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Re: Loop optimization bug with Ada front end on PPC (and probably Alpha)
I've committed the following simplification as execute/20011126-2.c.
/* Problem originally visible on ia64.
There is a partial redundancy of "in + 1" that makes GCSE want to
transform the final while loop to
p = in + 1;
tmp = p;
tmp = tmp + 1;
in = tmp;
if (in < p) goto top;
We miscalculate the number of loop iterations as (p - tmp) = 0
instead of (p - in) = 1, which results in overflow in the doloop
static const char *
test (const char *in, char *out)
if (*in == 'a')
const char *p = in + 1;
while (*p == 'x')
if (*p == 'b')
while (in < p)
*out++ = *in++;
int main ()
test ("aab", out);