[Bug gas/23647] New: ARM: Incorrect optimization of pseudo instruxtion ldr rx,=0 for -mcpu=cortex-m0plus

[johan.dahlberg at electrumab dot se]

https://sourceware.org/bugzilla/show_bug.cgi?id=23647

            Bug ID: 23647
           Summary: ARM: Incorrect optimization of pseudo instruxtion ldr
                    rx,=0 for -mcpu=cortex-m0plus
           Product: binutils
           Version: 2.30
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gas
          Assignee: unassigned at sourceware dot org
          Reporter: johan.dahlberg at electrumab dot se
  Target Milestone: ---

Hello,

When the startup assembly code for the NXP S32K116 processor is assembled with
gas bundled with gcc versions 6 and 7, the "ldr rx,=0" pseudo instruction is
incorrectly optimized into an invalid instruction for this CPU, "mov.w rx,#0"


Source code:

Reset_Handler:
    cpsid   i               /* Mask interrupts */

    /* Init the rest of the registers */
    ldr     r1,=0
    ldr     r2,=0
    ldr     r3,=0
    ...



Gas/Gcc version 6 and 7 generate the mov.w instruction, which does not exist
in the Cortex M0+ architecture. 
Below is the disassembled code for gas/gcc version 7 (GNU assembler (GNU Tools
for Arm Embedded Processors 7-2018-q2-update) 2.30.0.20180329):

00000000 <Reset_Handler>:
   0:   b672            cpsid   i
   2:   f04f 0100       mov.w   r1, #0
   6:   f04f 0200       mov.w   r2, #0
   a:   f04f 0300       mov.w   r3, #0



Gas/Gcc version 5 correctly generates the movs instruction:

00000000 <Reset_Handler>:
   0:   b672            cpsid   i
   2:   2100            movs    r1, #0
   4:   2200            movs    r2, #0
   6:   2300            movs    r3, #0



(As reference, the disassembled code for gas/gcc version 4.9, which
is less well optimized:

00000000 <Reset_Handler>:
   0:   b672            cpsid   i
   2:   4910            ldr     r1, [pc, #64]   ; (44 <JumpToSelf+0x2>)
   4:   4a0f            ldr     r2, [pc, #60]   ; (44 <JumpToSelf+0x2>)
   6:   4b0f            ldr     r3, [pc, #60]   ; (44 <JumpToSelf+0x2>)
)


Can you please fix this issue?
Meanwhile I stick with gas/gcc version 4 or 5...

Best regards,
/Johan Dahlberg

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