#2673 volatile handling bug in lospre

[Philipp Klaus Krause]

In current SDCC 3.6.9 #10093, the following code

struct
{
    volatile int x;
} s;

void f(void)
{
    s.x & 5;
    while(s.x & 5);
}

Reads s.x only once. This is probably a bug in lospre, since the generated asm seems correct when using --nolospre.

Philipp

P.S.: This issues was first found and reported by Daniel Drotos on the sdcc-user mailing list. I just verified, tested, created a code sample to reproduce the issue and filed the bug report.

[笑行天下]

confirmed on 3.7.0 and latest snapshot r10385, the following sample code also cause the problem:

void test1(volatile uint8_t* status)
{
    status[0] & 0x08;
    while (status[0] & 0x08) {}
}

void test2(volatile uint8_t* status)
{
    while (status[0] & 0x04) {}
    while (status[0] & 0x08) {}
}

[笑行天下]

Tried to modify SDCC source code, it seems that the patch in the attachment could fix the problem.

[Philipp Klaus Krause]

I'm looking into this, and hope to have a fix in the next few days. The patch would indeed fix the bug, but would also disable some valid optimizations, so I'll see if I can come up with a solution that allows for more optimizations on volatile variables.

Philipp

[Philipp Klaus Krause]

Fixed in [r10473].

Philipp