[Bug target/96769] New: -mpure-code produces suboptimal code for immediate generation for thumb-1

[Bug target/96769] New: -mpure-code produces suboptimal code for immediate generation for thumb-1

[clyon at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96769

            Bug ID: 96769
           Summary: -mpure-code produces suboptimal code for immediate
                    generation for thumb-1
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: clyon at gcc dot gnu.org
  Target Milestone: ---

As discussed in PR94538, -mpure-code produces switch tables for thumb-1.

int f3 (void) { return 0x11000000; }
int f3_2 (void) { return 0x12345678; }

Compiled with -O2 -mpure-code,
-mcpu=cortex-m0:
f3:
        movs    r0, #17
        @ sp needed
        lsls    r0, r0, #8
        lsls    r0, r0, #8
        lsls    r0, r0, #8
        bx      lr
f3_2:
        movs    r0, #18
        @ sp needed
        lsls    r0, r0, #8
        adds    r0, r0, #52
        lsls    r0, r0, #8
        adds    r0, r0, #86
        lsls    r0, r0, #8
        adds    r0, r0, #120
        bx      lr

-mcpu=cortex-m23:
f3:
        movs    r0, #136
        @ sp needed
        lsls    r0, r0, #21
        bx      lr
f3_2:
        movw    r0, #22136
        @ sp needed
        movt    r0, 4660
        bx      lr

Code for cortex-m23 is OK, but the code for cortex-m0 could be improved for
f3(). For f3_2(), code for cortex-m0 looks OK since that CPU does not have
movw/movt instructions.

[Bug target/96769] -mpure-code produces suboptimal code for immediate generation for thumb-1

[clyon at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96769

Christophe Lyon <clyon at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2020-09-03
             Status|UNCONFIRMED                 |ASSIGNED

--- Comment #1 from Christophe Lyon <clyon at gcc dot gnu.org> ---
Patch proposal sent:
https://gcc.gnu.org/pipermail/gcc-patches/2020-September/553196.html

[Bug target/96769] -mpure-code produces suboptimal code for immediate generation for thumb-1

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96769

--- Comment #2 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:2033a63cbd0aab27d3a8450b4a4a5b371d583c85

commit r11-3011-g2033a63cbd0aab27d3a8450b4a4a5b371d583c85
Author: Christophe Lyon <christophe.lyon@linaro.org>
Date:   Fri Sep 4 11:48:36 2020 +0000

    arm: Improve immediate generation for thumb-1 with -mpurecode [PR96769]

    This patch moves the move-immediate splitter after the regular ones so
    that it has lower precedence, and updates its constraints.

    For
    int f3 (void) { return 0x11000000; }
    int f3_2 (void) { return 0x12345678; }

    we now generate:
    * with -O2 -mcpu=cortex-m0 -mpure-code:
    f3:
            movs    r0, #136
            lsls    r0, r0, #21
            bx      lr
    f3_2:
            movs    r0, #18
            lsls    r0, r0, #8
            adds    r0, r0, #52
            lsls    r0, r0, #8
            adds    r0, r0, #86
            lsls    r0, r0, #8
            adds    r0, r0, #121
            bx      lr

    * with -O2 -mcpu=cortex-m23 -mpure-code:
    f3:
            movs    r0, #136
            lsls    r0, r0, #21
            bx      lr
    f3_2:
            movw    r0, #22136
            movt    r0, 4660
            bx      lr

    2020-09-04  Christophe Lyon  <christophe.lyon@linaro.org>

            PR target/96769
            gcc/
            * config/arm/thumb1.md: Move movsi splitter for
            arm_disable_literal_pool after the other movsi splitters.

            gcc/testsuite/
            * gcc.target/arm/pure-code/pr96769.c: New test.

[Bug target/96769] -mpure-code produces suboptimal code for immediate generation for thumb-1

[clyon at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96769

Christophe Lyon <clyon at gcc dot gnu.org> changed:

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

--- Comment #3 from Christophe Lyon <clyon at gcc dot gnu.org> ---
Fixed on trunk.