': ['pthread.h'],
'args': [i.size for i in pieces.threads if not is_integer(i.size)]
}
def _generate(self, exprs, exclude):
# E.g., extract `u.dx*a*b` and `u.dx*a*c` from `[(u.dx*a*b).dy`, `(u.dx*a*c).dy]`
def cbk_search(expr):
if isinstance(expr, EvalDerivative) and not expr.base.is_Function:
return expr.args
else:
return flatten(e for e in [cbk_search(a) for a in expr.args]
if e)
cbk_compose = lambda e: split_coeff(e)[1]
basextr = self._do_generate(exprs, exclude, cbk_search, cbk_compose)
if not basextr:
return
yield basextr
# E.g., extract `u.dx*a` from `[(u.dx*a*b).dy, (u.dx*a*c).dy]`
# That is, attempt extracting the largest common derivative-induced subexprs
mappers = [deindexify(e) for e in basextr.extracted]
counter = Counter(flatten(m.keys() for m in mappers))
groups = as_mapper(counter, key=counter.get)
grank = {
k: sorted(v, key=lambda e: estimate_cost(e), reverse=True)
for k, v in groups.items()
}
def cbk_search2(expr, rank):
ret = []
for e in cbk_search(expr):
mapper = deindexify(e)
for i in rank:
if i in mapper:
ret.extend(mapper[i])
break
return ret
candidates = sorted(grank, reverse=True)[:2]
for i in candidates:
lower_pri_elems = flatten([grank[j] for j in candidates if j != i])
cbk_search_i = lambda e: cbk_search2(e, grank[i] + lower_pri_elems)
yield self._do_generate(exprs, exclude, cbk_search_i, cbk_compose)
def cross_cluster_cse(clusters):
"""Apply CSE across an iterable of Clusters."""
clusters = clusters.unfreeze()
# Detect redundancies
mapper = {}
for c in clusters:
candidates = [i for i in c.trace.values() if i.is_unbound_temporary]
for v in as_mapper(candidates, lambda i: i.rhs).values():
for i in v[:-1]:
mapper[i.lhs.base] = v[-1].lhs.base
if not mapper:
# Do not waste time reconstructing identical expressions
return clusters
# Apply substitutions
for c in clusters:
c.exprs = [i.xreplace(mapper) for i in c.trace.values()
if i.lhs.base not in mapper]
return clusters
def _(expr):
args = [factorize_derivatives(a) for a in expr.args]
derivs, others = split(args, lambda a: isinstance(a, sympy.Derivative))
if not derivs:
return expr
# Map by type of derivative
# Note: `D0(a) + D1(b) == D(a + b)` <=> `D0` and `D1`'s metadata match,
# i.e. they are the same type of derivative
mapper = as_mapper(derivs, lambda i: i._metadata)
if len(mapper) == len(derivs):
return expr
args = list(others)
for v in mapper.values():
c = v[0]
if len(v) == 1:
args.append(c)
else:
args.append(c._new_from_self(expr=expr.func(*[i.expr for i in v])))
expr = expr.func(*args)
return expr
def callback(self, clusters, prefix):
if not prefix:
return clusters
d = prefix[-1].dim
subiters = flatten(
[c.ispace.sub_iterators.get(d, []) for c in clusters])
subiters = {i for i in subiters if i.is_Stepping}
if not subiters:
return clusters
# Collect the index access functions along `d`, e.g., `t + 1` where `t` is
# a SteppingDimension for `d = time`
mapper = DefaultOrderedDict(lambda: DefaultOrderedDict(set))
for c in clusters:
indexeds = [
a.indexed for a in c.scope.accesses if a.function.is_Tensor
]
for i in indexeds:
try:
iaf = i.indices[d]
except KeyError:
continue
# Sanity checks
sis = iaf.free_symbols & subiters
if len(sis) == 0:
continue
elif len(sis) == 1:
si = sis.pop()
else:
raise InvalidOperator(
"Cannot use multiple SteppingDimensions "
"to index into a Function")
size = i.function.shape_allocated[d]
assert is_integer(size)
mapper[size][si].add(iaf)
# Construct the ModuloDimensions
mds = []
for size, v in mapper.items():
