[Bug target/96882] Wrong assembly code generated with arm-none-eabi-gcc -flto -mfloat-abi=hard options

[emilie.feral at numworks dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96882

--- Comment #5 from emilie.feral at numworks dot com ---
When compiling without the lto using the command:
arm-none-eabi-gcc main.c -Os -mfloat-abi=hard -mthumb -mcpu=cortex-m4
-ffreestanding -nostdlib -lgcc -save-temps -o a.elf

I get the following instructions for CalledFunction:

Dump of assembler code for function CalledFunction:
   0x00008000 <+0>:     push    {r4, r5, lr}
   0x00008002 <+2>:     ldr     r5, [pc, #52]   ; (0x8038 <CalledFunction+56>)
   0x00008004 <+4>:     ldmia   r5!, {r0, r1, r2, r3}
   0x00008006 <+6>:     sub     sp, #100        ; 0x64
   0x00008008 <+8>:     add     r4, sp, #32
   0x0000800a <+10>:    stmia   r4!, {r0, r1, r2, r3}
   0x0000800c <+12>:    ldmia.w r5, {r0, r1, r2, r3}
   0x00008010 <+16>:    add     r5, sp, #32
   0x00008012 <+18>:    stmia.w r4, {r0, r1, r2, r3}
   0x00008016 <+22>:    ldmia   r5!, {r0, r1, r2, r3}
   0x00008018 <+24>:    add     r4, sp, #64     ; 0x40
   0x0000801a <+26>:    stmia   r4!, {r0, r1, r2, r3}
   0x0000801c <+28>:    ldmia.w r5, {r0, r1, r2, r3}
   0x00008020 <+32>:    stmia.w r4, {r0, r1, r2, r3}
   0x00008024 <+36>:    vldr    d0, [sp, #64]   ; 0x40
   0x00008028 <+40>:    vldr    d1, [sp, #72]   ; 0x48
   0x0000802c <+44>:    vldr    d2, [sp, #80]   ; 0x50
   0x00008030 <+48>:    vldr    d3, [sp, #88]   ; 0x58
   0x00008034 <+52>:    add     sp, #100        ; 0x64
   0x00008036 <+54>:    pop     {r4, r5, pc}
   0x00008038 <+56>:    strh    r0, [r3, #2]
   0x0000803a <+58>:    movs    r0, r0
End of assembler dump.

Which seems correct to me: the result is returned through registers d0-d3.

Interesting fact, if I keep the lto but remove the mfloat-abi=hard option:
arm-none-eabi-gcc main.c -Os -flto -mthumb -mcpu=cortex-m4 -ffreestanding
-nostdlib -lgcc -save-temps -o a.elf

The compilation also seems correct: the result is written at the address given
by r0 and the address is returned through r0.

Dump of assembler code for function CalledFunction:
   0x00008000 <+0>:     push    {r4, r5, r6, lr}
   0x00008002 <+2>:     ldr     r5, [pc, #20]   ; (0x8018 <CalledFunction+24>)
   0x00008004 <+4>:     mov     r6, r0
   0x00008006 <+6>:     mov     r4, r0
   0x00008008 <+8>:     ldmia   r5!, {r0, r1, r2, r3}
   0x0000800a <+10>:    stmia   r4!, {r0, r1, r2, r3}
   0x0000800c <+12>:    ldmia.w r5, {r0, r1, r2, r3}
   0x00008010 <+16>:    stmia.w r4, {r0, r1, r2, r3}
   0x00008014 <+20>:    mov     r0, r6
   0x00008016 <+22>:    pop     {r4, r5, r6, pc}
   0x00008018 <+24>:    strh    r0, [r5, #0]
   0x0000801a <+26>:    movs    r0, r0
End of assembler dump.