Loop Regions #1407

phschaad · 2023-10-24T15:45:08Z

This PR adds LoopRegions to SDFGs. This forms the second core element of the plan to make loops first class citizens of SDFGs.
LoopRegions are a special class of ControlFlowRegions that represent different types of loops, meaning the control flow region inside them is executed a parametric number of times.
A LoopRegion must have a conditional expression that determines whether the region is executed or not. It may additionally have:

an initialization expression that is run when the region is first executed (even if the condition to execute its contents does not hold)
an update expression, executed each time the execution of the region contents is finished
a flag indicating that it's inverted, meaning the contents are executed once before the condition is checked (condition is checked again after every execution)
a set of control flow blocks in its contents that, when reached, finish the execution of the region and do not execute it again even if the condition still holds (equivalent to break in C/Python)
a set of control flow blocks that end the execution of its contents and execute the update statement if there is one. After this, the condition is checked again and the contents may be run again (equivalent to continue in C/Python)

For more general information on control flow regions please refer to the documentation or the PR that introduced them.

An example of a tripple loop nest of regular for loops can be seen in the GEMM program below, showing that a proof-of-concept visualization for the introduced concepts is already available in the latest release version of the VSCode extension (version 1.6.0 and upwards):

As outlined by the project plan, these LoopRegions are currently not being used by any frontend. They can, however, already be manually used through the SDFG builder API. According to plan, most passes and transformations are not currently able to handle the use of such LoopRegions yet, so their use is still highly experimental. To allow traditional transformations and passes to work, as well as to be able to generate codes for SDFGs containing LoopRegions, a compatibility pass (InlineLoopRegions) is available, together with a utility function dace.sdfg.utils.inline_loop_blocks that inlines any LoopRegions to traditional state machine loops.

In summary, the PR includes:

Add LoopRegions to SDFGs, a special control flow region to represent loops
Pass / Utility function to remove all loop regions from a graph, turning them back into regular state machine loops (a.k.a., inlining)
Tests for inlining of loops
Tests for the functional correctness of different types of loops (regular for, while, do-while, do-for) and nested loops (gemm - tripple nested loop)

alexnick83

In general, looks good.

dace/sdfg/state.py

alexnick83 · 2023-11-09T12:49:59Z

dace/sdfg/state.py

@@ -1156,10 +1181,9 @@ def __init__(self, label=None, sdfg=None, debuginfo=None, location=None):
        """
        from dace.sdfg.sdfg import SDFG  # Avoid import loop
        OrderedMultiDiConnectorGraph.__init__(self)
-        ControlFlowBlock.__init__(self, label)
+        ControlFlowBlock.__init__(self, label, sdfg)


In case there is a discussion about using a single super call to initialize everything:

This is a good read: https://stackoverflow.com/questions/3277367/how-does-pythons-super-work-with-multiple-inheritance
My understanding is that super(SDFGState, self).__init__() will call in a sequence the inits of all the superclasses (recursively even if they also call super). To address the issue of different parameters, you could change the signatures of the inits to self, args, **kwargs.

However, my suggestion would be NOT to CHANGE anything, because IMHO it is unintuitive, and most people would just be confused.

alexnick83 · 2023-11-09T12:57:11Z

dace/sdfg/state.py

+
+@make_properties
+class LoopRegion(ControlFlowRegion):
+


I would add some documentation here. Some notes:

I don't like the name inverted because it doesn't sound to me to match the description. I also don't have a suggestion, but ask around for opinions.

Break and continue happen after completing execution of a break/continue state?

Correct on the break / continue. I will make sure to add the necessary documentation, thanks!

Added documentation

tbennun · 2023-11-04T17:41:47Z

dace/sdfg/sdfg.py

@@ -2170,6 +2171,10 @@ def compile(self, output_file=None, validate=True) -> 'CompiledSDFG':
            # if the codegen modifies the SDFG (thereby changing its hash)
            sdfg.build_folder = build_folder

+            # Convert any loop constructs with hierarchical loop regions into simple 1-level state machine loops.
+            # TODO (later): Adapt codegen to deal with hierarchical CFGs instead.
+            sdutils.inline_loop_blocks(sdfg)


This is not the right place to put this code. API calls such as generate_code will skip this. It’s better to add this to the codegen module, right after we validate before generating the code

tbennun · 2023-11-27T08:38:46Z

dace/sdfg/state.py

@@ -99,6 +99,10 @@ def in_degree(self, node: NodeT) -> int:
    def out_degree(self, node: NodeT) -> int:
        ...

+    @property
+    def sdfg(self) -> 'dace.sdfg.SDFG':


you should probably import dace.sdfg.SDFG in the TYPE_CHECKING clause (line 28)

tests/sdfg/loop_region_test.py

tests/transformations/control_flow_inline_test.py

tbennun · 2023-11-27T08:46:12Z

dace/transformation/interstate/control_flow_inline.py

+        init_edge = InterstateEdge()
+        if self.loop.init_statement is not None:
+            init_edge.assignments = {
+                self.loop.loop_variable: self.loop.init_statement.as_string.rpartition('=')[2].strip()


I am not super happy with this. There can be more than one statement in a codeblock, or a different statement entirely (i.e., that does not assign anything). Perhaps verify that there is only one ast.Assign in the can_be_applied method.