for si, iafs in list(v.items()):
# Offsets are sorted so that the semantic order (t0, t1, t2) follows
# SymPy's index ordering (t, t-1, t+1) afer modulo replacement so
# that associativity errors are consistent. This corresponds to
# sorting offsets {-1, 0, 1} as {0, -1, 1} assigning -inf to 0
siafs = sorted(iafs,
key=lambda i: -np.inf
if i - si == 0 else (i - si))
for iaf in siafs:
name = '%s%d' % (si.name, len(mds))
offset = uxreplace(iaf, {si: d.root})
mds.append(
ModuloDimension(name, si, offset, size, origin=iaf))
# Replacement rule for ModuloDimensions
def rule(size, e):
try:
return e.function.shape_allocated[d] == size
except (AttributeError, KeyError):
return False
# Reconstruct the Clusters
processed = []
for c in clusters:
# Apply substitutions to expressions
# Note: In an expression, there could be `u[t+1, ...]` and `v[t+1,
# ...]`, where `u` and `v` are TimeFunction with circular time
# buffers (save=None) *but* different modulo extent. The `t+1`
# indices above are therefore conceptually different, so they will
# be replaced with the proper ModuloDimension through two different
# calls to `xreplace_indices`
exprs = c.exprs
groups = as_mapper(mds, lambda d: d.modulo)
for size, v in groups.items():
mapper = {md.origin: md for md in v}
func = partial(xreplace_indices,
mapper=mapper,
key=partial(rule, size))
exprs = [e.apply(func) for e in exprs]
# Augment IterationSpace
ispace = IterationSpace(c.ispace.intervals, {
**c.ispace.sub_iterators,
**{
d: tuple(mds)
}
}, c.ispace.directions)
processed.append(c.rebuild(exprs=exprs, ispace=ispace))
return processed
def __init__(self, exprs):
self._mapper = {}
self._fixed = {}
# What Functions actually need a halo exchange?
need_halo = as_mapper(Scope(exprs).d_all, lambda i: i.function)
need_halo = {k: v for k, v in need_halo.items() if k.is_TensorFunction}
for i in exprs:
for f, v in i.dspace.parts.items():
if f not in need_halo:
continue
if f.grid is None:
raise RuntimeError("`%s` needs a `Grid` for a HaloScheme" %
f.name)
for d in f.dimensions:
r = d.root
if v[r].is_Null:
continue
elif d in f.grid.distributor.dimensions:
# Found a distributed dimension, calculate what and how
# much halo is needed
lsize = f._offset_domain[d].left - v[r].lower
if lsize > 0:
self._mapper.setdefault(f, []).append(
(d, LEFT, lsize))
rsize = v[r].upper - f._offset_domain[d].right
if rsize > 0:
self._mapper.setdefault(f, []).append(
(d, RIGHT, rsize))
else:
# Found a serial dimension, we need to determine where,
# along this dimension, the halo will have to be placed
fixed = self._fixed.setdefault(f, OrderedDict())
shift = int(any(d in dep.cause
for dep in need_halo[f]))
# Examples:
# u[t+1, x] = f(u[t, x]) => shift == 1
# u[t-1, x] = f(u[t, x]) => shift == 1
# u[t+1, x] = f(u[t+1, x]) => shift == 0
# In the first and second cases, the x-halo should be inserted
# at `t`, while in the last case it should be inserted at `t+1`
if i.ispace.directions[r] is Forward:
last = v[r].upper - shift
else:
last = v[r].lower + shift
if d.is_Stepping:
# TimeFunctions using modulo-buffered iteration require
# special handling
subiters = i.ispace.sub_iterators.get(r, [])
submap = as_mapper(subiters, lambda md: md.modulo)
submap = {
i.origin: i
for i in submap[f._time_size]
}
try:
handle = submap[d + last]
except KeyError:
raise HaloSchemeException
else:
handle = r + last
if handle is not None and handle != fixed.get(
d, handle):
raise HaloSchemeException
fixed[d] = handle or fixed.get(d)
