[JIT] ARM64 - Overflow check optimizations for division by TIHan · Pull Request #82924 · dotnet/runtime

TIHan · 2023-03-03T02:29:21Z

Description

This PR will not emit an arithmetic exception block if we know the dividend of a division operation is constant and not a MinValue.

This PR will also shorten the emitted code when testing for an overflow of a division operation.

Acceptance Criteria

CI passes

…tant that is a not a min value

ghost · 2023-03-03T02:29:32Z

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch, @kunalspathak
See info in area-owners.md if you want to be subscribed.

Issue Details

Will resolve #46010

At the moment, I haven't got rid of the redundant branch operations yet.

Author:	TIHan
Assignees:	-
Labels:	`area-CodeGen-coreclr`
Milestone:	-

…branch-opt

TIHan · 2023-03-06T20:52:59Z

@dotnet/jit-contrib @kunalspathak This is ready. Straight-forward change, should be an easy review. Diffs

EgorBo · 2023-03-06T20:58:52Z

+ }
+ }
+
+ if (checkDividend)


NOTE: this still leaves overflow block alive if it's unused but presumably it's a different issue

Hhm, won't it be dead code eliminated?

Throw helper blocks are marked as no-remove. This is because they aren't rooted in the normal flowgraph (the edges from the throwing nodes to the throw helper blocks are implicit).

Hhm, won't it be dead code eliminated?
these blocks are special, they have BBF_DONT_REMOVE or something like that. We spawn them early in importer/morph and then tie to corresponding divisions if needed, it's too late to remove them in codegen

I'm hopeful that this PR will resolve those cases as it's already happening today.

…branch-opt

EgorBo · 2023-03-06T22:48:10Z

+// Return Value:
+// true if the given tree is known to never be negative one
+//
+bool GenTree::IsNeverNegativeOne(Compiler* comp) const


this helper is only needed for division in one place it seems?

It's only in one place, but it does help make things clean.

TIHan · 2023-03-08T00:41:39Z

@dotnet/jit-contrib @BruceForstall This is ready again. Diffs

Co-authored-by: SingleAccretion <62474226+SingleAccretion@users.noreply.github.com>

…Flags. Use GetExceptionSetFlags to determine to add div-by-zero or overflow blocks for arm64.

TIHan · 2023-03-08T19:34:39Z

Thank you all for the feedback. The PR feels a lot better.

Since @SingleAccretion pointed me to OperExceptions, I realized we had another duplicate check.

I wonder if there are any more duplicate checks.

TIHan · 2023-03-08T22:08:35Z

@dotnet/jit-contrib ready again. Got more wins in full-opts compared to before: diffs
Current failure is not related.

BruceForstall

Wouldn't be a bad idea to run outerloop and/or jitstress

TIHan · 2023-03-09T02:03:45Z

/azp run runtime-coreclr jitstress gcstress

azure-pipelines · 2023-03-09T02:03:51Z

No pipelines are associated with this pull request.

TIHan · 2023-03-09T02:04:01Z

/azp run runtime-coreclr jitstress

azure-pipelines · 2023-03-09T02:04:18Z

Azure Pipelines successfully started running 1 pipeline(s).

TIHan · 2023-03-09T02:04:23Z

/azp run runtime-coreclr gcstress

azure-pipelines · 2023-03-09T02:04:29Z

No pipelines are associated with this pull request.

TIHan · 2023-03-09T17:27:28Z

/azp run fuzzlyn

azure-pipelines · 2023-03-09T17:27:45Z

Azure Pipelines successfully started running 1 pipeline(s).

TIHan · 2023-03-10T00:41:44Z

@jakobbotsch - I think it's fine that we do this optimization in min-opts, we were already doing it before. It's not going to hurt the debugging experience for users as its all generated internally; I don't see how this would impact anyone.

