8275847: Scheduling fails with "too many D-U pinch points" on small method #6131

nick-arm · 2021-10-27T06:25:22Z

Since around JDK 16 the following method cannot be compiled by C2 on AArch64:

  public double mergeSync() { return Math.log(Math.sin(value)); }

(Reduced from a slightly larger benchmark.)

  811 416 ! 3 Test::mergeSync (61 bytes)
  813 417 ! 4 Test::mergeSync (61 bytes)
  816 417 ! 4 Test::mergeSync (61 bytes) COMPILE SKIPPED: too many D-U pinch points (retry at different tier)
  816 418 ! 1 Test::mergeSync (61 bytes)

Scheduling::anti_do_def() will create temporary Nodes for each OptoReg killed by the MachProjs from the two runtime leaf calls. After SVE support was added these runtime calls kill more registers, and the number of new Nodes added by anti_do_def exceeds an internal limit (which is based on the LRG map size and roughly proportional to the method size).

X86 has the same problem if OptoScheduling is enabled because of the wide AVX registers.

The fix here is to ignore OptoRegs which correspond to the high slots of wide vectors (i.e. slots above 64 bits). The scheduler doesn't run on methods where C->max_vector_size() > 8, so we know these kills can't affect the scheduling result.

The added test fails on the current JDK with:

  compiler.lib.ir_framework.shared.TestRunException: Could not compile public double
  compiler.c2.irTests.TestScheduleSmallMethod.testSmallMethodTwoRuntimeCalls(double) at level C2
  after 10s. Last compilation level: 3

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Issue

JDK-8275847: Scheduling fails with "too many D-U pinch points" on small method

Reviewers

Tobias Hartmann (@TobiHartmann - Reviewer)
Vladimir Kozlov (@vnkozlov - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.java.net/jdk pull/6131/head:pull/6131
$ git checkout pull/6131

Update a local copy of the PR:
$ git checkout pull/6131
$ git pull https://git.openjdk.java.net/jdk pull/6131/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 6131

View PR using the GUI difftool:
$ git pr show -t 6131

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Download this PR as a diff file:
https://git.openjdk.java.net/jdk/pull/6131.diff

…ethod Since around JDK 16 the following method cannot be compiled by C2 on AArch64: public double mergeSync() { return Math.log(Math.sin(value)); } (Reduced from a slightly larger benchmark.) 811 416 ! 3 Test::mergeSync (61 bytes) 813 417 ! 4 Test::mergeSync (61 bytes) 816 417 ! 4 Test::mergeSync (61 bytes) COMPILE SKIPPED: too many D-U pinch points (retry at different tier) 816 418 ! 1 Test::mergeSync (61 bytes) Scheduling::anti_do_def() will create temporary Nodes for each OptoReg killed by the MachProjs from the two runtime leaf calls. After SVE support was added these runtime calls kill more registers, and the number of new Nodes added by anti_do_def exceeds an internal limit (which is based on the LRG map size and roughly proportional to the method size). X86 has the same problem if OptoScheduling is enabled because of the wide AVX registers. The fix here is to ignore OptoRegs which correspond to the high slots of wide vectors (i.e. slots above 64 bits). The scheduler doesn't run on methods where C->max_vector_size() > 8, so we know these kills can't affect the scheduling result. The added test fails on the current JDK with: compiler.lib.ir_framework.shared.TestRunException: Could not compile public double compiler.c2.irTests.TestScheduleSmallMethod.testSmallMethodTwoRuntimeCalls(double) at level C2 after 10s. Last compilation level: 3

bridgekeeper · 2021-10-27T06:26:32Z

👋 Welcome back ngasson! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2021-10-27T06:30:07Z

@nick-arm The following label will be automatically applied to this pull request:

hotspot-compiler

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

mlbridge · 2021-10-27T06:33:28Z

Webrevs

01: Full - Incremental (d9875679)
00: Full (dfa783f1)

TobiHartmann

While looking at the usages of is_concrete, I found that all current usages outside of asserts are dead:

jdk/src/hotspot/share/opto/buildOopMap.cpp

Line 234 in 1750a6e

if (false && r->is_reg() && !r->is_concrete()) {

jdk/src/hotspot/share/opto/buildOopMap.cpp

Line 315 in 1750a6e

if (b->is_stack() || b->is_concrete() || true ) {

jdk/src/hotspot/share/opto/buildOopMap.cpp

Line 320 in 1750a6e

if (b->is_stack() || b->is_concrete() || true ) {

jdk/src/hotspot/share/opto/buildOopMap.cpp

Line 350 in 1750a6e

if ( callee->is_concrete() || true ) {

I think we should clean that up.

src/hotspot/cpu/x86/vmreg_x86.hpp

nick-arm · 2021-10-29T07:40:44Z

While looking at the usages of is_concrete, I found that all current usages outside of asserts are dead:

Looks like it's been like that since the initial public commit in 2007. I folded the && false, || true uses.

