[avr-gcc-list] -O3 problem

[Dean Ferreyra]

Hi,

I am running into this problem:  I'm using a couple of layers of inline
functions.  When I compile with -O3 the generated assembly code changes the
value of r29 which is busy in this function as the frame pointer.  When the
function wants to return, this value gets copied back as the stack pointer
killing the stack.  I've included a distilled sample below that trigger the
problem and I've included the assembly output.  The problematic assignment
to r29 can be seen on the third line after the prolog.

I'm using CVS updates from May 16, 2001 for binutils and gcc.  My host is
cygwin.

My current workaround is to compile with -O2 or where possible change the
function so that avr-gcc does not use an explicit stack frame pointer.

Dean Ferreyra
address@hidden

--------------------
Makefile
--------------------
CC=avr-gcc
AR=avr-ar
CFLAGS=-Wall -O3 -mmcu=atmega103

%.s: %.c ; $(CC) $(CFLAGS) -S $*.c

bug01.s: bug01.c

--------------------
bug01.c
--------------------
void exec_cmd(unsigned cmd,
              const unsigned* cmd_data, char cmd_data_size,
              unsigned* reply_data, char reply_data_size);

inline static void set_a16(char cmd, char axis, unsigned value)
{
    exec_cmd(1, 0, 1, 0, 1);
}

inline static void set_source(char axis, char source)
{
    set_a16(1, axis, source);
}

void fn(void)
{
    unsigned data[10];
    data[0] = 0;

    set_source(1, 0);
    set_source(1, 0);
}

--------------------
bug01.s
--------------------
        .file   "bug01.c"
        .arch atmega103
__SREG__ = 0x3f
__SP_H__ = 0x3e
__SP_L__ = 0x3d
__tmp_reg__ = 0
__zero_reg__ = 1
_PC_ = 2
        .text
.global fn
        .type   fn,@function
fn:
/* prologue: frame size=20 */
        push r14
        push r15
        push r16
        push r17
        push r28
        push r29
        in r28,__SP_L__
        in r29,__SP_H__
        sbiw r28,20
        in __tmp_reg__,__SREG__
        cli
        out __SP_H__,r29
        out __SREG__,__tmp_reg__
        out __SP_L__,r28
/* prologue end (size=14) */
        std Y+1,__zero_reg__
        std Y+2,__zero_reg__
        ldi r29,lo8(1)
        clr r14
        clr r15
        mov r16,r29
        mov r19,r15
        mov r18,r14
        mov r20,r29
        mov r23,r15
        mov r22,r14
        ldi r24,lo8(1)
        ldi r25,hi8(1)
        call exec_cmd
        mov r19,r15
        mov r18,r14
        mov r20,r29
        mov r23,r15
        mov r22,r14
        ldi r24,lo8(1)
        ldi r25,hi8(1)
        call exec_cmd
/* epilogue: frame size=20 */
        adiw r28,20
        in __tmp_reg__,__SREG__
        cli
        out __SP_H__,r29
        out __SREG__,__tmp_reg__
        out __SP_L__,r28
        pop r29
        pop r28
        pop r17
        pop r16
        pop r15
        pop r14
        ret
/* epilogue end (size=13) */
/* function fn size 51 (24) */
.Lfe1:
        .size   fn,.Lfe1-fn
/* File bug01.c: code   51 = 0x0033 (  24), prologues  14, epilogues  13 */