dmd optimizer bug under linux

[Janzert]

Hi,

I've been chasing a bug for a few days and finally have it narrowed down
to the following example. Basically a branch that should always be false
is taken anyway.

The printf line below should never be executed, but it is if compiled
under linux with "dmd -release -O -inline badbranch.d".

I first started chasing this while using 1.043 but have since upgraded
to 1.052 and still see it. Not surprisingly I also see it with phobos or
tango. Unfortunately my assembly reading skills are poor enough that I
can't quite tell what is going on by looking at obj2asm output once the
optimizer is done with it.

Janzert

badbranch.d:
extern(C) int printf(char*, ...);

struct Container
{
    ulong[2] bits = [0UL, 1];
}

int called(ulong value)
{
    value = value * 3;
    return value;
}

int test(Container* c, int[] shift)
{
    int count = 0;
    if (c.bits[0])
        count = 1;
    count |= called(c.bits[1]) << shift[0];
    // This is always false, but is taken anyway.
    if (c.bits[0])
        printf("Impossible output %lld\n", c.bits[0]);

    return count;
}

int main(char[][] args)
{
    int[] shift = [0];
    Container c;
    return test(&c, shift);
}