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From: "joey.ye at arm dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug rtl-optimization/55757] Suboptimal interrupt prologue/epilogue for ARMv7-M (Cortex-M3)
Date: Fri, 21 Dec 2012 03:32:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55757

--- Comment #5 from Joey Ye <joey.ye at arm dot com> 2012-12-21 03:32:21 UTC ---
However, there is room to improve both performance and stack consumption in
case of Os:

extern void bar(int *);

void foo()
{
    int a;
    bar(&a);
}

Built with -mcpu=cortex-m3 -Os:
    push    {r0, r1, r2, lr}
    add    r0, sp, #4
    bl    bar
    pop    {r1, r2, r3, pc}

Apparently it should be optimized to save 8 bytes of stack consumption and two
stores:
    push    {r0, lr}
    mov    r0, sp
    bl    bar
    pop    {r1, pc}