Fixed - I'm allowing any number of assignments (but nothing else!) since this can be expressed with a valid SDFG (isedges can have an arbitrary number of assignments).

tbennun · 2023-11-27T08:47:00Z

dace/transformation/interstate/control_flow_inline.py

+        update_edge = InterstateEdge()
+        if self.loop.update_statement is not None:
+            update_edge.assignments = {
+                self.loop.loop_variable: self.loop.update_statement.as_string.rpartition('=')[2].strip()


dace/sdfg/state.py

Co-authored-by: Tal Ben-Nun <[email protected]>

This PR lets the Python and Fortran frontends (optionally) generate `LoopRegion`s for DaCe programs. This forms the third core element of the [plan to make loops first class citizens of SDFGs](https://github.com/orgs/spcl/projects/10). This PR is fully backwards compatible. `LoopRegion`s are always generated from new Python DaCe programs, and the legacy way of constructing a while / for loop is gone to remove complexity. To provide backwards compatibility, these `LoopRegion`s are by default immediately inlined into a traditional single level state machine loop as soon as program parsing is completed, before simplification and / or validation. However, an optional boolean parameter `use_experimental_cfg_blocks` can be set to True when declaring a DaCe program in Python to enable their use, which skips this inlining step. Example use: ```Python import dace import numpy N = dace.symbol('N') @dace.program(use_experimental_cfg_blocks=True): def mat_mult(A: dace.float64[N, N], B: dace.float64[N, N]): return A @ B # OR: mat_mult.use_experimental_cfg_blocks = True sdfg = mat_mult.to_sdfg() ``` The Fortran frontend similarly only utilizes `LoopRegions` if an additional parameter `use_experimenatl_cfg_blocks` is passed to the parser together with the program. Many passes and transformations (including in simplify) do not yet have the capability of handling the new, hierarchical SDFGs. To not break the pipeline and to provide backwards compatibility, a new decorator `@single_level_sdfg_only` has been added, which can be (and has been) placed over any pass or transformation that is not compatible with the new style SDFGs. Passes annotated with this decorator are skipped in all pipelines where they occur and instead generate warnings that they were skipped due to compatibility issues. For more information on `LoopRegion`s please refer to the [PR that introduced them](#1407). **Important Note about disabled tests:** Certain Python frontend loop tests have been disabled. Specifically, this concerns tests where either the loop structure (using continue/break) or other conditional statements cause the generation of control flow that looks irregular before the simplification pass is applied. The reason being that the frontend generates branches with one branch condition being set to constant `False` when generating continue / break / return, or while/for-else clauses. These branches are trivially removed during simplification, but not running simplification (as part of our CI does) leads to irregular control flow which is handled poorly by our codegen-time control flow detection. This error has so far gone unnoticed in these tests because of sheer luck, but is now exposed through a ever so slightly different state machine being generated by control flow region and loop inlining. The goal is for a subsequent PR to completely adapt codegen to make use of the control flow region constructs, thereby fixing this issue and re-enabling the tests. For more information about the issue, see #635 and #1586. Linked to: https://github.com/orgs/spcl/projects/10/views/4?pane=issue&itemId=42047238 and https://github.com/orgs/spcl/projects/10/views/4?pane=issue&itemId=42151188

phschaad added enhancement New feature or request core labels Oct 24, 2023

phschaad added 5 commits November 3, 2023 10:22

Add validation and inlining

e549d62

wip

1ca71e7

Add tests

ea9af8c

Add inlining test for breaks and continue

dbd2e82

Fix missing subgraph view sdfg prop

5573575

phschaad force-pushed the loop_architecture_pt_2 branch from 2d4c318 to 5573575 Compare November 3, 2023 09:23

phschaad added 3 commits November 3, 2023 10:59

Fix import

900f7b3

Test fixes

47d1e68

Remove stale API arg

ec79b29

phschaad marked this pull request as ready for review November 3, 2023 12:23

phschaad changed the title ~~Loop architecture pt 2~~ Loop Regions Nov 3, 2023

phschaad requested review from tbennun, alexnick83 and acalotoiu November 3, 2023 12:46

Merge branch 'master' into loop_architecture_pt_2

c5194aa

phschaad added the waiting for review label Nov 7, 2023

alexnick83 approved these changes Nov 9, 2023

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tbennun requested changes Nov 27, 2023

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phschaad and others added 4 commits November 27, 2023 12:12

Update tests/sdfg/loop_region_test.py

380cb0f

Co-authored-by: Tal Ben-Nun <[email protected]>

Update tests/sdfg/loop_region_test.py

5a66789

Co-authored-by: Tal Ben-Nun <[email protected]>

Update tests/transformations/control_flow_inline_test.py

13303e4

Co-authored-by: Tal Ben-Nun <[email protected]>

Update tests/transformations/control_flow_inline_test.py

ce2452e

Co-authored-by: Tal Ben-Nun <[email protected]>

phschaad removed the waiting for review label Nov 27, 2023

phschaad added 2 commits November 27, 2023 12:14

Merge branch 'master' into loop_architecture_pt_2

f270852

Address review comments

fba7e87

phschaad requested a review from tbennun November 27, 2023 13:14

tbennun approved these changes Nov 27, 2023

View reviewed changes

phschaad merged commit d157346 into master Nov 27, 2023
9 checks passed

phschaad deleted the loop_architecture_pt_2 branch November 27, 2023 16:18

phschaad mentioned this pull request Dec 11, 2023

Add loop regions to the frontend's capabilities #1475

Merged

phschaad mentioned this pull request Jun 13, 2024

Loops and SDFG Scope Blocks #1356

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Loop Regions #1407

Loop Regions #1407

phschaad commented Oct 24, 2023 •

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Loop Regions #1407

Loop Regions #1407

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phschaad commented Oct 24, 2023 • edited Loading

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phschaad commented Oct 24, 2023 •

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