[Bug rtl-optimization/42155] New: Optimizer generates bad code for ARM7 THUMB mode (local variable lost)

["heavy at smtp dot ru" <gcc-bugzilla@gcc.gnu.org>]

Hello.

I've found bug in GCC 4.4.1 for ARM7TDMI in THUMB mode.
Test code:
void foo(char *bar);
char test()
{
    char tmp;
    foo(&tmp);
    return tmp;
}

Compiled with: arm-elf-gcc -S -mcpu=arm7tdmi -O2 -mthumb test.c

Then using -O2 or -O3 optimization, assembler code looks like:
1:test:
2:        push    {r4, lr}
3:        sub     sp, sp, #4
4:        mov     r4, sp
5:        add     r4, r4, #3
6:        mov     r0, r4
7:        bl      foo
8:        add     sp, sp, #4
9:        ldrb    r0, [r4]
10:       @ sp needed for prologue
11:       pop     {r4, pc}

So, if interrupt or task switching occurs between line 8 and line 9,
local variable in stack (referenced by r4) will be garbaged by service routine,
because stack rewinds before usage of local variable.


This code works fine with -O1:
1:test:
2:        push    {r4, lr}
3:        sub     sp, sp, #4
4:        mov     r4, sp
5:        add     r4, r4, #3
6:        mov     r0, r4
7:        bl      foo
8:        ldrb    r0, [r4]
9:        add     sp, sp, #4
10:       @ sp needed for prologue
11:       pop     {r4, pc}


-- 
           Summary: Optimizer generates bad code for ARM7 THUMB mode (local
                    variable lost)
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: heavy at smtp dot ru
 GCC build triplet: arm-elf
  GCC host triplet: i486-linux-gnu
GCC target triplet: arm-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42155