Do not emit overflow check for div if we know first operand is a cons…
983523c
…tant that is a not a min value

ghost added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Mar 3, 2023

ghost assigned TIHan Mar 3, 2023

Remove redundant branch
81d7666

TIHan changed the title ~~[ARM64] Overflow check optimizations~~[JIT] ARM64 - Overflow check optimizationsMar 3, 2023

TIHan added 2 commits March 3, 2023 12:59

Update codegenarm64.cpp
0017311

Try to use subs, zr, dividendReg, 1 to determine overflow in division
844ceff

TIHan changed the title ~~[JIT] ARM64 - Overflow check optimizations~~[JIT] ARM64 - Overflow check optimizations for divisionMar 3, 2023

TIHan added 2 commits March 6, 2023 10:16

Merge remote-tracking branch 'upstream/main' into redundant-overflow-…
28da6ca
…branch-opt

Cleanup
1cb5b75

TIHan marked this pull request as ready for review March 6, 2023 20:51

EgorBo reviewed Mar 6, 2023
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Comment threadsrc/coreclr/jit/morph.cpp Outdated

EgorBo reviewed Mar 6, 2023
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TIHan added 4 commits March 6, 2023 13:19

Merge remote-tracking branch 'upstream/main' into redundant-overflow-…
96bdde8
…branch-opt

Use IsNeverNegative to help not emit overflow checks
ffae5be

Fix check
1b90874

Added helper functions
07b9e6f

EgorBo reviewed Mar 6, 2023
View reviewed changes

TIHan added 2 commits March 6, 2023 15:03

Use main node instead of op1 for type check
0c19463

Add 64-bit check
91e657b

BruceForstall suggested changes Mar 7, 2023
View reviewed changes

Comment threadsrc/coreclr/jit/gentree.cpp Outdated
Comment threadsrc/coreclr/jit/emitarm64.cpp Outdated

ghost added the needs-author-action An issue or pull request that requires more info or actions from the author. label Mar 7, 2023

Use cmp instead of subs since it is an alias
3ff0e20

ghost removed the needs-author-action An issue or pull request that requires more info or actions from the author. label Mar 7, 2023

TIHan added 2 commits March 6, 2023 17:58

Handle 32-bit arch division for LONG.
1f63cb2

Additional checks
99e972a

This was referenced Mar 7, 2023
Infra improvements for Helix #68176
Closed
Methodical_others test JIT/Methodical/Coverage/copy_prop_byref_to_native_int crashing #69832
Open

TIHan commented Mar 8, 2023
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Comment threadsrc/coreclr/jit/morph.cpp Outdated

SingleAccretion reviewed Mar 8, 2023
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Comment threadsrc/coreclr/jit/gentree.h Outdated
Comment threadsrc/coreclr/jit/morph.cpp Outdated
Comment threadsrc/coreclr/jit/gentree.cpp Outdated

TIHanand others added 3 commits March 8, 2023 09:43

Update src/coreclr/jit/gentree.cpp
72d4713
Co-authored-by: SingleAccretion <62474226+SingleAccretion@users.noreply.github.com>

Flip meaning of check flags. Rename OperExceptions to GetExceptionSet…
84bb667
…Flags. Use GetExceptionSetFlags to determine to add div-by-zero or overflow blocks for arm64.

Use GetExceptionSetFlags in arm64 codegen
722b820

jakobbotsch reviewed Mar 8, 2023
View reviewed changes

Comment threadsrc/coreclr/jit/gentree.cpp Outdated

TIHan added 4 commits March 8, 2023 11:09

Revert name
6b8fc40

Use GTF_DIV_MOD_NO_OVERFLOW_CHK in CanDivOrModPossiblyOverflow
b164f0b

Fix build
f25f1ed

Rename flags by removing '_CHK'
0117364

BruceForstall approved these changes Mar 9, 2023
View reviewed changes

Comment threadsrc/coreclr/jit/gentree.cpp Outdated

Remove break
2431635

build-analysisBot mentioned this pull request Mar 9, 2023
Tracking issue for CI build timeouts #76454
Closed

TIHan merged commit 9364575 into dotnet:mainMar 10, 2023

TIHan deleted the redundant-overflow-branch-opt branch March 10, 2023 00:42

TIHan mentioned this pull request Mar 14, 2023
ARM64: Left over dead code for special throw blocks #37675
Closed

kunalspathak mentioned this pull request Apr 4, 2023
What's new in .NET 8 Preview 3 dotnet/core#8135
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TIHan commented Mar 3, 2023•
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