TobiHartmann

Looks good to me but a second review would be good.

/reviewers 2

openjdk · 2021-11-01T08:15:11Z

@nick-arm This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8275847: Scheduling fails with "too many D-U pinch points" on small method

Reviewed-by: thartmann, kvn

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 139 new commits pushed to the master branch:

b01f107: 8276252: java/nio/channels/Channels/TransferTo.java failed with OOM java heap space error
92d2176: 8273967: gtest os.dll_address_to_function_and_library_name_vm fails on macOS12
a74a839: 8276571: C2: pass compilation options as structure
c393ee8: 8276632: Use blessed modifier order in security-libs code
7023b3f: 8276628: Use blessed modifier order in serviceability code
b933136: 8276641: Use blessed modifier order in jshell
0616d86: 8276635: Use blessed modifier order in compiler code
d95299a: 8276634: Remove usePlainDatagramSocketImpl option from the test DatagramChannel/SendReceiveMaxSize.java
3c0faa7: 8276173: Clean up and remove unneeded casts in HeapDumper
323d201: 8275506: Rename allocated_on_stack to allocated_on_stack_or_embedded
... and 129 more: https://git.openjdk.java.net/jdk/compare/9f75d5ce500886b32175cc541939b7f0eee190ca...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

vnkozlov

Seems fine to me but I need to run testing before approval.

vnkozlov

Testing results look good.

nick-arm · 2021-11-08T06:38:55Z

Thanks for the reviews. The Windows x64 build failure looks to be spurious, I re-ran the GitHub actions here: https://github.com/nick-arm/jdk/runs/4133872978

nick-arm · 2021-11-08T06:39:45Z

/integrate

openjdk · 2021-11-08T06:41:05Z

Going to push as commit 3934fe5.
Since your change was applied there have been 147 commits pushed to the master branch:

44047f8: 8274328: C2: Redundant CFG edges fixup in block ordering
8849154: 8275846: read_base_archive_name() could read past the end of buffer
2653cfb: 8276688: Remove JLinkReproducibleXXXTest from ProblemList.txt
c7095b2: 8276207: Properties.loadFromXML/storeToXML works incorrectly for supplementary characters
ed7ecca: 8254739: G1: Optimize evacuation failure for regions with few failed objects
59c3dcc: 8276746: Add section on reproducible builds in building.md
0e0dd33: 8276129: PretouchTask should page-align the chunk size
a472433: 8276572: Fake libsyslookup.so library causes tooling issues
b01f107: 8276252: java/nio/channels/Channels/TransferTo.java failed with OOM java heap space error
92d2176: 8273967: gtest os.dll_address_to_function_and_library_name_vm fails on macOS12
... and 137 more: https://git.openjdk.java.net/jdk/compare/9f75d5ce500886b32175cc541939b7f0eee190ca...master

Your commit was automatically rebased without conflicts.

openjdk · 2021-11-08T06:41:19Z

@nick-arm Pushed as commit 3934fe5.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

openjdk bot added the rfr Pull request is ready for review label Oct 27, 2021

openjdk bot added the hotspot-compiler hotspot-compiler-dev@openjdk.org label Oct 27, 2021

TobiHartmann reviewed Oct 28, 2021

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src/hotspot/cpu/x86/vmreg_x86.hpp Outdated Show resolved Hide resolved

Remove dead uses of is_concrete

d987567

TobiHartmann approved these changes Nov 1, 2021

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openjdk bot added the ready Pull request is ready to be integrated label Nov 1, 2021

vnkozlov reviewed Nov 5, 2021

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vnkozlov approved these changes Nov 5, 2021

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openjdk bot closed this Nov 8, 2021

openjdk bot added integrated Pull request has been integrated and removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Nov 8, 2021

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8275847: Scheduling fails with "too many D-U pinch points" on small method #6131

8275847: Scheduling fails with "too many D-U pinch points" on small method #6131

nick-arm commented Oct 27, 2021 •

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8275847: Scheduling fails with "too many D-U pinch points" on small method #6131

8275847: Scheduling fails with "too many D-U pinch points" on small method #6131

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nick-arm commented Oct 27, 2021 • edited by openjdk bot

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