8287373: remove unnecessary paddings in generated code #8453

bulasevich · 2022-04-28T14:46:57Z

The goal is to remove unnecessary paddings in generated code. The alignment of the [Stub Code] section is determined by the same value as the alignment of the [Entry Point] section: the CodeEntryAlignment parameter with default values 64B on AARCH, and 32B on AMD.

Large entry alignment values are questionable for entry section. For example, Arm Neoverse N1 Software Optimization Guide recommends to align subroutines to 32B, while static compilers uses an even smaller value of 16B. However, with this change, I suggest to apply different (and smaller) values for [Constants] and [Stub Code] section alignments. This makes overall code 2% smaller on AARCH.

The correctness of the changes is checked by jtreg. Performance tested by Renaissance and SpecJBB benchmarkds on AARCH and AMD.

Example. Dummy method disassembly on AARCH, before vs after:

[Verified Entry Point]                          |  [Verified Entry Point]
  78c63b80:   nop                               |    7437e480:   nop
  78c63b84:   sub     x9, sp, #0x20, lsl #12    |    7437e484:   sub     x9, sp, #0x20, lsl #12
  78c63b88:   str     xzr, [x9]                 |    7437e488:   str     xzr, [x9]
  78c63b8c:   sub     sp, sp, #0x20             |    7437e48c:   sub     sp, sp, #0x20
  78c63b90:   stp     x29, x30, [sp, #16]       |    7437e490:   stp     x29, x30, [sp, #16]
  78c63b94:   orr     w1, wzr, #0x10            |    7437e494:   orr     w1, wzr, #0x10
  78c63b98:   bl      78343e00                  |    7437e498:   bl      73a61980
  78c63b9c:   .inst   0x00000000 ; undefined    |    7437e49c:   .inst   0x00000000 ; undefined
  78c63ba0:   .inst   0x00000000 ; undefined    |
  78c63ba4:   .inst   0x00000000 ; undefined    |
  78c63ba8:   .inst   0x00000000 ; undefined    |
  78c63bac:   .inst   0x00000000 ; undefined    |
  78c63bb0:   .inst   0x00000000 ; undefined    |
  78c63bb4:   .inst   0x00000000 ; undefined    |
  78c63bb8:   .inst   0x00000000 ; undefined    |
  78c63bbc:   .inst   0x00000000 ; undefined    |
[Stub Code]                                     |  [Stub Code]
  78c63bc0:   ldr     x8, 78c63bc8              |    7437e4a0:   ldr     x8, 7437e4a8
  78c63bc4:   br      x8                        |    7437e4a4:   br      x8
  78c63bc8:   .inst   0x78343e00 ; undefined    |    7437e4a8:   .inst   0x73a61980 ; undefined
  78c63bcc:   .inst    ; undefined              |    7437e4ac:   .inst    ; undefined
[Exception Handler]                             |  [Exception Handler]
  78c63bd0:   b       783ee080                  |    7437e4b0:   b       73b0c100
[Deopt Handler Code]                            |  [Deopt Handler Code]
  78c63bd4:   adr     x30, 78c63bd4             |    7437e4b4:   adr     x30, 7437e4b4
  78c63bd8:   b       78343ac0                  |    7437e4b8:   b       73a61620
  78c63bdc:   .inst   0x00000000 ; undefined    |    7437e4bc:   .inst   0x00000000 ; undefined

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Issue

JDK-8287373: remove unnecessary paddings in generated code

Reviewers

Vladimir Kozlov (@vnkozlov - Reviewer) ⚠️ Review applies to 630f9c9c
@eastig (no known github.com user name / role) ⚠️ Review applies to 630f9c9c

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Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk pull/8453/head:pull/8453
$ git checkout pull/8453

Update a local copy of the PR:
$ git checkout pull/8453
$ git pull https://git.openjdk.org/jdk pull/8453/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 8453

View PR using the GUI difftool:
$ git pr show -t 8453

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Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/8453.diff

bridgekeeper · 2022-04-28T14:48:35Z

👋 Welcome back bulasevich! 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 · 2022-04-28T14:51:21Z

@bulasevich The following label will be automatically applied to this pull request:

hotspot

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.

eastig · 2022-05-04T15:52:19Z

src/hotspot/cpu/aarch64/globals_aarch64.hpp

@@ -37,7 +37,7 @@ define_pd_global(bool, TrapBasedNullChecks,  false);
 define_pd_global(bool, UncommonNullCast,         true);  // Uncommon-trap NULLs past to check cast

 define_pd_global(uintx, CodeCacheSegmentSize,    64 COMPILER1_AND_COMPILER2_PRESENT(+64)); // Tiered compilation has large code-entry alignment.
-define_pd_global(intx, CodeEntryAlignment,       64);


This change looks reasonable to me. I found the following in the N1 Opt Guide:

Consider aligning subroutine entry points and branch targets to 32B boundaries, within the bounds of the code-density requirements of the program. This will ensure that the subsequent fetch can maximize bandwidth following the taken branch by bringing in all useful instructions

I have rolled back CodeEntryAlignment 64->32 change as it shows different results on ARM platforms. I think it should be done in a separate PR. It can be tuned in vm_version after CPU architecture check.

src/hotspot/share/asm/codeBuffer.hpp

…de,stubs) have got its own alignment

…nerate_handler_blob asks a 1KB buffer, actually CodeBuffer::initialize reserves the given size with some extra bytes; with the new formula (code_size + align + slop * SECT_LIMIT) the extra bytes number is reduced, causing the handler_blob generator buffer to overflow. Solution: double the code_size estimate for handler_blob generator buffer (the temporary buffer size is not really important)

mlbridge · 2022-06-07T15:49:22Z

Webrevs

vnkozlov

Why you changed tested alignment to 8 for JVMCI tests?

vnkozlov · 2022-06-07T16:11:59Z

src/hotspot/cpu/x86/sharedRuntime_x86_32.cpp

@@ -2632,7 +2632,7 @@ SafepointBlob* SharedRuntime::generate_handler_blob(address call_ptr, int poll_t

  // allocate space for the code
  // setup code generation tools
-  CodeBuffer   buffer("handler_blob", 1024, 512);
+  CodeBuffer   buffer("handler_blob", 2048, 1024);


Why you need to double the size?

I did it to fix the CodeBuffer overflow assert on x86 build. SharedRuntime::generate_handler_blob asks a 1KB buffer -
actually CodeBuffer::initialize reserves the given size with some extra bytes; with the new formula (code_size + align + slop * SECT_LIMIT) the extra bytes number is reduced, causing the handler_blob generator buffer to overflow. My solution is to double the code_size estimate for handler_blob generator buffer. The same 2048/1024 numbers we can see on other platforms - aarch, pcc, amd, riscv.

vnkozlov · 2022-06-07T17:28:44Z

src/hotspot/share/jvmci/jvmciCodeInstaller.cpp

+  int total_size = align_up(_constants_size, CodeSection::alignment(CodeBuffer::SECT_INSTS)) +
+                   align_up(_code_size, CodeSection::alignment(CodeBuffer::SECT_STUBS)) +
+                   stubs_size;


At first look it is messed up. I understand that you are trying to take into account space between sections. It assumed the order of sections.
Add comment.

Ok. Thank you

src/hotspot/share/asm/codeBuffer.cpp

bulasevich · 2022-06-07T21:28:13Z

Why you changed tested alignment to 8 for JVMCI tests?

HotSpotCompiledCode.dataSectionAlignment value was changed to 8 to correspond the new CodeBuffer.constants code section alignment.

The jtreg tests issue was repoduced as "invalid data section alignment" JVMCI error in CodeInstaller::initialize_fields

vnkozlov · 2022-06-07T22:23:28Z

test/hotspot/jtreg/compiler/jvmci/errors/TestInvalidCompilationResult.java

@@ -85,9 +85,11 @@ public boolean equals(Object obj) {
        }
    }

+    static final int validDataSectionAlignment = 8;


Add comment to explain where 8 comes from.

fixed. thanks!

openjdk-notifier · 2022-06-09T09:21:22Z

@bulasevich Please do not rebase or force-push to an active PR as it invalidates existing review comments. All changes will be squashed into a single commit automatically when integrating. See OpenJDK Developers’ Guide for more information.

src/hotspot/share/jvmci/jvmciCodeInstaller.cpp

eastig

lgtm

vnkozlov · 2022-06-09T23:55:48Z

test/hotspot/jtreg/compiler/jvmci/errors/TestInvalidCompilationResult.java

@@ -85,9 +85,12 @@ public boolean equals(Object obj) {
        }
    }

+    // DataSectionAlignment value matches the alignment of the CodeBuffer::SECT_CONSTS code section


the alignment sizeof(jdouble) of the

vnkozlov

Looks good. I will test it before approval.

vnkozlov

My tier1-4 testing passed.

openjdk · 2022-06-10T05:06:26Z

@bulasevich 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:

8287373: remove unnecessary paddings in generated code

Reviewed-by: 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 166 new commits pushed to the master branch:

900d967: 8287924: Avoid redundant HashMap.containsKey call in EnvHelp.mapToHashtable
d482d7f: 8286160: (fs) Files.exists returns unexpected results with C:\pagefile.sys because it's not readable
edff51e: 8284858: Start of release updates for JDK 20
2671443: 8286171: HttpClient/2 : Expect:100-Continue blocks indefinitely when response is not 100
59b0de6: 8288048: Build failure with GCC 6 after JDK-8286562
db4405d: 8288078: linux-aarch64-optimized build fails in Tier5 after JDK-8287567
7e948f7: 8287903: Reduce runtime of java.math microbenchmarks
3fa9984: 8287854: Dangling reference in ClassVerifier::verify_class
4285e3d: 8288023: AArch64: disable PAC-RET when preview is enabled
560e292: 8287738: [PPC64] jdk/incubator/vector/*VectorTests failing
... and 156 more: https://git.openjdk.org/jdk/compare/784697138182f104c30f8365b01f67be4d28083c...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.

bulasevich · 2022-06-10T07:48:18Z

My tier1-4 testing passed.

