[Bug target/99988] New: aarch64: GCC generates excessive consecutive bti j instructions

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* [Bug target/99988] New: aarch64: GCC generates excessive consecutive bti j instructions
@ 2021-04-09 10:13 acoplan at gcc dot gnu.org
  2021-04-09 10:23 ` [Bug target/99988] " acoplan at gcc dot gnu.org
                   ` (8 more replies)
  0 siblings, 9 replies; 10+ messages in thread
From: acoplan at gcc dot gnu.org @ 2021-04-09 10:13 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99988

            Bug ID: 99988
           Summary: aarch64: GCC generates excessive consecutive bti j
                    instructions
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: acoplan at gcc dot gnu.org
  Target Milestone: ---

Created attachment 50535
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50535&action=edit
minimal reproducer

For the attached testcase (reduced from the linux kernel), GCC generates
multiple redundant sequences of back-to-back bti j instructions, the longest of
which is 262 instructions long.

To reproduce:

$ aarch64-linux-gnu-gcc -c test.c -S -o - -O2 -mbranch-protection=standard |
uniq -c | grep "bti j" | sort -nr
    262         hint    36 // bti j
      7         hint    36 // bti j
      6         hint    36 // bti j
      4         hint    36 // bti j
      4         hint    36 // bti j
      3         hint    36 // bti j
      2         hint    36 // bti j
      2         hint    36 // bti j
      2         hint    36 // bti j
      2         hint    36 // bti j
      2         hint    36 // bti j
      2         hint    36 // bti j
      2         hint    36 // bti j

^ permalink raw reply	[flat|nested] 10+ messages in thread

* [Bug target/99988] aarch64: GCC generates excessive consecutive bti j instructions
  2021-04-09 10:13 [Bug target/99988] New: aarch64: GCC generates excessive consecutive bti j instructions acoplan at gcc dot gnu.org
@ 2021-04-09 10:23 ` acoplan at gcc dot gnu.org
  2021-04-09 11:29 ` acoplan at gcc dot gnu.org
                   ` (7 subsequent siblings)
  8 siblings, 0 replies; 10+ messages in thread
From: acoplan at gcc dot gnu.org @ 2021-04-09 10:23 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99988

Alex Coplan <acoplan at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |10.3.1, 9.3.1

--- Comment #1 from Alex Coplan <acoplan at gcc dot gnu.org> ---
GCC 10 and 9 are also affected.

^ permalink raw reply	[flat|nested] 10+ messages in thread

* [Bug target/99988] aarch64: GCC generates excessive consecutive bti j instructions
  2021-04-09 10:13 [Bug target/99988] New: aarch64: GCC generates excessive consecutive bti j instructions acoplan at gcc dot gnu.org
  2021-04-09 10:23 ` [Bug target/99988] " acoplan at gcc dot gnu.org
@ 2021-04-09 11:29 ` acoplan at gcc dot gnu.org
  2021-04-21 13:42 ` cvs-commit at gcc dot gnu.org
                   ` (6 subsequent siblings)
  8 siblings, 0 replies; 10+ messages in thread
From: acoplan at gcc dot gnu.org @ 2021-04-09 11:29 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99988

Alex Coplan <acoplan at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |acoplan at gcc dot gnu.org
   Last reconfirmed|                            |2021-04-09

--- Comment #2 from Alex Coplan <acoplan at gcc dot gnu.org> ---
Taking a look at this.

^ permalink raw reply	[flat|nested] 10+ messages in thread

* [Bug target/99988] aarch64: GCC generates excessive consecutive bti j instructions
  2021-04-09 10:13 [Bug target/99988] New: aarch64: GCC generates excessive consecutive bti j instructions acoplan at gcc dot gnu.org
  2021-04-09 10:23 ` [Bug target/99988] " acoplan at gcc dot gnu.org
  2021-04-09 11:29 ` acoplan at gcc dot gnu.org
@ 2021-04-21 13:42 ` cvs-commit at gcc dot gnu.org
  2021-04-21 13:46 ` acoplan at gcc dot gnu.org
                   ` (5 subsequent siblings)
  8 siblings, 0 replies; 10+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-04-21 13:42 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99988

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Alex Coplan <acoplan@gcc.gnu.org>:

https://gcc.gnu.org/g:fe11882ae34c49f6214f93867783ed1332f35f0f

commit r12-34-gfe11882ae34c49f6214f93867783ed1332f35f0f
Author: Alex Coplan <alex.coplan@arm.com>
Date:   Wed Apr 21 14:42:04 2021 +0100

    aarch64: Avoid duplicating bti j insns for jump tables [PR99988]

    This patch fixes PR99988 which shows us generating large (> 250)
    sequences of back-to-back bti j instructions.

