Dear all,
I am having the problem, that since GCC 8 in the following code the if-section is optimized away for any optimization levels above 0.
But actually for a negative value of 'a', the value of 'ret' will overflow and thus 'ret' will be < 0, so the if-section cannot be optimized away.
#include <stdint.h>
int32_t foo(int32_t a)
{
int32_t ret = INT32_MAX - a;
if (ret < 0) {
ret -= 50;
}
return ret;
}
I am guessing, this is due to the fact, that signed integer overflow is undefined behavior in C/C++ and thus the compiler assumes this is prevented. Can you confirm this?
Can you give a hint, if this is a correct assumption and why this was introduced?
Which part of GCC 8 release notes represents this optimization?
Best regards
Lars
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