Precise dependencies compatibility

doc/ref_kernel.rst

@@ -460,6 +460,10 @@ Loopy's expressions are a slight superset of the expressions supported by
 TODO: Functions
 TODO: Reductions
 
+Dependencies
+^^^^^^^^^^^^
+.. automodule:: loopy.kernel.dependency
+
 Function Call Instructions
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 

loopy/kernel/dependency.py

@@ -0,0 +1,120 @@
+"""
+.. autofunction:: add_lexicographic_happens_after
+"""
+
+__copyright__ = "Copyright (C) 2023 Addison Alvey-Blanco"
+
+__license__ = """
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+"""
+
+import islpy as isl
+from islpy import dim_type
+
+from loopy import LoopKernel
+from loopy.kernel.instruction import HappensAfter
+from loopy.translation_unit import for_each_kernel
+
+
+@for_each_kernel
+def add_lexicographic_happens_after(knl: LoopKernel) -> LoopKernel:
+    """Construct a sequential dependency specification between each instruction
+    and the instruction immediately before it. This takes the order of statements
+    in :attr:`loopy.LoopKernel.instructions` and considers the inames (loops) within
+    which each statement is nested. Within the sequence of statements,
+    each iname must apply to a contiguous region, allowing us to speak of
+    a 'loop entry' and a 'loop exit' point. Loops/inames must nest properly,
+    i.e. entry and exit points of a loop/iname must occur nested within
+    the same outer loop structure.
+
+    Based on this understanding of the presented kernel, this routine adds
+    a dependency structure (see :class:`~loopy.HappensAfter`) copmatible
+    with a C program consisting of the same loop nest, i.e. statements
+    within the same loop nest obeying *lexicographic* ordering.
+
+    If inames are perfectly nested (i.e. both entry/exit points coincide),
+    the nesting of the two loops is undefined.
+    """
+
+    new_insns = []
+    for iafter, insn_after in enumerate(knl.instructions):
+        if iafter == 0:
+            new_insns.append(insn_after)
+
+        else:
+            insn_before = knl.instructions[iafter-1]
+
+            domain_before = knl.get_inames_domain(insn_before.within_inames)
+            domain_after = knl.get_inames_domain(insn_after.within_inames)
+
+            shared_inames = insn_before.within_inames & insn_after.within_inames
+
+            happens_after = isl.Map.from_domain_and_range(
+                    domain_before,
+                    domain_after)
+
+            for idim in range(happens_after.dim(dim_type.out)):
+                happens_after = happens_after.set_dim_name(
+                        dim_type.out,
+                        idim,
+                        happens_after.get_dim_name(dim_type.out, idim) + "'")
+
+            shared_inames_order_before = [
+                    domain_before.get_dim_name(dim_type.out, idim)
+                    for idim in range(domain_before.dim(dim_type.out))
+                    if domain_before.get_dim_name(dim_type.out, idim)
+                    in shared_inames]
+
+            shared_inames_order_after = [
+                    domain_after.get_dim_name(dim_type.out, idim)
+                    for idim in range(domain_after.dim(dim_type.out))
+                    if domain_after.get_dim_name(dim_type.out, idim)
+                    in shared_inames]
+
+            assert shared_inames_order_after == shared_inames_order_before
+            shared_inames_order = shared_inames_order_after
+
+            affs_in = isl.affs_from_space(happens_after.domain().space)
+            affs_out = isl.affs_from_space(happens_after.range().space)
+
+            lex_map = isl.Map.empty(happens_after.space)
+            for iinnermost, innermost_iname in enumerate(shared_inames):
+                innermost_map = affs_in[innermost_iname].lt_map(
+                        affs_out[innermost_iname + "'"])
+
+                for outer_iname in shared_inames_order[:iinnermost]:
+                    innermost_map = innermost_map & (
+                            affs_in[outer_iname].eq_map(
+                                affs_out[outer_iname + "'"]))
+
+                lex_map = lex_map | innermost_map
+
+            happens_after = happens_after & lex_map
+
+            new_happens_after = {
+                    insn_before.id: HappensAfter(None, happens_after)}
+
+            insn_after = insn_after.copy(happens_after=new_happens_after)
+
+            new_insns.append(insn_after)
+
+    return knl.copy(instructions=new_insns)
+
+
+# vim: foldmethod=marker

test/test_dependencies.py

@@ -0,0 +1,51 @@
+__copyright__ = "Copyright (C) 2023 Addison Alvey-Blanco"
+
+__license__ = """
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+"""
+
+import sys
+
+import loopy as lp
+from loopy.kernel.dependency import add_lexicographic_happens_after
+
+
+def test_lex_dependencies():
+    knl = lp.make_kernel(
+            [
+                "{[a,b]: 0<=a,b<7}",
+                "{[i,j]: 0<=i,j<n and 0<=a,b<5}",
+                "{[k,l]: 0<=k,l<n and 0<=a,b<3}"
+                ],
+            """
+            v[a,b,i,j] = 2*v[a,b,i,j]
+            v[a,b,k,l] = 2*v[a,b,k,l]
+            """)
+
+    knl = add_lexicographic_happens_after(knl)
+
+
+if __name__ == "__main__":
+    if len(sys.argv) > 1:
+        exec(sys.argv[1])
+    else:
+        from pytest import main
+        main([__file__])
+
+# vim: foldmethod=marker