    The fix is simply to avoid inserting bti j instructions at the target of
    a jump table if we've already inserted one for a given label.

    gcc/ChangeLog:

            PR target/99988
            * config/aarch64/aarch64-bti-insert.c (aarch64_bti_j_insn_p): New.
            (rest_of_insert_bti): Avoid inserting duplicate bti j insns for
            jump table targets.

    gcc/testsuite/ChangeLog:

            PR target/99988
            * gcc.target/aarch64/pr99988.c: New test.

^ permalink raw reply	[flat|nested] 10+ messages in thread

* [Bug target/99988] aarch64: GCC generates excessive consecutive bti j instructions
  2021-04-09 10:13 [Bug target/99988] New: aarch64: GCC generates excessive consecutive bti j instructions acoplan at gcc dot gnu.org
                   ` (2 preceding siblings ...)
  2021-04-21 13:42 ` cvs-commit at gcc dot gnu.org
@ 2021-04-21 13:46 ` acoplan at gcc dot gnu.org
  2021-04-22 12:46 ` cvs-commit at gcc dot gnu.org
                   ` (4 subsequent siblings)
  8 siblings, 0 replies; 10+ messages in thread
From: acoplan at gcc dot gnu.org @ 2021-04-21 13:46 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99988

--- Comment #4 from Alex Coplan <acoplan at gcc dot gnu.org> ---
Fixed on trunk. Keeping open for backports (once it's had some decent baking
time).

^ permalink raw reply	[flat|nested] 10+ messages in thread

* [Bug target/99988] aarch64: GCC generates excessive consecutive bti j instructions
  2021-04-09 10:13 [Bug target/99988] New: aarch64: GCC generates excessive consecutive bti j instructions acoplan at gcc dot gnu.org
                   ` (3 preceding siblings ...)
  2021-04-21 13:46 ` acoplan at gcc dot gnu.org
@ 2021-04-22 12:46 ` cvs-commit at gcc dot gnu.org
  2021-05-11 15:15 ` cvs-commit at gcc dot gnu.org
                   ` (3 subsequent siblings)
  8 siblings, 0 replies; 10+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-04-22 12:46 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99988

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Christophe Lyon <clyon@gcc.gnu.org>:

https://gcc.gnu.org/g:d44d8ed6b4e6fb2d0cf7566214e2e8281dd44cf0

commit r12-58-gd44d8ed6b4e6fb2d0cf7566214e2e8281dd44cf0
Author: Christophe Lyon <christophe.lyon@linaro.org>
Date:   Thu Apr 22 12:43:25 2021 +0000

    testsuite/aarch64: Run pr99988.c test under lp64 only

    The new test fails with -mabi=ilp32:
    sorry, unimplemented: return address signing is only supported for
'-mabi=lp64'

    2021-04-22  Christophe Lyon  <christophe.lyon@linaro.org>

            gcc/testsuite/
            PR target/99988
            * gcc.target/aarch64/pr99988.c: Skip if not lp64 target.

^ permalink raw reply	[flat|nested] 10+ messages in thread

* [Bug target/99988] aarch64: GCC generates excessive consecutive bti j instructions
  2021-04-09 10:13 [Bug target/99988] New: aarch64: GCC generates excessive consecutive bti j instructions acoplan at gcc dot gnu.org
                   ` (4 preceding siblings ...)
  2021-04-22 12:46 ` cvs-commit at gcc dot gnu.org
@ 2021-05-11 15:15 ` cvs-commit at gcc dot gnu.org
  2021-05-12  9:58 ` cvs-commit at gcc dot gnu.org
                   ` (2 subsequent siblings)
  8 siblings, 0 replies; 10+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-05-11 15:15 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99988

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Alex Coplan
<acoplan@gcc.gnu.org>:

https://gcc.gnu.org/g:1011bb8bc67cf34c45a9237d72a801a14ad9ef0f

commit r11-8379-g1011bb8bc67cf34c45a9237d72a801a14ad9ef0f
Author: Alex Coplan <alex.coplan@arm.com>
Date:   Wed Apr 21 14:42:04 2021 +0100

    aarch64: Avoid duplicating bti j insns for jump tables [PR99988]

    This patch fixes PR99988 which shows us generating large (> 250)
    sequences of back-to-back bti j instructions.

    The fix is simply to avoid inserting bti j instructions at the target of
    a jump table if we've already inserted one for a given label.

    Co-Authored-By: Christophe Lyon <clyon@gcc.gnu.org>

    gcc/ChangeLog:

            PR target/99988
            * config/aarch64/aarch64-bti-insert.c (aarch64_bti_j_insn_p): New.
            (rest_of_insert_bti): Avoid inserting duplicate bti j insns for
            jump table targets.

    gcc/testsuite/ChangeLog:

            PR target/99988
            * gcc.target/aarch64/pr99988.c: New test.

