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.
