Help with SH2E -O2 instruction ordering with volatile

[Alex Brown]

Hi,

I have some asm being generated that I am having trouble
understanding. The following example compiled with GCC 5.3 using -O2:

typedef struct {
    unsigned a;
    unsigned b;
    unsigned c;
    unsigned d;
    unsigned e;
} peripheral_t;

volatile peripheral_t peripheral;

extern void lock() ;
extern void unlock() ;

void
update(unsigned a, int x, int y, char c, unsigned color, unsigned char size)
{
  lock();
  char text[2] = { c, 0};
  peripheral.a = a;
  peripheral.b = x;
  peripheral.c = y;
  peripheral.d = color;
  peripheral.e = (unsigned)text;
  unlock();
}

Generated code is:

_update:
        mov.l   r8,@-r15
        mov     r6,r8
        mov.l   r9,@-r15
        mov     r5,r9
        mov.l   r10,@-r15
        mov     r4,r10
        mov.l   r11,@-r15
        exts.b  r7,r11              ; Move the value of "c" to r11
        mov.l   .L3,r1
        sts.l   pr,@-r15
        jsr     @r1
        add     #-4,r15
        mov.l   .L4,r1
        mov     #0,r0
        mov.l   @(24,r15),r3
        mov.l   r10,@r1
        mov.l   r9,@(4,r1)
        mov.l   r8,@(8,r1)
        mov.l   r3,@(12,r1)
        mov.l   r15,@(16,r1)   ; Move r15 to "peripheral.e"
        mov.l   .L5,r1
        mov.b   r11,@r15       ; Move r11 to @R15  ; text[0] = c
        jsr     @r1
        mov.b   r0,@(1,r15)    ; Move 0 to @R15+1  ; text[1] = 0
        add     #4,r15
        lds.l   @r15+,pr
        mov.l   @r15+,r11
        mov.l   @r15+,r10
        mov.l   @r15+,r9
        rts
        mov.l   @r15+,r8

I can fix this in various ways, (see below), but the question I am
asking: is my original code wrong ?

Regards

Alex

Working versions:

void
update(unsigned a, int x, int y, char c, unsigned color, unsigned char size)
{
  char text[2] = { c, 0};
  lock();
  peripheral.a = a;
  peripheral.b = x;
  peripheral.c = y;
  peripheral.d = color;
  peripheral.e = (unsigned)text;
  unlock();
}

void
update(unsigned a, int x, int y, char c, unsigned color, unsigned char size)
{

  lock();
  volatile char text[2] = { c, 0};
  peripheral.a = a;
  peripheral.b = x;
  peripheral.c = y;
  peripheral.d = color;
  peripheral.e = (unsigned)text;
  unlock();
}