[Bug target/96767] New: -mpure-code produces indirect loads for thumb-1

[Bug target/96767] New: -mpure-code produces indirect loads for thumb-1

[clyon at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96767

            Bug ID: 96767
           Summary: -mpure-code produces indirect loads 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 described in PR94538, -mpure-code produces suboptimal code for thumb-1 CPUs.

int x;
int f1 (void) { return x; }
Compiled with -O2 -mpure-code,
-mcpu=cortex-m0:
        movs    r3, #:upper8_15:#.LC0
        lsls    r3, #8
        adds    r3, #:upper0_7:#.LC0
        lsls    r3, #8
        adds    r3, #:lower8_15:#.LC0
        lsls    r3, #8
        adds    r3, #:lower0_7:#.LC0
        @ sp needed
        ldr     r3, [r3]
        ldr     r0, [r3]
        bx      lr
-> extra indirection, there should be only one ldr

For reference, -mcpu=cortex-m[347] and m23 produce:
        movw    r3, #:lower16:.LANCHOR0
        movt    r3, #:upper16:.LANCHOR0
        ldr     r0, [r3]
        bx      lr

[Bug target/96767] -mpure-code produces indirect loads for thumb-1

[clyon at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96767

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2020-09-08

[Bug target/96767] -mpure-code produces indirect loads for thumb-1

[clyon at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96767

--- Comment #1 from Christophe Lyon <clyon at gcc dot gnu.org> ---
Patch sent for review:
https://gcc.gnu.org/pipermail/gcc-patches/2020-September/554956.html

[Bug target/96767] -mpure-code produces indirect loads for thumb-1

[clyon at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96767

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

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

--- Comment #2 from Christophe Lyon <clyon at gcc dot gnu.org> ---
The master branch has been updated by Christophe Lyon <clyon@gcc.gnu.org>:

https://gcc.gnu.org/g:4d9af90d6a216822fe117337fb9836ba656dc3af

commit r11-4598-g4d9af90d6a216822fe117337fb9836ba656dc3af
Author: Christophe Lyon <christophe.lyon@linaro.org>
Date:   Mon Nov 2 07:31:22 2020 +0000

    arm: Avoid indirection with -mpure-code on v6m (PR96967)

    With -mpure-code on v6m (thumb-1), to avoid a useless indirection when
    building the address of a symbol, we want to consider SYMBOL_REF as a
    legitimate constant. This way, we build the address using a series of
    upper/lower relocations instead of loading the address from memory.

    This patch also fixes a missing "clob" conds attribute for
    thumb1_movsi_insn, needed because that alternative clobbers the flags.

    2020-11-02  Christophe Lyon  <christophe.lyon@linaro.org>

            gcc/
            PR target/96967
            * config/arm/arm.c (thumb_legitimate_constant_p): Add support for
            disabled literal pool in thumb-1.
            * config/arm/thumb1.md (thumb1_movsi_symbol_ref): Remove.
            (*thumb1_movsi_insn): Add support for SYMBOL_REF with -mpure-code.

            gcc/testsuite
            PR target/96967
            * gcc.target/arm/pure-code/pr96767.c: New test.