Thank you!

bulasevich · 2022-06-15T09:09:40Z

/integrate

openjdk · 2022-06-15T09:10:59Z

Going to push as commit 68b2057.
Since your change was applied there have been 222 commits pushed to the master branch:

2471f8f: 8287647: VM debug support: find node by pattern in name or dump
33f34d5: 8288207: Enhance MalformedURLException in Uri.parseCompat
444a0d9: 8284977: MetricsTesterCgroupV2.getLongValueEntryFromFile fails when named value doesn't exist
08400f1: 8287349: AArch64: Merge LDR instructions to improve C1 OSR performance
fe80721: 8287917: System.loadLibrary does not work on Big Sur if JDK is built with macOS SDK 10.15 and earlier
bbaeacb: 8265586: [windows] last button is not shown in AWT Frame with BorderLayout and MenuBar set.
0f58097: 8288134: Super class names don't have envelopes
fb29770: 8287186: JDK modules participating in preview
0530f4e: 8288094: cleanup old _MSC_VER handling
1a65332: 8287906: Rewrite of GitHub Actions (GHA) sanity tests
... and 212 more: https://git.openjdk.org/jdk/compare/784697138182f104c30f8365b01f67be4d28083c...master

Your commit was automatically rebased without conflicts.

openjdk · 2022-06-15T09:11:16Z

@bulasevich Pushed as commit 68b2057.

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

dougxc · 2022-09-19T10:53:13Z

src/hotspot/share/asm/codeBuffer.hpp

@@ -702,4 +706,19 @@ inline bool CodeSection::maybe_expand_to_ensure_remaining(csize_t amount) {
  return false;
 }

+inline int CodeSection::alignment(int section) {
+  if (section == CodeBuffer::SECT_CONSTS) {
+    return (int) sizeof(jdouble);


This breaks Graal which puts data items larger than a jdouble (e.g. 32-byte vector masks) into the constants section.

I opened https://bugs.openjdk.org/browse/JDK-8293999 to track this.

openjdk bot added the hotspot hotspot-dev@openjdk.org label Apr 28, 2022

bulasevich force-pushed the InteriorEntryAlignment branch 3 times, most recently from c802b1e to a631841 Compare April 30, 2022 06:51

eastig reviewed May 5, 2022

View reviewed changes

bulasevich force-pushed the InteriorEntryAlignment branch 2 times, most recently from ea4483c to 7237201 Compare May 25, 2022 14:31

bulasevich changed the title ~~remove unnecessary paddings within the generated code~~ 8287373: remove unnecessary paddings within the generated code May 26, 2022

bulasevich and others added 4 commits June 1, 2022 07:36

use InteriorEntryAlignment for code sections

9dfad7c

Undo CodeEntryAlignment modification. Each code section (constants,co…

a72cd3b

…de,stubs) have got its own alignment

jtreg/compiler tests update

20f2299

rollback InteriorEntryAlignment change

0f052d1

bulasevich force-pushed the InteriorEntryAlignment branch from 7237201 to 0f052d1 Compare June 1, 2022 07:36

bulasevich changed the title ~~8287373: remove unnecessary paddings within the generated code~~ 8287373: remove unnecessary paddings in generated code Jun 1, 2022

bulasevich marked this pull request as ready for review June 7, 2022 15:22

openjdk bot added the rfr Pull request is ready for review label Jun 7, 2022

vnkozlov reviewed Jun 7, 2022

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eastig reviewed Jun 7, 2022

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cleanup and comments

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eastig reviewed Jun 9, 2022

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src/hotspot/share/jvmci/jvmciCodeInstaller.cpp Outdated Show resolved Hide resolved

typo fix

630f9c9

eastig approved these changes Jun 9, 2022

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vnkozlov reviewed Jun 9, 2022

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vnkozlov approved these changes Jun 10, 2022

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openjdk bot added the ready Pull request is ready to be integrated label Jun 10, 2022

comment fix

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openjdk bot added the integrated Pull request has been integrated label Jun 15, 2022

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8287373: remove unnecessary paddings in generated code #8453

8287373: remove unnecessary paddings in generated code #8453

bulasevich commented Apr 28, 2022 •

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8287373: remove unnecessary paddings in generated code #8453

8287373: remove unnecessary paddings in generated code #8453

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