^ permalink raw reply	[flat|nested] 10+ messages in thread

* [Bug target/99988] aarch64: GCC generates excessive consecutive bti j instructions
  2021-04-09 10:13 [Bug target/99988] New: aarch64: GCC generates excessive consecutive bti j instructions acoplan at gcc dot gnu.org
                   ` (5 preceding siblings ...)
  2021-05-11 15:15 ` cvs-commit at gcc dot gnu.org
@ 2021-05-12  9:58 ` cvs-commit at gcc dot gnu.org
  2021-05-12 15:03 ` cvs-commit at gcc dot gnu.org
  2021-05-12 15:08 ` acoplan at gcc dot gnu.org
  8 siblings, 0 replies; 10+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-05-12  9:58 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99988

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Alex Coplan
<acoplan@gcc.gnu.org>:

https://gcc.gnu.org/g:419c243dfb9aba51aceb1370a241db082847eeb5

commit r10-9818-g419c243dfb9aba51aceb1370a241db082847eeb5
Author: Alex Coplan <alex.coplan@arm.com>
Date:   Wed Apr 21 14:42:04 2021 +0100

    aarch64: Avoid duplicating bti j insns for jump tables [PR99988]

    This patch fixes PR99988 which shows us generating large (> 250)
    sequences of back-to-back bti j instructions.

    The fix is simply to avoid inserting bti j instructions at the target of
    a jump table if we've already inserted one for a given label.

    Co-Authored-By: Christophe Lyon <clyon@gcc.gnu.org>

    gcc/ChangeLog:

            PR target/99988
            * config/aarch64/aarch64-bti-insert.c (aarch64_bti_j_insn_p): New.
            (rest_of_insert_bti): Avoid inserting duplicate bti j insns for
            jump table targets.

    gcc/testsuite/ChangeLog:

            PR target/99988
            * gcc.target/aarch64/pr99988.c: New test.

    (cherry picked from commit 1011bb8bc67cf34c45a9237d72a801a14ad9ef0f)

^ permalink raw reply	[flat|nested] 10+ messages in thread

* [Bug target/99988] aarch64: GCC generates excessive consecutive bti j instructions
  2021-04-09 10:13 [Bug target/99988] New: aarch64: GCC generates excessive consecutive bti j instructions acoplan at gcc dot gnu.org
                   ` (6 preceding siblings ...)
  2021-05-12  9:58 ` cvs-commit at gcc dot gnu.org
@ 2021-05-12 15:03 ` cvs-commit at gcc dot gnu.org
  2021-05-12 15:08 ` acoplan at gcc dot gnu.org
  8 siblings, 0 replies; 10+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-05-12 15:03 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99988

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-9 branch has been updated by Alex Coplan
<acoplan@gcc.gnu.org>:

https://gcc.gnu.org/g:52a09050fdfafb0e41d56b6adf1625264f315b82

commit r9-9528-g52a09050fdfafb0e41d56b6adf1625264f315b82
Author: Alex Coplan <alex.coplan@arm.com>
Date:   Wed Apr 21 14:42:04 2021 +0100

    aarch64: Avoid duplicating bti j insns for jump tables [PR99988]

    This patch fixes PR99988 which shows us generating large (> 250)
    sequences of back-to-back bti j instructions.

    The fix is simply to avoid inserting bti j instructions at the target of
    a jump table if we've already inserted one for a given label.

    Co-Authored-By: Christophe Lyon <clyon@gcc.gnu.org>

    gcc/ChangeLog:

            PR target/99988
            * config/aarch64/aarch64-bti-insert.c (aarch64_bti_j_insn_p): New.
            (rest_of_insert_bti): Avoid inserting duplicate bti j insns for
            jump table targets.

    gcc/testsuite/ChangeLog:

            PR target/99988
            * gcc.target/aarch64/pr99988.c: New test.

    (cherry picked from commit 1011bb8bc67cf34c45a9237d72a801a14ad9ef0f)

^ permalink raw reply	[flat|nested] 10+ messages in thread

* [Bug target/99988] aarch64: GCC generates excessive consecutive bti j instructions
  2021-04-09 10:13 [Bug target/99988] New: aarch64: GCC generates excessive consecutive bti j instructions acoplan at gcc dot gnu.org
                   ` (7 preceding siblings ...)
  2021-05-12 15:03 ` cvs-commit at gcc dot gnu.org
@ 2021-05-12 15:08 ` acoplan at gcc dot gnu.org
  8 siblings, 0 replies; 10+ messages in thread
From: acoplan at gcc dot gnu.org @ 2021-05-12 15:08 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99988

Alex Coplan <acoplan at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #9 from Alex Coplan <acoplan at gcc dot gnu.org> ---
Fixed everywhere.

^ permalink raw reply	[flat|nested] 10+ messages in thread

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