Swift Optimizer: add `EscapeInfo`, a new utility for escape analysis #42242

eeckstein · 2022-04-07T08:32:33Z

This PR is the first step of replacing the old EscapeAnalysis with a new utility, implemented in Swift (instead of C++) and with a much simple design.
While the old EscapeAnalysis builds a connection graph, the new EscapeInfo just performs a simple def-use and use-def walk in the SIL.
The EscapeInfo does not need to analyze the whole function (like the EscapeAnalysis does), but just the relevant value which is inspected. Therefore EscapeInfo is not an Analysis which caches its result across optimization passes - it’s not needed.

To do inter-procedural escape analysis, the new compute-effects pass derives escape information for function arguments and adds those effects in the function. Those effects can then be used by EscapeInfo to get escape-information of called functions.

The EscapeInfo utility is tested with the help of the dump-escape-info and dump-addr-escape-info passes, which dump escape information for the SIL in the corresponding test files.

All the utilities and passes in this PR only compute escape information, but don't use it, yet. So, regarding the generated code it's still a NFC. The second step for completely replacing EscapeAnalysis with the new EscapeInfo is here: #39438

eeckstein · 2022-04-07T11:21:49Z

@swift-ci test

eeckstein · 2022-04-07T11:59:25Z

@swift-ci test

eeckstein · 2022-04-07T12:32:47Z

@swift-ci test

eeckstein · 2022-04-07T20:15:32Z

@swift-ci test

eeckstein · 2022-04-08T08:33:34Z

@swift-ci test

eeckstein · 2022-04-12T16:32:24Z

@swift-ci test

eeckstein · 2022-04-12T18:25:19Z

@swift-ci test linux

eeckstein · 2022-04-20T18:36:28Z

@swift-ci smoke test

atrick

A couple of minor comments on the first 2 commits

atrick · 2022-04-20T17:20:51Z

SwiftCompilerSources/Sources/SIL/SmallProjectionPath.swift

+      if k.isClassField {
+        neededBits = totalBits
+        totalBits += numBits
+      } else {
+        totalBits += numBits
+        if !k.isValueField { neededBits = totalBits }


It looks like the isClassField check should have been removed since the code already checks !isValueField.

isValueField is not !isClassField because .anything is not neither a class field nor a value field.
I'll add a comment.

isValueField is not !isClassField because .anything is not neither a class field nor a value field.

ok, sure, but isn't isClassField a subset of !isValueField?

atrick · 2022-04-20T17:38:04Z

include/swift/SIL/TypeLowering.h

+/// Types for which this property is not known, e.g. generic types, it is
+/// assumed that the type has not a Builtin.RawPointer.


I wasn't sure how to read this and suspected a typo. It could be more clear

HasRawPointer is true only for types that are known to contain Builtin.RawPointer. It is not assumed true for generic or resilient types.

* rename `matchesAllValueFields` -> `topMatchesAnyValueField` * add `hasSingleClassIndirection` and `hasClassProjection` * add `popLastClassAndValuesFromTail`

…RawPointer This is needed for the new escape analysis

It’s a replacement for the old `EscapeAnalysis`, implemented in Swift (instead of C++) and with a much simple design and implementation. While the old EscapeAnalysis builds a connection graph, the new EscapeInfo just performs a simple def-use and use-def walk in the SIL. The EscapeInfo does not need to analyze the whole function (like the EscapeAnalysis does), but just the relevant value which is inspected. Therefore EscapeInfo is not an `Analysis` which caches its result across optimization passes - it’s not needed.

And add test files which uses the passes for verification of EscapeInfo

The ComputeEffects pass derives escape information for function arguments and adds those effects in the function. This needs a lot of changes in check-lines in the tests, because the effects are printed in SIL

eeckstein · 2022-04-21T06:46:35Z

@swift-ci smoke test

atrick · 2022-04-21T18:00:23Z

SwiftCompilerSources/Sources/Optimizer/Utilities/EscapeInfo.swift

+            case is DestructureStructInst, is DestructureTupleInst:
+              val = inst.operands[0].value
+              // TODO: only push the specific result index.
+              // But currently there is no O(0) method to get the result index
+              // from a result value.
+              p = p.popAllValueFields().push(.anyValueFields)


@eeckstein this really needs to be fixed because our goal is to migrate to destructures as much as possible for ownership forwarding. There shouldn't be any hidden downstream performance effects of one vs. the other. destructure vs. extract should be equivalent for all analysis that doesn't care about ownership! The result index is embedded in the result value. That won't work?

You are right. Somehow I didn't realize that. I'll change it

done in #42571

compnerd · 2022-04-22T03:29:26Z

This seems to have caused a regression on Windows: https://ci-external.swift.org/job/oss-swift-windows-toolchain-x86_64-vs2019/547/console

compnerd · 2022-04-22T03:30:36Z

CC: @shahmishal the CI didnt trigger here

This reverts commit c05e064, reversing changes made to c1534d5. This caused a regression on Windows.

Revert "Merge pull request #42242 from eeckstein/escapeinfo"

atrick · 2022-05-09T08:49:34Z

I'm using the following design document to review the escape analysis design that was introduced in this PR:
https://gist.github.com/atrick/562c0b69b44230dd7b04e0898514d806

eeckstein requested a review from atrick April 7, 2022 08:32

eeckstein force-pushed the escapeinfo branch 3 times, most recently from 3e87303 to ce2ea6b Compare April 7, 2022 09:45

eeckstein force-pushed the escapeinfo branch from ce2ea6b to 001d897 Compare April 8, 2022 08:33

eeckstein force-pushed the escapeinfo branch from 001d897 to b48f846 Compare April 12, 2022 16:31

eeckstein force-pushed the escapeinfo branch from b48f846 to 730106d Compare April 20, 2022 18:36

atrick reviewed Apr 20, 2022

View reviewed changes

eeckstein force-pushed the escapeinfo branch from 730106d to 588e7c8 Compare April 21, 2022 06:40

eeckstein added 5 commits April 21, 2022 08:45

Swift SIL: a few small addition to SmallProjectionPath

003fdec

* rename `matchesAllValueFields` -> `topMatchesAnyValueField` * add `hasSingleClassIndirection` and `hasClassProjection` * add `popLastClassAndValuesFromTail`

TypeLowering: add a recursive property to check if a type contains a …

3b2e409

…RawPointer This is needed for the new escape analysis

add passes to dump the results of EscapeInfo

4d5987c

And add test files which uses the passes for verification of EscapeInfo

add the ComputeEffects pass

700412b

The ComputeEffects pass derives escape information for function arguments and adds those effects in the function. This needs a lot of changes in check-lines in the tests, because the effects are printed in SIL

eeckstein force-pushed the escapeinfo branch from 588e7c8 to 700412b Compare April 21, 2022 06:46

eeckstein merged commit c05e064 into swiftlang:main Apr 21, 2022

eeckstein deleted the escapeinfo branch April 21, 2022 09:09

atrick reviewed Apr 21, 2022

View reviewed changes

compnerd added a commit to compnerd/apple-swift that referenced this pull request Apr 22, 2022

Revert "Merge pull request swiftlang#42242 from eeckstein/escapeinfo"

218ef58

This reverts commit c05e064, reversing changes made to c1534d5. This caused a regression on Windows.

shahmishal added a commit that referenced this pull request Apr 22, 2022

Merge pull request #42562 from compnerd/42242

b4fa721

Revert "Merge pull request #42242 from eeckstein/escapeinfo"

eeckstein mentioned this pull request Apr 22, 2022

Swift Optimizer: add EscapeInfo, a new utility for escape analysis (2nd try) #42571

Merged

		/// Types for which this property is not known, e.g. generic types, it is
		/// assumed that the type has not a Builtin.RawPointer.

Swift Optimizer: add EscapeInfo, a new utility for escape analysis #42242

Swift Optimizer: add EscapeInfo, a new utility for escape analysis #42242

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eeckstein commented Apr 7, 2022

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Swift Optimizer: add `EscapeInfo`, a new utility for escape analysis #42242

Swift Optimizer: add `EscapeInfo`, a new utility for escape analysis #42242